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Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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3

Independent Assessment of Styrene

The committee’s task had two parts. The first was to review the styrene substance profile as it was presented in the National Toxicology Program (NTP) 12th Report on Carcinogens (RoC) (NTP 2011a). In Chapter 2 of this report, the committee considered only literature that was available to NTP (literature published by June 10, 2011). It reviewed the primary literature, assessed NTP’s description and analysis of that literature, and determined whether NTP’s arguments support the conclusion that styrene is “reasonably anticipated to be a human carcinogen”.

To address the second part of its task, the committee carried out an independent assessment of styrene carcinogenicity, which is the focus of the present chapter. The committee used its peer review in Chapter 2 and the background document that supports the styrene profile in the 12th RoC as a starting point. The present chapter provides a brief summary of informative studies and highlights key data that informed its independent assessment of styrene. The reader is also referred to the background document (NTP 2008) for a more detailed discussion of study methodologies, strengths, and weaknesses for literature published prior to 2011 and to the primary literature.

The committee’s independent assessment of styrene carcinogenicity was based on literature that included primary data; however, the committee used published peer-reviewed review articles and reviews by other authoritative bodies to ensure that relevant literature was not missed and that all plausible interpretations of primary data were considered. The committee also considered comments and arguments that were presented during its first meeting, comments received from outside stakeholders during the study process, and independent literature searches carried out by National Research Council staff. The goal of the literature searches was to identify relevant literature that may have missed inclusion in the 12th RoC and relevant literature that was published after the release of the 12th RoC. Each search began on January 1, 2008, the year in which the background document for styrene was published (Bucher 2013). The search was first run on May 28, 2013, and it was updated on November 13,

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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2013.1 Databases searched were PubMed, Medline (Ovid), Embase (Ovid), Scopus, and Web of Science. The search strategy for each database and the exclusion criteria are described in greater detail in Appendix D. After identifying the relevant body of literature up to November 13, 2013, the committee reviewed the primary data and applied the RoC listing criteria to human, experimental animal, and mechanistic studies. It then integrated the evidence to develop its own independent listing recommendation for styrene. Consideration was given to all relevant information, including “dose response, route of exposure, chemical structure, metabolism, pharmacokinetics, sensitive sub-populations, genetic effects, or other data relating to mechanism of action or factors that may be unique to a given substance” (NTP 2011b).

In accordance with the listing criteria, expert judgment was used to interpret and apply the RoC listing criteria to evidence in human and animal studies. A substance can be classified in the RoC as “known to be a human carcinogen” if “there is sufficient evidence of carcinogenicity from studies in humans, which indicates a causal relationship between exposure to the agent, substance, or mixture, and human cancer” (NTP 2008, p. v). A substance can be classified in the RoC as “reasonably anticipated to be a human carcinogen” if at least one of the following three criteria are fulfilled (NTP 2008, p. v):

  • “There is limited evidence of carcinogenicity from studies in humans, which indicates that causal interpretation is credible, but that alternative explanations, such as chance, bias, or confounding factors, could not adequately be excluded.”
  • “There is sufficient evidence of carcinogenicity from studies in experimental animals, which indicates there is an increased incidence of malignant and/or a combination of malignant and benign tumors (1) in multiple species or at multiple tissue sites, or (2) by multiple routes of exposure, or (3) to an unusual degree with regard to incidence, site, or type of tumor, or age at onset.”
  • “There is less than sufficient evidence of carcinogenicity in humans or laboratory animals; however, the agent, substance, or mixture belongs to a well-defined, structurally related class of substances whose members are listed in a previous Report on Carcinogens as either known to be a human carcinogen or reasonably anticipated to be a human carcinogen, or there is convincing relevant information that the agent acts through mechanisms indicating it would likely cause cancer in humans.”

_____________________

1The cut-off date for the literature search was chosen to allow the committee time to review the literature within the time constraints of the project schedule.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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As discussed in Chapter 2, the type of information needed to meet the criterion for sufficient evidence in experimental animals is clear and transparent. The type of information needed to meet the criterion for limited or sufficient evidence in humans required more interpretation and expert judgment on behalf of the committee. In its evaluation of the epidemiology literature, the committee described the information it used to identify informative studies and to evaluate those studies.

This chapter begins with a section on metabolism and toxicokinetics. It then reviews cancer studies in humans, cancer studies in experimental animals, and mechanistic data. The chapter ends with a section that summarizes the evidence and provides a final conclusion and listing recommendation for styrene that is based on the listing criteria published in the 12th RoC.

METABOLISM AND TOXICOKINETICS

The absorption, distribution, metabolism, and excretion of styrene have been reviewed by several organizations (Sumner and Fennell 1994; IARC 2002; Vodicka et al. 2006; NTP 2008). In brief, as expected for a lipid-soluble hydrocarbon, styrene is absorbed after inhalation, ingestion, or dermal exposure. Increased blood concentrations of styrene or styrene metabolites have been observed in experimental subjects and workers exposed to styrene. Concentrations of styrene in the blood increase rapidly after the onset of exposure and decay over the course of several hours after termination of the exposure (see the background document for styrene [NTP 2008] for more information). Styrene is extensively metabolized, and metabolites are excreted in urine. Humans and rodents differ quantitatively in whole-body metabolism and excretion, but styrene metabolic pathways are qualitatively similar in rodents and humans (IARC 2002; Vodicka et al. 2006). Several pharmacokinetic and physiologically based pharmacokinetic models of inhaled styrene absorption and metabolism have been developed (Filser et al. 2002; Sarangapani et al. 2002; Chen et al. 2008; NTP 2008; Verner et al. 2012).

Metabolic activation is thought to be essential for styrene toxicity and carcinogenicity (IARC 2002; Vodicka et al. 2006; NTP 2008, 2011a). The balance between the metabolic activation rate and the detoxification rate in a specific target tissue is critical in determining the ultimate response. This section provides information on styrene phase I metabolism (metabolic activation), information on phase II (detoxification) pathways, and then a summary.

Multiple target sites are relevant to the carcinogenic hazard posed by styrene. In humans, styrene exposure is associated with cancer of the lymphohematopoietic system, esophagus, pancreas, and kidney (see the section “Epidemiologic Studies” below). In mice, styrene causes lung tumors, but statistically significant increases in tumor burden were not observed for other sites. The metabolic pathways that are likely to be important in the carcinogenic response are fairly well defined (and described below), but there is no comprehensive information on activation and detoxification rates in potential target tissues in the human.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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Phase I: Metabolism

Styrene is metabolically activated by cytochrome P450 monooxygenase (CYP450)-dependent oxidation on the side chain to form styrene-7,8-oxide (see Figure 3-1). Because this molecule contains an asymmetric carbon, there are two enantiomers, R- and S-styrene-7,8-oxide. Styrene aromatic ring metabolites are also formed, including 4-vinylphenol (presumably through styrene-1,2-oxide) and 2-vinylphenol (presumably through styrene-2,3-oxide). Of those pathways, styrene-7,8-oxide and 4-vinylphenol have been the most studied. It is possible that styrene-7,8-oxide and its initial detoxification products are further metabolized, perhaps through ring oxidation, and that 4-vinylphenol is also metabolized (Carlson et al. 2001; Carlson 2004, 2012; Cruzan et al. 2012, 2013). In the rodent, 14C-labeled CO2 is exhaled after 14C-styrene administration; this suggests that aromatic ring–opened metabolites are formed (Boogaard et al. 2000a). The precise structures and toxicologic roles of those downstream metabolites are not fully characterized.

In humans, styrene-7,8-oxide-based metabolic products form over 90% of the excreted metabolites of styrene (see below). That is clear evidence that styrene-7,8-oxide is the primary phase I metabolite in humans. Ring oxidation to 4-vinylphenol also occurs but to a much smaller extent. Sulfate and glucuronide conjugates of 4-vinylphenol have been identified in urine of humans but at low concentrations (less than 1% of the excreted metabolites) (IARC 2002; Vodicka et al. 2002a; NTP 2008). Aromatic ring metabolites may be critical with respect to cytotoxic or genotoxic effects in specific target organs even though they constitute only a minor pathway with respect to whole-body metabolism of styrene.

Multiple forms of human CYP450 are reported to catalyze styrene oxidation, albeit with different activities, including CYP1A2, CYP2A6, CYP2A13, CYP2B6, CYP2C8, CYP2E1, CYP2F1, CYP2S1, CYP3A3, CYP3A4, CYP3A5, and CYP4B1 (Nakajima et al. 1994; Vodicka et al. 2006; Carlson 2008; Fukami et al. 2008; NRC USCG 2008; Bui and Hankinson 2009). Multiple recent studies have shown associations of polymorphisms in selected CYPs with the pattern of urinary styrene metabolite excretion; although the studies suggest a role of CYPs in styrene metabolism, they did not examine associations with disease outcome. Two CYP2E1 binding sites with allosteric interactions result in a shift to more efficient metabolism as styrene concentration increases. Many of the aforementioned CYPs are expressed in nonhepatic tissues, and this indicates that styrene may be metabolically activated in multiple organs in humans. Because styrene produces lung tumors in mice, a focus of investigation has been on pulmonary metabolism in mice. Styrene is extensively metabolized in the mouse liver and lung (primarily in Clara cells) by multiple forms of CYP, including CYP2E1 and CYP2F2 (Carlson 2004, 2008, 2012; Shen et al. 2010; Cruzan et al. 2012, 2013). Both side chain and aromatic ring metabolites are probably formed in the lung. In the mouse, CYP2F2 may be particularly important in activation of styrene (Cruzan et al. 2012, 2013). Investigations of the role of CYP2F2 in the pulmonary response to styrene have focused solely on

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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cytotoxicity and short-term cell proliferation, and its role is critical in both these processes in the mouse lung. It is important to consider, however, that cytotoxicity and short-term cell proliferation responses may not be the sole determinants of the ultimate tumorigenic response and, in this context, the role of this CYP in lung tumorigenicity in mice remains uncertain.

images

FIGURE 3-1 Primary metabolic pathways of styrene. Main pathways are indicated by thick arrows. Metabolites that have been extensively studied are highlighted in the boxes. This figure is not a complete depiction of all known metabolites. A similar figure can be found in the background document for styrene (NTP 2008). GSH, glutathione. Source: Adapted from IARC (2002).

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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Styrene-7,8-oxide is genotoxic (see below). Metabolites derived from styrene-7,8-oxide are excreted in urine after styrene exposure; this is a clear indication that it is formed in humans. Moreover, styrene-7,8-oxide is detected in venous blood in humans and rodents after styrene exposure (NTP 2008), so it can probably migrate from the organ in which it was formed. The presence of styrene-7,8-oxide in the blood indicates widespread exposure to this genotoxic metabolite throughout the body. In humans, styrene-7,8-oxide–hemoglobin adducts and styrene-7,8-oxide–DNA adducts in lymphocytes have been observed, possibly because of circulating styrene-7,8-oxide or the generation of styrene-7,8oxide in circulating blood cells (NTP 2008, 2011a). Nonenzymatic epoxidation of styrene, perhaps via oxyhemoglobin, may occur in erythrocytes (Tursi et al. 1983).

As in the human, styrene-7,8-oxide is present in blood of both rats and mice exposed to styrene. Styrene exposure does not induce tumors in the rat and a statistically significant increase in tumors was only observed in the lungs of mice. The reasons for this are unclear. Styrene-7,8-oxide-based DNA adducts are formed in mouse lung after styrene exposure (Boogaard et al. 2000b), but their role in lung tumorigenesis in mice is not known. The amount of DNA adducts found in the lung vs liver in the mouse or in the rat lung vs mouse lung does not correlate with the target organ or a specific-species tumor response (Cruzan et al. 2009). However, inasmuch as adduct formation is the first of multiple steps of tumor development, a direct relationship between adduct concentrations and tumor response among species or organs is not necessary. The lack of direct concordance between styrene-7,8-oxide-adduct concentrations and tumor formation does not exclude the potential role of these adducts in the pulmonary carcinogenic response in mice.

Styrene is also metabolized via oxidation of its aromatic ring. Although a minor component, 4-vinylphenol-derived metabolites are present in urine after styrene exposure (NTP 2008, 2011a; Linhart et al. 2010, 2012). The aromatic ring–derived metabolite 4-vinylphenol is more potent than styrene or styrene-7,8-oxide in inducing pulmonary toxicity (Carlson 2002, 2004; Cruzan et al. 2005). This metabolite is thought to be formed by CYP2E1 and CYP2F2 in rodents (Carlson et al. 2001). 4-Vinylphenol is further metabolized by epoxidation in the rodent liver and lung (Zhang et al. 2011). Although it is not known with absolute certainty, aromatic ring–derived metabolites are likely important in the pneumotoxicity of styrene in mice (Cruzan et al. 2009, 2012, 2013). Information is not available on target organ–specific formation of aromatic ring metabolites in humans. The genotoxicity of these metabolites has not been extensively investigated.

Phase II: Detoxification

The side-chain–based or aromatic ring–based phase I metabolic oxidative products of styrene can be detoxified by hydrolysis via epoxide hydrolase or glutathione conjugation. Styrene-7,8-oxide is metabolized by epoxide hydrolase to

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

form styrene glycol, which can be converted to mandelic acid and phenylglyoxylic acid (Figure 3-1). Those two products are excreted in urine and account for more than 90% of the excreted styrene metabolites in humans (Vodicka et al. 2006; NTP 2008, 2011a). Information is not available on the pharmacogenetics of epoxide hydrolase relative to styrene disposition in humans; however, microsomal epoxide hydrolase knockout mice are more sensitive to styrene-induced cytotoxicity, and this highlights its potentially important role (Carlson 2010b, 2011a). Glutathione-based conjugates of styrene metabolites are also formed; they account for less than 10% of the excreted metabolites in humans but may account for more than 30% of the excreted metabolites in rodents (NTP 2008; Vodicka et al. 2006). Studies in mice that are deficient in glutathione-S-transferase P1P2 (-/-) suggest that this form is not important in styrene detoxification, but other forms of glutathione-S-transferase may still have a role in detoxification (Carlson 2011b). Some evidence suggests that expression of glutathione-S-transferase M1 and T1 in humans may contribute to individual variability in the fraction of styrene-7,8-oxide that is conjugated to glutathione (Haufroid et al. 2002; Teixeira et al. 2004; Fustinoni et al. 2008; Vodicka et al. 2006). Further information on the precise phase II activities of styrene in critical target cells is not available.

Summary of Styrene Metabolism and Toxicokinetics

Metabolism of styrene is key to its toxic and carcinogenic responses. The organ-specific tumorigenic responses to styrene will depend, in large part, on the balance between the rate of activation and the rate of detoxification in each organ. Thorough information on styrene activation and detoxification rates specific to target sites, particularly in the human, is not available. Given the wide array of CYP450 isozymes that can oxidize styrene, including forms that are known to be expressed in extrahepatic tissues (for example, CYP2E1 and CYP2A13), it is not possible to exclude the possibility that styrene bioactivation can occur in multiple target tissues. The presence of styrene-7,8-oxide in blood indicates that there is widespread tissue exposure to this genotoxic metabolite even in tissues that have low capacity for styrene activation. That highlights the importance of cellular detoxification capacities relative to organ-specific effects of styrene. In tissues that have low activity of epoxide hydrolase or glutathione-S-transferase, it might take only low levels of oxidation of styrene to produce cellular effects. The absence of marked toxicity in organs other than the liver or lung of mice (see the “Cytotoxicity” section) suggests detoxification capacities in that species are sufficient to prevent overt toxicity, except in the liver and lung. However, specific information on capacities for detoxification of styrene metabolites (such as epoxide hydrolase and glutathione-S-transferase) in critical target tissues in humans is not available. Therefore, the available information on styrene metabolism is insufficient to exclude any tissue from being a plausible target for styrene-induced cytotoxicity, which could contribute to carcinogenesis.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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EPIDEMIOLOGIC STUDIES

The literature was searched to identify relevant epidemiologic studies that had been published by November 13, 2013 (see Appendix D). The committee established exclusion criteria for the literature search and identified studies that were most informative for determining whether an association exists between styrene exposure and carcinogenesis. The committee then reviewed and evaluated the methods and results of those informative studies and applied the RoC listing criteria to the evidence.

Identification of Informative Studies

The committee established a set of attributes for identifying the most informative cohort and case–control studies. The most informative cohort studies were ones that had

  • Large cohorts that were exposed to high and varied concentrations of styrene.
  • Systematically assigned exposure estimates (such as the years in which exposure began and ended or job exposure matrices that coupled worker histories with exposure estimates according to occupation).
  • Styrene exposures that could be assessed apart from exposures to other potentially carcinogenic chemicals.
  • Systematically and reliably assigned cancer end points.
  • Internal comparisons, for example incidence rate ratios (IRRs) and mortality rate ratios (MRRs) that compared workers with different levels of exposure in the same cohort.

The most informative case–control studies were ones that had

 

  • Relatively large numbers of cases and controls.
  • Reliable assessments of styrene exposure based on specific job histories or other sources of information.
  • Interviews of cases and controls or their next of kin to collect occupational histories and data related to lifestyle (for example, smoking) and other important potential confounders.

On the basis of those attributes, the committee identified what it judged to be the 11 informative publications: six studies that used four cohorts in the reinforced-plastics industry that were conducted in Europe (Kogevinas et al. 1994; Kolstad et al. 1994, 1995) and the United States (Wong et al. 1994; Ruder et al. 2004; Collins et al. 2013) and five case–control studies conducted in Europe (Scélo et al. 2004; Seidler et al. 2007; Cocco et al. 2010; Karami et al. 2011) and

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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Canada (Gerin et al. 1998). See Table 3-1 for descriptions of the studies, including the salient strengths and weaknesses of each study. It should be noted that approximately one-third of the Kolstad et al. (1994) cohort in Denmark was included in the Kogevinas et al. (1994) European cohort. However, the two studies assessed different cancer outcomes (incidence and mortality, respectively), and the Kolstad et al. (1994) study only included male workers whereas the Kogevinas et al. (1994) study included male and female workers. It should also be noted that the Collins et al. (2013) study was an extension of the study by Wong et al. (1994). However, Wong et al. (1994) assessed somewhat different exposure metrics and necessarily focused on mortality that occurred closer to the time of high exposure.

The committee reviewed all epidemiologic studies that reported human exposure to styrene and an assessment of cancer end points and it identified several epidemiologic studies that it judged to be less informative compared to the 11 studies listed above. Reasons why the studies were judged as less informative studies and were excluded from Chapter 3 include small numbers of subjects, low concentrations of exposure to styrene, and simultaneous exposure of cohorts to other chemicals in addition to styrene (especially 1,2-butadiene), which prevented a clear characterization of styrene exposures. For an in-depth description of all epidemiology studies that were reviewed by NTP, see NTP (2008).

Evaluation of Informative Studies

After identifying studies that it deemed most informative, the committee evaluated the study data to inform its judgment of whether the evidence of carcinogenesis in humans after exposure to styrene is sufficient, limited, or inconclusive. The following factors were judged by the committee to increase the credibility of evidence on human carcinogenicity of styrene:

  • High estimates of MRRs, IRRs, standardized mortality ratios (SMRs), standardized incidence ratios (SIRs), or odds ratios (ORs). The committee considered a study to be particularly credible if a relative risk or its surrogate was ≥2.0 in an entire study cohort or a subset with high exposure (that is, a doubling of cancer mortality or incidence compared to the less exposed or unexposed comparison group). However, a relative risk estimate ≥1.5 also added credibility to the overall body of evidence, particularly if the relative risk was unlikely to be due to chance on the basis of the confidence interval (CI) around the estimate.
  • Exposure–response relationships for any reliably established exposure metric.
  • Consistency of the above two types of observations among independent cohort studies of the reinforced-plastics industry or between cohort and case–control studies. Some inconsistencies among findings in different populations is typical in the epidemiologic literature and can be the
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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TABLE 3-1 Summary of Most Informative Epidemiologic Studies Related to Styrene Exposure and Cancer

Study Design, Population, Outcomes, and Analytic Strategy Exposure Assessment and Exposure Metrics Strengths and Limitations
     
Kogevinas et al. 1994

(Included approximately one-third of subjects from Kolstad et al. 1994).

A retrospective cohort of 40,688 male and female workers ever employed in 660 reinforced-plastics plants in six countries (Denmark, Finland, Italy, Norway, Sweden, United Kingdom).

Mortality from all causes and specific causes.

SMRs and 95% CIs: External comparisons based on data from WHO, standardized by sex, age (5-year age groups), and calendar period (5-year periods).

Rate ratios and 95% CIs from Poisson regression: Internal comparisons limited to exposed subjects.

Cumulative exposure and average exposure assessed for each worker on the basis of individual job histories and country-, period-, and job-specific exposure estimates from personal sampling measurements and urine measurements.

 

  • 16,500 personal sampling measurements from 1955 to 1990.
  • 18,500 measurements of styrene metabolites in urine conducted in the 1980s.

Cumulative exposure (<75, 75–199, 200–499, ≥500 ppm–years).

Average exposure (<60, 60–99; 100–119; 120–199; ≥200 ppm).

Longest-held job collapsed into 5 job groups (laminators, n = 10,629; workers with unspecified tasks, n = 19,408; workers in other exposed jobs, n = 5,406; workers not exposed to styrene, n = 4,044; and workers with unknown job titles, n = 1,201).

Strengths
  • Large cohort with many workers involved in lamination.
  • Relatively long duration of followup (period of followup and employment varied by country, average followup = 13 years, 539,479 person–years at risk), with little loss to followup (3.0% of the cohort).
  • Cumulative exposure computed with and without a 5-year lag period.
  • Internal comparisons made—Poisson regression models included cumulative exposure, age, sex, calendar period, and time since first exposure.

Limitations

  • About 60% of the cohort was employed in the reinforced-plastics industry for <2 years.
  • No information on smoking, alcohol use, or other lifestyle factors.
 

Duration of exposure (assessed by combining data from payroll records and plant records showing the dates of production of reinforced plastics [in Denmark, pension-fund records were used]).

Time since first exposure (<10, 10–19, ≥20 years).

 
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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Kolstad et al. 1994

A retrospective cohort study of 36,525 male workers in 386 reinforced-plastics plants ever employed during 1964–1988 in Denmark and 14,254 workers not exposed to styrene in 166 industries not producing reinforced plastics, or company unknown.

Incidence of all cancers and specific lymphohematopoietic cancers.

SIRs and 95% CIs: External comparisons based on national incidence rates standardized for sex, age, and year of diagnosis.

SIRs and 95% CIs from Poisson regression (internal comparisons to unexposed workers; authors reported that results were similar to results based on external comparisons but data were not provided).

Pension-fund records were used to determine duration of employment (for exposed workers, only payments recorded during exposed employment were included).

Type of company (ever producing reinforced plastics, never producing reinforced plastics, and unknown production) and years since first employment (<10 vs ≥10 years).

For workers employed in plants producing reinforced plastics (n=36,525):

 

  • First year of employment (1964–1970, 1971–1975, 1976–1988) and years since first employment (<10 vs ≥10).
  • Years since first employment (<10 vs ≥10) and years of employment (<1 vs ≥1).

Analyses of a subset of workers in plants with styrene measurements (9,335 workers employed during the years of sampling). 2,473 personal air samples (not linked to workers or job titles) collected during 1964–1988; 1,814 of which were sampled in the 128 companies included in the study. These were averaged by company and dichotomized as follows: <50 ppm vs ≥50 ppm.

Strengths
  • Large cohort with relatively long followup (followup during 1970–1989, range of followup 0 to 20 years, mean = 10.9 years, 584,556 person–years at risk) and little loss (<2%) to followup.
  • Outcome of interest was cancer incidence instead of mortality, which avoids the issues related to cause of death categorization and different lengths of survival after cancer diagnosis.
  • Internal comparisons made and yielded similar results.

Limitations

  • Exposure assessment at plant level, with 12,837 workers from 287 companies in which it was estimated that ≥50% of workers were involved in reinforced-plastics production (included in Kogevinas et al. 1994) and 23,748 workers from 99 companies in which 1–49% of the workforce produced reinforced plastics); 60% of workers employed <1 year.
  • Personal sampling data available on a subset of the cohort, but not linked to workers or job titles.
  • No information on smoking, alcohol use, or other lifestyle factors.
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
Study Design, Population, Outcomes, and Analytic Strategy Exposure Assessment and Exposure Metrics Strengths and Limitations

Wong et al. 1994

Update of Wong 1990.

A retrospective cohort study of 15,826 male and female workers in 30 US reinforced-plastics facilities who were employed in areas exposed to styrene for ≥6 months during January 1, 1948–December 31, 1977.

Mortality from all causes and specific causes.

SMRs and 95% CIs: External comparisons based on US national age-, sex-, cause-, race-, and year-specific data (race missing from employment records, so the entire cohort was assumed to be white).

Coefficients and standard deviations from Cox proportional hazards model; internal comparisons for selected causes of death.

Because of scant historical monitoring data (Wong 1990), contractors collected monitoring data around 1980. Coupling the monitoring data to information about process changes, engineering controls, and personal protective equipment and employment histories, a job-exposure matrix (JEM) was used to estimate exposure for each plant, accounting for calendar time with 6 process categories:

 

  1. Open-mold processing.
  2. Mixing- and closed-mold processing.
  3. Finish and assembly.
  4. Plant office and support.
  5. Maintenance and preparation.
  6. Supervisory and professional.

Time since first exposure to styrene (<10, 10–19, ≥20 years).

Duration of employment (<1, 1–1.9, 2–4.9, 5–9.9, ≥10 years). Sensitivity analyses were done for workers employed >2 years in the 6 process categories.

Duration of exposure (<1, 1–1.9, 2–4.9, 5–9.9, ≥10 years).

Cumulative exposure (<10, 10–29.9, 30–99.9, ≥100 ppm–years).

Cumulative exposure and time since first exposure.

Strengths

  • 307,932 person–years at risk in the cohort during the followup period (through 1989), with little loss (3.5%) to followup (due to unknown vital status).
  • Internal comparisons made—Cox proportional hazards models with cumulative exposure, duration of exposure, sex, and age included as independent variables.

Limitations

  • 24% of the cohort was employed for <1 year and 27% for >5 years.
  • “Conservative” historical estimates of styrene exposure were reported by AD Little, Inc. (Little 1981). Exposures not assessed after 1977 (affecting 27% of the cohort). No assessment of average exposure. No information on departments or jobs worked for 3% of the cohort who were assigned the lowest exposure levels.
  • No information on smoking, alcohol use, or other lifestyle factors.
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

Kolstad et al. 1995

A retrospective-cohort study of 36,610 male workers in 386 reinforced-plastics plants ever employed during 1964–1988 in Denmark and 14,293 workers not exposed to styrene in similar industries.

Mortality from nonmalignant causes and incidence of total and specific solid cancers.

SMRs, SIRs, and 95% CIs: External comparisons based on age and calendar-specific national rates.

MRRs, IRRs, and 95% CIs from Poisson regression: Internal comparisons based on workers not exposed to styrene in similar industries.

Pension-fund records used to determine duration of employment.

Type of company. Companies classified as (1) high-probable exposure to styrene (producing reinforced plastics with ≥50% of the workforce involved in production) or (2) low-probable exposure to styrene (<50% of the workforce involved in production).

Year of first employment (≤1970 and >1970).

Duration of employment (year) (<1 and ≥1).

Years since first employment (<10 and ≥10).

Strengths

  • Large cohort with relatively long followup (followup during 1970–1990, 618,900 person–years at risk) and little loss to followup (<2.1%).
  • Internal comparisons made—Poisson regression models included exposure probability (unexposed, low, and high), age, year of first employment, duration of employment, and time since first employment, but results on exposure probability not reported.
  • Outcome of interest was cancer incidence instead of mortality, which avoids the issues related to cause of death categorization and different lengths of survival after cancer diagnosis.

Limitations

  • Exposure assessment at plant level.
  • No information on smoking, alcohol use, or other lifestyle factors.

Gerin et al. 1998

A population-based case–control study of men ages 35–70 years living in the metropolitan area of Montreal, Canada (3,730 cancer cases diagnosed during 1979–1986 in 19 major hospitals; 533 population controls age-stratified to cases; 533 cancer controls and 1,066 pooled controls).

Detailed questionnaires on working histories, including each job held. For each job, information about the company’s activities, the raw materials and final product, the machines used and responsibility for machine maintenance, the type of room or building in which the person worked, activities of surrounding workers, and presence of gases, fumes, or dusts.

A team of chemists and industrial hygienists estimated exposure for each job:

Strengths

  • High participation rates of cases—82% of cases agreed to participate, 82% of responses were obtained from study subjects and the rest from next of kin.
  • Population controls—71% of controls who were selected to participate were interviewed.
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
Study Design, Population, Outcomes, and Analytic Strategy Exposure Assessment and Exposure Metrics Strengths and Limitations

12 cancer sites.

ORs and 95% CIs from unconditional logistic regression.

  • Confidence that the exposure actually occurred (possible, probable, definite).
  • Frequency of exposure during a normal work week (<5%, 5–30%, >30% of the time).
  • Concentration in the environment (low, medium, high; relative to certain occupations that were used as reference points).
  • Frequency and concentration coded on an ordinal 1, 2, 3 scale and transformed to 1, 4, and 9 scores for estimating cumulative exposure.

Ever vs never exposed.

Cumulative exposure index estimated as the sum over all jobs of the product of duration, frequency, and concentration. Categorized as low, medium, or high (defined by cut-off points at the 70th and 90th percentiles of the distribution of all subjects; medium and high groups were collapsed when numbers were small).

  • Detailed retrospective exposure assessment, chemists and industrial hygienists responsible for exposure assessments were blinded to case–control status.
  • Adjustment for age, family income, ethnic group, cigarette smoking, and respondent status (self or proxy).
  • Separate analyses using cancer controls, population controls, and pooled controls (generally, authors reported that results were similar).
  • Single and multiple (styrene, benzene, toluene, and xylene) exposure models.

Limitations

  • Relatively low prevalence of exposure—2% of study population exposed to styrene. Era of first exposure: 0.6% before 1950; 0.8% during 1950–1960; 0.6% after 1960.
  • Sparse numbers of cases or controls by exposure status for some outcomes.

Ruder et al. 2004

Update of Okun et al. 1985.

A retrospective-cohort study of 5,204 male and female workers in two US reinforced-plastics boatbuilding plants who worked ≥1 day during 1959–1978.

Personnel records used to determine departments in which workers were employed and for which periods (no information on job titles). Industrial hygiene surveys were conducted to classify jobs and departments within plants according to level of styrene exposure (Okun et al. 1985).

Strengths

  • 135,588 person-years at risk in the cohort during the followup period (through 1998) with little loss to followup (n = 72) and few participants excluded because of missing data (n = 3).
  • Latency analysis conducted.
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

Mortality from all causes and specific causes (including cancers).

SMRs and 95% CI: External comparisons based on rates for Washington state and the United States standardized for sex, race, age, and calendar period. SMRs reported for the entire cohort, the high-exposure and low-exposure cohorts, and for workers who were employed for >1 year.

High-exposure subcohort (n = 2,063) included persons who ever worked in the fibrous-glass or lamination departments (TWA = 42.5 ppm/day in company A or TWA of 71.7ppm/day in company B).

Low-exposure subcohort (n = 3,141) included workers who never worked in fibrous-glass or lamination departments (TWA = 5ppm/day).

Latency (<15 years latency and ≥15 years latency defined as date of first exposure to date of death, date last known alive, or December 31,1998).

Years of employment (for high-exposure group, <1year vs >1 year).

Cumulative exposure (5 to <500, ≥500 to <5,000, ≥5,000 ppm*).

*The publication reported incorrect units for cumulative exposure.

Limitations

  • Cumulative exposure assessed for two departments at each plant and up to 1978; no information on previous or subsequent employment.
  • Mean duration of employment for the entire cohort = 1.59 + 3.0 years; mean duration of employment for the high-exposure subcohort = 1.10 + 2.1 years and for the low-exposure subcohort = 1.80 + 3.4 years.
  • No information on smoking, alcohol use, or other lifestyle factors.

Scélo et al. 2004

A multicenter case–control study in six central and eastern European countries and the United Kingdom (Liverpool). 2,861 newly diagnosed cases and 3,118 hospital-based controls that were frequency-matched to cases on age and sex. Two centers (Poland and Liverpool) recruited population-based controls.

Lung cancer.

ORs and 95% CIs from unconditional logistic regression.

In-person interviews on jobs held at ≥1 year using standardized questionnaires (specialized questionnaires were used for jobs and industries likely to entail exposures to known or suspected lung carcinogens).

Industrial hygienists at each center evaluated the frequency and intensity of exposure to 70 agents and indicated the level of confidence in their assessment.

Duration of exposure (not exposed and 1–6, 7–14, >14 years).

Strengths

  • Large case–control study with prospective ascertainment of cases during 1998–2002 from hospitals covering entire population except in Russia (exclusion of Russian cases did not alter results).
  • Hospital controls excluded cancer and tobacco-related diseases.
  • Detailed retrospective exposure assessment with standardized protocols across centers and industrial hygienists blinded to case–control status.
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
Study Design, Population, Outcomes, and Analytic Strategy Exposure Assessment and Exposure Metrics Strengths and Limitations
 

Weighted years of exposure (weighted by frequency of exposure in each job) (not exposed and 0.01–0.50, 0.51–3.00, >3.00).

Cumulative exposure (ppm-years). Frequency and intensity of exposures (2.5, 26, 100 ppm) were based on assigned midinterval weightings (2.5%, 17.5%, 65.0%).

Categorical analyses were based on tertiles of the distribution among exposed controls (subjects never exposed made up the referent category).

  • Reliability study (of a small number of jobs) indicated comparability among expert teams, although different levels of misclassification by agent.
  • Adjustment for center, sex, age, tobacco consumption, vinyl chloride, acrylonitrile, formaldehyde, and inorganic pigment dust.
  • Analyses also conducted with a 20-year lag and for jobs with high-confidence assessments (data not shown in publication).

Limitations

  • Use of hospital-based controls.
  • Low prevalence of styrene exposure (1.8% of cases and 1.5% of controls).

Seidler et al. 2007

A population-based case–control study of men and women ages 18–80 years living in 6 regions in Germany (710 lymphoma patients diagnosed during 1979–1986; 710 controls matched on sex, region, and age [±1 year of birth]).

Lymphoma (and lymphoma subentities).

ORs and 95% CIs from conditional logistics regression.

Interviewer-administered questionnaire to obtain information on jobs held for ≥ 1year; start and end dates of employment; and job title, industry, and specific job tasks. For specific occupations, job task-specific supplementary questions were administered. Industrial physician assessed the intensity and frequency of exposure for each job held.

  • Intensity of exposure assessed as low (0.5 to 5 ppm), medium (>5 to 50 ppm), and high (>50 ppm).

Strengths

  • Population-based case–control study with prospective ascertainment of cases and a case participation rate of 87.4%.
  • Detailed retrospective exposure assessment with industrial physician responsible for exposure assessment blinded to case–control status.
  • High prevalence of styrene exposure in controls (23.8%).
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
 
  • Frequency of exposure assessed as low (1 to 5%), medium (>5 to 30%), and high (>30%).
  • Confidence of exposure assessment (possible but not probable, probable, certain).

Cumulative exposure (ppm–years). For every job held, the sum of the product of the intensity (2.5 ppm for “low” intensity; 25 ppm for “medium” intensity; 100 ppm for “high” intensity), frequency (3% of the time for “low” frequency; 17.5% of the time for “medium” frequency; 65% of the time for “high” frequency), and duration of employment in the job. Cumulative exposure was categorized as 0; >0 to ≤1.5; 1.5 to ≤67.1; >67.1 ppm-years.

  • Adjustment for age, sex, region, smoking (pack years), and alcohol consumption (g/day) in unmatched analyses and adjustment for smoking and alcohol consumption in matched analyses.

Limitations

  • Relatively low participation rate of controls (44.3%).
  • Sparse numbers of cases or controls by exposure status for some outcomes.

Cocco et al. 2010

Multicenter case–control study in Czech Republic, France, Germany, Ireland, Italy, Spain (2,348 incident cases of lymphoma diagnosed during 1998–2004). 2,462 controls were randomly selected from the general population (Germany and Italy) and matched to cases by sex, 5-year age intervals, and residence areas or selected from hospital controls who were limited to diagnoses other than cancer, infectious diseases, or immune-deficient disease.

Lymphoma (by subtype).

ORs and 95% CIs from unconditional logistic regression.

In-person interviews on full-time jobs held for ≥1 year; information on activity of the company, tasks performed, machines used, and potential exposures were ascertained. There were14 modules for specific occupations to gather additional details.

Occupations were coded using the 1968 International Labour Organisation Standard Classification of Occupations and 4-digit codes of the 1996 European Economic Community Classification of Economic Activities, Revision 1.

Intensity of exposure (0 = unexposed, 1 = low, 2 = medium, 3 = high).

Frequency of exposure (proportion of work time involving contact with the agent; 0 = unexposed, 1 = 1–5% work time, 2 = 5–30% work time, 3 = >30% work time).

Strengths

  • Large case–control study with high participation rates of cases (88%) and hospital controls (81%), although lower participation rates of population controls (52%).
  • Specific histologic outcomes were studied.
  • Detailed retrospective exposure assessment.
  • Adjustment for age, sex, education, and center.
  • Correction for multiple comparisons.

Limitations

  • A relatively low percentage of subjects had styrene exposure assessed with high confidence (27% of cases and 33% of controls).
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
Study Design, Population, Outcomes, and Analytic Strategy Exposure Assessment and Exposure Metrics Strengths and Limitations
 

Confidence. Based on the probability of exposure (1 = possible but not probable, 2 = probable, 3 = certain) and proportion of workers exposed in a given job (1 = <40%; 2 = 40–90%; 3 = >90%) (low, medium, high).

Cumulative exposure score, Ci ∑(yi * fi/3)xi where ci = cumulative exposure score, i = study subject, y = duration of exposure, x = exposure intensity level, f = exposure frequency level; categorized into quartiles (unexposed, low, medium, and high).

  • Possibility for subjects to be occupationally exposed to multiple chemicals.
  • No adjustment for smoking.
  • Sparse numbers of cases or controls by exposure status for some outcomes.

Karami et al. 2011

A hospital-based case–control study with controls frequency-matched to cases on age, sex, place of residence in seven centers in central and eastern Europe (1,097 renal-cancer cases and 1,476 controls).

Renal cell cancer.

ORs and 95% CIs from unconditional logistic regression.

Jobs held ≥1 year (questionnaires were used to ascertain lifetime occupational histories: job title, tasks, working environment, time spent on each task, type of employer, and starting and ending dates of employment).

Specialized occupational questionnaires were administered for nine specific jobs and eight industries.

Industrial hygienists evaluated the frequency and intensity of exposure to PAHs and “plastics” specific to the dates of employment. They assigned a confidence score to their exposure assessment (possible <40%, probable 40–90%, or definite >90% exposure).

Ever vs never exposed.

Duration of exposure (years).

Cumulative exposure (ppm–years). Product of duration in each job, the midpoint of the frequency of exposure

Strengths

  • Large case–control study with high participation rates of cases (90–99%) and controls (90% –96%) across study centers, with additional controls from a study of head and neck cancer that likely increased power.
  • Specific histologic type of renal cancer was studied.
  • Detailed retrospective exposure assessment with industrial hygienists blinded to case–control status.
  • Adjustment for sex, age, center, smoking status, self-reported hypertension, body mass index, and family history of cancer.
  • Assessment of lag period and sensitivity analysis (restricted to exposures with a high level of confidence).
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
 

(3%, 17.5%, 65%), and the intensity weight of the job (low, 2.5 ppm; medium, 25 ppm; high, 100 ppm)**, summed across all of the subjects’ jobs.

Average exposure (ppm). Computed by dividing cumulative exposure by the number of years exposed.

** Weights not specified in Karami et al. (2011); assumed to be the same as those reported in Scélo et al. (2004).

Limitations

  • Use of hospital-based controls.
  • Relatively low prevalence of styrene exposure in cases (2.1%) and controls (1.2%).
  • Additional controls from a study of head and neck cancer made it difficult to assess the representativeness of the study.
  • Sparse numbers of cases or controls by exposure status for some exposure metrics.

Collins et al. 2013

Update of Wong et al. 1994.

A retrospective-cohort study of 15,826 male and female workers in 30 reinforced-plastics facilities in 16 US states who were employed in areas exposed to styrene for ≥6 months during 1948–1977.

Mortality from all causes and specific causes.

SMRs and 95% CIs: comparisons based on the US population standardized for sex, age, time interval.

Hazard ratios and 95% CIs from proportional-hazards models (for internal comparisons; cumulative exposure only).

See Wong et al. (1994) for details about the exposure assessment.

Time since first exposure to styrene (<15 vs ≥15 years).

Cumulative exposure (0–149.9, 150–399.9, 400–1,199.9, ≥1,200 ppm–months).

Peak exposure (0, 1–719***, 720–1,799, ≥1,800 days with 100 ppm or higher for 15 min).

Average exposure (cumulative exposure divided by duration; results reported in the text for pancreatic cancer and diabetes only).

Duration of exposure (years). Text indicates no increasing trends for any cause of death and duration of exposure.

***Corrected from publication: “1–179”.

Strengths

  • Long duration of followup (1948–2008) with 561,530 person–years at risk and little loss to followup (<1%).
  • Relatively long duration of exposure (mean = 4.3 years).
  • Proportional hazards models included adjustment for sex, year of hire, and year of birth.

Limitations

  • Exposure not assessed after 1977 (relevant for 27% of the cohort); average exposure in 1977 was 25 ppm vs 34 ppm a decade earlier.
  • Peak exposure defined as the average number of peaks over 100 ppm for 15 min of a working day with no details provided as to whether monitoring data or expert judgment was used to construct this exposure metric.
  • No information on smoking, alcohol use, or other lifestyle factors.

Abbreviations: CI, confidence interval; IRR, incidence rate ratio; MRR, mortality rate ratio; OR, odds ratio; SIR, standardized incidence ratio; SMR, standardized mortality ratio; TWA, time-weighted average; WHO, World Health Organization. Source: committee-generated.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
  • result of the variability across populations, the difficulty in controlling for all potential variables that could influence an observed association or lack thereof, and methods for selecting or retaining individuals in a study and collecting information from them.

  • At least two informative studies in independent populations or with varying study designs were needed for the committee to consider evidence for a particular cancer outcome to be credible. In the committee’s view, the presence of negative findings in other studies did not negate positive findings. The existence of conflicting findings was one reason why the committee considered the evidence for an association between styrene exposure and carcinogenesis to be limited instead of sufficient.

The committee judged the evidence to be limited if the epidemiology evidence was credible but chance, bias, and confounding could not adequately be excluded. The evidence was judged to be sufficient if the epidemiology evidence was credible and chance, bias, and confounding could be excluded as an alternative explanation for the observed association.

In addition, the committee considered the implications of traditional statistical significance, which is usually thought of in terms of a p value less than 0.05 and the exclusion of 1.0 in the 95% CI around an effect estimate. The committee considered some observations of increased frequency of disease to be informative in smaller studies if they did not reach traditional statistical significance but were consistent with those of other studies. For example, the National Institute for Occupational Safety and Health cohort described by Ruder et al. (2004) involved fewer person–years than the Kogevinas et al. (1994), Kolstad et al. (1994), and Wong et al. (1994) cohorts and in some instances found similar SMRs, albeit with wider CIs because of the lower statistical power. Given the nature of the styrene exposure assessment in many of the cohort studies, such misclassifications are likely. For example, there were no individual-based exposure data in Kolstad et al. (1994); rather, assigned exposure status was based on the proportion of employees in specific plants who were working in the production of reinforced plastics. Furthermore, as in most occupational studies, it is possible that the “healthy-worker effect” influenced observations of the cohort studies in ways that cannot be determined.

The committee also looked at the presence or absence of isolated associations. Each of the six cohort studies that the committee determined to be most informative included a multitude of statistical analyses of exposures and cancer outcomes, as is typical in occupational cohort studies. Similarly, many different comparisons were conducted in the five case–control studies that were judged informative by the committee, often involving different exposure metrics and specific types of cancer. Because of issues potentially related to multiple comparisons, associations that appeared to be isolated among the multiple studies were not judged to constitute evidence of human carcinogenicity. However, the committee notes that nondifferential exposure misclassification and other data errors that are independent of exposure or disease status tend to result in an at-

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

tenuation of observed relative risks and its surrogates; therefore, any strong associations repeatedly found in informative studies need to be given more weight.

Findings on Different Types of Cancers

In this section, the committee describes specific findings on cancers of the lymphohematopoietic system, kidney, pancreas, and esophagus. Tables 3-2 through 3-8 and the pages that follow present the salient observations in those studies on specific types of cancer.

Lymphohematopoietic Cancers Combined

As discussed in Chapter 2, the definition of lymphohematopoietic neoplasm has advanced in recent decades. Some of the advance has come from recognition of subtypes that were previously lumped together, some from reclassification of subtypes, and some from revisions of knowledge and capabilities for classification of the broad array of lymphohematopoietic cancers. Recognizing that the grouping of “all lymphohematopoietic cancers” includes many biologically distinct diagnoses in humans (NRC 2011), the committee has adopted a general approach of focusing on more detailed classification when it is feasible but using broader categories when needed. When detailed classification is possible, looking at the finer categories may reveal specific associations if an effect is present in some subcategories but not others. Thus, the committee discussions below begin with the broadest classification of lymphohematopoietic cancers and follow with more detailed classifications. The epidemiologic data provide credible but limited evidence that styrene is a risk factor for lymphohematopoietic cancers on the basis of two European cohort studies (Kogevinas et al. 1994; Kolstad et al. 1994), as the role of chance, bias, or confounding cannot be adequately excluded.

Kogevinas et al. (1994) studied 40,688 workers in Denmark, Finland, Italy, Norway, Sweden, and the United Kingdom and followed up in various countries during 1945–1991 (539,479 person–years and an average duration of followup of 13 years). The SMR for lymphohematopoietic cancers combined was 0.93 (95% CI 0.71–1.20, 60 deaths) (see Table 3-2). Their internal analysis, which used data obtained from workers within the study (instead of an external standard population) and compared workers with different levels of styrene exposure to each other, showed that a longer time since first exposure (at least 10 years vs less than 10 years) was associated with a significantly higher mortality due to combined lymphohematopoietic cancers (10–19 years: MRR = 2.90, 95% CI 1.29–6.48, 25 deaths; at least 20 years: MRR = 3.97, 95% CI 1.30–12.13, nine deaths; p value for the test of linear trend = 0.012). Compared with workers who had an average exposure of less than 60 ppm (seven deaths), the MRRs for those who had an average exposure of 60–99 ppm, 100–119 ppm, 120–199 ppm, and at least 200 ppm were 1.68 (95% CI 0.59–4.79, nine deaths), 3.11 (95% CI 1.07–9.06, 10 deaths), 3.08 (95% CI 1.04–9.08, 13 deaths), and 3.59 (95% CI

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

TABLE 3-2 Summary of Observations for Lymphohematopoietic Cancers Combined

Reference Observations (95% CI)
Reinforced-Plastics Industry Cohorts
Kogevinas et al. 1994 Full study cohort: SMR = 0.93 (0.71–1.20), n = 60
   
  Subgroups by job category:
  Laminators: SMR = 0.81 (0.43–1.39), n = 13
  Unspecified task: SMR = 1.19 (0.80–1.70), n = 30
  Other exposed jobs: SMR = 0.65 (0.26–1.34), n = 7
  Unexposed: SMR = 0.91 (0.41–1.72), n = 9
   
  Cumulative exposure (ppm–years):
  <75 as reference: n = 20
  75–199: MRR = 0.98 (0.43–2.26), n = 8
  200–499: MRR = 1.24 (0.57–2.72), n = 10
  ≥ 500: MRR = 0.84 (0.35–2.02), n = 9
  p for trend = 0.65
   
  Time since first exposure (years):
  <10 as reference: n = 13
  10–19: MRR = 2.90 (1.29–6.48), n = 25
  ≥20: MRR = 3.97 (1.30–12.13), n = 9
  p for trend = 0.012
   
  Average exposure (ppm):
  <60 as reference: n = 7
  60–99: MRR = 1.68 (0.59–4.79), n = 9
  100–119: MRR = 3.11 (1.07–9.06), n = 10
  120–199: MRR = 3.08 (1.04–9.08), n = 13
  ≥200: MRR = 3.59 (0.98–13.14), n = 8
  p for trend = 0.019
Kolstad et al. 1994 Full study cohort: SIR = 1.20 (0.98–1.44), n = 112
   
  Employees of companies with 1–49% reinforced-plastics workers: SIR = 1.24 (0.99–1.54), n = 81
Employees of companies with 50–100% reinforced plastics workers: SIR = 1.09 (0.74–1.55), n = 31
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
  Year of first employment:
  1964–1970: SIR = 1.32 (1.02–1.67), n = 6
  1971–1975: SIR = 1.12 (0.75–1.62), n = 28
  1976–1988: SIR = 0.97 (0.57–1.53), n = 18
   
  Time since first employment ≥10 years:
  Overall: SIR = 1.20 (0.92–1.53), n = 64
  Duration of employment <1 year: SIR = 1.65 (1.18–2.26), n = 39
  Duration of employment ≥1 year: SIR = 0.84 (0.54–1.24), n = 25
Wong et al. 1994 Full study cohort (CIs not reported): SMR = 0.82 (0.56–1.17), n = 31
   
  Subgroups by latency (that is, time since first exposure in years) (CIs not reported):
  <10: SMR = 0.81, n = 9
  10–19: SMR = 0.66, n = 10
  ≥20: SMR = 1.04, n = 12
   
  Subgroups by cumulative exposure (ppm–years) (CIs not reported):
  <10: SMR = 1.05, n = 9
  10–29.9: SMR = 0.56, n = 5
  30–99.9: SMR = 0.76, n = 8
  ≥100: SMR = 0.94, n = 9
   
  Employed for ≥2 years by processing category (CIs not reported):
  Open-mold processing: SMR = 1.41, n = 4
  Mixing and closed-mold processing: SMR = 0.71, n = 2
  Finish and assembly: SMR = 0.62, n = 4
  Plant office and support: SMR = 0.65, n = 3
  Maintenance and preparation: SMR = 0.93, n= 5
  Supervisory and professional: SMR = 1.02, n = 2
   
  In proportional-hazard models, cumulative exposure and duration of exposure to styrene were not significant (n = 31).
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
Reference Observations (95% CI)
Collins et al. 2013 Full study cohort: SMR = 0.84 (0.69–1.02), n = 106
  Latency ≥15 years: SMR = 0.87 (0.70–1.07), n = 93
   
  Subgroups by cumulative exposure (ppm–months):
  0–149.9: SMR = 0.85 (0.56–1.25), n = 26
  150–399.9: SMR = 0.80 (0.51–1.21), n = 23
  400–1199.9: SMR = 0.90 (0.60–1.29), n = 29
  ≥1,200: SMR = 0.80 (0.53–1.16), n = 28
   
  Cumulative exposure (ppm–months) p for trend = 0.819, hazard ratio = 0.994 (0.983–1.006)
Ruder et al. 2004 Full study cohort: SMR = 0.74 (0.42–1.20), n = 16
  High exposure: SMR = 0.72 (0.20–1.84), n = 4
Reference population = Washington state Low exposure: SMR = 0.74 (0.38–1.30), n = 12
  Workers who were employed >1 year:
  Overall: SMR = 0.54 (0.17–1.26), n = 5
  High exposure: SMR = 0.56 (0.01–3.09), n = 1
  Low exposure: SMR = 0.53 (0.15–1.37), n = 4
   
  High exposure by duration of employment:
  <1 year: SMR = 0.76 (0.15–2.50), n = 3
  ≥1 year: SMR = 0.58 (0.01–4.70), n = 1

Abbreviations: MRR, mortality rate ratio; n, number of cases or deaths in cohort studies or number of exposed cases in case–control studies; SMR, standardized mortality ratio; SIR, standardized incidence ratio. Source: committee-generated.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

0.98–13.14, eight deaths), respectively, with a p value of 0.019 for the test of linear trend. Cumulative exposure (ppm-years) did not appear to be associated with an increase in mortality due to combined lymphohematopoietic cancers in this cohort (Kogevinas et al. 1994).

The study by Kolstad et al. (1994) included 36,525 male workers who were employed in 386 reinforced-plastics plants in Denmark during 1964–1988 and 14,254 employees of similar industries who were not exposed to styrene, with followup from 1970 through 1989 (584,556 person–years and an average duration of followup of 10.9 years). Between this study and the one by Kogevinas et al. (1994), there was an overlap of 12,837 male workers who were employed in 287 Danish plants where more than 50% of the workforce manufactured reinforced plastics. Kolstad et al. (1994) found that the SIR for combined lymphohematopoietic cancers in workers in companies that produced reinforced plastics was 1.20 (95% CI 0.98–1.44, 112 observed cases) (see Table 3-2). When the analysis was stratified by year of first employment, those who were first employed during 1964–1970 had a significantly higher incidence of combined lymphohematopoietic cancers (SIR = 1.32, 95% CI 1.02–1.67, 6 cases), whereas the SIR was 1.12 (95% CI 0.75–1.62, 28 cases) for those first employed during 1971–1975 and 0.97 (95% CI 0.57–1.53, 18 cases) for those first employed during 1976–1988. That observation is consistent with a possible exposure–response relationship, inasmuch as 2,473 historical personal air samples from the cohort showed that average styrene concentrations decreased from 180 ppm in 1964–1970 to 43 ppm in 1976–1988 (Jensen et al. 1990). Workers employed for less than 1 year and with at least 10 years since first employment had a significantly higher incidence than the standard population (SIR = 1.65, 95% CI 1.18–2.26, 39 cases). The SIR in those who were employed for at least 1 year with at least 10 years since first employment was not increased. The phenomenon of high disease frequency in short-term workers is a frequent finding in occupational cohort studies of cancer outcomes. While Kolstad et al. (1994) acknowledged that it was possible for short-term workers to have carcinogenic exposures in other industries or less favorable lifestyle factors, they considered it “less likely since a comparison between the exposed and unexposed short-term employees does not yield lower ratios for leukemia” (p. 277). An internal analysis with Poisson regression was also conducted, but no details were provided except for a statement that the rate ratios were close to the results presented (Kolstad et al. 1994).

Wong et al. (1994) studied a cohort of 15,826 male and female employees who were exposed to styrene for at least 6 months during 1948–1977 in 30 participating reinforced-plastics manufacturing plants in the United States and included followup through 1989 (307,932 person–years). The study observed an SMR of 0.82 (95% CI 0.56–1.17, 31 deaths) for lymphohematopoietic cancers combined in the overall cohort (see Table 3-2). Additional subgroup analyses by latency, duration of employment, duration of exposure to styrene, cumulative styrene exposure (ppm–years), and latency and cumulative styrene exposure simultaneously did not suggest an association between styrene exposure and

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

mortality due to lymphohematopoietic cancers. An internal analysis with Cox proportional hazard regression—including age, sex, cumulative exposure, and duration of exposure to styrene as independent variables—did not support an association either (Wong et al. 1994).

The study by Collins et al. (2013) is an extension of the Wong et al. (1994) cohort with an additional 19 years of followup (through 2008) and a total number of 561,530 person–years. The SMR for lymphohematopoietic cancers combined was 0.84 (95% CI 0.69–1.02, 106 deaths). Additional analyses by latency, cumulative exposure (ppm–months), number of peak exposures, cumulative duration, and average exposure and an internal analysis did not indicate an association between occupational styrene exposure and mortality due to lymphohematopoietic cancers (Collins et al. 2013).

The study by Ruder et al. (2004) included 5,204 workers exposed to styrene during 1959–1978 in two reinforced-plastic boatbuilding plants in Washington state and followup through 1998 (135,707 person–years). Using the Washington state population as the standard, the investigators observed an SMR of 0.74 (95% CI 0.42–1.20, 16 deaths) for lymphohematopoietic cancers combined (see Table 3-2). The SMRs for people who had high and low exposures were 0.72 (95% CI 0.20–1.84, four deaths) and 0.74 (95% CI 0.38–1.30, 12 deaths), respectively. An additional analysis by duration of employment and another analysis focusing on workers who were employed for over 1 year did not support an association between styrene exposure and mortality due to lymphohematopoietic cancers combined. However, the cohort had a smaller sample and smaller number of person–years of followup than the other studies discussed here. The total number of deaths due to lymphohematopoietic cancers combined was only five in workers who were employed for more than 1 year (Ruder et al. 2004).

Studies of specific types of lymphohematopoietic cancer generate SMRs, SIRs, and MRRs with wider CIs because of the smaller number of observed events (cancer incidence or deaths). Findings on leukemia and non-Hodgkin lymphoma (NHL) are discussed below. Because Hodgkin lymphoma and multiple myeloma are rare and there is a paucity of data from existing studies, the committee concludes that there are insufficient data to assess whether exposure to styrene is associated with the frequency of these two malignancies.

Leukemia

The epidemiologic data provide credible but limited evidence that styrene exposure is associated with an increase in the frequency of leukemia on the basis of two European cohort studies (Kogevinas et al. 1994; Kolstad et al. 1994), as the role of chance, bias, or confounding cannot be adequately excluded. As reported by Kogevinas et al. (1994), workers in the reinforced-plastics industry who had a higher average exposure to styrene or a longer time since first exposure appeared to have a higher probability of dying from leukemia although none of the MRRs reached statistical significance (see Table 3-3). In the Danish cohort (Kolstad et al. 1994), workers who were first employed during 1964–

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

TABLE 3-3 Summary of Observations for Leukemia

Reference Observations (95% CI)
Reinforced-Plastics Industry Cohorts
Kogevinas et al. 1994 Full study cohort: SMR = 1.04 (0.69–1.50), n = 28
   
  Subgroups by job category:
  Laminators: SMR = 0.48 (0.10–1.39), n = 3
  Unspecified task: SMR = 1.40 (0.79–2.28), n = 16
  Other exposed jobs: SMR = 0.94 (0.26–2.40), n = 4
  Unexposed: SMR = 0.99 (0.27–2.54), n = 4
   
  Cumulative exposure (ppm–years):
  <75 as reference: n = 11
  75–199: MRR = 0.46 (0.10–2.09), n = 2
  200–499: MRR = 0.69 (0.19–2.53), n = 3
  ≥500: MRR = 0.86 (0.26–2.83), n = 5
  p for trend > 0.52
   
  Time since first exposure (years):
  <10 as reference: n = 5
  10–19: MRR = 3.01 (0.90–10.08), n = 12
  ≥20: MRR = 3.79 (0.70–20.59), n = 4
  p for trend = 0.094
   
  Average exposure (ppm)
  <60 as reference: n = 3
  60–99: MRR = 1.58 (0.32–7.79), n = 4
  100–119: MRR = 4.43 (0.98–20.03), n = 8
  120–199: MRR = 1.36 (0.22–8.48), n = 3
  ≥200: MRR = 2.16 (0.29–16.24), n = 3
  p for trend = 0.47
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
Reference Observations (95% CI)
Kolstad et al. 1994 Full study cohort: SIR = 1.22 (0.88–1.65), n = 42
   
  Employees of companies with 1–49% reinforced plastic workers: SIR = 1.15 (0.77–1.67), n = 28
  Employees of companies with 50–100% reinforced plastics workers: SIR = 1.38 (0.75–2.32), n = 14
   
  Year of first employment:
  1964–1970: SIR = 1.54 (1.04–2.19), n = 30
  1971–1975: SIR = 1.00 (0.46–1.90), n = 9
  1976–1988: SIR = 0.51 (0.11–1.50), n = 3
   
  Time since first employment ≥10 years:
  Overall: SIR = 1.57 (1.07–2.22), n = 32
  Duration of employment <1 year: SIR = 2.34 (1.43–3.61), n = 20
  Duration of employment ≥1 year: SIR = 1.01 (0.52–1.77), n = 12
Wong et al. 1994 Full study cohort: SMR = 0.74 (0.37–1.33), n = 11
   
  Subgroups by latency (time since first exposure in years) (CIs not reported):
  <10: SMR = 1.11, n = 5
  10–19: SMR = 0.68, n = 4
  ≥20: SMR = 0.46, n = 2
   
  Subgroups by cumulative exposure (ppm–years) (CIs not reported):
  <10: SMR = 0.30, n = 1
  10–29.9: SMR = 1.12, n = 4
  30–99.9: SMR = 0.73, n = 3
  ≥100: SMR = 0.80, n = 3
   
  Employed for ≥2 years by processing category (CIs not reported):
  Open-mold processing: SMR = 0.90, n = 1
  Mixing and closed-mold processing: n = 0
  Finish and assembly: SMR = 0.80, n = 2
   
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
  Plant office and support: SMR = 0.56, n = 1
  Maintenance and preparation: SMR = 0.48, n= 1
  Supervisory and professional: SMR = 1.33, n = 1
  In proportional-hazard models, cumulative exposure and duration of exposure to styrene were not significant (n = 11).
Collins et al. 2013 Full study cohort: SMR = 0.84 (0.60–1.14), n = 40
  Latency ≥15 years: SMR = 0.88 (0.61–1.22), n = 35
   
  Subgroups by cumulative exposure (ppm–months):
  0–149.9: SMR = 0.61 (0.25–1.26), n = 7
  150–399.9: SMR = 1.30 (0.71–2.18), n = 14
  400–1,199.9: SMR = 0.66 (0.28–1.30), n = 8
  ≥1,200: SMR = 0.83 (0.42–1.49), n = 11
   
  Cumulative exposure (ppm–months) p for trend = 0.908, hazard ratio = 0.996 (0.979–1.014)
Ruder et al. 2004 Full study cohort: SMR = 0.60 (0.19–1.40), n = 5
  High exposure: SMR = 0.47 (0.01–2.63), n = 1
reference population = Washington state Low exposure: SMR = 0.64 (0.18–1.65), n = 4

Abbreviations: MRR, mortality rate ratio; n, number of cases or deaths in cohort studies or number of exposed cases in case–control studies; SMR, standardized mortality ratio; SIR, standardized incidence ratio. Source: committee-generated.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

1970 had a significantly higher incidence of leukemia (SIR = 1.54, 95% CI 1.04–2.19, 30 cases) whereas the SIRs for workers first employed after 1970 were not above 1 (see Table 3-3). Given the substantial change in the concentration of styrene exposure in this cohort over time (Jensen et al. 1990), such a finding is consistent with a possible exposure–response relationship. In addition, workers who had more than 10 years of followup since their first employment in a participating plant also had a significantly higher incidence of leukemia (SIR =1.57, 95% CI 1.07–2.22, 32 cases) although the observed higher leukemia incidence was limited to short-term workers whose duration of employment was less than 1 year (SIR = 2.34, 95% CI 1.43–3.61, 20 cases) (Kolstad et al. 1994).

The findings by Wong et al. (1994) and Collins et al. (2013) did not support a leukemogenic role of styrene. The SMR for leukemia was 0.74 (95% CI 0.37–1.33, 11 deaths) and 0.84 (95% CI 0.60–1.14, 40 deaths), respectively, in the studies by Wong et al. (1994) and Collins et al. (2013). Additional analyses by latency, duration of exposure, and cumulative exposure also did not suggest an association between styrene and leukemia in these two studies.

There were only five deaths due to leukemia in the study by Ruder et al. (2004). The SMR for leukemia was 0.60 (95% CI 0.19–1.40) when the Washington state population was used as the standard for the overall cohort and similar for people who had high or low exposures. No additional analysis was conducted, probably because of the small number of deaths.

Non-Hodgkin Lymphoma

The epidemiologic data provide credible but limited evidence that styrene exposure is a risk factor for NHL on the basis of a cohort study (Kogevinas et al. 1994) and two case–control studies (Gerin et al. 1998; Cocco et al. 2010), as the role of chance, bias, or confounding cannot be adequately excluded. In the study by Kogevinas et al. (1994), the SMR for NHL was 0.77 (95% CI 0.43–1.28, 15 deaths) for the general cohort and 1.40 (95% CI 0.56–2.88, seven deaths) for laminators, who were expected to have greater exposure to styrene. Workers who had a higher average exposure to styrene or a longer time since first exposure consistently had higher mortality due to malignant lymphomas (the term probably meant both Hodgkin lymphoma and NHL), as reflected by MRRs in the range of 1.65–7.15 although only one of the six MRRs reached statistical significance (see Table 3-4). The p values for the test of linear trend were 0.052 and 0.072 for average exposure and time since first exposure, respectively. In the Kolstad et al. (1994) study, the SIR for NHL was 1.33 (95% CI 0.96–1.80, 42 cases) (see Table 3-4). The SIRs for different periods of first employment were all above 1 but imprecise in that all 95% CIs included 1 (Kolstad et al. 1994). The study by Wong et al. (1994) listed a total of four deaths due to lymphosarcoma and reticulosarcoma in Table 2 of the publication but 10 deaths due to NHL in Table 9. It is unclear which subtypes of hematopoietic cancers were

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

TABLE 3-4 Summary of Observations for Non-Hodgkin Lymphoma

Reference Observations (95% CI)
Reinforced-Plastics Industry Cohorts
Kogevinas et al. 1994 Full study cohort: SMR = 0.77 (0.43–1.28), n = 15
  Subgroups by job category:
  Laminators: SMR = 1.40 (0.56–2.88), n = 7
  Unspecified task: SMR = 0.55 (0.15–1.39), n = 4
  Other exposed jobs: SMR = 0.30 (0.01–1.67), n = 1
  Unexposed: SMR = 1.01 (0.21–2.94), n = 3
   
  Time since first exposure (years):
  <10: SMR = 0.51 (0.11–1.49), n = 3
  10–19: SMR = 0.76 (0.25–1.78), n = 5
  ≥20: SMR = 1.55 (0.42–3.97), n = 4
   
  Duration of exposure (years):
  <2: SMR = 0.60 (0.19–1.40), n = 5
  ≥2: SMR = 1.05 (0.42–2.17), n = 7
   
  Malignant lymphomas (probably include both NHL and Hodgkin lymphoma) Average exposure (ppm):
  <60 as reference: n = 3
  60–99: MRR = 2.51 (0.49–12.87), n = 4
  100–119: MRR = 1.65 (0.15–18.57), n = 1
  120–199: MRR = 7.15 (1.21–42.11), n = 8
  ≥200: MRR = 4.40 (0.42–45.99), n = 2
  p for trend = 0.052
Kolstad et al. 1994 Full study cohort: SIR = 1.33 (0.96–1.80), n = 42
   
  Employees of companies with 1–49% reinforced-plastic workers: SIR = 1.65 (1.15–2.28), n = 36
  Employees of companies with 50–100% reinforced-plastics workers: SIR = 0.62 (0.23–1.35), n = 6
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
Reference Observations (95% CI)
   
  Year of first employment:
  1964–1970: SIR = 1.54 (1.04–2.19), n = 30
  1971–1975: SIR = 1.00 (0.46–1.90), n = 9
  1976–1988: SIR = 0.51 (0.11–1.50), n = 3
   
  Time since first employment ≥10 years:
  Overall: SIR = 1.57 (1.07–2.22), n = 32
  Duration of employment <1 year: SIR = 2.34 (1.43–3.61), n = 20
  Duration of employment ≥1 year: SIR = 1.01 (0.52–1.77), n = 12
Wong et al. 1994 It is unclear how many deaths due to NHL were included in this study. Table 9 of the publication indicated 10, but earlier tables did not show this.
   
  In proportional-hazard models, cumulative exposure and duration of exposure to styrene were not significant (n = 10).
Collins et al. 2013 Full study cohort: SMR = 0.72 (0.50–1.00), n = 36
  Latency ≥15 years: SMR = 0.75 (0.52–1.06), n = 33
   
  Subgroups by cumulative exposure (ppm–months):
  0–149.9: SMR = 1.08 (0.58–1.85), n = 13
  150–399.9: SMR = 0.17 (0.02–0.64), n = 2
  400–1,199.9: SMR = 0.94 (0.49–1.64), n = 12
  ≥1,200: SMR = 0.65 (0.30–1.23), n = 9
   
  Cumulative exposure (ppm–months) p for trend = 0.766, hazard ratio = 0.994 (0.976–1.013)
Ruder et al. 2004 Referred to as lymphosarcoma and reticulosarcoma, not NHL

Reference population = Washington state

Full study cohort: SMR = 0.39 (0.01–2.19), n = 1
High exposure: n = 0
Low exposure: SMR = 0.53 (0.01–2.93), n = 1

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
Case–Control Studies 
Gerin et al. 1998 NHL, not otherwise specified.
   
  Ever occupationally exposed to styrene:
  Adjusted OR = 2.0 (0.8–4.8), number of exposed cases = 8; unadjusted OR = 2.1
   
  Adjusted for age, family income, ethnic group, cigarette smoking, and respondent status.
Seidler et al. 2007 B-cell NHL (ppm-years):
  >0 to ≤1.5: adjusted OR = 0.8 (0.6–1.2), number of exposed cases = 53; unadjusted OR = 0.8
  >1.5 to ≤67.1: adjusted OR = 1.2 (0.8–1.7), number of exposed cases = 62; unadjusted OR = 1.2
  >67.1: adjusted OR = 0.8 (0.4–1.8), number of exposed cases = 12; unadjusted OR = 0.9
  Test for trend: p = 0.18
   
  T-cell NHL (ppm-years):
  >0 to ≤1.5: adjusted OR = 1.3 (0.5–3.6), number of exposed cases = 6; unadjusted OR = 1.7
  >1.5 to ≤67.1: adjusted OR = 1.6 (0.5–4.8), number of exposed cases = 4; unadjusted OR = 1.4
  Test for trend: p = 0.41
   
  Large diffuse B-cell lymphoma (ppm-years):
  >0 to ≤1.5: adjusted OR = 0.8 (0.4–1.5), number of exposed cases = 15; unadjusted OR = 0.8
  >1.5 to ≤67.1: adjusted OR = 1.3 (0.7–2.3) number of exposed cases = 19; unadjusted OR = 1.3
  >67.1: adjusted OR = 1.5 (0.5–4.4), number of exposed cases = 5; unadjusted OR = 1.4
  Test for trend: p = 0.03
   
  Follicular lymphoma (ppm-years):
  > 0 to ≤1.5: adjusted OR =1.1 (0.5–2.1), number of exposed cases = 12; unadjusted OR = 1.3
  > 1.5 to ≤ 67.1: adjusted OR = 2.2 (1.2–4.0), number of exposed cases = 17; unadjusted OR = 2.3
  >67.1: adjusted OR = 1.6 (0.5–6.0) number of exposed cases = 3; unadjusted OR = 1.6
  Test for trend: p = 0.20
  .
  Chronic lymphocytic leukemia (ppm-years):
  > 0 to ≤1.5: adjusted OR = 1.0 (0.5–2.2) number of exposed cases = 10; unadjusted OR = 0.8
  > 1.5 to ≤ 67.1: adjusted OR = 1.1 (0.5–2.2) number of exposed cases = 11; unadjusted OR = 1.1
  >67.1: adjusted OR = 0.5 (0.2–2.3), number of exposed cases = 2; unadjusted OR = 0.8
  Test for trend: p = 0.37
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
Reference Observations (95% CI)
  Marginal-zone lymphoma (ppm-years):
  > 0 to ≤1.5: adjusted OR = 1.0 (0.3–3.0), number of exposed cases = 4; unadjusted OR = 0.8
  > 1.5 to ≤ 67.1: adjusted OR = 0.8 (0.2–2.6), number of exposed cases = 3; unadjusted OR = 0.8
  Test for trend: p = 0.28
   
  All analyses used “no exposure, i.e., cumulative exposure = 0” as the reference group. All ORs adjusted for age, sex, region, smoking, and alcohol consumption.
Cocco et al. 2010 B-cell NHL:
   
  Ever exposed to styrene occupationally:
  Adjusted OR = 1.6 (1.1–2.3), number of exposed cases = 66; unadjusted OR = 1.6
   
  Cumulative exposure score based on confidence, intensity of exposure, frequency of exposure:
p for trend = 0.000096
   
  Adjusted for age, sex, education, and center

Abbreviations: MRR, mortality rate ratio; n, number of cases or deaths in cohort studies or number of exposed cases in case–control studies; NHL, non-Hodgkin lymphoma; OR, odds ratio; SMR, standardized mortality ratio; SIR, standardized incidence ratio. Source: committee-generated.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

considered NHL. In the proportional-hazard model that included 10 NHL deaths (Table 9 of the publication), duration of styrene exposure and cumulative exposure to styrene were not associated with mortality due to NHL (Wong et al. 1994). In the study by Collins et al. (2013), the SMR for NHL was 0.72 (95% CI 0.50–1.00, 36 deaths). Additional analyses by latency, cumulative exposure (ppm–months), number of peak exposures, cumulative duration, and average exposure and an internal analysis that used Cox proportional-hazard regression did not suggest an association between occupational styrene exposure and mortality due to NHL. The cohort study by Ruder et al. (2004) had only one observed death due to lymphosarcoma and reticulosarcoma and did not use the term non-Hodgkin lymphoma. The SMR for lymphosarcoma and reticulosarcoma was 0.39 (95% CI 0.01–2.19) when the Washington state population was used as the standard. No additional analysis was conducted.

Gerin et al. (1998) conducted a population-based case–control study in Montreal, Canada, that ascertained newly diagnosed incident cancer cases from 19 sites between 1979 and 1986 and population controls. For cases with a specific type of cancer (for example, 215 cases of NHL), three different control groups were used: cancer controls who had cancers other than NHL (n = 2,341), population controls (n = 533), and pooled controls (n = 1,066) that consisted of 533 cancer controls randomly selected from the total of 2,341 cancer controls and 533 population controls. All three control groups were used for comparisons with cases, but most of the findings presented by the authors were derived from the comparisons between cases and pooled controls. Based on a logistic regression model adjusted for age, family income, ethnic group, cigarette smoking, and respondent status, subjects who had occupational exposure to styrene appeared to have a higher odds of NHL than those who were not occupationally exposed to styrene (adjusted odds ratio [OR] = 2.0), although the association did not reach statistical significance (95% CI 0.8–4.8). It should be noted that the crude, unadjusted OR was 2.1, which was very close to the adjusted OR derived from the model that controlled for multiple covariates.

A population-based case–control study of lymphoma was conducted in six regions of Germany during 1998–2003 (Becker et al. 2004). Seidler et al. (2007) analyzed the relationship between solvent exposure and malignant lymphoma in the Becker et al. (2004) study, which included 554 incident cases of B-cell NHL and 35 incident cases of T-cell NHL who were diagnosed at the age of 18–80 years and an equal number of gender-, region-, and age-matched population controls (Seidler et al. 2007). Using job task-specific supplementary questionnaires, a trained industrial physician assessed the exposure to styrene and other solvents. The intensity and frequency of exposure to styrene were categorized semi-quantitatively as low, medium, and high, and a cumulative exposure was calculated by incorporating duration, intensity, and frequency of exposure. Compared with subjects without occupational styrene exposure, those who had varying levels of cumulative exposure to styrene had similar frequencies of B-cell NHL and T-cell NHL based on an unconditional logistic regression model that adjusted for age, sex, region, smoking, and alcohol consumption (Table 3-

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

4). Additional analyses by specific subtypes of B-cell NHL produced similar findings in general, although the trend test for diffuse large B-cell lymphoma (n = 158) was significant (p = 0.03), and elevated ORs for follicular lymphoma were observed for subjects with higher levels of cumulative exposure to styrene (Table 3-4). It should be noted that multiple myeloma was included in this study as a subtype of B-cell NHL, while it is usually considered a separate entity and a distinct type of cancer by itself.

Cocco et al. (2010) conducted a multicenter case–control study of lymphomas in the Czech Republic, France, Germany, Ireland, Italy, and Spain from 1998 to 2004. The study included 1,127 cases of B-cell NHL; 66 of the cases had occupational exposure to styrene. Three independent exposure metrics were used: intensity, frequency, and duration of exposure. Statistical analyses adjusted for age, sex, education, and center. Compared with people who had no exposure to styrene in an occupational setting, those who were exposed to styrene at work had a higher odds of B-cell NHL (adjusted OR = 1.6, 95% CI 1.1–2.3). The test for trend by increasing levels of the three independent exposure metrics yielded a p value of 0.000096, which was lower than a preset p value of 0.000125 chosen by the authors as the threshold for rejecting the null hypothesis. The authors chose a lower threshold than the usual 0.05 to account for multiple comparisons. Supplementary tables available online showed significant trends with frequency and duration of exposure to styrene (p = 0.04 and p = 0.03, respectively) (Cocco et al. 2010). It should be noted that subjects exposed to styrene could have been exposed to other solvents, but of the different subgroups of solvents evaluated in this study, exposure to styrene showed the highest OR of 1.6, with the ORs for exposure to other groups of solvents ranging from 1.0 to 1.2. In addition, the list of covariates adjusted for in Cocco et al. (2010) was not as extensive as in Gerin et al. (1998) and Seidler et al. (2007), but the unadjusted and adjusted ORs in the latter studies were very close for NHL (Gerin et al. 1998) or B-cell NHL (Seidler et al. 2007) (Table 3-4), which suggests that the covariates adjusted for did not have a strong confounding effect. Overall, the findings of Cocco et al. (2010) are consistent with an association between occupational exposure to styrene and B-cell NHL.

Kidney Cancer

The epidemiologic data provide credible but limited evidence that styrene is a carcinogen for the kidney (see Table 3-5) on the basis of the US cohort studies and a European case–control study. The US study of Wong et al. (1994) found a kidney-cancer SMR of 1.75 (95% CI 0.98–2.89); the strongest association was in workers who had been exposed for at least 2 years to open-mold processing (SMR = 4.57, CI not given, three cases). Collins et al. (2013) published an update of the Wong et al. (1994) study with about twice as many person–years of followup. The authors analyzed cumulative exposures (ppm–months), duration of exposure,

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

TABLE 3-5 Summary of Observations for Kidney Cancer

Reference Observations (95% CI)
Reinforced-Plastics Industry Cohorts
Kogevinas et al. 1994 Full study cohort: SMR = 0.77 (0.44–1.25), n=16
   
  Industrial process SMRs (95% CI)
  Laminators: 0.90 (0.25–2.32), n = 4
  Unspecified task: 0.75 (0.30–1.54), n = 7
  Other exposed jobs: 0.29 (0.01–1.61), n = 1
  Unexposed: 0.69 (0.08–2.51), n = 2
   
  Cumulative exposure (ppm–years):
  <75 reference: n=2
  100–199: MRR = 4.40 (0.71–27.2), n = 3
  200–499: MRR = 3.30 (0.42–25.6), n = 2
  ≥500: MRR = 6.04 (0.74–49.5), n = 3
  trend p = 0.12
Wong et al. 1994 Full study cohort: SMR= 1.75 (0.99–2.89), n = 15
   
  SMRs by latency (years) (CIs not reported):
  <10: 1.67, n = 3
  10–19: 1.41, n = 5
  ≥20: 2.18, n = 7
   
  SMRs by duration of exposure to styrene (years) (CIs not reported):
  <1: 1.89, n = 3
  1–1.9: 1.96, n = 3
  2–2.9: 1.51, n = 3
  5–9.9: 1.26, n = 2
  ≥10: 2.15, n = 4
   
  SMRs by cumulative styrene exposure (ppm–years) (CIs not reported):
  <10: 0.54, n = 1
  10–29.9: 2.06, n = 4
  30–99.9: 1.67, n = 4
  ≥100: 2.55, n = 6
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
Reference Observations (95% CI)
  SMRs employed ≥2 years in processing categories (CIs not reported):
  Open-mold processing: 4.57, n = 3
  Mixing and closed-mold processing: n = 0
  Finish and assembly: 1.94, n = 3
  Plant office and support: 1.72, n = 2
  Maintenance and preparation: 2.14, n = 3
  Supervisory and professional: 1.85, n = 1
   
  Proportional-hazard models, cumulative exposure, duration of exposure to styrene were not significant.
Kolstad et al. 1995 Full study cohort: SIR = 0.93 (0.65–1.28), n = 37
Ruder et al. 2004 Full study cohort: SMR = 1.43 (0.57–2.95), n = 7
  High exposure: SMR = 3.60 (0.98–9.20), n = 4
reference population = Washington state Low exposure: SMR = 0.80 (0.16–2.33), n = 3
  SMRs for those employed >1 year:
  Total: 1.38 (0.28–4.04), n = 3
  High exposure: 5.11 (0.62–18.4), n = 2
  Low exposure: 0.56 (0.01–3.12), n = 1
  SMRs for duration of exposure in high-exposure department (year)
  <1: 2.35 (0.26–10.2), n = 2
  >1: 4.91 (0.55–21.3), n = 2
Collins et al. 2013 Total cohort: SMR = 1.18 (0.83–1.62), n = 38
  ≥15 years latency: SMR= 1.18 (0.82–1.65), n = 34
  Cumulative exposure SMRs (ppm–months):
  0.0–149.9: 0.76 (0.28–1.66), n = 6
  150–399.9: 1.09 (0.47–2.15), n = 8
  400–1,199.9: 0.98 (0.42–1.94), n = 8
  ≥1,200: 1.79 (1.02–2.91), n = 16
  Test for trend: p = 0.045
  Proportional-hazard model: hazard ratio for styrene exposure = 1.009 (1.000–1.017)
  SMR (days with ≥15 min of styrene at >100 ppm):
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
  0: 0.88 (0.50–1.42), n = 16
  1–719*: 1.08 (0.49–2.04), n = 9
  720–1,799: 2.73 (1.17–5.38), n = 8
  ≥1,800: 1.82 (0.59–4.24), n = 5
  Test for trend: p = 0.054
   
  *Corrected from publication: “1–179”.
Case–Control Studies
Gerin et al. 1998 Kidney cancer: all histologies combined
   
  Ever exposed:
  Adjusted OR = 0.3 (0.0-2.0), n=1; unadjusted OR = 0.3
   
  Adjusted for age, family, income, ethnic group, cigarette smoking, and respondent status.
Karami et al. 2011 Renal-cell carcinoma
   
  All exposed cases:
  Adjusted OR = 1.7 (0.8–3.6), n = 17; unadjusted OR = 1.76
   
  Cumulative exposure** (years x frequency x ppm):
  ≤1.40: adjusted OR = 0.56 (0.19-1.67), n = 5; unadjusted OR = 0.66
  >1.40: adjusted OR = 6.65 (1.82–24.27), n = 12; unadjusted OR = 5.79
   
  Average exposure** (frequency x ppm):
  ≤0.175:adjusted OR = 1.09 (0.41–2.93), n = 8; unadjusted OR = 1.29
  >0.175: adjusted OR = 3.05 (0.99–9.42), n = 9; unadjusted OR = 2.61
   
  Duration of exposure** (years):
  ≤10:adjusted OR = 1.26 (1.47–3.39), n = 8; unadjusted OR = 1.29
  >10: adjusted OR = 2.57 (0.83–7.95), n = 9; unadjusted OR = 2.61
   
  Adjusted for center, sex, age, body-mass index, self-reported hypertension, smoking status (ever/never), and family history of cancer.
   
  **OR obtained from S. Karami on July 29, 2013, in response to a request from the Committee to Review the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens.

Abbreviations: MRR, mortality rate ratio; n, number of cases or deaths in cohort studies or number of exposed cases in case–control studies; OR, odds ratio; CI, confidence interval; SMR, standardized mortality ratio; SIR, standardized incidence ratio. Source: committee-generated.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

average exposure, and number of days with at least 15 min exceeding 100 ppm (“number of peak exposure days”) and calculated proportional hazard ratios. Although the SMR in the combined cohort of Collins et al. (2013) was 1.18 (95% CI 0.83–1.62), the authors observed an increased and positive association between styrene exposure and kidney cancer (proportional hazards ratio = 1.009, 95% CI 1.000–1.017) and exposure–response trends for cumulative exposure (ppm–months) (p = 0.045) and for number of peak exposure days (p = 0.054). The relatively small study of Ruder et al. (2004) in Washington state found an SMR of 1.43 with a wide 95% CI (0.57–2.95) on the basis of seven cases. However, the SMRs for the high-exposure subsets were 3.60 (95% CI 0.98–9.20) overall and 5.11 (95% CI 0.62–18.4) for workers who had been employed for more than 1 year. The European cohort studies (Kogevinas et al. 1994; Kolstad et al. 1995) were either inconsistent with the above observations or had sparse but suggestive data that were based on cumulative exposure–response analysis, as noted in Table 3-5.

An interview-based case–control study focusing on occupational exposure to polycyclic aromatic hydrocarbons and plastics was published by Karami et al. (2011) as part of the Central and Eastern European Renal Cell Carcinoma study. It fell outside the time window for NTP’s background document for styrene (NTP 2008) and was not reviewed in the substance profile for styrene (NTP 2011a). The interviews that were part of this study design enabled the authors to control for factors, such as smoking, which could not be controlled for in the cohort studies described above. The study also had the advantage that it included only renal-cell carcinomas whereas the cohort studies described previously in this section apparently also included other histologic types of kidney cancer, such as transitional-cell carcinomas. For study participants who were ever exposed vs never exposed to styrene, an increased OR was observed (OR = 1.7, 95% CI 0.8–3.6). Relative to the unexposed group and after adjustment for location, smoking, family history, hypertension, body-mass index, sex, and age, the ORs were 0.6 (95% CI 0.2–1.7) for exposed persons below the median value of cumulative exposure and 6.7 (95% CI 1.8–24.3) for exposed persons above the median value of cumulative exposure; the p for trend of ORs with cumulative exposure was 0.02. Analysis by average concentration and by duration also yielded higher associations with greater styrene exposure (Table 3-5), including some associations that approached or reached statistical significance and some associations with high ORs. The committee notes that the adjusted ORs, including the one with adjustment for smoking, were similar to or higher than the unadjusted ORs. Limitations of the study included the use of hospital-based controls, excluding patients who had other urologic conditions or diagnoses related to smoking; past cancer diagnosis of nonurologic cancer in the controls was possible. Kidney-cancer survival rates are relatively high and have been increasing over the last several decades (NCI 2014), so studies based on death certificates have the limitation that they do not capture some incident cases, and this can introduce a bias if case survival rates vary among groups with varied degrees of exposure. A smaller population-based case–control study in a Canadian popula-

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

tion included 177 cases in all of various histological types of kidney cancer and found no association with styrene exposure. The adjusted OR was the same as the unadjusted OR.

Overall, the observations for kidney cancer include repeated observations of associations with styrene exposure for various metrics, including independent populations and contrasting study designs, high estimates of risk, and exposure–response relationships. However, the role of chance, bias, or confounding cannot be adequately excluded. Therefore, the evidence fulfills NTP’s listing criteria for limited evidence and not sufficient evidence for an association between exposure to styrene and kidney cancer.

Pancreatic Cancer

The epidemiologic data on pancreatic cancer constitute credible but limited evidence that styrene exposure is associated with pancreatic cancer on the basis of four cohort studies (see Table 3-6). High case-fatality rates in pancreatic cancer make mortality a reliable index of incidence. Kogevinas et al. (1994) found an SMR of 1.48 (95% CI 0.76–2.58) for the highest-exposure group (laminators). The cumulative ppm–years analysis showed an exposure–response trend of p = 0.068 (MRR = 2.56 for exposures greater than 500 ppm, 95% CI 0.90–7.31, 10 cases). Kolstad et al. (1995) found a statistically significant pancreatic-cancer excess incidence in the subgroup that had the highest probability of exposure (IRR = 2.2, 95% CI 1.1–4.5). Ruder et al. (2004) found an SMR of 1.43 (95% CI 0.78–2.41) in the overall cohort and 1.88 (95% CI 0.51–4.81) in the high-exposure subgroup. The Wong et al. (1994) study did not find an association of styrene with pancreatic cancer. The update by Collins et al. (2013) found an overall SMR close to expected (SMR = 0.96, 95% CI 0.73–1.22), but found a significantly increased proportional hazard ratio of 1.008 (95% CI 1.002–1.015) that was based on cumulative exposure and a monotonic “increasing risk with increasing average exposure…with SMRs of 0.75, 0.83, 1.46, and 1.52” (Collins et al. 2013, p. 201). No large case–control studies of pancreatic cancer that include an assessment of styrene have been reported, but the committee did review a small population-based case–control study in Canada that included 116 cases of pancreatic cancer (Gerin et al. 1998). The authors did not find an association of cancer with exposure to styrene.

Overall, the observations for pancreatic cancer demonstrated exposure–response relationships with styrene exposure estimates in cohort mortality studies conducted in both the United States and Europe and in the Danish incidence study. However, the role of chance, bias, or confounding cannot be adequately excluded. Therefore, the evidence fulfills NTP’s listing criteria of limited evidence, not sufficient evidence, for an association between exposure to styrene and pancreatic cancer. The committee notes that the study by Collins et al. (2013) has been recently published and was not included in the background document or substance profile.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

TABLE 3-6 Summary of Observations for Pancreatic Cancer

Reference Observations (95% CI)
Reinforced-Plastics Industry Cohorts
Kogevinas et al. 1994 Full study cohort: SMR = 1.00 (0.71–1.38), n = 37
  ≥20 years after first exposure: SMR = 2.05 (0.58-7.29), n = 9
   
  Industrial process SMRs:
  Laminators: 1.48 (0.76–258), n = 12
  Unspecified task: 1.17 (0.68–1.88), n = 17
  Other exposed jobs: 0.30 (0.04–1.10), n = 2
  Unexposed: 0.79 (0.26–1.86), n = 5
   
  Cumulative exposure (ppm–years):
  <75 reference: n = 9
  100–199: MRR = 1.44 (0.48–4.34) n = 5
  200–499: MRR = 1.90 (0.65–5.53), n = 6
  ≥500: MRR = 2.56 (0.90–7.31), n = 10
  Trend p = 0.068
Wong et al. 1994 Full study cohort: SMR = 1.13 (0.68–1.77), n = 19
   
  SMRs by latency (years) (CIs not reported):
  <10: 1.45, n = 5
  10–19: 0.87, n = 6
  ≥20: 1.25, n = 8
   
  SMRs by duration of exposure to styrene (years) (CIs not reported):
  <1: 2.03, n = 6
  1–1.9: 1.04, n = 3
  2–4.9: 1.29, n = 5
  5–9.9: n = 0
  ≥10: 1.30, n = 5
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
   
  SMRs by cumulative styrene exposure (ppm–years) (CIs not reported):
  <10: 1.40, n = 5
  10–29.9: 1.61, n = 6
  30–99.9: 0.63, n = 3
  ≥100: 1.06, n = 5
   
  SMRs employed ≥2 years in processing categories (CIs not reported):
  Open-mold processing: 0.80 n = 1
  Mixing and closed-mold processing: 1.57, n = 2
  Finish and assembly: 0.93, n = 3
  Plant office support: 0.44, n = 1
  Maintenance and preparation: 0.34, n = 1
  Supervisory and professional: n = 0
Kolstad et al. 1995 Full study cohort: SIR = 1.20 (0.86–1.63), n = 41
   
  Incidence rate ratio based on exposure probability:
  Low: 1.1(0.6–2.2), n = 24
  High: 2.2 (1.1–4.5), n = 17
Ruder et al. 2004 Full study cohort: SMR = 1.43 (0.78–2.41), n = 14
  High exposure: SMR = 1.88 (0.51–4.81), n = 4
  Low exposure: SMR = 1.31 (0.63–2.41), n = 10
   
  SMRs for those employed >1 year:
  Total: 1.54 (0.62–3.17), n = 7
  High exposure: 1.23 (0.03–6.85), n = 1
  Low exposure: 1.60 (0.59–3.49), n = 6
Collins et al. 2013 Total cohort: SMR = 0.96 (0.73–1.22), n = 63
  ≥15 years latency: SMR= 0.90 (0.67–1.17), n = 53
   
  Cumulative exposure SMRs (ppm-months):
  0.0–149.9: 0.90 (0.49–1.51), n = 14
  150–399.9: 1.15 (0.67–1.84), n = 17
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
Reference Observations (95% CI)
  400–1,199.9: 0.53 (0.24–1.01), n = 9
  ≥1,200: 1.24 (0.78–1.86), n = 23
  Test for trend: p = 0.274
  Proportional-hazards model: hazard ratio for styrene exposure = 1.008 (1.002–1.015)
   
  SMR (number of days with ≥15 min of styrene at >100 ppm):
  None: 0.84 (0.58–1.19), n = 32
  1–719*: 1.21 (0.74–1.87), n = 20
  720–1,799: 0.52 (0.11–1.51), n = 3
  ≥1,800: 1.45 (0.63–2.85), n = 8
  Test for trend: p = 0.337
   
  *Corrected from publication “1–179”.
   
  SMRs, with increasing average exposure = 0.75, 0.83, 1.46, 1.52.
Case–Control Study
Gerin et al. 1998 Ever exposed: OR = 0.3 (0.0-2.6) n = 1
   
  Adjusted for age, family, income, ethnic group, cigarette smoking, and respondent status.

Abbreviations: MRR, mortality rate ratio; n, number of cases or deaths in cohort studies or number of exposed cases in case–control studies; CI, confidence interval; SMR, standardized mortality ratio; SIR, standardized incidence ratio. Source: committee-generated.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

Esophageal Cancer

The committee judged there to be credible but limited evidence that high exposure to styrene in workers is associated with esophageal cancer on the basis of observations from Kogevinas et al. (1994), Wong et al. (1994), and Ruder et al. (2004) (see Table 3-7). For esophageal cancer, as for pancreatic cancer, mortality is a relatively reliable index of incidence because of the typically high mortality and short survival of patients.

An internal analysis in the Kogevinas et al. (1994) mortality study found exposure–response patterns among the higher-exposed subjects and an SMR of 5.8 (1.0–34) after 20 years following the first exposure on the basis of six cases. The Kolstad et al. (1994) study did not find any association in the full cohort and did not report on highly exposed subgroups. Wong et al. (1994) observed an SMR of 1.92 (95% CI 1.05–3.22) that was based on 14 cases, but subgroup analyses, all with small numbers, did not show clear patterns. The updated publication of Collins et al. (2013) did not include data on esophageal cancer; its unpublished background report (Collins et al. 2012) indicated that no increased SMRs were found for esophageal cancer. No proportional hazard analyses like those reported for pancreatic cancer and kidney cancer were included. The Ruder et al. (2004) study found an SMR of 2.30 (95% CI 1.19–4.02) with 12 cases in the full cohort (the highest-exposure subgroup had a similar SMR but only two cases). The committee did not identify any large case–control studies of esophageal cancer that included an assessment of styrene exposure, but it did identify a Canadian population-based case–control study that reported 99 cases of esophageal cancer (Gerin et al. 1998). The study authors did not report an association between esophageal cancer and styrene exposure.

Overall, while the epidemiologic evidence is weaker for esophageal cancer than for kidney or pancreatic cancer, there are nevertheless repeated observations of mortality associations with styrene among two independent U.S. cohorts, each with relative risk estimates of approximately double what was expected in the comparison group. Therefore, the evidence fulfills NTP’s listing criteria of limited evidence, not sufficient evidence, for an association between exposure to styrene and esophageal cancer.

Lung and Breast Cancers

The committee does not consider there to be credible epidemiologic evidence of an association of styrene exposure and lung or breast cancer (Table 3-8). However, it decided to summarize the data from the most informative studies because lung cancers and breast cancers have been observed in experimental animals after treatment with styrene (see review below). For lung cancer (that is, cancer of the lung, bronchus, or trachea), the Wong et al. (1994) and Collins et al. (2013) studies found statistically significant increases in their combined

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

TABLE 3-7 Summary of Observations for Esophageal Cancer

Reference Observations (95% CI)
Reinforced-Plastics Industry Cohorts
Kogevinas et al. 1994 Full study cohort: SMR = 0.82 (0.47–1.31), n = 1
  ≥20 years after first exposure: SMR = 5.82 (1.0-33.91), n = 6
   
  Industrial process SMRs:
  Laminators: 1.81 (0.87–3.34), n = 0
  Unspecified task: 0.83 (0.27–1.93), n = 5
  Other exposed jobs: no = 0
  Unexposed: 0.82 (0.47–1.31), n = 17
   
  Cumulative exposure (ppm–years):
  <75 reference: n = 5
  100–199: MRR = 1.01 (0.20–5.23), n = 2
  200–499: MRR = 1.67 (0.39–7.18), n = 3
  ≥500: MRR = 1.76 (0.42–7.30), n = 4
  Test for trend p = 0.31
Wong et al. 1994 Full study cohort: SMR = 1.92 (1.05–3.22), n = 14
   
  SMRs by latency (years) (CIs not reported):
  <10: 1.43, n = 2
  10–19: 2.66, n = 8
  ≥20: 1.38, n = 4
   
  SMRs by duration of exposure to styrene (years) (CIs not reported):
  <1: 1.55, n = 2
  1–1.9: 2.37, n = 3
  2–4.9: 2.41, n = 4
  5–9.9: 0.73, n = 1
  ≥10: 2.34, n = 4
   
  SMRs by cumulative styrene exposure (ppm–years) (CIs not reported):
  <10: 2.51, n = 4
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
  10–29.9: 1.24, n = 2
  30–99.9: 2.95, n = 6, p < 0.05
  ≥100: 0.97, n = 2
   
  SMRs employed ≥2 years in processing categories (CIs not reported):
  Open-mold processing: 3.57, n = 2
  Mixing and closed-mold processing: n = 0
  Finish and assembly: 3.01, n = 4
  Plant office support: 0.98, n = 1
  Maintenance and preparation: 2.30, n = 3
  Supervisory and professional: 1.99, n = 1
   
  Proportional-hazard models, cumulative exposure, duration of exposure to styrene were not significant.
Kolstad et al. 1995 Full study cohort: SIR = 0.92 (0.50–1.57), n = 13
Ruder et al. 2004 Full study cohort: SMR = 2.30 (1.19–4.02), n = 12
  High exposure: SMR = 1.85 (0.22–6.67), n = 2
  Low exposure: SMR = 2.42 (1.16–4.44), n = 10
   
  SMRs for those employed >1 year:
  Total: 1.27 (0.26–3.72), n = 3
  High exposure: 2.71 (0.07–15.0), n = 1
  Low exposure: 1.01 (0.12–3.64), n = 2
   
  SMRs for duration of exposure in high-exposure department (years)
  <1: 1.18 (0.02–9.61), n = 1
  >1: 2.74 (0.04–22.3), n = 1
Case–Control Study
Gerin et al. 1998 Ever exposed: OR = 1.0 (0.0–3.5), n = 3
   
  Adjusted for age, family, income, ethnic group, cigarette smoking, and respondent status.

Abbreviations: MRR, mortality rate ratio; n, number of cases or deaths in cohort studies or number of exposed cases in case–control studies; CI, confidence interval; SMR, standardized mortality ratio; SIR, standardized incidence ratio. Source: committee-generated.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

cohort on the basis of 162 and 556 cases, respectively. In the analysis by Wong et al. (1994), the most highly exposed subgroup, which consisted of people who worked in open-mold processing for at least 2 years, did not have an excess SMR (eight cases). A previous nested case–control analysis by Wong (1990) that was based on the same cohort found a strong association with smoking (Mantel-Haenszel Relative Risk = 7.33, chi-square = 4.27, p = 0.04) but no association with styrene exposure (Mantel-Haenszel Relative Risk = 0.63, chi-square = 1.11, p = 0.29). Collins et al. (2013) observed an increased SMR for lung cancer (SMR = 1.34, 95% CI 1.23–1.46) but reported inverse linear trends for cumulative exposure (p < 0.001). The proportional hazard ratio was below 1.0, and the 95% CI included 1.0. Ruder et al. (2004) found marginally increased lung-cancer SMRs (see Table 3-8). The Danish and European cohort studies found no evidence of an association between styrene exposure and lung cancer. Scélo et al. (2004) conducted a case–control study of industrial exposures and lung cancer in which there were no increased ORs associated with having been ever exposed to styrene or with the highest category of exposure duration, duration weighted by frequency, or cumulative ppm–years.

For breast cancer, no increase in the frequency of disease was observed in the reinforced-plastics industry; all three cohorts that included women (Kogevinas et al. 1994; Wong et al. 1994; Ruder et al. 2004; Collins et al. 2013) found lower than expected SMRs for breast cancer. When high-exposure subsets were analyzed for breast cancer, no indication of an exposure–response relationship was observed. The paucity of exposed women in the cohorts limits the conclusions that can be drawn. No pertinent case–control studies have been identified. In addition, the mortality data used in those studies comprise a less reliable index of breast cancer compared to incidence data.

Conclusion on Epidemiologic Literature

After identifying the most informative epidemiologic studies and evaluating their results, the committee found that there is limited evidence for the carcinogenicity of styrene on the basis of epidemiologic studies. A causal interpretation is credible, but alternative explanations—such as chance, bias, and confounding factors—cannot adequately be excluded.

CANCER STUDIES IN EXPERIMENTAL ANIMALS

Several studies have been published in which the tumor response to styrene-exposed animals has been measured, but as described in Appendix D, no relevant studies were identified after publication of the RoC. In general, the committee considered studies to be more informative when they included more than one dose, well-matched controls, chronic exposure, treatment groups of

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

TABLE 3-8 Summary of Observations for Lung, Bronchial, and Tracheal Cancers (Unless Otherwise Indicated)

Reference Observations (95% CI)
Reinforced-Plastics Industry Cohorts
Kogevinas et al. 1994 Full study cohort: SMR = 0.99 (0.87–1.13), n = 235
   
  Industrial process SMRs:
  Laminators: 1.06 (0.81–1.36), n = 60
  Unspecified task: 0.99 (0.78–1.24), n = 78
  Other exposed jobs: 0.89 (0.65–1.21), n = 42
  Unexposed: 0.84 (0.58–1.16), n = 37
   
  Cumulative exposure (ppm–years):
  <75 reference: n = 73
  100–199: MRR = 0.75 (0.47–1.19), n = 25
  200–499: MRR = 0.74 (0.47–1.16), n = 26
  ≥500: MRR = 0.90 (0.58–1.38), n = 37
  Test for trend p < 0.43 (sic)
Wong et al. 1994 Full study cohort: SMR = 1.41 (1.20–1.64), n = 162
   
  SMRs by latency (years) (CIs not reported):
  <10: 1.07, n = 23
  10–19: 1.46, n = 70, p < 0.01
  ≥20: 1.51, n = 69, p < 0.01
   
  SMRs by duration of exposure to styrene (years) (CIs not reported):
  <1: 1.83, n = 37, p < 0.01
  1–1.9: 1.25, n = 25
  2–4.9: 1.68, n = 44, p < 0.01
  5–9.9: 1.37, n = 30
  ≥10: 0.97, n = 26
   
  SMRs by cumulative styrene exposure (ppm-years) (CIs not reported):
  <10: 1.50, n = 37, p < 0.05
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
  10–29.9: 1.88, n = 48, p < 0.01
  30–99.9: 1.33, n = 43
  ≥100: 1.04, n = 34
   
  SMRs employed ≥2 years in processing categories (CIs not reported):
  Open-mold processing: 0.90, n = 8
  Mixing and closed-mold processing: 1.24, n = 10
  Finish and assembly: 1.43, n = 31
  Plant office support: 1.07, n = 17
   
  Maintenance and preparation: 1.49, n = 30, p < 0.05
  Supervisory and professional: 0.66, n = 5
   
  Proportional-hazard models, cumulative exposure, duration of exposure to styrene were not significant.
   
  Nested case control from same cohort at earlier period (Wong 1990):
  Direct exposure to styrene: Mantel-Haenszel Relative Risk = 0.63, n exposed cases = 15, p = 0.29
  Smoking: Mantel-Haenszel Relative Risk = 7.33, n exposed cases = 30, p = 0.04
Kolstad et al. 1995 Full study cohort: SIR = 1.12 (0.98–1.26), n = 248
   
  Incidence Rate Ratio by exposure probability:
  Unexposed controls: n = 123
  Low probability: 0.9 (0.7–1.1), n = 176
  High probability: 1.0 (0.7–1.3), n = 72
  All reinforced-plastics workers: 0.9 (0.7–1.1), n = 248
Ruder et al. 2004 Full study cohort: SMR = 1.14 (0.90–1.43), n = 76
  High exposure: SMR = 1.29 (0.76–2.04), n = 18
  Low exposure: SMR = 1.10 (0.84–1.43), n = 58
   
  SMRs for those employed >1 year:
  Total: 0.99 (0.67–1.41), n = 31
  High exposure: 1.11 (0.40–2.41), n = 6
  Low exposure: 0.97 (0.62–1.43), n = 25
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
  SMRs for duration of exposure in high-exposure department (years):
  <1: 1.40 (0.77–2.39), n = 14
  >1: 0.73 (0.20–2.03), n = 4
Collins et al. 2013 Total cohort: SMR = 1.34 (1.23–1.46), n = 556
  ≥15 years latency: SMR= 1.35 (1.24–1.48), n = 501
  Cumulative exposure SMRs (ppm–months):
  0.0–149.9: 1.60 (1.36–1.87), n = 157
  150–399.9: 1.41 (1.18–1.67), n = 131
  400–1,199.9: 1.31 (1.10–1.55), n = 138
  ≥1,200: 1.10 (0.92–1.31), n = 130
  Test for trend: p = 0.003 for inverse trend
  Proportional-hazard model: hazard ratio for styrene exposure = 0.997 (0.993–1.002)
   
  SMR (number of days with ≥15 min of styrene at >100 ppm):
  None: 1.32 (1.18–1.47), n = 314
  1–719*: 1.50 (1.28–1.76), n = 154
  720–1799: 1.34 (1.00–1.77), n = 49
  ≥1800: 1.06 (0.76–1.46), n = 39
  Test for trend: p = 0.201 for inverse trend
   
  *Corrected from publication, which printed “1–179”.
Case–Control Study
Gerin et al. 1998 Low exposure to styrene: OR = 0.3 (0.1–1.9), n = 5
  Medium / high exposure to styrene: OR = 0.9 (0.2–3.3), n = 5
   
  Adjusted for age, family income, ethnic group, cigarette smoking, respondent status, arsenic, asbestos, chromium VI, nickel, crystalline silica,
  beryllium, cadmium, and polycyclic aromatic hydrocarbons.
Scélo et al. 2004 Ever exposed to styrene: OR = 0.70 (0.42–1.18), n = 51
   
  Exposure duration OR (years):
  1–6: 0.98 (0.37–2.61), n = 13
  7–14: 0.72 (0.33–1.59), n = 19
  ≥14: 0.59 (0.26–1.34), n = 19
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
Reference Observations (95% CI)
   
  Duration x frequency of exposure OR (years):
  0.01–0.50: 0.67 (0.28–1.56), n = 13
  0.51–3.00: 1.19 (0.52–2.73), n = 21
  ≥3.00: 0.38 (0.13–1.03), n = 17
   
  Cumulative exposure (years x frequency x ppm) OR:
  0.01–2.75: 1.15 (0.55–2.41), n = 22
  2.76–12.50: 0.37 (0.13–1.08), n = 9
  ≥12.50: 0.53 (0.20–1.43), n = 20
   
  All ORs adjusted for center, sex, age, tobacco consumption, vinyl chloride, acrylonitrile, formaldehyde, and inorganic pigment dust.

Abbreviations: MRR, mortality rate ratio; n, number of cases or deaths in cohort studies or number of exposed cases in case–control studies; CI, confidence interval; OR, odds ratio; SMR, standardized mortality ratio; SIR, standardized incidence ratio. Source: committee-generated.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

adequate size, the use of well-characterized test material of high purity, thorough necropsy and pathologic evaluation of tissues according to established criteria, and statistical evaluation of tumor data with accepted methods. The quality of the studies varied considerably; the value of some of them is limited by the numbers of animals treated, exposure duration, observation period, dose selection, or incomplete reporting of methods or results. Studies were considered less informative if any of those attributes were missing or could not be verified from the study description.

Studies of Styrene

Despite weaknesses in some individual studies, the overall body of evidence is sufficient to permit an evaluation of evidence on carcinogenicity. The strongest evidence of a tumorigenic response to styrene is in the mouse lung. Inhalation exposure to styrene has been observed to produce significant increases in alveolar and bronchiolar tumors in both male and female CD-1 mice (Cruzan et al. 2001; Cohen et al. 2002), including a significant increase in malignant tumors in females at the highest dose. CD-1 mice (70 males and females) were exposed to styrene vapor 5 days/week for 6 hours/day. Two groups of 10 mice were sacrificed after 52 and 78 weeks, and the remaining 50 were exposed for 104 weeks (males) or 98 weeks (females). Styrene concentrations were 0, 20, 40, 80, or 160 ppm. Complete necropsies were performed on all animals. The major organs in all organ systems (respiratory, gastrointestinal, cardiovascular, urinary, reproductive, nervous, lymphohematopoietic, endocrine, musculoskeletal, and cutaneous) and grossly abnormal tissues in the control and high-dose groups were examined histopathologically. Selected organs and grossly abnormal tissues were examined histopathologically in intermediate-dose groups. After 24 months, the incidence of bronchiolar and alveolar adenomas was increased significantly in males exposed to styrene at 40 ppm or higher and in females exposed at 20, 40, or 160 ppm (see Table 3-9). The incidence of carcinomas alone was significantly increased only in females exposed at 160 ppm. The lung tumors occurred late in the study, and no increases were observed in subgroups of animals terminated after 52 and 78 weeks of exposure.

After oral exposure by gavage, a significant increase in alveolar and bronchiolar tumors combined was observed in male mice at the highest dose, and there was a significant dose-related trend (NCI 1979a). B6C3F1 mice (50 males and 50 females) were given styrene in a corn-oil vehicle by oral gavage 5 days/week for 78 weeks in doses of 150 or 300 mg/kg. Mice (20 males and 20 females) given corn-oil vehicle alone served as controls. Mice in all treatment groups were euthanized 13 weeks after the last dose. Complete necropsies were performed on all animals. The major organs in all organ systems (respiratory, gastrointestinal, cardiovascular, urinary, reproductive, nervous, lymphohematopoietic, endocrine, musculoskeletal, and cutaneous) and grossly abnormal tissues were examined histopathologically in all groups with the exception of some

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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TABLE 3-9 Lung-Tumor Incidence in CD-1 Mice Exposed to Styrene by Inhalation1

Sex Lung Tumor Type Tumor Incidence by Styrene Concentration
0 ppm 20 ppm 40 ppm 80 ppm 160 ppm
Males Bronchioalveolar adenoma 15/50 (30%) 21/50 (42%) 35/50 (70%)2 30/50 (60%)2 33/50 (66%)2
Bronchioloalveolar carcinoma 4/50 (8%) 5/50 (10%) 3/50 (6%) 6/50 (12%) 7/50 (14%)
Females Bronchioalveolar adenoma 6/50 (12%) 16/50 (32%)2 16/50 (32%)2 11/50 (22%) 24/50 (48%)2
Bronchioloalveolar carcinoma 0/50 (0%) 0/50 (0%) 2/50 (4%) 0/50 (0%) 7/50 (14%)2

1Source: Data from Tables 5 and 6 in NCI (1979a). Observations are expressed as number of animals with the indicated tumor over the number of animals examined.

2p < 0.05. Source: Data from Table 4 in Cruzan et al. 2001.

moribund animals. A significant increase in combined adenoma and carcinoma of the lung was observed in male mice at the higher styrene dose compared with controls (Table 3-10). The authors of this National Cancer Institute (NCI 1979a) study also compared their results with those in historical controls that were treated differently (dietary controls rather than mice treated with corn-oil vehicle) and found that the lung-tumor incidences were similar (an average of 12%—incidences were as high as 20% in two studies). That appears to have led the authors to discount to some extent the male mouse lung-tumor findings. The authors concluded that “the findings of an increased incidence of a combination of adenomas and carcinomas of the lung provided suggestive evidence for the carcinogenicity of styrene in male B6C3F1 mice” but also stated, “However, it is concluded that, under the conditions of this bioassay, no convincing evidence for the carcinogenicity of the compound was obtained in Fischer 344 rats or B6C3F1 mice of either sex” (p. VIII).

With respect to the male mouse lung-tumor findings in the NCI (1979a) study, the committee considers the use of the historical controls to be inappropriate in that they were not well matched to the treatment conditions of the study. As discussed in Chapter 2, many factors are related to the genetic makeup of the animals and husbandry practices that can influence tumor incidences in control and treated animals. They can include such details as the strain and substrain of experimental animal, the specific supplier, and even the subpopulation within the colony from which the animals were derived. Caging conditions, ventilation, diet, drinking water, and treatment vehicle are also important (Haseman et al. 1984; Festing and Altman 2002; Keenan et al. 2009). For those reasons, controls must be carefully matched, and the best opportunity to do this is almost always with concurrent controls. Although attempts were made by both NCI

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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TABLE 3-10 Lung-Tumor Incidence in B6C3F1 Mice Exposed to Styrene by Gavage1

Sex Alveolar and Bronchiolar Tumor Incidence
Vehicle Control 150 mg/kg 300 mg/kg
Male Adenoma 0/20 (0%) 3/44 (7%) 4/43 (9%)
Carcinoma 0/20 (0%) 3/44 (7%) 5/43 (11%)
Combined 0/20 (0%),
p = 0.023
6/44 (14%) 9/43 (20%),
p = 0.024
Female Adenoma 0/20 (0%) 1/43 (2%) 3/43 (7%)
Carcinoma 0/20 (0%) 0/43 (0) 0/43 (0)
Combined 0/20 (0%) 1/43 (2%) 3/43 (7%)

1Source: Data from Tables 5 and 6 in NCI (1979a). Control data from concurrent controls. Initial numbers of mice: 20 controls and 50 in each dose group. Statistical comparison results in each treatment group were from comparison with controls by one-tailed Fischer’s exact test. Results were not significant unless otherwise stated. Probability value for trend from Cochran Armitage test is shown below vehicle control results. No results for trend were presented for adenomas alone.

(1979a) and NTP (2008) to compare results with historical controls, neither documented the extent to which experimental conditions of the historical controls varied from those of the treated groups in the NCI study. The NTP historical-control group included studies in different laboratories, and this raises the possibility that genetic and husbandry factors were not well matched; the NCI historical control comparison included animals treated differently (that is, without corn-oil vehicle treatment). The committee views concurrent controls as an appropriate basis of comparison and interprets the findings of the NCI study, with respect to lung tumors after oral exposure in male mice, as being positive. No significant increases in lung tumors were observed in females, and tumors at other sites were not significantly increased in male or female mice.

In view of the importance of the observation of increased lung tumors in mice following oral exposure in the NCI (1979a) study, the committee took the additional step of confirming that the increases would be statistically significant if contemporary statistic tests were applied. With input from a statistical consultant, the committee applied an age-adjusted analysis of alveolar and bronchiolar tumors for male and female mice using information provided in the NCI report. Tumor incidences in styrene-treated mice were compared with concurrent study controls. On the basis of data included in the report, it was difficult to determine the time of death for animals that did not reach the end of the study, which precluded the use of the poly-3 trend test. However, given that all tumor-bearing mice were identified at terminal sacrifice, the Peto test could be applied using survival curve data and estimates of the numbers of missing or unexamined animals in each treatment group. For some groups, it was possible to infer the number of animals examined in specific treatment groups on the basis

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

of the data presented in the publication. In other groups, there were several possibilities for the number of animals examined in specific treatment groups, and each possibility was considered. As a result, comparisons between groups resulted in a range of p-values rather than a single value. The p-values obtained from the Peto test are summarized in Table 3-11. Alveolar and bronchiolar adenomas or carcinomas were significantly increased in the high-dose group, and the trend with dose was also statistically significant. Those results are consistent with the results obtained using the statistical test in the original NCI (1979a) report and indicate that the same conclusion is reached using a more modern statistical approach.

Studies of short-term exposure of pregnant mice and their progeny to high doses of styrene (Ponomarkov and Tomatis 1978) are not as well suited as the longer-term studies discussed above to assess tumor induction caused by chronic exposure. However, the short-term studies do provide some limited support for a tumorigenic effect of styrene on the lung. O20 and C57BL pregnant mice were orally exposed to styrene, and carcinogenic and developmental toxic effects were investigated (Ponomarkov and Tomatis 1978). O20 (29 treated) and C57BL (15 treated) mice were exposed at 1,350 mg/kg and 300 mg/kg, respectively, on gestation day 17. After weaning, progeny were exposed once a week at the same doses as dams for each strain; O20 mice were exposed for 16 weeks (discontinued because of toxicity), and C57BL for 120 weeks or until death. The authors indicate that all surviving animals were necropsied with histopathologic examination of all major organs, but the specific organs that were included in the examination were not stated. The preweaning mortality of the O20 mice (43%) was significantly increased compared with controls in which an olive-oil vehicle was used (22%); no difference in postweaning mortality was observed. The O20 strain had a significantly increased total lung-tumor incidence in both sexes compared with vehicle controls (p < 0.01). There was no significant increase in preweaning or postweaning mortality or tumor incidence in the C57BL mice in either dams or male and female progeny.

TABLE 3-11 Statistical Comparison of Mouse Lung Tumor Data from the 1979 NCI Study Using the Peto Test

Tumor Comparison P-value
Males Alveolar/Bronchiolar Carcinoma Low Dose vs. Control 0.296 – 0.318
High Dose vs. Control 0.110 – 0.115
Trend 0.057 – 0.067
Alveolar/Bronchiolar Adenoma Low Dose vs. Control 0.081 – 0.094
or Carcinoma High Dose vs. Control 0.015 – 0.017
Trend 0.011 – 0.014
Females Alveolar/Bronchiolar Low Dose vs. Control 0.684 – 0.690
Adenoma High Dose vs. Control 0.304 – 0.304
Trend 0.124 – 0.126
Alveolar/Bronchiolar Carcinoma 1 1

1No alveolar/bronchiolar carcinomas observed. Source: committee generated.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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A/J mice (25 females) were given an intraperitoneal injection three times a week for a total of 20 doses, which equaled a total exposure of 200 µmol of styrene (about 100 mg/kg); 4-(N-Nitrosomethylamino-)-1-(3-pyridyl)-1-butanone was used as a positive control (Brunnemann et al. 1992). Mice were sacrificed 20 weeks after their last injection. Complete necropsies were performed on all animals. Some of the major organs and sites (head, lung, heart, liver, spleen, pancreas, kidney, and adrenal) and grossly abnormal tissues were preserved and examined histopathologically in all groups. Lung adenomas were observed in three styrene-treated mice and one control; the difference was not statistically significant.

In contrast with the positive findings of lung tumors in mice, styrene exposure of rats by both oral and inhalation routes has had consistently negative results except for mammary tumors. Sprague-Dawley rats (30 males and 30 females in each dose group and 60 male and 60 female controls) were exposed to styrene vapor by inhalation (at 25, 50, 100, 200, and 300 ppm) 4 hours/day, 5 days/week for 52 weeks and then observed until death (Conti et al. 1988). Complete necropsies were performed on all animals. The major organs in all organ systems (respiratory, gastrointestinal, cardiovascular, urinary, reproductive, nervous, lymphohematopoietic, endocrine, musculoskeletal, and cutaneous) and grossly abnormal tissues were examined histopathologically in all groups. There was no significant difference in mortality or body weight between any group and controls. A nonsignificant increase in total malignant tumors was observed in both males and females at 100 ppm but not at the higher concentrations tested. There was a significant increase in malignant mammary tumors in females in all exposure groups.

Cruzan et al. (1998) exposed Sprague-Dawley rats (70 males and 70 females) to styrene vapor at 0, 50, 200, 500, and 1,000 ppm 6 hours/day, 5 days/week for 104 weeks. Rats were sacrificed at 105 and 107 weeks. Complete necropsies were performed on all animals. The major organs in all organ systems (respiratory, gastrointestinal, cardiovascular, urinary, reproductive, nervous, lymphohematopoietic, endocrine, musculoskeletal, and cutaneous) and grossly abnormal tissues were examined histopathologically in the control and high-dose groups. Selected organs and grossly abnormal tissues were examined histopathologically in the intermediate-dose groups. Body-weight gains were lower in the male 500- and 1,000-ppm groups and in the female 200-, 500-, and 1,000-ppm groups compared with controls. There were no significant increases in any tumor type in males or females.

Ponomarkov and Tomatis (1978) gave 21 pregnant BD IV rats an oral gavage with 1,350 mg/kg of styrene in olive oil on gestation day 17. After weaning, progeny (73 males and 71 females) were given styrene at 500 mg/kg via a gastric tube once a week throughout their lifespan or until 120 weeks, when they were sacrificed. The authors indicated that all surviving animals were necropsied with histopathologic examination of all major organs, but the specific organs that were examined were not stated. There was no difference in litter size, body weight, or tumor incidence between the treated and control groups.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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NCI (1979a) gave F344 rats (50 males and 50 females) an oral gavage 5 days/week for 103 weeks at 500 mg/kg or for 78 weeks at 1,000 or 2,000 mg/kg. Complete necropsies were performed on all animals. The major organs in all organ systems (respiratory, gastrointestinal, cardiovascular, urinary, reproductive, nervous, lymphohematopoietic, endocrine, musculoskeletal, and cutaneous) and grossly abnormal tissues were examined histopathologically in all groups except for some moribund animals. The 53-week survival of the males in the high-dose group was six of 50, and the 70-week survival of the females in the high-dose group was seven of 50. The 90-week survival in the medium-dose group was 44 of 50 in both males and females and in the low-dose group 47 of 50 in both sexes. No differences in tumor incidence were observed in either sex at any of the doses compared with the corn-oil vehicle controls.

Conti et al. (1988) used Sprague-Dawley rats (40 males and 40 females) to test oral exposure to styrene at 50 and 250 mg/kg via a gastric tube. Rats were exposed 4 or 5 days/week for 52 weeks and then observed until death. Complete necropsies were performed on all animals. The major organs in all organ systems (respiratory, gastrointestinal, cardiovascular, urinary, reproductive, nervous, lymphohematopoietic, endocrine, musculoskeletal, and cutaneous) and grossly abnormal tissues were examined histopathologically in all groups. Increased mortality was observed in the females in the high-dose group compared with the olive-oil vehicle controls; no significant difference was observed in males. There was no significant difference in body weight or tumor incidences in either sex.

Beliles et al. (1985) used Sprague-Dawley rats (50 treated males, 70 treated females, 76 control males, and 106 control females) to study drinking-water exposure to styrene. Rats were exposed via drinking water for 2 years at 125 or 250 ppm. In males, the daily doses were estimated to be 7.7 and 14.0 mg/kg for the low and high doses, respectively. In females, the daily doses were estimated to be 12.0 and 21.0 mg/kg for the low and high doses, respectively. Complete necropsies were performed on all animals. The major organs in all organ systems (respiratory, gastrointestinal, cardiovascular, urinary, reproductive, nervous, lymphohematopoietic, endocrine, musculoskeletal, and cutaneous) and grossly abnormal tissues were examined histopathologically in the control and high-dose groups, including moribund animals. No observed effects on mortality, tumor rates, or type of tumors were reported. A separate analysis of the data (Huff 1984) found a dose-related increase in combined mammary tumors in females that was significant in terms of trend (p = 0.032) and when the high-dose group was compared to controls (p = 0.039).

Conti et al. (1988) gave Sprague-Dawley rats (40 males and 40 females) four intraperitoneal injections at 2-month intervals (200 mg total); no significant differences in tumor incidence were observed when the exposed rats were compared with the olive-oil vehicle controls. In the same study, the researchers gave

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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Sprague-Dawley rats (40 males and 40 females) a single subcutaneous injection of 50 mg of styrene at the age of 13 weeks and observed them until death; no significant differences were observed when the exposed rats were compared with the olive-oil vehicle controls.

As evident from the study descriptions above, a styrene effect on mammary tumors in rats is contradictory. Rats exposed to styrene by inhalation were reported to have a significant increase in malignant mammary tumors (Conti et al.1988) although inconsistencies in reporting of the data render this observation inconclusive (IARC 1994a). Huff (1984) analyzed data from oral exposure of Sprague-Dawley rats to styrene in the same study and found a significant increase in combined mammary tumors in high-dose females and a significant trend with dose. In contrast with those suggestive findings, no increase in mammary tumors was observed in the NCI (1979a) oral study of styrene-exposed rats, and the inhalation study by Cruzan et al. (1998) found a significant inverse trend between dose and mammary gland carcinoma after styrene inhalation in Sprague-Dawley rats (that is, the incidence decreased with increasing styrene concentration in air). There is no evidence from mouse and rat bioassays of increased cancer incidence at other sites.

Studies of Styrene-7,8-oxide and Styrene Mixtures

A bioassay was conducted with a mixture of 70% styrene and 30% betanitrostyrene in B6C3F1 mice and F344 rats (NCI 1979b). The mixture was administered to male rats by gavage in corn oil at 150 or 300 mg/kg and to female rats at 75 or150 mg/kg. The mixture was administered to mice by gavage in corn oil at 87.5 and 175 mg/kg for mice of both sexes. Each dose group consisted of 50 males and 50 females, and the controls were 20 males and 20 females that were given only corn oil. Rats were exposed for 79 weeks and observed for an additional 29 weeks, and mice were exposed for 78 weeks and observed for an additional 14 weeks. No significant increases in tumors at any site were observed in rats. Significant increases in alveolar or bronchiolar carcinoma and alveolar and bronchiolar adenoma were observed in the low-dose male mice but not the high-dose male mice, which experienced high mortality. Because the bioassay involved a combination of styrene with another substance (betanitrostyrene), the interpretation of findings with respect to potential styrene carcinogenicity is confounded, and the committee did not include it in its evaluation.

Styrene-7,8-oxide, a metabolite of styrene, was evaluated in a cancer bioassay. Styrene-7,8-oxide is the principal metabolite of styrene in rodents and humans, and its carcinogenicity is potentially relevant as supporting information in a determination of the carcinogenicity of styrene in humans. Four studies

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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evaluated tumor response to administration by gavage. In one, B6C3F1 mice and F344 rats (52 males and 52 females per treatment group per species) were given styrene-7,8-oxide by gavage in corn oil 3 days/week for 104 weeks (Lijinsky 1986). Doses were 0, 375, and 750 mg/kg for mice and 0, 275, and 550 mg/kg for rats. Significant increases in forestomach tumors were observed after both high and low doses in both species and sexes. Similarly, significant increases in forestomach tumors were observed in male and female Sprague-Dawley rats (40 per treatment group per sex) that were given styrene-7,8-oxide by gavage in corn oil at 50 or 250 mg/kg for 52 weeks (Conti et al. 1988). Significant increases in forestomach tumors were also observed in BD IV rats given styrene-7,8-oxide by gavage in olive oil at 200 mg/kg (Ponomarkov et al. 1984). The only other tumor response observed was a significant increase in hepatocellular neoplasms in B6C3F1 mice given styrene-7,8-oxide by gavage at 375 mg/kg (but not 750 mg/kg) (Lijinsky 1986).

Styrene-7,8-oxide is a reactive compound, so it is not surprising that tumors occurred primarily in tissues proximal to the site of administration—in the case of gavage, the forestomach. If administered by a different route, or when styrene-7,8-oxide is formed from metabolism of styrene, the distribution of styrene-7,8-oxide in the body would probably be substantially different and would plausibly lead to different sites of tumorigenesis. In view of that, despite the discordant sites of tumors between styrene (lung) and styrene-7,8-oxide (forestomach), positive findings with styrene-7,8-oxide are considered supporting evidence of the carcinogenicity of styrene.

Summary of Evidence from Studies in Animals

In summary, the committee identified studies that showed positive findings of lung tumors in mice after both inhalation and oral administration of styrene in well-conducted chronic bioassays (NCI 1979a; Cruzan et al. 2001). Results of another study that is more limited in value for assessing carcinogenicity (Ponomarkov and Tomatis 1978) are also reasonably consistent with the production of lung tumors in mice after styrene exposure. Contradictory findings on mammary tumors have been observed in rats. For other tumor sites, rats exposed to styrene by both oral and inhalation routes have been consistently negative (Jersey et al. 1978; NCI 1979a; Beliles et al. 1985; Conti et al. 1988; Cruzan et al. 1998); the tumorigenic response appears to be species-specific.

MECHANISTIC AND OTHER RELEVANT DATA

Genotoxicity

Styrene is a highly reactive chemical whose potential for genotoxicity has been investigated for 3 decades. Many studies have been designed to determine

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

whether styrene or styrene-7,8-oxide—its reactive epoxide metabolic product—elicits DNA damage that leads to mutagenic and clastogenic events in animal and human cells or in animals and humans exposed to styrene or styrene-7,8oxide. A comprehensive review of data with respect to carcinogenicity of styrene-7,8-oxide was conducted by the International Agency for Research on Cancer (IARC 1994b). The formal evaluation at that time was that there was sufficient evidence of the carcinogenicity of styrene-7,8-oxide in experimental animals. A later review by IARC (2002) concluded that exposure of humans to styrene leads to the generation of styrene-7,8-oxide-induced DNA adducts and other forms of DNA damage. The overall evaluation by IARC, which attached heavy weight to the evidence of genotoxicity, was that styrene is possibly carcinogenic in humans. NTP also reviewed styrene-7,8-oxide and in 2002 listed it as “reasonably anticipated to be a human carcinogen” (NTP 2002).

DNA adducts are considered mechanism-based biomarkers of exposure to chemical carcinogens and have been used to identify people and populations at risk for cancer and to set exposure limits for occupational carcinogens (Swenberg et al. 2008; Jarabek et al. 2009). The presence of DNA adducts in target tissues reflects the formation of reactive metabolites, such as styrene-7,8-oxide, that bind covalently to DNA and to proteins (Poirier 2012). The presence of structurally modified DNA bases substantially increases the probability that polymerase errors during DNA synthesis will create mutations in genes that may lead to cancer (Knobel and Marti 2011).

There are also reports that oxidative DNA damage, mediated by reactive oxygen species, is caused by exposure of tissues to styrene-7,8-oxide and contributes to its genotoxic effects. A study by Laffon et al. (2002a) that suggested exposure to styrene may result in oxidative DNA damage was cited in the background document for styrene; however, Gamer et al. (2004), using 8-oxoguanine as a biomarker, found no evidence of oxidative stress. In a comparative study of styrene-exposed workers and unexposed clerks (Manini et al. 2009), exposed workers showed lower concentrations of 8-oxoguanine adducts in white blood cell DNA but higher concentrations of 8-oxoguanine in urine. Similar results were obtained by Wongvijitsuk et al. (2011). Considering that 8-oxoguanine is a weak mutagen and is efficiently repaired by base-excision repair, it seems unlikely that oxidative DNA damage plays a strong role in styrene-associated genotoxicity.

The mutagenic and carcinogenic effects of DNA adducts are affected by the efficiency of DNA repair (both base-excision repair, as in the case of oxidative DNA damage, and nucleotide-excision repair of adducts derived from styrene). Thus, susceptibility to styrene genotoxicity may be affected at the individual level by DNA-repair capacity, some aspects of which may be inducible (Vodicka et al. 2004a, 2006).The effects of single-nucleotide polymorphisms on styrene genotoxicity in vivo have been comprehensively reviewed by Vodicka et al. (2006).

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

Evaluation of Genotoxicity Evidence

The committee’s charge was to “integrate the level-of-evidence conclusions, and consider…all relevant information in accordance with RoC listing criteria” (see Appendix B). The RoC includes “studies on genotoxicity (ability to damage genes) and biological mechanisms” for each substance listed (NTP 2011c, p. 3). That information is evaluated with other relevant evidence to address the RoC listing criteria. Specifically, “data derived from studies of tissues or cells obtained from humans exposed to the substance in question, which is particularly valuable in evaluating whether a relevant cancer mechanism is operating in humans,” constitute one of several lines of evidence used to establish whether there is sufficient or limited evidence of carcinogenicity from studies in humans (NTP 2011c).

The committee reviewed the relevant literature, including all recently published studies, with the goal of determining whether it is biologically plausible for styrene to act as a carcinogen through a genotoxic mechanism. The committee’s comprehensive review of scientific peer-reviewed literature on the genotoxicity and mutagenicity of styrene and the dates covered by the search are described in Appendix D. As noted in the Environmental Protection Agency Cancer Guidelines (EPA 2005), one must go beyond simply counting the numbers of studies that report statistically significant results or statistically nonsignificant results on carcinogenesis and related modes of action to reach credible conclusions about the relative strength of the evidence and the likelihood of causality. Accordingly, the committee first categorized evidence pertaining to styrene and styrene-7,8-oxide genotoxic and clastogenic mechanistic events into tables on DNA damage (Table 3-12), sister-chromatid exchanges (Table 3-13), micronuclei (Table 3-14), and chromosomal aberrations (Table 3-15). Studies in each table were categorized as positive if a statistically significant effect was observed. Studies were categorized as negative if they reported an absence of a particular effect (that is, no statistically significant difference from the appropriate control group). Committee members exercised their scientific judgment in categorizing studies, but they did not perform a formal quality assessment of each individual study or make critical judgments regarding study design or methodology, recognizing that all studies cited have been subjected to some form of peer review. Table 3-16 summarizes the evidence. For each mechanistic event (Tables 3-13 to 3-15), the committee used a set of causal criteria (EPA 2005) as general guidance to determine the strength of the overall evidence of causality.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

TABLE 3-12 Studies of DNA Damage Associated with Styrene or Styrene-7,8-oxide (Including Adducts and Strand Breaks)a

Styrene Styrene-7,8-oxide
Positive Negative Positive Negative
  In vitro Bastlová et al. 1995 Vodicka et al. 1996 Marczynski et al. 1997b Pauwels and Veulemans 1998 Laffon et al. 2001b Laffon et al. 2002b Vodicka et al. 2002a Laffon et al. 2003b Cemeli et al. 2009c Fabiani et al. 2012c
Human In vivob Brenner et al. 1991 Maki-Paakkanen et al. 1991 Vodicka et al. 1993 Vodicka et al. 1994 Vodicka et al. 1995 Marczynski et al. 1997a Somorovska et al. 1999 Vodicka et al. 1999 Laffon et al. 2002a Migliore et al. 2002 Shamy et al. 2002 Buschini et al. 2003 Fracasso et al. 2009c Manini et al. 2009c Mikes et al. 2010c Wongvijitsuk et al. 2011c Costa et al. 2012c Holz et al. 1995 Vodicka et al. 2004a Godderis et al. 2004 Hanova et al. 2010c Teixeira et al. 2010c Hanova et al. 2011c
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
Styrene Styrene-7,8-oxide
Positive Negative Positive Negative
  In vitro Sina et al. 1983 Sina et al. 1983 Liu et al. 1988a Dypbukt et al. 1992 Bjørge et al. 1996 Herrero et al. 1997
Rodent In vivob Walles and Orsen 1983d Byfält -Nordqvist et al. 1985d Cantoreggi and Lutz 1993 Pauwels et al. 1996d Vaghef and Hellman 1998d Boogaard et al. 2000b Vodicka et al. 2001b Otteneder et al. 2002 Mikes et al. 2009c Gate et al. 2012c Kligerman et al. 1993 Walles and Orsen 1983d Byfalt-Nordqvist et al. 1985d Lutz et al. 1993e Sasaki et al. 1997d Vaghef and Hellman 1998d Tsuda et al. 2000d Gate et al. 2012c

aStudies were categorized as positive if a statistically significant effect was observed. Studies were categorized as negative if there was an absence of a particular effect (that is, no statistically significant change from the appropriate control group); bRoute of administration is inhalation unless noted otherwise; cIdentified through committee’s literature search; dDenotes chemical administration through intraperitoneal injection; eDenotes chemical administration through oral gavage.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

TABLE 3-13 Studies of Sister-Chromatid Exchanges Associated with Styrene or Styrene-7 8-oxidea

Styrene Styrene-7,8-oxide
Positive Negative Positive Negative
  In vitro Norppa et al. 1980a Norrpa et al. 1983a Norppa and Vainio 1983 Norppa and Tursi 1984 Chakrabarti et al. 1993 Lee and Norppa 1995 Norppa et al. 1980a Norppa et al. 1983a Pohlova et al. 1984 Pohlova and Sram 1985 Zhang et al. 1993 Lee and Norppa 1995 Uüskula et al. 1995 Chakrabarti et al. 1997 Ollikainen et al. 1998 Laffon et al. 2001b
Human In vivob Andersson et al. 1980 Camurri et al. 1983 Camurri et al. 1984 Yager et al. 1993 Hallier et al. 1994 Tates et al. 1994 Artuso et al. 1995 Karakaya et al. 1997 Biro et al. 2002 Laffon et al. 2002a Teixeira et al. 2004 Teixeira et al. 2010e Costa et al. 2012e Meretoja et al. 1978a Watanabe et al. 1981 Watanabe et al. 1983 Hansteen et al. 1984 Maki-Paakkanen 1987 Kelsey et al. 1990 Brenner et al. 1991 Maki-Paakkanen et al. 1991 Sorsa et al. 1991 Van Hummelen et al. 1994 Holz et al. 1995 Rappaport et al. 1996
Rodent In vitro De Raat 1978 Norppa and Tursi 1984 Norppa et al. 1983b De Raat 1978 Nishi et al. 1984 Von der Hude et al. 1991
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
Styrene Styrene-7,8-oxide
Positive Negative Positive Negative
Rodent In vivob Conner et al. 1979 Conner et al. 1980 Sharief et al. 1986f Kligerman et al. 1992 Preston and Abernethy 1993d Conner et al. 1982c Sinsheimer et al. 1993c,f Norppa et al. 1979c Conner et al. 1982c

aStudies were categorized as positive if a statistically significant effect was observed. Studies were categorized as negative if there was an absence of a particular effect (that is, no statistically significant change from the appropriate control group); bRoute of administration is inhalation unless noted otherwise; cIdentified from IARC (1994b); dIdentified from IARC (2002); eIdentified through committee’s literature search; fDenotes chemical administration through intraperitoneal injection.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

TABLE 3-14 Studies of Micronuclei Associated with Styrene or Styrene-7,8-oxidea

Styrene Styrene-7,8-oxide
Positive Negative Positive Negative
  In vitro Linnainmaa et al. 1978b Linnainmaa et al. 1978a Linnainmaa et al. 1978b Laffon et al. 2001b Speit et al. 2012d
Human In vivob Meretoja et al. 1977 Hogstedt et al. 1983 Nordenson and Beckman 1984 Brenner et al. 1991 Tates et al. 1994 Holz et al. 1995 Laffon et al. 2002a Godderis et al. 2004 Teixeira et al. 2004 Vodicka et al. 2004a Migliore et al. 2006a Maki-Paakkanen 1987 Hagmar et al. 1989 Maki-Paakkanen et al. 1991 Sorsa et al. 1991 Tomanin et al. 1992 Yager et al. 1993 Van Hummelen et al. 1994 Anwar and Shamy 1995 Karakaya et al. 1997 Hanova et al. 2010d Teixeira et al. 2010d Costa et al 2012d
  In vitro Turchi et al 1981
Rodent In vivob Penttila et al. 1980c Norppa 1981c,e Kligerman et al. 1992 Gate et al. 2012d Fabry et al. 1978c Penttila et al. 1980c Gate et al. 2012d

aStudies were categorized as positive if a statistically significant effect was observed. Studies were categorized as negative if there was an absence of a particular effect (that is, no statistically significant change from the appropriate control group); bRoute of administration is inhalation unless noted otherwise; cIdentified from Scott and Preston (1994a); dIdentified through committee’s literature search; eDenotes chemical administration through intraperitoneal injection.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

TABLE 3-15 Studies of Chromosomal Aberrations Associated with Styrene or Styrene-7,8-oxidea

Styrene Styrene-7,8-oxide
Positive Negative Positive Negative
  In vitro Linnainmaa et al. 1978a Linnainmaa et al. 1978b Pohlova et al. 1984g Pohlova and Sram et al. 1985 Jantunen et al. 1986 Linnainmaa et al. 1978a Linnainmaa et al. 1978b Fabry et al. 1978 Norppa et al. 1981 Pohlova et al. 1984g Pohlova and Sram 1985
Human In vivob Meretoja et al. 1977 Meretoja et al. 1978a Fleig and Thiess 1978 Hogstedt et al. 1979 Andersson et al. 1980 Dolmierski et al. 1983 Camurri et al. 1983 Camurri et al. 1984 Hansteen at al. 1984 Forni et al. 1988 Tomanin et al. 1992 Tates et al. 1994 Artuso et al. 1995 Anwar and Shamy 1995 Lazutka et al. 1999 Somorovska et al. 1999 Helal and Elshaf 2013f Thiess et al. 1980 Watanabe et al. 1981 Watanabe et al. 1983 Nordenson and Beckman 1984 Pohlova and Sram 1985 Maki-Paakkanen 1987 Jablonicka et al. 1988 Hagmar et al. 1989 Maki-Paakkanen et al. 1991 Sorsa et al. 1991 Oberheitmann et al. 2001 Biro et al. 2002 Vodicka et al. 2004a Vodicka et al. 2004c Migliore et al. 2006b
Rodent In vitro Matsuoka et al. 1979 Ishidate andYoshikawa 1980 Matsuoka et al. 1979 Turchi et al. 1981
Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×
Rodent In vivob Meretoja et al. 1978be Loprieno et al. 1978e,h Norppa et al. 1980be Sbrana et al. 1983e,h Sinha et al. 1983e Sharief et al. 1986e Kligerman et al. 1992 Preston and Abernethy 1993d Loprieno et al. 1978e,h Sinsheimer et al. 1993c,e Fabry et al. 1978e Norppa et al. 1979e

aStudies were categorized as positive if a statistically significant effect was observed. Studies were categorized as negative if there was an absence of a particular effect (that is, no statistically significant change from the appropriate control group); bRoute of administration is inhalation unless noted otherwise; cIdentified from IARC (1994a,b); dIdentified from IARC (2002); eIdentified from Scott and Preston (1994a); fIdentified through committee’s literature search; gDenotes chemical administration through intraperitoneal injection; hDenotes chemical administration through oral gavage.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

TABLE 3-16 Summary of Genotoxic Effects of Styrene in Humans and Rodents

DNA Damage Sister-Chromatid Exchanges Micronucli Chromoso Abberational
Styrene SO Styrene SO Styrene SO Styrene SO
Human In vitro N/A + (10/0) + (6/0) + (10/0) + (1/0) + (4/0) + (5/0) + (6/0)
In vivo +/- (17/6) N/A +/- (13/12) N/A -/+ (11/12) N/A +/- (17/15) N/A
Rodent In vitro + (1/0) + (5/0) + (3/0) + (3/0) N/A + (1/0) +/- (2/1) + (1/0)
In vivo + (10/1) + (6/1) + (4/1) +/- (2/2) +/- (2/2) - (0/3) - (1/7) +/- (2/2)

“+” All or most of the studies indicate the effect.

“+/-” Most of the studies indicate the effect, although many studies show lack thereof.

“-/+” Most of the studies indicate lack of the effect, although many positive studies have been published.

“-” All or most of the studies indicate lack of the effect.

Parentheses indicate total number of studies demonstrating the effect or lack thereof.

N/A, no studies identified.

Abbreviations: SO, styrene-7,8-oxide.

Genotoxic and Clastogenic Effects of Styrene and Styrene-7,8-Oxide on in Vitro Human and Rodent Cells

The evidence available on all forms of DNA and genetic damage shows clearly that DNA damage (Table 3-12) and clastogenic effects (Tables 3-13 through 3-15) are observed when human or rodent cells are incubated in the presence of styrene or styrene-7,8-oxide. Studies conducted in various in vitro model systems, including freshly isolated human blood cells and whole blood, were consistently strong (one negative study identified among dozens of positive studies). Furthermore, positive effects were observed in connection with many types of mechanistic events that pertain to genotoxicity.

DNA adducts initiate carcinogenesis; however, those adducts may be undetectable in target tissues in later stages of the carcinogenesis process. DNA adducts also form in non-target tissues and bioactivation may occur at sites other than the target organ (Swenberg et al. 2008). Additionally, mutations induced by a specific adduct may require additional mutations to produce cancer (Vogelstein et al. 2013). The committee considered this mechanistic information in evaluating whether styrene,7-8,oxide–DNA adducts contribute to the development of human cancer.

The committee made several observations about evidence in the in vitro studies that used human and rodent cells. All studies that were evaluated in this category used purified styrene or styrene-7,8-oxide; thus, chemical specificity was firmly established. Most studies used positive and negative controls, and this strengthens the chemical specificity of the associations between exposure and genotoxicity. Temporality of the observed associations between styrene, styrene-7,8-oxide, and genotoxicity was clearly established. And concentration–response relationships between genotoxic effects and styrene or styrene-7,8oxide were observed in studies that were designed to measure such effects.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

The committee concludes that the evidence of genotoxicity and clastogenicity of styrene and styrene-7,8-oxide in human and rodent cells in vitro is consistent, strong, and specific with respect to exposure to styrene or styrene-7,8oxide. Temporal and exposure–response relationships have been established. These mechanistic events have been studied extensively in human cells, and the results are consistent with those found in cells obtained from rodents.

Genotoxic and Clastogenic Effects in Animals or Humans Exposed to Styrene and in Rodents Exposed to Styrene-7,8-Oxide

Many studies have attempted to evaluate the genotoxicity and clastogenicity of styrene in humans exposed in an occupational setting. Styrene-induced DNA damage was found in many of the studies (Table 3-12). Most studies in rodents demonstrate sister-chromatid exchanges after exposure to styrene or styrene-7,8-oxide, but only about half of the human studies that examined styrene exposure demonstrated the same effects (Table 3-13). With respect to micronuclei, studies of humans or rodents exposed to styrene are also equally divided; however, formation of micronuclei was not observed in three studies of rodents exposed to styrene-7,8-oxide (Table 3-14). For chromosomal aberrations (Table 3-15), about half of the studies of humans exposed to styrene show a significant effect. In exposed rodents, formation of chromosomal aberrations was not found in most of the studies of styrene exposure or in half studies of styrene-7,8-oxide exposure.

In rodent studies of styrene and styrene-7,8-oxide, evidence was less strong but mostly positive for DNA damage, sister-chromatid exchanges, and micronuclei; however, the total number of rodent studies was less than the number of studies of exposed humans. Effects of styrene or styrene-7,8-oxide were well documented, and this helps to establish that exposure to styrene or styrene-7,8-oxide was associated with the positive and negative observations. Studies of rodents provided evidence of a temporal relationship for the observed association in that effects were observed only after exposure to the agents in question. Studies of rodents also provided strong evidence of a genotoxic concentration–response relationship.

Evidence of genotoxicity and clastogenicity of styrene in exposed humans is generally strong, although some studies reported no effects. The strongest positive observations involved DNA-damage end points found in studies of diverse cohorts of subjects exposed to styrene in various occupations. Various assays were used to evaluate the mechanistic events, and the statistical significance of the effects was firmly established in the positive studies. Some investigators established exposure to styrene through biomonitoring, but many of their studies were of occupational groups and the contributions from other toxic agents cannot be excluded. An exposure–response association for several biomarkers of genotoxicity and clastogenicity was demonstrated through workplace dosimetry (Fracasso et al. 2009) or the use of urinary biomarkers of exposure (Teixeira et al. 2010).

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

The committee concludes that the biologic plausibility of genotoxic and clastogenic effects of styrene, as observed in exposed animals and humans, is supported by solid and extensive observational evidence. Several negative studies notwithstanding, the evidence is generally strong and specific with respect to styrene or styrene-7,8-oxide exposure. Both temporal and exposure–response relationships have been clearly established by diverse studies, including studies of exposed humans. That most of the observational evidence used in this evaluation is derived from studies of humans exposed to styrene substantially strengthens the relevance of the mechanistic evidence to the epidemiologic findings.

Summary of Evidence on Genotoxicity of Styrene

Styrene requires metabolic activation to electrophilic intermediates (for example, styrene-7,8-oxide) for it to be able to form covalent adducts with DNA. DNA damage, reflected by the presence of styrene-7,8-oxide-derived DNA adducts in human tissues, is highly likely to generate mutations, some of which may occur in genes that lead to cancer in susceptible people. The presence of DNA adducts—occurring predominantly at the N7, N2, and O6 positions of guanine—has been amply demonstrated in cell culture, experimental animals, and, most important, lymphocytes of workers occupationally exposed to styrene (Table 3-12). These findings have been reproduced in many laboratories and provide strong evidence of the genotoxic effects of styrene.

Unless removed by nucleotide excision repair, styrene-7,8-oxide DNA adducts invariably serve as a substrate for DNA polymerases, including specialized lesion-bypass polymerases that may either block DNA synthesis at the lesion site or catalyze the introduction of nucleotides that lead to mutational changes. Evidence of the mutagenicity of styrene and styrene-7,8-oxide was established early on in studies of bacteria and other nonmammalian systems (IARC 1994a, 2002). Consistently positive results, with or without metabolic activation, have been reported for gene-mutation end points in bacteria and other model organisms exposed to styrene-7,8-oxide. In studies with styrene, results were less consistent in the absence of metabolic activation; positive results were reported in Salmonella typhimurium strains TA1530 or TA1535 with the addition of an exogenous metabolic activation system (IARC 2002). Additional evidence of the mutagenic potential of styrene or styrene-7,8-oxide includes studies of Chinese hamster (V79) cells, mouse lymphoma (L5178Y), and human T lymphocytes (HPRT locus) (Vodicka et al. 2006). Moreover, many studies of occupationally exposed workers report a positive association between styrene exposure and frequency of sister-chromatid exchanges, micronuclei, and chromosomal aberrations (Tables 3-13 to 3-15). Although the evidence for and against an association of clastogenic effects with styrene exposure in humans is nearly equally divided, the diversity of studies, exposure scenarios, and methodology support the biologic plausibility of the genotoxicity of styrene in exposed humans. Even low-concentration occupational exposure to styrene was shown to result in an increase in various genotoxic effects (Wongvijitsuk et al. 2011).

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

Genotoxic effects have been explored in comparisons with structurally related epoxides, many of which are classified as human carcinogens or as likely to be human carcinogens (Fabiani et al. 2012).

The committee concludes that the genotoxicity and mutagenicity of styrene has been thoroughly and comprehensively investigated. The evidence reviewed by the committee also indicates that styrene-7,8-oxide, a major reactive metabolite of styrene that is produced in exposed humans, reacts with DNA to form covalent adducts and other premutagenic forms of DNA damage, which result in genotoxic effects. The committee recognizes that styrene-7,8-oxide may not be the only genotoxic metabolite of styrene. For example, styrene-3,4oxide may also be mutagenic (Watabe et al. 1982). However, to the committee’s knowledge, the potential contribution of styrene-3,4-oxide to the carcinogenic response to styrene and the potential contribution of other aromatic-ring metabolites of styrene in addition to styrene-7,8-oxide have not been investigated.

Overall, the observations in various studies performed over the last 3 decades have been consistent. Temporal and exposure–response relationships have been established. Not only is the experimental evidence extensive, it is likely to be relevant to all target tissues that have been associated with cancer after exposure to styrene. Causality is strengthened by the large amount of evidence obtained from studies of exposed humans.

Immunosuppression

The human immune system plays a critical role in defending the body against external pathogens and in being on perpetual alert against internally transforming (premalignant) or transformed malignant cells (cancers). The concept of “immune surveillance” describes those functions specifically and relies on the involvement of a network of white blood cells, also known as leukocytes. There are two basic types of leukocytes: phagocytes (including neutrophils, monocytes, and macrophages, which are important in innate immunity) and lymphocytes (including T, B, and natural killer [NK] cells that allow the immune system to recognize, memorize, and specifically respond to previous invaders). NK lymphocytes are critical for the innate and adaptive immune systems because they can destroy virus-infected or malignantly transformed cells. Therefore, they are extremely important in immunosurvillance. When deficiency is present in one or more immune components as a result of congenital or acquired conditions, immunodeficiency or immunosuppression might occur and the incidence of malignancies might increase. For example, Kaposi sarcoma, NHL, and cervical cancers occur at a higher rate in people who have acquired immunodeficiency syndrome (AIDS) as a result of infection by human immunodeficiency virus (HIV) (Labarga 2013). In addition, all de novo neoplasms have a greater incidence in renal-transplantation patients because of antilymphocytic treatment (Andrés 2005).

As discussed in Chapter 2, NTP identified immunosuppression as a possible mechanism by which styrene exposure could lead to malignancies, but the

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

background document and the substance profile lack strong evidence to support this mechanism. Therefore, the committee undertook an independent literature search to identify research that would inform the topic (see Appendix D). The committee considered studies relevant if they reported data on changes in basic hematologic measures, such as white blood cell (WBC) count and WBC differential count.2 The committee also included studies that reported such measures as weight of lymphoid organs and expression of functional markers. Efforts were made to identify and include studies that reported effects on local, systemic, innate, and adaptive immunity in exposed animals or humans. Studies that reported genotoxic measures were excluded from this section because they are discussed in more detail in the genotoxicity sections of Chapter 2 and the present chapter. The committee’s literature search yielded 233 results, 19 of which were relevant articles that were not already cited in the background document for styrene. Eight of the studies documented hematologic effects in experimental animal models or in animal cells (Table 3-17), and 11 described hematologic effects in humans or human cells (Table 3-18). Those studies were reviewed in detail by the committee and are discussed below.

Animal Studies

Leukocytopenia and Lymphocytopenia

Two studies described hematologic effects in peripheral blood that were consistent with leukocytopenia and lymphocytopenia. Brondeau et al. (1990) observed a transient decrease in WBCs (leukopenia) in rats exposed to styrene for 4 hours. Seidel et al. (1990) observed decreased lymphocyte counts (lymphocytopenia) in peripheral blood of female C57BL/6 x DBA/2 hybrid mice after exposure to styrene.

Systemic vs Localized Lymphoid Organs

In animal models, the response of lymphocytic organs to styrene exposure can vary at different locations. For example, the weight of the spleen was significantly lower in mice exposed to styrene than in controls, whereas the weights of peripheral lymph nodes were higher in exposed mice than in controls (Dogra et al. 1989). Lymphocytic proliferation in the spleen was significantly lower in styrene-7,8-oxide-exposed C57BL/6 mice than in styrene-exposed mice; this indicates that an active intermediate form of styrene may be needed for systemic inhibition to occur (Grayson and Grill 1986). In contrast, allergic responses

_____________________

2A differential blood count gives the relative percentage of white blood cell types, such as neutrophils, lymphocytes, monocytes, eosinophils, and basophils.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

TABLE 3-17 Immune Effects of Inhalation or Intraperitoneal Exposure to Styrene in Animals

Cell Type Hematologic Effects Reference
RBC ↑ erythroid by inhalation Nano et al. 2000
No change by intraperitoneal administration Nano et al. 2000
WBC ↓ by 4h exposure, but innate rather than specific effects cannot be ruled out Brondeau et al. 1990
Neutrophils ↓ numbers of promyelocytes and myelocytes temporarily by inhalation (chronic) but unchanged by intraperitoneal administration (acute) Nano et al. 2000
Monocytes ↓ nitro-blue tetrazolium, monocyte attachment, phagocytic activity Dogra et al. 1989
NK cells ↓ activity by styrene, styrene-7,8-oxide Grayson and Gill 1986
Lymphocyte ↓ numbers Seidel et al. 1990
↓ spleen weight Dogra et al. 1989
↓ splenic lymphocyte counts vs no change in lymphocyte counts in regional or peripheral lymph nodes or bone marrow Dogra et al. 1989
T cells ↑ interferon-gamma in local lymph nodes by inhalation Ban et al. 2003
↑ T-helper lymphocyte cytokine and interleukin level Ban et al. 2006
↑mitogen-stimulated proliferation Sharma et al. 1981; Dogra et al. 1989
↑ delayed-type hypersensitivity Dogra et al. 1989
B cells ↓ immunoglobulin M plaque-forming unit Dogra et al. 1989
↑ mitogen-stimulated proliferation at lowest and middle doses Dogra et al. 1989
Stem cells Unaffected in CFU-S and CFU-C but lower in BFU-E and CFU-E although statistical difference could not be reached Seidel et al. 1990

Abbreviation: BFU-E, burst-forming unit-erythroid; CFU-C, colony-forming unit in culture; CFU-E, colony-forming unit-erythrocyte; CFU-S, colony-forming unit-spleen; NK, natural killer cell; RBC, red blood cell; WBC, white blood cell.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

TABLE 3-18 Immune Effects of Inhalation Exposure to Styrene in Humans

Cell type Hematologic Effects Reference
RBC ↓ RBC and hermatocrit Checkoway and Williams 1982
WBC ↓ absolute neutrophils Checkoway and Williams 1982
No difference in CBC Hagmar et al. 1989; Tulinska et al. 2000; Biro et al. 2002; Jahnova et al. 2002
↑ WBC Somorovska et al. 1999
Monocytes ↑ adherent molecule expression Somorovska et al. 1999
↑ percentage Hagmar et al. 1989; Stengel et al. 1990; Tulinska et al. 2000; Jahnova et al. 2002
↓ percentage Khristeva 1986
↑ necrosis, apoptosis, increased bcl-2 and raf-1 proteins Diodovich et al. 2004
Lymphocyte ↓ lymphocytes Tulinska et al. 2000
No change Biro et al. 2002
↑ lymphocytes Khristeva 1986
T cells ↓ numbers Tulinska et al. 2000
↑ CD4+ T (Th) cells Mutti et al. 1992; Bergamaschi et al. 1995; Biro et al. 2002
No difference in mitogen-induced proliferation of lymphocytes Hagmar et al. 1989; Somorovska et al. 1999
↓ mitogen-induced proliferation of lymphocytes Somorovska et al. 1999; Tulinska et al. 2000; Jahnova et al. 2002
↓ large-granule lymphocytes Somorovska et al. 1999
NK cells ↑ NK cells Mutti et al. 1992; Bergamaschi et al. 1995
↓ NK function (K562 cell lysis) Bergamaschi et al. 1995
B cells No change in numbers Mutti et al. 1992; Tulinska et al. 2000
↑ CD25+ expression in B cells Bergamaschi et al. 1995
No change in mitogen-induced proliferation of lymphocytes Hagmar et al. 1989; Tulinska et al. 2000; Jahnova et al. 2002

Abbreviation: CBC, complete blood count; CD4, cluster of differentiation 4; NK, natural killer cell; RBC, red blood cell; WBC, white blood cell.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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through such mechanisms as increased interferon-gamma, interleukin (specifically IL-4, IL-5, and IL-13), and immunoglobulin E (IgE) production were observed more in lung and lymph nodes than in those produced from lymphocytes in the spleen of female BALB/c mice (Ban et al. 2003, 2006).

Innate vs Adaptive Immunity

Immune responses are typically divided into two categories—innate (nonspecific) responses and adaptive (antigen-specific) responses. Monocytes, macrophages, neutrophils, and NK cells are the main effector cells in innate immunity, and T and B lymphocytes are part of adaptive immunity. In the studies reviewed by the committee, styrene generally had more suppressive effects than stimulatory effects on innate immunity. For example, a substantial impairment was observed in macrophage and monocyte functional studies and resulted in a reduction in nitroblue tetrazolium, changes in surface attachment, and changes in phagocytic indexes in mice exposed to styrene (Dogra et al 1989). In addition, in a dose-dependent manner, styrene and styrene-7,8-oxide were strong suppressors of NK-cell activity in exposed mice, whereas cytotoxic T-cell activity was not affected (Grayson and Grill 1986).

In contrast, styrene exerted more stimulatory effects on adaptive cellular immunity in mice by enhancing delayed hypersensitivity (also known as type IV hypersensitivity) (Dogra et al. 1989), mitogen-stimulated lymphoblastic transformation (Sharma et al. 1981), increased production of interferon-gamma and cytokines, and increased production of interleukins by T-helper type 2 lymphocytes (Sharma et al. 1981; Dogra et al. 1989; Ban et al. 2003, 2006). For B lymphocytes, Dogra et al. (1989) observed reduced IgM plaque-forming colonies but increased liposaccharide-stimulated proliferation.

Hematopoietic Malignancy

The committee found two animal studies that provided information on hematopoietic measures of malignancies (Seidel et al. 1990; Nano et al. 2000). Animals exposed to styrene had reduced erythroid lineage colony-forming function (specifically, burst-forming unit erythroid [BFU-E] and colony-forming unit erythroid [CFU-E]), but normal colony-forming unit function in the spleen (CFU-S) and colony-forming unit function in culture (CFU-C) (Seidel et al. 1990). Nano et al. (2000) aimed to determine whether there was a higher frequency of malignancies in hematopoietic tissues of rats treated with styrene by either injection or inhalation; they did not observe an increase in the frequency of preleukemic or leukemic disorders in rats exposed to styrene, although decreased promyelocytes and myelocytes were observed after exposure by inhalation (Nano et al. 2000).

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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Human Studies

Leukocytopenia and Lymphocytopenia

The studies of humans exposed to styrene reported inconsistent results for WBC and lymphocyte counts. Abnormal WBC differential was identified in two studies (Somorovska et al. 1999; Jahnova et al. 2002), but more results showed either normal complete blood counts or increased WBCs in exposed people (Hagmar et al. 1989; Somorovska et al. 1999; Tulinska et al. 2000; Biro et al. 2002; Jahnova et al. 2002).

Systemic vs Localized Lymphoid Organs

The committee did not identify any studies of humans that reported systemic vs localized effects on the immune system after exposure to styrene.

Innate vs Adaptive Immunity

The committee identified studies that reported effects on the innate immune system following exposure to styrene. Increases in monocytes or monocytosis were reported in five of seven studies (Hagmar et al. 1989; Stengel et al. 1990; Somorovska et al. 1999; Tulinska et al. 2000; Jahnova et al. 2002). Only one study found a decrease in monocytes (Khristeva 1986) and another found that necrosis and apoptosis were increased in monocytes (Diodovich et al. 2004). For NK cells, two studies found that the number of NK cells were increased in workers exposed to styrene (Mutti et al. 1992; Bergamaschi et al. 1995). Bergamaschi et al. (1995) also performed a functional study of NK cells (that is, in vitro lysis of leukemia cell lines) and demonstrated that workers exposed to styrene had significantly lower cytotoxic activity toward leukemia cells than the control group. On the basis of those results, styrene might have suppressive effects on NK cells, but more studies are needed before a stronger conclusion can be reached.

Among the studies that investigated effects of styrene on adaptive immunity, inconsistent results were observed between the number of lymphocytes in workers exposed to styrene and the number in controls. For example, Khristeva (1986) reported an increase in the number of lymphocytes, but Tulinska et al. (2000) observed a decrease in the number of lymphocytes and Biro et al. (2002) found no change. Three studies found a decrease in mitogen-induced T-cell proliferation (Somorovska et al. 1999; Tulinska et al. 2000; Jahnova et al. 2002), and two found no difference between exposed and non-exposed groups (Hagmar et al. 1989; Somorovska et al. 1999). Most of the studies found no change in the number of B lymphocytes and no change in mitogen-induced proliferation of B lymphocytes in workers exposed to styrene (Hagmar et al. 1989; Mutti et al. 1992; Bergamaschi et al. 1995; Tulinska et al. 2000; Jahnova et al. 2002).

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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Conclusions on Immunosuppression Evidence

As mentioned in Chapter 2 and above, the background document and the substance profile lack strong evidence to support immunosuppression as a potential mechanism of carcinogenesis, so the committee undertook a literature search (see Appendix D). No relevant studies of the immunosuppressive effects of styrene were identified that were not available to NTP (that is, all relevant articles were published by June 10, 2011). After reviewing the relevant studies, the committee determined that the evidence on immune effects after exposure to styrene varies and is inconsistent. In animals, inhibitory effects were observed mainly on the innate immune system, including decreases in lymphocyte counts and weights in the spleen, suppressed monocyte and macrophage activity, and suppressed NK-cell activity. In adaptive immunity, stimulatory effects were observed in cellular immunity, including increased type IV hypersensitivity and increased production of cytokines, interferon-gamma, and interleukins. In contrast, effects on humoral immunity in styrene-exposed animals varied. For example, IgM plaque-forming cells were decreased, but lipopolysaccharideinduced proliferation was increased. In humans exposed to styrene, effects were more varied and both suppressive and stimulatory effects were observed. Additional research is needed to understand the effects of styrene on the immune system and to explore whether immunosuppression is a possible mechanism for styrene-induced carcinogenesis.

Cytotoxicity

The use of cytotoxic responses to investigate the mode of action by which exposure to metabolically activated compounds, such as styrene, produces tumors depends on a clear definition of the conditions that render a specific organ or tissue susceptible to injury. As outlined in the section “Metabolism and Toxicokinetics” above, many factors contribute to those conditions. Recent literature regarding cytotoxicity of styrene addresses three general questions: Which isozymes of the cytochrome P450 mono-oxygenase system are involved in metabolic activation? What are the chemical nature and reactivity of the metabolites? Which antioxidants and phase II enzymes interact with the reactive metabolites to modulate toxicity?

Pulmonary and Hepatic Toxicity

Recent studies of the mechanisms by which styrene produces cytotoxic injury have relied on the cytotoxic response in the lungs, and occasionally the liver, of one species: the mouse. The relevance of bioactivation (by cytochrome P450 mono-oxygenases) and detoxification (by glutathione S-transferases and epoxide hydrolases) pathways has been evaluated by using relatively nonspecific assays (Carlson 2010b, 2011a,b, 2012; Meszka-Jordan et al. 2009; Shen et al.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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2010). For substances released into the airway space, bronchoalveolar-lavage fluid has been analyzed for protein, cells, and succinic dehydrogenase. For the liver, serum has been analyzed for sorbitol dehydrogenase. Although those nonspecific approaches appear to provide reliable screening tools and reflect the overall responses of the organs, they lack sufficient specificity to define the response in the presumed target cells for styrene, the Clara cells. That is especially true in the mouse lung, in which cells that have high metabolic potential are not restricted to the terminal bronchioles but are distributed throughout the airway tree, with some activity in the gas-exchange area (Buckpitt et al. 1995). Studies with another CYP450-activated cytotoxic aromatic hydrocarbon, naphthalene, have also documented that acute Clara cell injury increases in terminal bronchioles as the intraperitoneal dose is elevated and that injury extends about as far as lobar bronchi at higher doses (Plopper et al. 1992). When naphthalene is administered via inhalation, acute injury is equal to or greater in proximal bronchi than that produced in terminal bronchioles (West et al. 2001).

Other studies of styrene have assessed toxicity by examining proliferation in the presumed target area (terminal bronchioles). Toxicity was determined on the basis of differential counts of cells that have undergone proliferation and that have incorporated and expressed a DNA precursor (5-bromo-2’-deoxyuridine, BrdU) (Cruzan et al. 2012, 2013). The committee notes that restricting the histopathologic and quantitative analysis to terminal bronchioles may not accurately characterize the full response, because the cells that are most likely to be undergoing replication, and most of their daughter cells, are also the cells that are most likely to be damaged by bioactivated cytotoxicants. In addition, at higher doses, the level of cell death may be so high that repopulation of distal airways is principally by progenitor cells that are found in more proximal airways and at airway bifurcations (Stripp et al. 1995; Lawson et al. 2002).

Kaufmann et al. (2005) reported high levels of labeled cells in proximal bronchi following 3 days of exposure to styrene and two of its metabolites, styrene-7,8-oxide and 4-vinylphenol. Further complicating the interpretation of BrdU–incorporation studies of styrene cytotoxicity is the fact that epithelial cells injured by initial exposure to a cytotoxic agent undergo a cycle of necrosis and exfoliation of injured cells and squamation and proliferation of surviving cells, followed by migration and differentiation of newly produced cells to repopulate injured sites. The first phase is usually complete by 2 to 3 days following a single exposure and the second phase by 5 to 7 days following exposure. The timing depends on the route and concentration of the toxicant exposure. This process has been well documented for the oxidant gas ozone (Paige and Plopper 1999; Plopper et al. 2001) and for naphthalene (Van Winkle et al. 1995; Lawson et al. 2002), and seems to be the case for styrene based on observations by Kaufmann et al. (2005). When this injury–repair cycle occurs in the presence of elevated levels of the cytotoxicant, as are produced by repeated daily exposures, the repaired population becomes tolerant to further injury, obviating the need for proliferation and repair, even at doses approaching the LD50 (the dose that is lethal to 50% of the test organisms). The production of tolerance has been doc-

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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umented for ozone (Paige and Plopper 1999; Plopper et al. 2001), nitrogen dioxide (Kubota et al. 1987), naphthalene (O’Brien et al. 1989; West et al. 2003), 4-ipomeanol (Boyd et al. 1981), and coumarin (Born et al. 1999). Assessments of metabolite reactivity and cellular antioxidant responses have relied on direct assays of relevant cellular chemicals either in isolated target cells or in organ homogenates or serum (Carlson 2010a; Harvilchuck and Carlson 2009; Harvilchuck et al. 2008, 2009).

Bioactivation by Cytochrome P450 Mono-oxygenases

A review cited in the background document for styrene listed a substantial number of CYP450 isozymes that have been identified in the lungs and liver of mice, rats, and humans as having the ability to metabolize styrene to styrene-7,8-oxide and other metabolites (Vodicka et al. 2006). A more recent review summarizes the large number of isozymes found in human lung (Carlson 2008). Although the specific CYP450 mono-oxygenases capable of catalyzing the metabolism of styrene have been reported, the committee found almost no available information on the kinetics of the process or an evaluation of the catalytic efficiencies of the enzymes involved (that is, Kcat/Km). Thus, it is still not known which isozymes are critical for the generation of metabolites that result in cytotoxicity. Of further concern is the inadequate characterization of possible compensatory changes in gene expression in the CYP2F2–null animals. No data were identified that demonstrated how the null animals differed from the wild-type in terms of disposition kinetics of styrene or styrene-7,8-oxide.

A recent in vitro study that used lung and liver microsomes, principally from mice, has identified additional phenolic metabolites whose production appears to be based primarily on the activity of two CYP450 isozymes, CYP2F2 and CYP2E1, on the basis of modestly selective CYP450 inhibitors, and on the basis of studies that used very high substrate concentrations (500 µM) (Shen et al. 2010). The study also strongly emphasized that there is active metabolism of styrene in both the liver and the lung. However, the toxicity of the metabolites was tested only in the mouse lung and only at concentrations that did not generate toxicity by the parent compounds, styrene and styrene-7,8-oxide, or by any of the phenols except 4-vinylphenol. It is not clear how the liver would respond to those metabolites or to what degree production of the metabolites by the liver might contribute to toxic responses in the lung.

Three studies that used the same strain of CYP2F2 knockout mice demonstrated that metabolism by the 2F2 isozyme is critical for the production of high levels of distal bronchiolar cytotoxicity in lungs of mice, whether styrene is administered via intraperitoneal injection (Carlson 2012; Cruzan et al. 2012, 2013) or orally (Cruzan et al. 2012). Liver toxicity was also present in both deficient and wild-type mice (Carlson 2012). Metabolism of styrene to the R- and S-styrene oxide enantiomers was identical in the liver of wild-type and knockout mice but markedly reduced in the lungs of knockout mice (Carlson 2012). Although CYP2F2 knockout mice appear to be insensitive to styrene exposure,

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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leading the authors to conclude that this is a key enzyme associated with the metabolic activation of styrene, no data were presented to demonstrate a change in the rates of metabolism in airways of knockout mice compared with wild-type mice. Furthermore, although the knockout animals were characterized to determine whether there were compensatory changes in the concentration of CYP450s, no attempts were made to evaluate alterations in proteins associated with detoxification. It is not clear what the full metabolic potential of the lungs and liver of the knockout animals are for metabolizing styrene to other metabolites.

On the basis of an assay of bronchiolar epithelial proliferation, bronchiolar toxicity, produced by both styrene-7,8-oxide enantiomers, was markedly lower in knockout than in wild-type mice and is equal to that of carrier-treated controls (Cruzan et al. 2012). Whether this was true for epithelium in other airways that were more proximal was not assessed. The study also found that the portion of bronchiolar epithelial cells, which contained BrdU labelling, actually decreased at higher doses of styrene, and this suggests that cells that have the potential for replication may be lost as part of the toxic response at higher doses. In CYP2F2-/mice in which a transgene for three human CYP450 mono-oxygenases (CYP2F1, 2A13, and 2B6) was inserted, lung toxicity, on the basis of the same proliferation assay, was observed with 4-vinylphenol but not styrene or the R- or S-styrene oxides (Cruzan et al. 2013). A major deficiency of these studies is that there were no quantitative measurements of the differences in metabolic capacity of the airways in wild-type and transgenic mice. How the presence of the CYP450 isozymes in the liver and other organs affected their response was not addressed. In knockout mice deficient in hepatic CYP450 reductase, which is critical for CYP450 function, lavage and serum markers of lung and liver toxicity were higher than in carrier-treated controls (Carlson 2012). Although the metabolism of styrene to the R- or S-styrene oxides was markedly reduced in the liver, production of the R-styrene oxide in the lungs doubled, and S-styrene oxide production was unchanged compared with controls.

The literature suggests that more than one CYP450 isozyme is involved in generating cytotoxic metabolites from styrene. More organs than the lung appear to serve as sites for both metabolic activation and cytotoxic injury, and the responses in different organs are unique to the organ. However, a clear understanding of the roles of CYP450s in the cytotoxicity of styrene will require further studies with a more comprehensive approach, including comparisons of not only liver and lung but other organs.

Cellular Oxidative Stress Response

Styrene and its principle metabolites, R- and S-styrene oxide and 4-vinylphenol, have been used to define markers of oxidative stress and the cellular stress response only in Clara cells in mice. Expression of Clara cell secretory protein (CC10) mRNA was affected differently when exposure to those compounds was in vitro (expression was increased by R- and S-styrene oxide and

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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decreased by 4-vinylphenol) as opposed to in vivo by intraperitoneal injection (expression was decreased by racemic and R-styrene oxide over a time course) (Harvilchuck et al. 2008). Expression of CC10 protein followed the same pattern. Reactive oxygen species were increased in Clara cells by both short-term in vitro and in vivo exposure to styrene, racemic styrene oxide, R-styrene oxide, and S-styrene oxide, but not 4-vinylphenol (Harvilchuck et al. 2009). Cellular markers of oxidative stress (8-hydroxydeoxyguanosine and superoxide dismutase) and indicators of apoptosis (bax/bcl-2 and caspase 3) were also increased by styrene or R-styrene oxide. Expression of all four markers returned to control values over an extended postexposure period after R-styrene oxide treatment but not in all cases for styrene. Repeated exposures to styrene and R-styrene oxide produced different short-term responses for the expression of CC10 mRNA and bax/bcl-2 mRNA (Harvilchuck and Carlson 2009). None of those studies addressed oxidative stress in other organs created by the presence of circulating styrene and its metabolites. To define mechanisms by which the metabolites of styrene react with potential target cells more clearly, future studies will need to address oxidative stress in other cell populations that have different levels of susceptibility in the lungs and in other organs, such as the liver.

Cellular Antioxidants

Extracellular pools of the antioxidant glutathione were markedly altered in mice by exposure to a single intraperitoneal dose of styrene or R-styrene oxide (Carlson 2010a). Depletion in both bronchoalveolar lavage fluid and plasma ranged from 30% up to 90%. Replenishment to steady-state concentrations after exposure to either compound required about 24 hours. Systemic pretreatment with known antioxidants to increase cellular antioxidant pools modulated styrene toxicity differently in two of the principal target organs (lung and liver) (Meszka-Jordan et al. 2009). On the basis of exposure to the most toxic metabolite, R-styrene oxide, glutathione pretreatment reduced liver toxicity without altering toxicity in the lungs. N-Acetylcysteine pretreatment had the same effect on the liver and a partial reductive effect on lung toxicity. Administration of a synthetic tetrapeptide analogue of glutathione, 4-methoxy-L-tyrosinyl-g-L-glutamyl-L-cysteinyl-glycine (UPF1), for a week before R-styrene oxide treatment enhanced toxicity in both lung and liver. Glutathione appears to play a role in modulating cellular toxicity produced by styrene metabolites, but a clear definition of the roles of the cellular and extracellular pools requires further studies that compare responses in a number of cell populations and organs that have different degrees of susceptibility.

Detoxification Pathways

The role of enzyme systems responsible for the detoxification of styrene and its metabolites has not been clearly defined for most potential target organs.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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Recent work that focused on the glutathione conjugation pathway used mice that were deficient in glutathione S-transferase pi (GST P1P2-/-), one of the three classes of glutathione S-transferases (Carlson 2011b). The results demonstrated that absence of this form did not alter the liver or lung toxicity of styrene (Carlson 2011b). The toxicity of racemic styrene oxide was not altered in the liver but was increased in the lungs of deficient mice. That was also the case for 4-vinylphenol. Depletion of glutathione in the lung and liver by styrene or 4-vinylphenol was unaltered in deficient mice. Expression of peroxiredoxin VI (a bifunctional enzyme) in the liver of GST P1P2-/- mice was substantially increased in comparison to wild-type mice (Kitteringham et al. 2003), and the effect of this change on metabolism and cytotoxicity, and possibly other alterations in protein concentration, is unclear.

Microsomal epoxide hydrolase is thought to play a critical role in the detoxification of styrene by the hydrolysis of styrene-7,8-oxide to styrene glycol. Mice deficient in microsomal epoxide hydrolase do not exhibit a difference in the metabolism of styrene to the R- or S-styrene oxides in either the liver or the lung (Carlson 2010b). Metabolism of styrene-7,8-oxide to glycol is reduced for R- and S-styrene oxide in the liver and for R-styrene oxide in the lung. The toxicity of styrene is substantially higher in both the lung and liver of deficient mice than in wild-type mice. However, the toxic response to racemic styrene-7,8oxide did not differ in the liver and lung between deficient and wild-type mice. Depletion of glutathione by styrene was increased in the liver of deficient mice but not in the lung. There was a difference between the toxic responses to R- and S-styrene oxide in microsomal epoxide hydrolase–deficient mice (Carlson 2011a). Neither enantiomer produced liver toxicity, but S-styrene oxide produced greater lung toxicity. R-styrene oxide substantially depleted liver glutathione, but S-styrene oxide did not.

The glutathione S-transferases and epoxide hydrolase pathways appear to play a role in the detoxification of reactive styrene metabolites. Their contributions to cellular injury will require more comprehensive studies that compare activity and responses in multiple organs that have different levels of susceptibility.

Summary of Cytotoxicity Evidence

In summary, the studies cited above, in combination with those included in the background document for styrene (NTP 2008), suggest that the mode of action by which styrene produces toxicity is highly complex. The final cellular outcome associated with exposure to a metabolically activated chemical, particularly with chemicals present at relatively low concentrations in the environment, is highly dependent on both the catalytic efficiency of the enzymes involved in the activation and detoxification processes and the amount of protein present in target cells. Establishing the mode of action for styrene on the basis of cytotoxicity and later proliferation at injured sites will depend on a comprehensive approach to identify

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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the cellular, metabolic, and chemical processes involved in different organs and to define rigorously how their interactions modulate the toxic response. Although research points to the importance of CYP2F2 in biomarker alterations (that is, BrdU labeling indices) that have been observed in styrene-exposed mice, the committee judged the studies to generally lack the scientific rigor necessary to ensure the validity of the conclusions. All the studies noted above relied on the intraperitoneal injection of styrene and its metabolites into the model species, the mouse, with the exception of Cruzan et al. (2012) study, which exposed mice via gavage. Consequently, the response of the candidate target organ, the lung, is based on the concentration of the compound delivered to it by the circulation. In none of the studies were the circulating concentrations determined. Other organ systems in the animal were exposed at the same time. When the response in another organ, the liver, was compared with that in the lung, it became clear that at least two organs are targets for cytotoxicity produced by styrene and its circulating metabolites. Studies of workers in the styrene industry found styrene or its metabolites in both blood and urine and identified a number of additional target organs in at least three other systems—the lymphohematopoietic system (bone marrow, lymph nodes, and spleen), gastrointestinal system (esophagus and pancreas), and urinary system (kidney and bladder)—that should be included in mechanistic studies that use animal models. The need to study other organs in addition to the lungs is especially true for studies in which metabolic capabilities of the model are altered by eliminating the genes for specific activation and detoxification enzymes in the animal as a whole. Additional studies that compare the kinetics of styrene metabolism using a range of recombinant P450 proteins, including CYP2F1 (the human orthologue of CYP2F2), are needed to establish the catalytic efficiency of these proteins with styrene. When both liver and lung were assessed in the studies evaluated in this section, the metabolic function and toxic response in both organs were altered. When gene manipulation was restricted to one organ, the liver, the toxic response in the other, the lung, was altered. Circulating concentrations of key compounds in the toxic response (when evaluated) were also altered. Taken as a whole, this evidence suggests that the activities and toxic responses of multiple organs may play a role in modulating the circulating concentrations of styrene, its metabolites, and other key compounds, such as glutathione, and in affecting the toxic response of other organs in the same individual.

SUMMARY OF EVIDENCE AND CONCLUSIONS

The statement of task (Appendix B) directed the committee to “integrate the level-of-evidence conclusions, and considering all relevant information in accordance with the RoC listing criteria, make an independent listing recommendation for styrene and provide scientific justification for its recommendation.” As discussed throughout this report, a substance can be categorized as reasonably anticipated to be a human carcinogen on the basis of sufficient evidence in animals or limited evidence in humans and a substance can be catego-

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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rized as known to be a human carcinogen on the basis of sufficient evidence in humans (see Box 1-2). Guided by the RoC listing criteria, the committee integrated data from individual studies to determine whether the evidence in experimental animals reached the level of limited or sufficient and to determine whether the evidence in humans reached the level of limited or sufficient. Supporting information was provided from mechanistic studies. The RoC listing criteria do not provide guidance on the integration of information across data streams (that is, across human, experimental animal, and mechanistic information) or the reconciliation of cross-data inconsistencies, so the committee only integrated information within data streams to derive a listing recommendation.

The committee identified evidence of styrene exposure that would potentially lead to carcinogenicity through genotoxic and mutagenic mechanisms, and that evidence is considered strong, inasmuch as it has been found in vivo and in vitro in both humans and rodents. The genotoxic mechanism is probably relevant for all target tissues associated with cancer after exposure to styrene. Identification of styrene metabolites, such as styrene-7,8-oxide, strongly supports the production of reactive intermediates in a variety of tissues in both humans and animals. The reactive metabolites, which may be produced in one organ and transported to produce toxicity in other sites, have been identified in the blood of humans exposed to styrene. Animal toxicology and carcinogenesis studies clearly support the possibility that multiple organs can be affected regardless of their capacity for metabolic activation. In humans, evidence of carcinogenicity in multiple organs is credible but limited. Those findings were based on large occupational cohort studies in the reinforced-plastics industry and on case–control studies.

In sum, the committee finds that compelling evidence exists to support a listing of styrene as, at a minimum, reasonably anticipated to be a human carcinogen. That conclusion is based on credible but limited evidence of carcinogenicity in traditional epidemiologic studies, on sufficient evidence of carcinogenicity in animals, and on convincing evidence that styrene is genotoxic in exposed humans.

The listing criteria state that a substance should be classified as known to be a human carcinogen if “there is sufficient evidence of carcinogenicity from studies in humans”. The footnote associated with that sentence states that “this evidence can include data derived from the study of tissues or cells from humans exposed to [styrene] that can be useful for evaluating whether a relevant cancer mechanism is operating in people”. The evidence of styrene genotoxicity in exposed humans is convincing, so a strong argument could be made to support the listing of styrene as a known human carcinogen if data derived from the study of tissues or cells from humans in and of themselves are considered sufficient for making such a determination. The committee notes that there is ambiguity with respect to weighing the mechanistic evidence in applying the listing criteria.

The types of evidence that are available to determine the listing and classification of substances in the RoC continue to evolve. In the future, there will

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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probably be more powerful mechanistic evidence in exposed humans to use for cancer hazard evaluation. Similarly, improvements in exposure-assessment methods may be developed to improve the identification and characterization of exposed persons. This is true not only for styrene and styrene-7,8-oxide, but for all substances in the RoC. Thus, the committee finds that further clarification and expanded guidance by NTP regarding the types and strength of mechanistic evidence and the use of that evidence in the context of the RoC listing criteria are warranted.

REFERENCES

Andersson, H.C., E.A. Tranberg, A.H. Uggla, and G. Zetterberg. 1980. Chromosomal aberrations and sister-chromatid exchanges in lymphocytes of men occupationally exposed to styrene in a plastic-boat factory. Mutat. Res. 73(2):387-401.

Andrés, A. 2005. Cancer incidence after immunosuppressive treatment following kidney transplantation. Crit. Rev. Oncol. Hematol. 56(1):71-85.

Anwar, W.A., and M.Y. Shamy. 1995. Chromosomal aberrations and micronuclei in reinforced plastics workers exposed to styrene. Mutat. Res. 327(1-2):41-47.

Artuso, M., G. Angotzi, S. Bonassi, S. Bonatti, M. De Ferrari, D. Gargano, L. Lastrucci, L. Miligi, C. Sbrana, and A. Abbondandolo. 1995. Cytogenetic biomonitoring of styrene-exposed plastic boat builders. Arch. Environ. Contam. Toxicol. 29(2):270-274.

Ban, M., D. Hettich, and P. Bonnet. 2003. Effect of inhaled industrial chemicals on systemic and local immune response. Toxicology 184(1):41-50.

Ban, M., I. Langonne, N. Huguet, E. Pepin, and G. Morel. 2006. Inhaled chemicals may enhance allergic airway inflammation in ovalbumin-sensitised mice. Toxicology 226(2-3):161-171.

Bastlová, T., P. Vodicka, K. Peterková, K. Hemminki, and B. Lambert. 1995. Styrene oxide-induced HPRT mutations, DNA adducts and DNA strand breaks in cultured human lymphocytes. Carcinogenesis 16(10):2357-2362.

Becker, N., E. Deeq, and A. Nieters. 2004. Population-based study of lymphoma in Germany: Rationale, study design and first results. Leuk. Res. 28(7):713-724.

Beliles, R.P., J.H. Butala, C.R. Stack, and S. Makris. 1985. Chronic toxicity and three-generation reproduction study of styrene monomer in the drinking water of rats. Fundam. Appl. Toxicol. 5(5):855-868.

Bergamaschi, E., A. Smargiassi, A. Mutti, I. Franchini, and R. Lucchini. 1995. Immunological changes among workers occupationally exposed to styrene. Int. Arch. Occup. Environ. Health 67(3):165-171.

Biro, A., E. Pallinger, J. Major, M.G. Jakab, T. Klupp, A. Falus, and A. Tompa. 2002. Lymphocyte phenotype analysis and chromosome aberration frequency of workers occupationally exposed to styrene, benzene, polycyclic aromatic hydrocarbons or mixed solvents. Immunol. Lett. 81(2):133-140.

Bjørge, C., G. Brunborg, R. Wiger, J.A. Holme, T. Scholz, E. Dybing, and E.J. Søderlund. 1996. A comparative study of chemically induced DNA damage in isolated human and rat testicular cells. Reprod. Toxicol. 10(6):509-519.

Boogaard, P.J., K.P. de Kloe, S.C. Sumner, P.A. van Elburg, and B.A. Wong. 2000a. Disposition of [ring-U-14C] styrene in rats and mice exposed by recirculating nose-only inhalation. Toxicol. Sci. 58(1):161-172.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

Boogaard, P.J., K.P. de Kloe, B.A. Wong, S.C. Sumner, W.P. Watson, and N.J. van Sittert. 2000b. Quantification of DNA adducts formed in liver, lungs, and isolated lung cells of rats and mice exposed to 14C-styrene by nose-only inhalation. Toxicol. Sci. 57(2):203-216.

Born, S.L., A.S. Fix, D. Caudill, and L.D. Lehman-McKeeman. 1999. Development of tolerance to Clara cell necrosis with repeat administration of coumarin. Toxicol. Sci. 51(2):300-309.

Boyd, M.R., L.T. Burka, B.J. Wilson, and B.V. Sastry. 1981. Development of tolerance to the pulmonary toxin, 4-ipomeanol. Toxicology 19(2):85-100.

Brenner, D.D., A.M. Jeffrey, L. Latriano, L. Wazneh, D. Warburton, M. Toor, R.W. Pero, L.R. Andrews, S. Walles, and F.P. Perera. 1991. Biomarkers in styrene-exposed boatbuilders. Mutat. Res. 261(3):225-236.

Brondeau, M.T., P. Bonnet, J.P. Guenier, P. Simon, and J. de Ceaurriz. 1990. Adrenal-dependent leucopenia after short-term exposure to various airborne irritants in rats. J. Appl. Toxicol. 10(2):83-86.

Brunnemann, K.D., A. Rivenson, S.C. Cheng, V. Saa, and D. Hoffmann. 1992. A study of tobacco carcinogenesis. XLVII. Bioassays of vinylpyridines for genotoxicity and for tumorigenicity in A/J mice. Cancer Lett. 65(2):107-113.

Bucher, J.R. 2013. Follow-up Questions Submitted by the NAS Committee on Review of the Formaldehyde Assessment in the NTP 12th RoC and the NAS Committee on Review of the Styrene Assessment in the NTP 12th RoC, April 2, 2013.

Buckpitt, A., A.M. Chang, A. Weir, L. Van Winkle, Z. Duan, R. Philpot, and C. Plopper. 1995. Relationship of cytochrome P450 activity to Clara cell cytotoxicity. IV. Metabolism of naphthalene and naphthalene oxide in microdissected airways from mice, rats, and hamsters. Mol. Pharmacol. 47(1):74-81.

Bui, P.H., and O. Hankinson. 2009. Functional characterization of human cytochrome P450 2S1 using a synthetic gene-expressed protein in Escherichia coli. Mol. Pharmacol. 76(5):1031-1043.

Buschini, A., G. De Palma, P. Poli, A. Martino, C. Rossi, P. Mozzoni, E. Scotti, L. Buzio, E. Bergamaschi, and A. Mutti. 2003. Genetic polymorphism of drug-metabolizing enzymes and styrene-induced DNA damage. Environ. Mol. Mutagen. 41(4):243-252.

Byfält Nordqvist, M., A. Löf, S. Osterman-Golkar, and S.A. Walles. 1985. Covalent binding of styrene and styrene-7,8-oxide to plasma proteins, hemoglobin and DNA in the mouse. Chem. Biol. Interact. 55(1-2):63-73.

Camurri, L., S. Codeluppi, C. Pedroni, and L. Scarduelli. 1983. Chromosomal aberrations and sister-chromatid exchanges in workers exposed to styrene. Mutat. Res. 119(3):361-369.

Camurri, L., S. Codeluppi, L. Scarduelli, and S. Candela. 1984. Sister chromatid exchanges in workers exposed to low doses of styrene. Basic Life Sci. 29(Pt. B):957-963.

Cantoreggi, S., and W.K. Lutz. 1993. Covalent binding of styrene to DNA in rat and mouse. Carcinogenesis 14(3):355-360.

Carlson, G.P. 2002. Effect of the inhibition of the metabolism of 4-vinylphenol on its hepatotoxicity and pneumotoxicity in rats and mice. Toxicology 179(1-2):129-136.

Carlson, G. 2004. Influence of selected inhibitors on the metabolism of the styrene metabolite 4-vinylphenol in wild-type and CYP2E1 knockout mice. J. Toxicol. Environ. Health A 67(12):905-909.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

Carlson, G.P. 2008. Critical appraisal of the expression of cytochrome P450 enzymes in human lung and evaluation of the possibility that such expression provides evidence of potential styrene tumorigenicity in humans. Toxicology 254(1-2):1-10.

Carlson, G.P. 2010a. Depletion by styrene of glutathione in plasma and bronchioalveolar lavage fluid of non-Swiss albino (NSA) mice. J. Toxicol. Environ. Health A 73(11):766-772.

Carlson, G.P. 2010b. Metabolism and toxicity of styrene in microsomal epoxide hydrolase-deficient mice. J. Toxicol. Environ. Health A 73(24):1689-1699.

Carlson, G.P. 2011a. Comparison of styrene oxide enantiomers for hepatotoxic and pneumotoxic effects in microsomal epoxide hydrolase-deficient mice. J. Toxicol. Environ. Health A 74(6):347-350.

Carlson, G.P. 2011b. Hepatotoxicity and pneumotoxicity of styrene and its metabolites in glutathione S-transferase-deficient mice. Drug Chem. Toxicol. 34(4):440-444.

Carlson, G.P. 2012. Modification of the metabolism and toxicity of styrene and styrene oxide in hepatic cytochrome P450 reductase deficient mice and CYP2F2 deficient mice. Toxicology 294(2-3):104-108.

Carlson, G.P., A.A. Perez Rivera, and N.A. Mantick. 2001. Metabolism of the styrene metabolite 4-vinylphenol by rat and mouse liver and lung. J. Toxicol. Environ. Health A 63(7):541-551.

Cemeli, E., E. Mirkova, G. Chiuchiarelli, E. Alexandrova, and D. Anderson. 2009. Investigation on the mechanisms of genotoxicity of butadiene, styrene and their combination in human lymphocytes using the Comet assay. Mutat. Res. 664(1-2):69-76.

Chakrabarti, S., M.A. Duhr, M. Senécal-Quevillon, and C.L. Richer. 1993. Dose-dependent genotoxic effects of styrene on human blood lymphocytes and the relationship to its oxidative and metabolic effects. Environ. Mol. Mutagen. 22(2):85-92.

Chakrabarti, S., X.X. Zhang, and C.L. Richer. 1997. Influence of duration of exposure to styrene oxide on sister chromatid exchanges and cell-cycle kinetics in cultured human blood lymphocytes in vitro. Mutat. Res. 395(1):37-45.

Checkoway, H., and T.M. Williams. 1982. A hematology survey of workers at a styrene-butadiene synthetic rubber manufacturing plant. Am. Ind. Hyg. Assoc. J. 43(3):164-169.

Chen, C.C., M.C. Shih, K.Y. Wu, and P.K. Sen. 2008. Exterior exposure estimation using a one-compartment toxicokinetic model with blood sample measurements. J. Math. Biol. 56(5):611-633.

Cocco, P., A. t'Mannetje, D. Fadda, M. Melis, N. Becker, N., S. de Sanjose, L. Foretova, J. Mareckova, A. Staines, S. Kleefeld, M. Maynadie, A. Nieters, P. Brennan, and P. Boffetta. 2010. Occupational exposure to solvents and risk of lymphoma subtypes: Results from the Epilymph case-control study. Occup. Environ. Med. 67(5):341-347.

Cohen, J.T., G. Carlson, G. Charnley, D. Coggon, E. Delzell, J.D. Graham, H. Greim, D. Krewski, M. Medinsky, R. Monson, D. Paustenbach, B. Petersen, S. Rappaport, L. Rhomberg, P.B. Ryan, and K. Thompson. 2002. A comprehensive evaluation of the potential health risks associated with occupational and environmental exposure to styrene. J. Toxicol. Environ. Health B Crit. Rev. 5(1-2):1-265.

Collins, J.J., K.M. Bodner, and J. Bus. 2012. Cancer Mortality of Workers Exposed to Styrene in the U.S. Reinforced Plastics and Composite Industry. Final Report, April 3, 2012.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

Collins, J.J., K.M. Bodner, and J.S. Bus. 2013. Cancer mortality of workers exposed to styrene in the U.S. Reinforced plastics and composite industry. Epidemiology 24(2):195-203.

Conner, M.K., Y. Alarie, R.L. Dombroske. 1979. Sister chromatid exchange in regenerating liver and bone marrow cells of mice exposed to styrene. Toxicol. Appl. Pharmacol. 50(2):365-367.

Conner, M.K., Y. Alarie, R.L. Dombroske. 1980. Sister chromatid exchange in murine alveolar macrophages, bone marrow and regenerating liver cell induced by styrene inhalation. Toxicol. Appl. Pharmacol. 55(1):37-42.

Conner, M.K., Y. Alarie, and R.L. Dombroske, 1982. Multiple tissue comparisons of sister chromatid exchanges induced by inhaled styrene. Environ. Sci. Res. 25:433-441.

Conti, B., P. Maltoni, G. Perino, and A. Ciliberti. 1988. Long-term carcinogenicity bioassays on styrene administered by inhalation, ingestion and injection and styrene oxide administered by ingestion in Sprague-Dawley rats, and para-methylstyrene administered by ingestion in Sprague-Dawley rats and Swiss mice. Ann. NY Acad. Sci. 534:203-234.

Costa, C., S. Costa, S. Silva, P. Coelho, M. Botelho, J. Gaspar, J. Rueff, B. Laffon, and J.P. Taixeira. 2012. DNA damage and susceptibility assessment in industrial workers exposed to styrene. J. Toxicol. Environ. Health A 75(13-15):735-746.

Cruzan, G., J.R. Cushman, L.S. Andrews, G.C. Granville, K.A. Johnson, C.J. Hardy, D.W. Coombs, P.A. Mullins, and W.R. Brown. 1998. Chronic toxicity/oncogenicity study of styrene in CD rats by inhalation exposure for 104 weeks. Toxicol. Sci. 46(2):266-281.

Cruzan, G., J.R. Cushman, L.S. Andrews, G.C. Granville, K.A. Johnson, C. Bevan, C.J. Hardy, D.W. Coombs, P.A. Mullins, and W.R. Brown. 2001. Chronic toxicity/oncogenicity study of styrene in CD-1 mice by inhalation exposure for 104 weeks. J. Appl. Toxicol. 21(3):185-198.

Cruzan, G., G.P. Carlson, M. Turner, and W. Mellert. 2005. Ring-oxidized metabolites of styrene contribute to styrene-induced Clara-cell toxicity in mice. J. Toxicol. Environ. Health A 68(3):229-237.

Cruzan, G., J. Bus, M. Banton, R. Gingell, and G. Carlson. 2009. Mouse specific lung tumors from CYP2F2-mediated cytotoxic metabolism: An endpoint/toxic response where data from multiple chemicals converge to support a mode of action. Regul. Toxicol. Pharmacol. 55(2):205-218.

Cruzan, G., J. Bus, J. Hotchkiss, J. Harkema, M. Banton, and S. Sarang. 2012. CYP2F2generated metabolites, not styrene oxide, are a key event mediating the mode of action of styrene-induced mouse lung tumors. Regul. Toxicol. Pharmacol. 62(1):214-220.

Cruzan, G., J. Bus, J. Hotchkiss, R. Sura, C. Moore, G. Yost, M. Banton, and S. Sarang. 2013. Studies of styrene, styrene oxide and 4-hydroxystyrene toxicity in CYP2F2 knockout and CYP2F1 humanized mice support lack of human relevance for mouse lung tumors. Regul. Toxicol. Pharmacol. 66(1):24-29.

de Raat, W.K. 1978. Induction of sister chromatid exchanges by styrene and its presumed metabolite styrene oxide in the presence of rat liver homogenate. Chem. Biol. Interact. 20(2):163-170.

Diodovich, C., M.G. Bianchi, G. Bowe, F. Acquati, R. Taramelli, D. Parent-Massin, and L. Gribaldo. 2004. Response of human cord blood cells to styrene exposure: Evaluation of its effects on apoptosis and gene expression by genomic technology. Toxicology 200(2-3):145-157.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

Dogra, R.K., S. Khanna, S.N. Srivastava, L.J. Shukla, and R. Shanker. 1989. Styrene-induced immunomodulation in mice. Int. J. Immunopharmacol. 11(5):577-586.

Dolmierski, R., M. Szczepanik, G. Danielewicz-Garbalinska, D. Kunikowska, W. Mickiewicz, M. Chomicz, and R. Glosnicka. 1983. Mutagenic action of styrene and its metabolites. 1. Chromosome aberration in persons exposed to the action of styrene. Introductory investigations. Bull. Inst. Marit. Trop. Med. Gdynia 34(1-2):89-93.

Dypbukt, J.M., L.G. Costa, L. Manzo, S. Orrenius, and P. Nicotera. 1992. Cytotoxic and genotoxic effects of styrene-7,8-oxide in neuroadrenergic Pc 12 cells. Carcinogenesis 13(3):417-424.

EPA (U.S. Environmental Protection Agency). 2005. Guidelines for Carcinogen Risk Assessment. EPA/630/P-03/001F. Risk Assessment Forum, U.S. Environmental Protection Agency, Washington, DC [online]. Available: http://www.epa.gov/raf/publications/pdfs/Cancer_Guidelines_Final_3-25-05.pdf [accessed Jan. 23, 2014].

Fabiani, R., P. Rosignoli, A. De Bartolomeo, R. Fuccelli, and G. Morozzi. 2012. Genotoxicity of alkene epoxides in human peripheral blood mononuclear cells and HL60 leukemia cells evaluated with the comet assay. Mutat. Res. 47(1):1-6.

Fabry, L., A. Léonard, and M. Roberfroid. 1978. Mutagenicity tests with styrene oxide in mammals. Mutat. Res. 51(3):377-381.

Festing, M.F., and D.G. Altman. 2002. Guidelines for the design and statistical analysis of experiments using laboratory animals. ILAR J. 43(4):244-258.

Filser, J.G., W. Kessler, and G.A. Csanády. 2002. Estimation of a possible tumorigenic risk of styrene from daily intake via food and ambient air. Toxicol. Lett. 126(1):1-18.

Fleig, I., and A.M. Thiess. 1978. Mutagenicity study of workers employed in the styrene and polystyrene processing and manufacturing industry. Scand. J. Work Environ. Health 4(suppl. 2):254-258.

Forni, A., E. Goggi, E. Ortisi, R. Cacchetti, G. Cortona, G. Sesana, and L. Alessio. 1988. Cytogenic findings in styrene workers in relation to exposure. Pp. 159-162 in Enviromental Hygiene, N.H. Seemayer, and W. Hadnagy, eds. Berlin, Germany: Springer.

Fracasso, M.E., D. Doria, M. Carrieri, G.B. Bartolucci, S. Quantavalle, and E. De Rosa. 2009. DNA single and double-strand breaks by alkaline- and immune-comet assay in lymphocytes of workers exposed to styrene. Toxicol. Lett. 185(1):9-15.

Fukami, T., M. Katoh, H. Yamazaki, T. Yokoi, and M. Nakajima. 2008. Human cytochrome P450 2A13 efficiently metabolizes chemicals in air pollutants: Naphthalene, styrene, and toluene. Chem. Res. Toxicol. 21(3):720-725.

Fustinoni, S., L. Campo, A. Manini, M. Buratt, S. Waidyanatha, G. De Palma, A. Mutti, V. Foa, A. Colombi, and S.M. Rappaport. 2008. An integrated approach to biomonitoring exposure to styrene and styrene-(7,8)-oxide using a repeated measurements sampling design. Biomarkers 13(6):560-578.

Gamer, A.O., E. Leibold, K. Deckardt, B. Kittel, W. Kaufmann, H.A. Tennekes, and B. van Ravenzwaay. 2004. The effects of styrene on lung cells in female mice and rats. Food Chem. Toxicol. 42(10):1655-1667.

Gate, L., J.C. Micillino, S. Sebillaud, C. Langlais, F. Cosnier, H. Nunge, C. Darne, Y. Guichard, and S. Binet. 2012. Genotoxicity of styrene-7,8-oxide and styrene in Fisher 344 rats: A 4-week inhalation study. Toxicol. Lett. 211(3):211-219.

Gerin, M., J. Siemiatychi, M. Desy, and D. Krewski. 1998. Associations between several sites of cancer and occupational exposure to benzene, toluene, xylene, and styrene: Results of a case-control study in Montreal. Am. J. Ind. Med. 34(2):144-156.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

Godderis, L., M. De Boeck, V. Haufroid, M. Emmery, R. Mateuca, S. Gardinal, M. Kirsch-Volders, H. Veulemans, and D. Lison. 2004. Influence of genetic polymorphisms on biomarkers of exposure and genotoxic effects in styrene-exposed workers. Environ. Mol. Mutagen. 44(4):293-303.

Grayson, M.H., and S.S. Gill. 1986. Effect of in vitro exposure to styrene, styrene oxide, and other structurally related compounds on murine cell-mediated immunity. Immunopharmacology 11(3):165-173.

Hagmar, L., B. Hogstedt, H. Welinder, A. Karlsson, and F. Rassner. 1989. Cytogenetic and hematological effects in plastics workers exposed to styrene. Scand. J. Work Environ. Health 15(2):136-141.

Hallier, E., H.W. Goergens, K. Hallier, and H.M. Bolt. 1994. Intervention study on the influence of reduction of occupational exposure to styrene on sister chromatid exchanges in lymphocytes. Int. Arch. Occup. Environ. Health 66(3):167-172.

Hanova, M., R. Stetina, L. Vodickova, R. Vaclavikova, P. Hlavac, Z. Smerhovsky, A. Naccarati, V. Polakova, P. Soucek, M. Kuricova, P. Manini, R. Kumar, K. Hemminki, and P. Vodicka. 2010. Modulation of DNA repair capacity and mRNA expression levels of XRCC1, hoGG1, and XPC genes in styrene-exposed workers. Toxicol. Appl. Pharmacol. 248(3):194-200.

Hanova, M. L. Vodickova, R. Vaclavikova, Z. Smerhovsky, R. Stetina, P. Hlavac, A. Naccarati, J. Slyskova, V. Polakova, P. Soucek, R. Kumar, K. Hemminki, and P. Vodicka. 2011. DNA damage, DNA repair rates and mRNA expression levels of cell cycle genes (TP53, p21(CDKN1A), BCL2 and BAX) with respect to occupational exposure to styrene. Carcinogenesis 32(1):74-79.

Hansteen, I.L., O. Jelmert, T. Torgrimsen, and B. Forsund. 1984. Low human exposure to styrene in relation to chromosome breaks, gaps and sister chromatid exchanges. Hereditas 100(1):87-91.

Harvilchuck, J.A., and G.P. Carlson. 2009. Effect of multiple doses of styrene and R-styrene oxide on CC10, bax, and bcl-2 expression in isolated Clara cells of CD-1 mice. Toxicology 259(3):149-152.

Harvilchuck, J.A., R.J. Zurbrugg, and G.P. Carlson. 2008. CC10 mRNA and protein expression in Clara cells of CD-1 mice following exposure to styrene or its metabolites styrene oxide or 4-vinylphenol. Toxicol. Lett. 183(1-3):28-35.

Harvilchuck, J.A., X. Pu, J.E. Klaunig, and G.P. Carlson. 2009. Indicators of oxidative stress and apoptosis in mouse whole lung and Clara cells following exposure to styrene and its metabolites. Toxicology 264(3):171-178.

Haseman, J.K., J. Huff, and G.A. Boorman. 1984. Use of historical control data in carcinogenicity students in rodents. Toxicol. Pathol. 12(2):126-135.

Haufroid, V., M. Jakubowski, B. Janasik, D. Ligocka, J.P. Buchet, E. Bergamaschi, P. Manini, A. Mutti, S. Ghittori, M. Arand, N. Hangen, F. Oesch, A. Hirvonen, and D. Lison. 2002. Interest of genotyping and phenotyping of drug-metabolizing enzymes for the interpretation of biological monitoring of exposure to styrene. Pharmacogenetics 12(9):691-702.

Helal, S.F., and W.S. Elshafy. 2013. Health hazards among workers in plastic industry. Toxicol. Ind. Health 29(9):812-819.

Herrero, M.E., M. Arand, J.G. Hengstler, and F. Oesch. 1997. Recombinant expression of human microsomal epoxide hydrolase protects V79 Chinese hamster cells from styrene oxide- but not from ethylene oxide-induced DNA strand breaks. Environ. Mol. Mutagen. 30(4):429-439.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

Hogstedt, B., K. Hedner, E. Mark-Vendel, F. Mitelman, A. Schutz, and S. Skerfving. 1979. Increased frequency of chromosome aberrations in workers exposed to styrene. Scand. J. Work Environ. Health 5(4):333-335.

Hogstedt, B., B. Akesson, K. Axell, B. Gullberg, F. Mitelman, R.W. Pero, S. Skerfving, and H. Welinder. 1983. Increased frequency of lymphocyte micronuclei in workers producing reinforced polyester resin with low exposure to styrene. Scand. J. Work Environ. Health 9(3):241-246.

Holz, O., G. Scherer, S. Brodtmeier, F. Koops, K. Warncke, T. Krause, A. Austen, J. Angerer, A.R. Tricker, F. Adlkofer, and H.F. Rüdiger. 1995. Determination of low level exposure to volatile aromatic hydrocarbons and genotoxic effects in workers at a styrene plant. Occup. Environ. Med. 52(6):420-428.

Huff, J.E. 1984. Styrene, styrene oxide, polystyrene, and β-nitrostyrene/styrene carcinogenicity in rodents. Pp. 227-238 in Industrial Hazards of Plastics and Synthetic Elastomers, J. Järvisalo, P. Pfäffli, and H. Vainio, eds. New York: Alan R. Liss.

IARC (International Agency for Research on Cancer). 1994a. Styrene. Pp. 233-320 in Some Industrial Chemicals. IARC Monographs on the Evaluation of the Carcinogenic Risk to Humans, Vol. 60. Lyon, France: IARC Press [online]. Available: http://monographs.iarc.fr/ENG/Monographs/vol60/mono60.pdf [accessed Feb. 12, 2014].

IARC (International Agency for Research on Cancer). 1994b. Styrene-7,8-oxide. Pp. 321-346 in Some Industrial Chemicals. IARC Monographs on the Evaluation of the Carcinogenic Risk to Humans, Vol. 60. Lyon, France: IARC Press [online]. Available: http://monographs.iarc.fr/ENG/Monographs/vol60/mono60.pdf [accessed Feb. 12, 2014].

IARC (International Agency for Research on Cancer). 2002. Styrene. Pp. 437-550 in Some Traditional Herbal Medicines, Some Mycotoxins, Naphthalene and Styrene. IARC Monographs on the Evaluation of the Carcinogenic Risk to Humans Vol. 82. Lyon, France: IARC Press [online]. Available: http://monographs.iarc.fr/ENG/Monographs/vol82/mono82.pdf [accessed Feb. 12, 2014].

Ishidate, M., Jr., and K. Yoshikawa. 1980. Chromosome aberration tests with Chinese hamster cells in vitro with and without metabolic activation--a comparative study on mutagens and carcinogens. Arch. Toxicol. Suppl. 4:41-44.

Jablonicka, A., J. Karelova, H. Polakova, and M. Vargova. 1988. Analysis of chromosomes in peripheral blood lymphocytes of styrene-exposed workers. Mutat. Res. 206(2):167-169.

Jahnova, E., J. Tulinska, S. Weissova, M. Dusinska, and L. Fuortes. 2002. Effects of occupational exposure to styrene on expression of adhesion molecule on leukocytes. Hum. Exp. Toxicol. 21(5):235-240.

Jantunen, K., J. Mäki-Paakkanen, and H. Norppa. 1986. Induction of chromosome aberrations by styrene and vinylacetate in cultured human lymphocytes: Dependence on erythrocytes. Mutat. Res. 159(1-2): 109-116.

Jarabek, A.M., L.H. Pottenger, L.S. Andrews, D. Casciano, M.R. Embry, J.H. Kim, R.J. Preston, M.V. Reddy, R. Schoeny, D. Shuker, J. Skare, J. Swenberg, G.M. Williams, and E. Zeiger. 2009. Creating context for the use of DNA adduct data in cancer risk assessment. Crit. Rev. Toxicol. 39(8):659-678.

Jensen, A.A., N.O. Breum, J. Bacher, and E. Lynge. 1990. Occupational exposures to styrene in Denmark 1955-88. Am. J. Ind. Med. 17(5):593-606.

Jersey, G.C., M.F. Balmer, J.F. Quast, C.N. Park, D.J. Schuetz, J.E. Beyer, K.J. Olson, S.B. McCollister, and L.W. Rampy. 1978. Two-Year Chronic Inhalation Toxicity

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

         and Carcinogenicity Study on Monomeric Styrene in Rats. Final Report. The Dow Chemical Company, Midland, MI.

Karakaya, A.E., B. Karahalil, M. Yilmazer, N. Aygün, S. Sardas, and S. Burgaz. 1997. Evaluation of genotoxic potential of styrene in furniture workers using unsaturated polyester resins. Mutat. Res. 392(3): 261-268.

Karami, S., P. Boffetta, P. Brennan, P.A. Stewart, D. Zaridze, V. Matveev, V. Janout, H. Kollarova, V. Bencko, M. Navratilova, N. Szeszenia-Dabrowska, D. Mates, J.P. Gromiec, R. Sobotka, W.H. Chow, N. Rothman, and L.E. Moore. 2011. Renal cancer risk and occupational exposure to polycyclic aromatic hydrocarbons and plastics. J. Occup. Environ. Med. 53(2):218-223.

Karami, S. 2013. National Cancer Institute at the National Institutes of Health. Unpublished material. Request for information to Dr. Karami from the Committee to Review the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Received on July 29, 2013.

Kaufmann, W., W. Mellert, B. van Ravenzwaay, R. Landsiedel, and A. Poole. 2005. Effects of styrene and its metabolites on different compartments of the mouse: Cell proliferation and histomorphology. Regul. Toxicol. Pharmacol. 42(1): 24-36.

Keenan, C., S. Elmore, S. Francke-Carroll, R. Kemp, R. Kerlin, S. Peddada, J. Pletcher, M. Rinke, S.P. Schmidt, I. Taylor, and D.C. Wolf. 2009. Best practices for use of historical control data of proliferative rodent lesions. Toxicol. Pathol. 37(5):679-693.

Kelsey, K.T., T.J. Smith, S.K. Hammond, R. Letz, and J.B. Little. 1990. Sister-chromatid exchanges in lymphocytes from styrene-exposed boat builders. Mutat. Res. 241(2):215-221.

Khristeva, V. 1986. Changes in the peripheral blood of workers engaged in ethylbenzenestyrene and synthetic rubber and latex manufacture [in Bulgarian]. Probl. Khig. 11:90-95.

Kitteringham, N.R., H. Powell, R.E. Jenkins, J. Hamlett, C. Lovatt, R. Elsby, C.J. Henderson, C.R. Wolf, S.R. Pennington, and B.K. Park. 2003. Protein expression profiling of glutathione S-transferase pi null mice as a strategy to identify potential markers of resistence to paracetamol-induced toxicity in the liver. Proteomics 3(2):191-207.

Kligerman, A.D., J.W. Allen, M.F. Bryant, J.A. Campbell, B.W. Collins, R.L. Doerr, G.L. Erexson, P. Kwanyuen, and D.L. Morgan. 1992. Cytogenetic studies of mice exposed to styrene by inhalation. Mutat. Res. 280(1):35-43.

Kligerman, A.D., J.W. Allen, G.L. Erexson, and D.L. Morgan. 1993. Cytogenetic studies of rodents exposed to styrene by inhalation. Pp. 217-224 in Butadiene and Styrene: Assessment of Health Hazards, M. Sorsa, K. Peltonen, H. Vainio, and K. Hemminki, eds. IARC Scientific Publications No. 127. Lyon, France: International Agency for Research on Cancer.

Knobel, P.A., and T.M. Marti. 2011. Translesion DNA synthesis in the context of cancer research. Cancer Cell Int. 11:39.

Kogevinas, M., G. Ferro, A. Andersen, T. Bellander, M. Biocca, O. Coggon, V. Gennaro, S. Hutchings, H. Kolstad, I. Lundberg, E. Lynge, T. Partanen, and R. Saracci. 1994. Cancer mortality in a historical cohort study of workers exposed to styrene. Scand. J. Work Environ. Health 20(4):251-261.

Kolstad, H.A., E. Lynge, J. Olsen, and N. Breum. 1994. Incidence of lymphohematopoietic malignancies among styrene-exposed workers of the reinforced plastics industry. Scand. J. Work Environ. Health 20(4):272-278.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

Kolstad, H.A., K. Juel, J. Olsen, and E. Lynge. 1995. Exposure to styrene and chronic health effects: Mortality and incidence of solid cancers in the Danish reinforced plastics industry. Occup. Environ. Med. 52(5):320-327.

Kubota, K., M. Murakami, S. Takenaka, K. Kawai, and H. Kyono. 1987. Effects of long-term nitrogen dioxide exposure on rat lung: Morphological observations. Environ. Health Perspect. 73:157-169.

Labarga, P. 2013. Cancer in HIV patients. AIDS Rev. 15(4):237-238.

Laffon, B., E. Pásaro, and J. Méndez. 2001b. Genotoxic effects of styrene-7,8-oxide in human white blood cells: Comet assay in relation to the induction of sister-chromatid exchanges and micronuclei. Mutat. Res. 491(1-2):163-172.

Laffon, B., E. Pásaro, and J. Méndez. 2002a. Evaluation of genotoxic effects in a group of workers exposed to low levels of styrene. Toxicology 171(2-3):175-186.

Laffon, B., E. Pásaro, and J. Méndez. 2002b. DNA damage and repair in human leukocytes exposed to styrene-7,8-oxide measured by the comet assay. Toxicol. Lett. 126(1):61-68.

Laffon, B., B. Pérez-Cadahia, E. Pásaro, and J. Méndez. 2003b. Effect of epoxide hydrolase and glutathione S-tranferase genotypes on the induction of micronuclei and DNA damage by styrene-7,8-oxide in vitro. Mutat. Res. 536(1-2):49-59.

Lawson, G.W., L.S. Van Winkle, E. Toskala, R.M. Senior, W.C. Parks, and C.G. Plopper. 2002. Mouse strain modulates the role of the ciliated cell in acute tracheobronchial airway injury-distal airways. Am. J. Pathol. 160(1):315-327.

Lazutka, J.R., R. Lekevicius, V. Dedonytë, L. Maciuleviciutë-Gervers, J. Mierauskienë, S. Rudaitienë, and G. Slapšytë. 1999. Chromosomal aberrations and sister-chromatid exchanges in Lithuanian populations: Effects of occupational and environmental exposures. Mutat. Res. 445(2):225-239.

Lee, S.H., and H. Norppa. 1995. Effects of indomethacin and arachidonic acid on sister chromatid exchange induction by styrene and styrene-7,8-oxide. Mutat. Res. 348(4):175-181.

Lijinsky, W. 1986. Rat and mouse forestomach tumors induced by chronic oral administration of styrene oxide. J. Natl. Cancer Inst. 77(2):471-476.

Linhart, I., J. Mraz, J. Scharff, J. Krouzelka, S. Duskova, H. Nohova, and L. Vodickova. 2010. New urinary metabolites formed from ring-oxidized metabolic intermediates of styrene. Chem. Res. Toxicol. 23(1):251-257.

Linhart, I., J. Mraz, L. Dabrowska, M. Malis, J. Krouzelka, and M. Korinek. 2012. Vinylphenylmercapturic acids in human urine as biomarkers of styrene ring oxidation. Toxicol. Lett. 213(2):260-265.

Linnainmaa, K., T. Meretoja, M. Sorsa, and H. Vainio. 1978a. Cytogenetic effects of styrene and styrene oxide on human lymphocytes and Allium cepa. Scand. J. Work Environ. Health 4 (suppl. 2):156-162.

Linnainmaa, K., T. Meretoja, M. Sorsa, and H. Vainio. 1978b. Cytogenetic effects of styrene and styrene oxide. Mutat. Res. 58(2-3):277-286.

Little, Inc. 1981. Industrial Hygiene Evaluation of Retrospective Mortality Study Plants. A.D. Little, Inc., Boston, MA

Liu, S.F., S.M. Rappaport, J. Rasmussen, and W.J. Bodell. 1988a. Detection of styrene oxide-DNA adducts by 32P-postlabeling. Carcinogenesis 9(8):1401-1404.

Loprieno, N., S. Presciuttini, I. Sbrana, G. Stretti, L. Zaccaro, A. Abbondandolo, S. Bonatti, R. Fiorio, and A. Mazzaccaro. 1978. Mutagenicity of industrial compounds. VII. Styrene and styrene oxide: II. Point mutations, chromosome aberrations and DNA repair induction analyses. Scand. J. Work Environ. Health 4(suppl. 2):169-178.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

Lutz, W.K., S. Cantoreggi, and I. Velic. 1993. DNA binding and stimulation of cell division in the carcinogenicity of styrene 7,8-oxide. Pp. 245-252 in Butadiene and Styrene: Assessment of Health Hazards, M. Sorsa, K. Peltonen, H. Vainio, and K. Hemminki, eds. IARC Scientific Publications No. 127. Lyon, France: International Agency for Research on Cancer.

Maki-Paakkanen, J. 1987. Chromosome aberrations, micronuclei and sister-chromatid exchanges in blood lymphocytes after occupational exposure to low levels of styrene. Mutat. Res. 189(4):399-406.

Maki-Paakkanen, J., S. Walles, S. Osterman-Golkar, and H. Norppa. 1991. Single-strand breaks, chromosome aberrations, sister-chromatid exchanges, and micronuclei in blood lymphocytes of workers exposed to styrene during the production of reinforced plastics. Environ. Mol. Mutagen. 17(1):27-31.

Manini, P., G. De Palma, R. Andreoli, B. Marczynski, M. hanova, P. Mozzoni, A. Naccarati, L. Vodickova, P. Hlavac, A. Mutti, and P. Vodicka. 2009. Biomarkers of nucleic acid oxidation, polymorphism in, and expression of, hOGG1 gene in styrene-exposed workers. Toxicol. Let. 190(1):41-47.

Marczynski, B., P. Rozynek, H.J. Elliehausen, M. Korn, and X. Baur. 1997a. Detection of 8-hydroxydeoxyguanosine, a marker of oxidative DNA damage, in white blood cells of workers occupationally exposed to styrene. Arch. Toxicol. 71(8):496-500.

Marczynski, B., M. Peel, and X. Baur. 1997b. Changes in high molecular weight DNA fragmentation following human blood exposure to styrene-7,8-oxide. Toxicology 120(2):111-117.

Matsuoka, A., M. Hayashi, and M. Ishidate, Jr. 1979. Chromosomal aberration tests on 29 chemicals combined with S9 mix in vitro. Mutat. Res. 66(3):277-290.

Meretoja, T., H. Vainio, M. Sorsa, and H. Harkonen. 1977. Occupational styrene exposure and chromosomal aberrations. Mutat. Res. 56(2):193-197.

Meretoja, T., H. Jarventaus, M. Sorsa, and H. Vainio. 1978a. Chromosome aberrations in lymphocytes of workers exposed to styrene. Scand. J. Work Environ. Health 4(suppl. 2):259-264.

Meretoja, T., H. Vainio, and H. Jarventaus. 1978b. Clastogenic effects of styrene exposure on bone marrow cells of rat. Toxicol. Lett. 1(5-6):315-318.

Meszka-Jordan, A., R. Mahlapuu, U. Soomets, and G.P. Carlson. 2009. Oxidative stress due to (R)-styrene oxide exposure and the role of antioxidants in non-Swiss albino (NSA) mice. J. Toxicol. Environ. Health A 72(10):642-650.

Migliore, L., A. Naccarati, A. Zanello, R. Scarpato, L. Bramanti, and M. Mariani. 2002. Assessment of sperm DNA integrity in workers exposed to styrene. Hum. Reprod. 17(11):2912-2918.

Migliore, L., A. Naccarati, F. Coppede, E. Bergamaschi, G. De Palma, A. Voho, P. Manini, H. Jarventaus, A. Mutti, H. Norppa, and A. Hirvonen. 2006a. Cytogenetic biomarkers, urinary metabolites and metabolic gene polymorphisms in workers exposed to styrene. Pharmacogenet. Genomics 16(2):87-99.

Migliore, L., R. Colognato, A. Naccarati, and E. Bergamaschi. 2006b. Relationship between genotoxicity biomarkers in somatic and germ cells: Findings from a biomonitoring study. Mutagenesis 21(2):149-152.

Mikes, P., M. Korinek, I. Linhart, J. Krouzelka, E. Frantik, L. Vodickova, and L. Neufussova. 2009. Excretion of urinary N7 guanine and N3 adenine DNA adducts in mice after inhalation of styrene. Toxicol. Lett. 184(1):33-37.

Mikes, P., M. Korínek, I. Linhart, J. Krouzelka, L. Dabrowská, V. Stránský, and J. Mráz. 2010. Urinary N3 adenine DNA adducts in humans occupationally exposed to styrene. Toxicol. Lett. 197(3):183-187.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

Mutti, A., C. Buzio, F. Perazzoli, E. Bergamaschi, M.C. Bocchi, L. Selis, F. Mineo, and I. Franchini. 1992. Lymphocyte subpopulations in workers exposed occupationally to styrene [in Italian]. Med. Lav. 83(2):167-177.

Nakajima, T., R.S. Wang, E. Elovaara, F.J. Gonzalez, H.V. Gelboin, H. Vainio, and T. Aoyama. 1994. CYP2C11 and CYP2B1 are major cytochrome P450 forms involved in styrene oxidation in liver and lung microsomes from untreated rats, respectively. Biochem. Pharmacol. 48(4):637-642.

Nano, R., A. Rossi, C. Fenoglio, and P. de Piceis Polver. 2000. Evaluation of a possible styrene-induced damage to the haematopoietic tissues in the rat. Anticancer Res. 20(3A):1615-1619.

NCI (National Cancer Institute). 1979a. Bioassay of Styrene for Possible Carcinogenicity. Technical Report No. 185. NIH 79-1741. National Cancer Institute, National Institute of Health, Bethesda, MD.

NCI (National Cancer Institute). 1979b. Bioassay of a Solution of beta-Nitrostyrene and Styrene for Possible Carcinogenicity. Technical Report No. 170. NCI-CG-TR-170. National Cancer Institute, National Institute of Health, Bethesda, MD.

NCI (National Cancer Institute). 2014. Surveillance, Epidemiology, and End Results Program (SEERP) Stat Fact Sheets: Kidney and Renal Pelvis Cancer [online]. Available: http://seer.cancer.gov/statfacts/html/kidrp.html [accessed Mar. 4, 2014].

Nishi, Y., M.M. Hasegawa, M. Taketomi, Y. Ohkawa, and N. Inui. 1984. Comparison of 6-thioguanine-resistant mutation and sister chromatid exchanges in Chinese hamster V79 cells with forty chemical and physical agents. Cancer Res. 44(8):3270-3279.

Nordenson, I., and L. Beckman. 1984. Chromosomal aberrations in lymphocytes of workers exposed to low levels of styrene. Hum. Hered. 34(3):178-182.

Norppa, H. 1981. Styrene and vinyltoluene induce micronuclei in mouse bone marrow. Toxicol. Lett. 8(4-5):247-251.

Norppa, H., and F. Tursi. 1984. Erythrocyte-mediated metabolic activation detected by SCE. Pp. 547-559 in Sister Scromatid Exchange, Vol. 29B, R.R. Tice, and A. Hollander, eds. New York: Plenum Press.

Norppa, H., and H. Vainio. 1983. Induction of sister-chromatid exchanges by styrene analogues in cultured human lymphocytes. Mutat. Res. 116(3-4):379-387.

Norppa, H., E. Elovaara, K. Husgafvel-Pursiaiòen, M. Sorsa, and H. Vainio. 1979. Effects of styrene oxide on chromosome aberrations, sister chromatid exchange and hepatic drug biotransformation in Chinese hamsters in vivo. Chem. Biol. Interact. 26(3):305-315.

Norppa, H., M. Sorsa, P. Pfaeffli, and H. Vainio. 1980a. Styrene and styrene oxide Induce SCEs and are metabolized in human lymphocyte cultures. Carcinogenesis 1(4):357-361.

Norppa, H., M. Sorsa, and H. Vainio. 1980b. Chromosomal aberrations in bone marrow of Chinese hamsters exposed to styrene and ethanol. Toxicol. Lett. 5(3-4):241-244.

Norppa, H., K. Hemminki, M. Sorsa, and H. Vainio. 1981. Effect of monosubstituted epoxides on chromosome aberrations and SCE in cultured human lymphocytes. Mutat. Res. 91(3):243-250.

Norppa, H., H. Vainio, and M. Sorsa. 1983a. Metabolic activation of styrene by erythrocytes detected as increased sister chromatid exchanges in cultured human lymphocytes. Cancer Res. 43(8):3579-3582.

Norppa, H., F. Tursi, and P. Einistö. 1983b. Erythrocytes as a metabolic activation system in mutagenicity studies. Pp. 35-50 in Mutagenesis and Genetic Toxicology, P. Janiaud, D. Averbeck, and E. Moustacchi, eds. Paris, France: INSERM.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

NRC (National Research Council). 2011. Review of the Environmental Protection Agency’s Draft IRIS Assessment of Formaldehyde. Washington, DC: The National Academies Press.

NRC (National Research Council). 2014. Review of EPA’s Integrated Risk Information System (IRIS) Process. Washington, DC: The National Academies Press.

NRC USCG (National Response Center U.S. Coast Guard). 2008. Query results for styrene. NRC FOIA Data. National Response Center, U.S. Coast Guard [online]. Available: http://www.nrc.uscg.mil/apex/f?p=109:2:6333530711141909:pg_R_1810817102655439:NO&pg_min_row=1&pg_max_rows=20&pg_rows_fetched=20 [accessed May 13, 2008] (as cited in NTP 2011).

NTP (National Toxicology Program). 2002. Report on Carcinogens, 10th Ed. U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program, Research Triangle Park, NC.

NTP (National Toxicology Program). 2008. Report on Carcinogens Background Document for Styrene, September 29, 2008. U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program, Research Triangle Park, NC [online]. Available: http://ntp.niehs.nih.gov/NTP/roc/twelfth/2010/FinalBDs/Styrene_Final_508.pdf [accessed Aug. 14, 2013].

NTP (National Toxicology Program). 2011a. Styrene. Pp. 383-392 in Report on Carcinogens, 12th Ed. U.S. Department of Health and Human Services, National Toxicology Program, Research Triangle Park, NC [online]. Available: http://ntp.niehs.nih.gov/ntp/roc/twelfth/profiles/Styrene.pdf [accessed Aug. 14, 2013].

NTP (National Toxicology Program). 2011b. Listing Criteria [online]. Available: http://ntp.niehs.nih.gov/?objectid=47B37760-F1F6-975E-7C15022B9C93B5A6 [accessed Feb. 24, 2014].

NTP (National Toxicology Program). 2011c. Report on Carcinogens, 12th Ed. U.S. Department of Health and Human Services, National Toxicology Program, Research Triangle Park, NC [online]. Available: http://ntp.niehs.nih.gov/ntp/roc/twelfth/roc12.pdf [accessed Aug. 14, 2013].

Oberheitmann, B., R. Frentzel-Beyme, and W. Hoffmann. 2001. An application of the challenge assay in boat builders exposed to low levels of styrene - a feasibility study of a possible biomarker for acquired susceptibility. Int. J. Hyg. Environ. Health 204(1):23-29.

O’Brien, K.A., C. Suverkropp, S. Kanekal, C.G. Plipper, and A.R. Buckpitt. 1989. Tolerance to multiple doses of the pulmonary toxicant, naphthalene. Toxicol. Appl. Pharmacol. 99(3):487-500.

Okun, A.H., J.J. Beaumont, T.J. Meinhardt, and M.S. Crandall. 1985. Mortality patterns among styrene-exposed boat builders. Am. J. Ind. Med. 8(3):193-205.

Ollikainen, T., A. Hirvonen, and H. Norppa. 1998. Influence of GSTT1 genotype on sister chromatid exchange induction by styrene-7,8-oxide in cultured human lymphocytes. Environ. Mol. Mutagen. 31(4):311-315.

Otteneder, M., U. Lutz, and W.K. Lutz. 2002. DNA adducts of styrene-7,8-oxide in target and non-target organs for tumor induction in rat and mouse after repeated inhalation exposure to styrene. Mutat Res. 500(1-2):111-116.

Paige, R.C., and C.G. Plopper. 1999. Acute and chronic effects of ozone in animal models. Pp. 531-557 in Air Pollution and Health, S.T. Holgate, J.M. Samet, H.S. Koren, and R.L. Maynard, eds. London: Academic Press.

Pauwels, W., and H. Veulemans. 1998. Comparison of ethylene, propylene and styrene 7,8-oxide in vitro adduct formation on N-terminal valine in human haemoglobin and on N-7-guanine in human DNA. Mutat. Res. 418(1):21-33.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

Pauwels, W., P. Vodicèka, M. Severi, K. Plná, H. Veulemans, and K. Hemminki. 1996. Adduct formation on DNA and haemoglobin in mice intraperitoneally administered with styrene. Carcinogenesis 17(12):2673-2680.

Penttila, M., M. Sorsa, and H. Vainio. 1980. Inability of styrene to induce nondisjunction in Drosophila or a positive micronucleus test in the Chinese hamster. Toxicol. Lett. 6(2):119-123.

Plopper, C.G., J. Macklin, S.J. Nishio, D.M. Hyde, and A.R. Buckpitt. 1992. Relationship of cytochrome P450 activity to Clara cell cytotoxicity. III. Morphometric comparison of changes in the epithelial populations of terminal bronchioles and lobar bronchi in mice, hamsters, and rats after parenteral administration of naphthalene. Lab. Invest. 67(5):553-565.

Plopper, C.G., R. Paige, E. Schelegle, A. Buckpitt, V. Wong, B. Tarkington, L. Putney, and D. Hyde. 2001. Time-response profiles: Implications for injury, repair, and adaptation to ozone. Pp. 23-37 in Relationship Between Acute and Chronic Effects of Air Pollution, U. Heinrich and U. Mohr, eds. Washington, DC: ILSI Press.

Pohlova, H., and R.J. Sram. 1985. Cytogenetic analysis of peripheral blood lymphocytes of workers occupationally exposed to styrene. J. Hyg. Epidemiol. Microbiol. Immunol. 29(2):155-161.

Pohlova, H., P. Rossner, and R.J. Sram. 1984. Cytogenetic analysis of human peripheral blood lymphocytes in culture exposed in vitro to styrene and styrene oxide. J. Hyg. Epidemiol. Microbiol. Immunol. 29(3):269-274.

Poirier, M.C. 2012. Chemical-induced DNA damage and human cancer risk. Discov. Med. 14(77):283-288.

Ponomarkov, V., and L. Tomatis. 1978. Effects of long-term oral administration of styrene to mice and rats. Scand. J. Work Environ. Health 4(suppl. 2):127-135.

Ponomarkov, V., J.R. Cabral, J. Wahrendorf, and D. Galendo. 1984. A carcinogenicity study of styrene-7,8-oxide in rats. Cancer Lett. 24(1):95-101.

Preston, R.J., and D.J. Abernethy. 1993. Studies of the induction of chromosomal aberration and sister chromatid exchange in rats exposed to styrene by inhalation. Pp. 225-233 in Butadiene and Styrene: Assessment of Health Hazards, M. Sorsa, K. Peltonen, H. Vainio, and K. Hemminki, eds. IARC Scientific Publications No. 127. Lyon: IARC Press.

Rappaport, S.M., K. Yeowell-O’Connell, W. Bodell, J.W. Yager, and E. Symanski. 1996. An investigation of multiple biomarkers among workers exposed to styrene and styrene-7,8-oxide. Cancer Res. 56(23): 5410-5416.

Ruder, A.M., E.M. Ward, M. Dong, A.H. Okun, and K. Davis-King. 2004. Mortality patterns among workers exposed to styrene in the reinforced plastic boatbuilding industry: An update. Am. J. Ind. Med. 45(2):165-176.

Sarangapani, R., J.G. Teeguarden, G. Cruzan, H.J. Clewell, and M.E. Andersen. 2002. Physiologically based pharmacokinetic modeling of styrene and styrene oxide respiratory-tract dosimetry in rodents and humans. Inhal. Toxicol. 14(8):789-834.

Sasaki, Y.F., F. Izumiyama, E. Nishidate, N. Matsusaka, and S. Tsuda. 1997. Detection of rodent liver carcinogen genotoxicity by the alkaline single-cell gel electrophoresis (Comet) assay in multiple mouse organs (liver, lung, spleen, kidney, and bone marrow). Mutat. Res. 391(3):201-214.

Sbrana, I., D. Lascialfari, A.M. Rossi, N. Loprieno, M. Bianchi, M. Tortoreto, and C. Pantarotto. 1983. Bone marrow cell chromosomal aberrations and styrene transformation in mice given styrene on repeated oral schedule. Chem. Biol. Interact. 45(3):349-357.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

Scélo, G., V. Constantinescu, I. Csiki, D. Zaridze, N. Szeszenia-Dabrowska, P. Rudnai, J. Lissowska, E. Fabiánová, A. Cassidy, A. Slamova, L. Foretova, V. Janout, J. Fevotte, T. Fletcher, A. Mannetje, P. Brennan, and P. Boffetta. 2004. Occupational exposure to vinyl chloride, acrylonitrile and styrene and lung cancer risk (Europe). Cancer Causes Control 15(5):445-452.

Scott, D., and R.J. Preston. 1994a. A re-evaluation of the cytogenetic effects of styrene. Mutat. Res. 318(3):175-203.

Seidel, H.J., J. Herkommer, D. Seitz, L. Weber, and E. Barthel. 1990. Haemopoitic stem cells in mice chronically exposed to styrene vapour. Arch. Toxicol. 64(6):466-469.

Seidler, A., M. Mohner, J. Berger, B. Mester, E. Deeg, G. Elsner, A. Nieters, and N. Becker. 2007. Solvent exposure and malignant lymphoma: A population-based case-control study in Germany. J. Occup. Med. Toxicol. 2:2.

Shamy, M.Y., H.H. Osman, K.M. Kandeel, N.M. Abdel-Moneim, and K.F. El Said. 2002. DNA single strand breaks induced by low levels of occupational exposure to styrene: The gap between standards and reality. J. Environ. Pathol. Toxicol. Oncol. 21(1):57-61.

Sharief, Y., A.M. Brown, L.C. Backer, J.A. Campbell, B. Westbrook-Collins, A.G. Stead, and J.W. Allen. 1986. Sister chromatid exchange and chromosome aberration analysis in mice after in vivo exposure to acrylonitrile, styrene, or butadiene monoxide. Environ. Mutagen. 8(3):439-448.

Sharma, R.P., F.A. Smith, and P.J. Gehring. 1981. Styrene epoxide intermediate as a possible stimulant of lymphocytic function. J. Immunopharmacol. 3(1):67-78.

Shen, S., F. Zhang, L. Gao, S. Zeng, and J. Zheng. 2010. Detection of phenolic metabolites of styrene in mouse liver and lung microsomal incubations. Drug Metab. Dispos. 38(11):1934-1943.

Sina, J.F., C.L. Bean, G.R. Dysart, V.I. Taylor, and M.O. Bradley. 1983. Evaluation of the alkaline elution/rat hepatocyte assay as a predictor of carcinogenic/mutagenic potential. Mutat. Res. 113(5): 357-391.

Sinha, A.K., G.C. Jersey, V.A. Linscombe, R.L. Adams, A.M. Mueller, and M.L. McClintock. 1983. Cytogenetic evaluation of bone marrow cells from rats exposed to styrene vapor for one year. Fundam. Appl. Toxicol. 3(2):95-98.

Sinsheimer, J.E., R. Chen, S.K. Das, B.H. Hooberman, S. Osorio, and Z. You. 1993. The genotoxicity of enantiomeric aliphatic epoxides. Mutat. Res. 298(3):197-206.

Somorovská, M., E. Jahnová, J. Tulinská, M. Zámecníková, J. Šarmanová, A. Terenová, L. Vodicková, A. Líšková, B. Vallová, P. Soucek, K. Hemminki, H. Norppa, A. Hirvonen, A.D. Tates, L. Fuortes, M. Dušinská, and P. Vodicka. 1999. Biomonitoring of occupational exposure to styrene in a plastics lamination plant. Mutat. Res. 428(1-2):255-269.

Sorsa, M., A. Anttila, H. Jarventaus, R. Kubiak, H. Norppa, L. Nylander, K. Pekari, P. Pfaffli, and H. Vainio. 1991. Styrene revisited - exposure assessment and risk estimation in reinforced plastics industry. Prog. Clin. Biol. Res. 372:187-195.

Speit, G., R. Linsenmeyer, P. Schutz, and S. Kuehner. 2012. Insensitivity of the in vitro cytokinesis-block miconucleaus assay with human lymphocutes for the detection of DNA damage present at the start of the cell culture. Mutagenesis 27(6):743-747.

Stengel, B., A. Touranchet, H.L. Boiteau, H. Harousseau, L. Mandereau, and D. Hemon. 1990. Hematological findings among styrene-exposed workers in the reinforced plastics industry. Int. Arch. Occup. Environ. Health 62(1):11-18.

Stripp, B.R., K. Maxson, R. Mera, and G. Singh. 1995. Plasticity of airway cell proliferation and gene expression after acute naphthalene injury. Am. J. Physiol. 269(6 Pt.1):791-799.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
×

Sumner, S.J., and T.R. Fennell. 1994. Review of the metabolic fate of styrene. Crit. Rev. Toxicol. 24(suppl.):S11-S33.

Swenberg, J.A., E. Fryar-Tita, Y.C. Jeong, G. Boysen, T. Starr, V.E. Walker, and R.J. Albertini. 2008. Biomarkers in toxicology and risk assessment: Informing critical dose response relationships. Chem. Res. Toxicol. 21(1):253-265.

Tates, A.D., T. Grummt, F.J. van Dam, F. de Zwart, F.J. Kasper, R. Rothe, H. Stirn, A.H. Zwinderman, and A.T. Natarajan. 1994. Measurement of frequencies of HPRT mutants, chromosomal aberrations, micronuclei, sister-chromatid exchanges and cells with high frequencies of SCEs in styrene/dichloromethane-exposed workers. Mutat. Res. 313(2-3):249-262.

Teixeira, J.P., J. Gaspar, S. Silva, J. Torres, S.N. Silva, M.C. Azevedo, P. Neves, B. Laffon, J. Méndez, C. Gonçalves, O. Mayan, P.B. Farmer, and J. Rueff. 2004. Occupational exposure to styrene: Modulation of cytogenetic damage and levels of urinary metabolites of styrene by polymorphisms in genes CYP2E1, EPHX1, GSTM1, GSTT1 and GSTP1. Toxicology 195(2-3):231-242.

Teixeira, J.P., J. Gaspar, P. Coelho, C. Costa, S. Pinho-Silva, S. Costa, S. Da Silva, B. Laffon, E. Psaro, J. Rueff, and P. Farmer. 2010. Cytogenetic and DNA damage on workers exposed to styrene. Mutagenesis 25(6):617-621.

Thiess, A.M., H. Schwegler, and I. Fleig. 1980. Chromosome investigations in lymphocytes of workers employed in areas in which styrene-containing unsaturated polyester resins are manufactured. Am. J. Ind. Med. 1(2):205-210.

Tomanin, R., C. Ballarin, G.B. Bartolucci, E. De Rosa, G. Sessa, G. Iannini, A.R. Cupiraggi, and F. Sarto. 1992. Chromosome aberrations and micronuclei in lymphocytes of workers exposed to low and medium levels of styrene. Int. Arch. Occup. Environ. Health 64(3):209-215.

Tsuda, S., N. Matsusaka, H. Madarame, Y. Miyamae, K. Ishida, M. Satoh, K. Sekihashi, and Y.F. Sasaki. 2000. The alkaline single cell electrophoresis assay with eight mouse organs: Results with 22 mono-functional alkylating agents (including 9 dialkyl N-nitrosoamines) and 10 DNA crosslinkers. Mutat. Res. 467(1):83-98.

Tulinska, J., M. Dusinska, E. Jahnova, A. Liskova, M. Kuricova, P. Vodicka, I. Vodickova, M. Sulcova, and L. Fuortes. 2000. Changes in cellular immunity among workers occupationally exposed to styrene in a plastics lamination plant. Am. J. Ind. Med. 38(5):576-583.

Turchi, G., S. Bonatti, L. Citti, P.G. Gervasi, and A. Abbondandolo. 1981. Alkylating properties and genetic activity of 4-vinylcyclohexene metabolites and structurally related epoxides. Mutat. Res. 83(3): 419-430.

Tursi, F., M. Samaia, M. Salmona, and G. Belvedere. 1983. Styrene oxidation to styrene oxide in human erythrocytes is catalyzed by oxyhemoglobin. Experientia 39(6):593-594.

Uüskula, M., H. Järventaus, A. Hirvonen, M. Sorsa, and H. Norppa. 1995. Influence of GSTM1 genotype on sister chromatid exchange induction by styrene-7,8-oxide and 1,2-epoxy-3-butene in cultured human lymphocytes. Carcinogenesis 16(4):947-950.

Vaghef, H., and B. Hellman. 1998. Detection of styrene and styrene oxide-induced DNA damage in various organs of mice using the comet assay. Pharmacol. Toxicol. 83(2):69-74.

Van Hummelen, P., M. Severi, W. Pauwels, D. Roosels, H. Veulemans, and M. Kirsch-Volders. 1994. Cytogenetic analysis of lymphocytes from fiberglass-reinforced plastics workers occupationally exposed to styrene. Mutat. Res. 310(1):157-165.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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Van Winkle, L.S., A.R. Buckpitt, S.J. Nishio, J.M. Isaac, and C.G. Plopper. 1995. Cellualar response in naphthalene-induced Clara cell injury and bronchiolar epithelial repair in mice. Am. J. Physiol. 269(6 Pt 1):800-818.

Verner, M.A., R. McDougall, and G. Johanson. 2012. Using population physiologically based pharmacokinetic modeling to determine optimal sampling times and to interpret biological exposure markers: The example of occupational exposure to styrene. Toxicol. Lett. 213(2):299-304.

Vodicka, P., L. Vodickova, and K. Hemminki. 1993. 32P-postlabeling of DNA adducts of styrene-exposed lamination workers. Carcinogenesis 14(10):2059-2061.

Vodicka, P., L. Vodicková, K. Trejbalová, R.J. Srám, and K. Hemminki. 1994. Persistence of O6-guanine DNA adducts in styrene-exposed lamination workers determined by 32P-postlabelling. Carcinogenesis 15(9):1949-1953.

Vodicka, P., T. Bastlová, L. Vodicková, K. Peterková, B. Lambert, and K. Hemminki. 1995. Biomarkers of styrene exposure in lamination workers: Levels of O6guanine DNA adducts, DNA strand breaks and mutant frequencies in the hypoxanthine guanine phosphoribosyltransferase gene in T-lymphocytes. Carcinogenesis 16(7):1473-1481.

Vodicka, P., R. Stetina, R. Kumar, K. Plna, and K. Hemminki. 1996. 7-Alkylguanine adducts of styrene oxide determined by 32P-postlabeling in DNA and human embryonal lung fibroblasts (HEL). Carcinogenesis 17(4):801-808.

Vodicka, P., T. Tvrdik, S. Osterman-Golkar, L. Vodicková, K. Peterková, P. Soucek, J. Šarmanová, P.B. Farmer, F. Granath, B. Lambert, and K. Hemminki. 1999. An evaluation of styrene genotoxicity using several biomarkers in a 3-year follow-up study of hand-lamination workers. Mutat. Res. 445(2):205-224.

Vodicka, P., M. Koskinen, L. Vodicková, R. Štetina, P. Šmerák, I. Bárta, and K. Hemminki. 2001b. DNA adducts, strand breaks and micronuclei in mice exposed to styrene by inhalation. Chem. Biol. Interact. 137(3):213-227.

Vodicka, P., M. Koskinen, M. Arand, F. Oesch, and K. Hemminki. 2002a. Spectrum of styrene-induced DNA adducts: The relationship to other biomarkers and prospects in human biomonitoring. Mutat. Res. 511(3):239-254.

Vodicka, P., J. Tuimala, R. Stetina, R. Kumar, P. Manini, A. Naccarati, L. Maestri, L. Vodickova, M. Kuricova, H. Jarventaus, Z. Majvaldova, A. Hirvonen, M. Imbriani, A. Mutti, L. Migliore, H. Norppa, and K. Hemminki. 2004a. Cytogenetic markers, DNA single-strand breaks, urinary metabolites, and DNA repair rates in styrene-exposed lamination workers. Environ. Health Perspect. 112(8):867-871.

Vodicka, P., R. Kumar, R. Stetina, L. Musak, P. Soucek, V. Haufroid, M. Sasiadek, L. Vodickova, A. Naccarati, J. Sedikova, S. Sanyal, M. Kuricova, V. Brsiak, H. Norppa, J. Buchancova, and K. Hemminki. 2004c. Markers of individual susceptibility and DNA repair rate in workers exposed to xenobiotics in a tire plant. Environ. Mol. Mutagen. 44(4):283-292.

Vodicka, P., M. Koskinen, A. Naccarati, B. Oesch-Bartlomowicz, L. Vodickova, K. Hemminki, and F. Oesch. 2006. Styrene metabolism, genotoxicity, and potential carcinogenicity. Drug Metab. Rev. 38(4):805-853.

Vogelstein, B., N. Papadopoulos, V.E. Velculescu, S. Zhou, L.A. Diaz, Jr., and K.W. Kinzler. 2013. Cancer genome landscapes. Science. 339(6127):1546-1558.

von der Hude, W., S. Carstensen, and G. Obe. 1991. Structure-activity relationships of epoxides: Induction of sister-chromatid exchanges in Chinese hamster V79 cells. Mutat. Res. 249(1):55-70.

Walles, S.A.S., and I. Orsen. 1983. Single-strand breaks in DNA of various organs of mice induced by styrene and styrene oxide. Cancer Lett. 21(1):9-15.

Suggested Citation:"3 Independent Assessment of Styrene." National Research Council. 2014. Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens. Washington, DC: The National Academies Press. doi: 10.17226/18725.
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Watabe, T., N. Ozawa, and K.Yoshikawa. 1982. Studies on metabolism and toxicity of styrene. V. The metabolism of styrene, racemic, (R)-(+)-, and (S)-(–)-phenyloxiranes in the rat. J. Pharmacobiodyn. 5(2):129–133.

Watanabe, T., A. Endo, K. Sato, T. Ohtsuki, M. Miyasaka, A. Koizumi, and M. Ikeda. 1981. Mutagenic potential of styrene in man. Ind. Health 19(1):37-45.

Watanabe, T., A. Endo, M. Kumai, and M. Ikeda. 1983. Chromosome aberrations and sister chromatid exchanges in styrene-exposed workers with reference to their smoking habits. Environ. Mutagen. 5(3): 299-309.

West, J.A., G. Pakenhham, D. Morin, C.A. Fleschner, A.R. Buckpitt, and C.G. Plopper. 2001. Inhaled naphthalene causes dose dependent Clara cell cytotoxicity in mice but nor rats. Toxicol. Appl. Pharmacol. 173(2):114-119.

West, J.A., L.S. Van Winkle, D. Morin, C.A. Fleschner, H.J. Forman, and C.G. Plopper. 2003. Repeated inhalation exposures to the bioactivated cytotoxicant naphthalene (NA) produce airway-specific Clara cell tolerance in mice. Toxicol. Sci. 75(1):161-168.

Wong, O. 1990. A cohort mortality study and a case-control study of workers potentially exposed to styrene in the reinforced plastics and composites industry. Br. J. Ind. Med. 47(11):753-762.

Wong, O., L.S. Trent, and M.D. Whortont. 1994. An updated cohort mortality study of workers exposed to styrene in the reinforced plastics and composites industry. Occup. Environ. Med. 51(6):386-396.

Wongvijitsuk, S, P. Navasumrit, U. Vattanasit, V. Parniob, and M. Ruchirawat. 2011. Low level occupational exposure to styrene: Its effects on DNA damage and DNA repair. Int. J. Hyg. Environ. Health 214(2):127-137.

Yager, J.W., W.M. Paradisin, and S.M. Rappaport. 1993. Sister-chromatid exchanges in lymphocytes are increased in relation to longitudinally measured occupational exposure to low concentrations of styrene. Mutat. Res. 319(3):155-165.

Zhang, F., E.R. Lowe, D.L. Rick, X. Qiu, E. Leibold, G. Cruzan, and M.J. Bartels. 2011. In vitro metabolism, glutathione conjugation, and CYP isoform specificity of epoxidation of 4-vinylphenol. Xenobiotica 41(1):6-23.

Zhang, X.X., S. Chakrabarti, A.M. Malick, and C.L. Richer. 1993. Effects of different styrene metabolites on cytotoxicity, sister-chromatid exchanges and cell-cycle kinetics in human whole blood lymphocytes in vitro. Mutat. Res. 302(4):213-218.

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Next: Appendix A: Biographic Information on the Committee to Review the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens »
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Many people in the United States are exposed to styrene. Sources of environmental exposure included food (from migration of styrene from polymer packaging materials), cigarette smoke, vehicle exhaust and other forms of combustion and incineration of styrene polymers. Occupational exposure to humans can occur during the industrial processing of styrene. It is used to create a broad spectrum of products, including latex paints and coatings; synthetic rubbers; construction materials, such as pipes, fittings, and lighting fixtures; packaging; household goods, such as synthetic marble, flooring, and molded furnishings; and automotive parts. In 2011, the National Toxicology Program (NTP) listed styrene as "reasonably anticipated to be a human carcinogen" in its 12th Report on Carcinogens, marking the first time that the substance was listed. Congress directed the Department of Health and Human Services to arrange for the National Academy of Sciences to independently review the substance profile of styrene and it listing in the NTP report.

Review of the Styrene Assessment in the National Toxicology Program 12th Report on Carcinogens concurs with the NTP determination that there is limited but credible evidence that exposure to styrene in some occupational settings is associated with an increase in the frequency of lymphohematopoietic cancers. Additionally, the NRC report authoring committee independently reviewed the scientific evidence from studies in humans, experimental animals, and other studies relevant to the mechanisms of carcinogenesis and made level-of-evidence conclusions. Based on credible but limited evidence of carcinogenicity in traditional epidemiologic studies, on sufficient evidence of carcinogenicity in animals, and on convincing evidence that styrene is genotoxic in exposed humans, this report finds that compelling evidence exists to support a listing of styrene as, at a minimum, "reasonably anticipated to be a human carcinogen."

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