7

Solvents

Solvents have a variety of uses in the military, and many of them were shipped in large quantities to the Persian Gulf. Some of the known uses for the military’s various solvents include the maintenance of vehicles and equipment, cleaning, and degreasing. However, there is little information on which solvents were used in the Gulf War and the Post-9/11 conflicts, for what purposes, and in what quantity.

Although Congress identified several of the insecticides and other toxicants for study in the legislation on Gulf War exposures, it did not identify the specific solvents that should be examined by the committees of the Gulf War and Health series. The Volume 2 committee identified a large number of solvents sent to the Gulf War (see Appendix D in Volume 2), many of which have been extensively studied. To identify the solvents used in the Gulf War, the committee gathered information from several sources, including veterans’ testimony and reports from the Office of the Special Assistant for Gulf War Illnesses (OSAGWI, 2000) and the Department of Defense (DoD) Defense Logistics Agency. Through its research the committee ultimately identified 53 solvents for review (see Table 7-1, adapted from Appendix D in Volume 2).

As the Volume 11 committee had a defined period in which to complete its review, the decision was made to update the toxicological and epidemiological information on the solvents discussed in Volume 2 and to add any solvents that were sent to the Gulf in large quantities (more than 1,000 liters) and that had a threshold limit value¹ (TLV) of less than or equal to 100 ppm. However, solvents for which little or no information was available on the reproductive or developmental effects of the chemical (e.g., amyl acetate) were not given further consideration by the Volume 11 committee. The committee found no specific information on the exposures of Post-9/11 service members to solvents during deployment. The solvents considered by the Volume 11 committee are listed in Table 7-1.

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¹Threshold limit values (TLVs^®) refer to airborne concentrations of chemical substances and represent conditions under which it is believed that nearly all workers may be repeatedly exposed, day after day, over a working lifetime, without adverse effects. TLVs are not regulatory standards, but rather recommendations developed and maintained by the American Conference of Governmental Industrial Hygienists.

TABLE 7-1 Solvents Sent to the 1990–1991 Gulf War

TABLE 7-1 Continued

NOTES: kL=kiloliter; OSAGWI=Office of the Special Assistant for Gulf War Illnesses.

^a These solvents were reviewed by the Volume 2 committee (IOM, 2003).

^b Reproductive and/or developmental toxicity data regarding the effects of these solvents were reported by the Volume 2 committee (IOM, 2003).

^c These solvents were present during Gulf War deployment according to reports from veterans (OSAGWI, 2000).

^d Solvents sent to the theater of operations as indicated by DoD Defense Logistics Agency (OSAGWI, 2000).

^e Threshold limit value (TLV) is an occupational exposure limit set by the American Conference of Governmental Industrial Hygienists to represent the upper limit of exposure considered safe for humans over a lifetime. Lower values represent more toxic substances (ACGIH, 2018).

^f Reproductive (R) or developmental (D) toxicity data available from either an Agency for Toxic Substances and Disease Registry toxicological profile (A) or from a U.S. Environmental Protection Agency (E) document such as a support document for the Integrated Risk Integration System database or a human health assessment.

** Not discussed in Volume 11.

The most thoroughly documented solvent exposure involved the spray painting of military vehicles with chemical-agent-resistant coating (CARC) (IOM, 2003). Thousands of military vehicles deployed to the Gulf War were painted with tan CARC to provide camouflage protection for the desert environment as well as to provide a surface that could be easily decontaminated. Not all military personnel involved in CARC painting were trained in spray painting operations, and some might not have had or used all the necessary personal protective equipment, thus increasing their potential exposure to the cleaning solvents and paints (IOM, 2003). Personnel who participated in CARC painting were likely exposed to solvents in the CARC formulations, paint thinners, and cleaning products. As noted in a report by the Office of the Special Assistant for Gulf War Illnesses (OSAGWI), some of the solvents used to clean painting equipment might have been purchased locally and therefore not identified (OSAGWI, 2000).

In addition to the solvents sent to the Gulf War or Post-9/11 conflicts in large quantities or of great toxicity, in some cases exposure to volatile organic compounds (VOCs) and to the solvents themselves in ambient air were the result of incomplete combustion from diesel exhaust and burn pits. There is overlap between the two sources. For example, trichloroethylene (TCE) and tetrachloroethylene (PCE) were sent to the Gulf as solvents but were detected in air monitoring samples collected at Joint Base Balad (JBB), one of the largest U.S. military bases in Iraq, as the result of the operation of a large burn pit there. Several VOCs were detected only in air samples from JBB and were not sent to the Middle East as solvents (e.g., hexane); these VOCs are not discussed in depth in this volume, but more information on their health impacts may be found in the Institute of Medicine report Long-Term Health Consequences of Exposure to Burn Pits in Iraq and Afghanistan (IOM, 2011).

It is important to note that many of the epidemiologic studies that examine the potential reproductive and developmental effects of solvents—particularly in occupational settings or during the course of environmental exposures—involve a mixture of solvents, although investigators generally attempt either to measure levels of specific solvents or to use job matrices to estimate exposures. Because of the variety of uses for these solvents in the Gulf War and Post-9/11 conflicts, there were a number of possible routes of exposure for service members, including—in descending order of likelihood based on the described uses—inhalation, dermal, and oral pathways. These routes of exposure are associated with differing rates of systemic exposure, metabolism, and elimination from the body. The lack of precise exposure information for each solvent is a significant weakness for many of the studies considered in this section, and it adds uncertainty in extrapolating from occupational and environmental exposures, such as working in a dry cleaning facility or automotive repair facility, to the exposures that may have been experienced by veterans during deployment. Furthermore, many of the occupational studies report on exposure to several or many toxicants. Where there are studies of reproductive or developmental effects as a result of exposure to several of the committee’s toxicants of concern, the Volume 11 committee cites the study for each relevant solvent.

The Volume 11 committee began its consideration of the reproductive and developmental effects of solvents by reviewing the findings of the 2003 Volume 2 committee. Although the Volume 2 committee reached conclusions on the category of association for specific solvents and most reproductive and developmental health outcomes (e.g., that there was evidence of a causal association between benzene exposure and acute leukemia in adults), it was unable to reach a consensus on the category of association for parental preconception exposure to solvents and the developmental health effect of childhood leukemia. The Volume 2 committee did reach a consensus that there was inadequate/insufficient evidence to determine whether an association existed for:

• Solvents and male or female infertility after the cessation of exposure;
• Parental preconception exposure to solvents and neuroblastoma and childhood brain cancers;

• Parental preconception exposure to solvents and spontaneous abortion or other adverse pregnancy outcomes; and
• Parental preconception exposure to solvents and congenital malformations.

In the following sections, the Volume 11 committee considers the epidemiologic and toxicologic information available on benzene, toluene, xylene, TCE, PCE, and glycols and glycol ethers derived from reports by authoritative bodies such as the Environmental Protection Agency (EPA) and the Agency for Toxic Substances and Disease Registry (ATSDR) and from literature searches for scientific studies published since Volume 2. It is important to note that the committee did not consider human or animal studies where the exposures attempted to mimic those of abuse scenarios such as solvent sniffing or “huffing.” This exposure scenario was considered to be nonrepresentative of those that might be encountered by male or female veterans while on deployment.

BENZENE

Benzene is an aromatic hydrocarbon. It was widely used as a solvent in the past, and it was reported to be among the solvents used by Gulf War veterans (IOM, 2003); the Volume 11 committee was unable to identify any information on its use in the Post-9/11 conflicts. This hydrocarbon is also considered to be a VOC due to its physicochemical properties. Benzene is a known human carcinogen and causes leukemia (IARC, 2012). Although no longer used as a general purpose solvent because of concerns regarding its toxicity, benzene continues to be used in the synthesis of other chemicals, and it is a component of gasoline, diesel fuel, and JP-8 jet fuel. The Occupational Safety and Health Administration’s permissible exposure level for benzene in workplace air is 1 ppm (time-weighted average) (OSHA, 2018).

Benzene was also one of the 12 most frequently measured pollutants in air samples taken at JBB in 2007 and 2009 (IOM, 2011). The base was home to a large airstrip and a large burn pit for waste. Air sampling, conducted by the U.S. Army to determine if service members on base were exposed to hazardous substances as a result of the burning of waste in the large burn pit, showed average benzene concentrations of 2.7 to 9.1 μg/m³ (0.85 to 2.85 ppb), depending on the year (2007 or 2009) of sampling and sampling location.

These data show that both Gulf War and Post-9/11 service members may have been exposed, voluntarily and involuntarily, to benzene from several sources during their deployment, whether from its use as a solvent, as a component of jet and vehicle fuels, or as a byproduct of waste disposal in burn pits. Benzene is also a component of tobacco smoke. Environmental tobacco smoke is the single greatest source of indoor benzene concentrations, with emissions from cigarette smoking ranging from 430 to 590 μg per cigarette (Singer et al., 2003; WHO, 2010).

The epidemiologic studies reviewed below are summarized in Table 7-2 at the end of the section.

Reproductive Effects

Reproductive Effects in Men and Women

The Volume 2 committee reviewed several studies that assessed the risk of spontaneous abortions in the partners of men who were occupationally exposed to benzene in Finland (Lindbohm et al., 1991), France (Stucker et al., 1994), and China (Xu et al., 1998). The risk of spontaneous abortion was not significantly increased with low-level benzene exposures (concentrations not measured) for the Finnish workers exposed prior to conception (odds ratio [OR]=1.0, 95% confidence interval [CI] 0.7–1.3) or

for the French workers exposed to 5 ppm (relative risk [RR]=1.1, 95% CI 0.6–2.0). However, female workers in the Chinese petrochemical industry exposed to undefined levels of benzene had a significantly increased risk of spontaneous abortion (RR=2.5, 95% CI 1.7–3.7) (Xu et al., 1998).

The 2007 ATSDR Toxicological Profile for Benzene and the 2015 Addendum to the Toxicological Profile for Benzene (ATSDR, 2007a, 2015a) reviewed numerous studies on the reproductive effects of benzene in humans. In one study, male workers with occupational exposure to benzene showed no statistically significant changes in the volume, appearance, pH, viscosity, or liquefaction of their semen compared with unexposed workers. However, when the men were stratified according to their duration of exposure, there were significant effects which included decreases in total sperm count and sperm motility, increased percentages of morphologically abnormal sperm, and increased sperm comet tail length (a measure of deoxyribonucleic acid [DNA] integrity) across all exposure groups (0–5 years, 5–10 years, and 10–15 years) compared with unexposed controls. The study did not include an evaluation of reproductive success in these workers (Katukam et al., 2012). ATSDR (2015a) reported that occupational exposure to benzene was also associated with genotoxic effects in sperm, including increased rates of chromosomal aberrations (e.g., breaks, deletions, translocations, and aneuploidy) for a number of sperm chromosomes (Ji et al., 2012; Kim et al., 2010; Marchetti et al., 2012; Schmid et al., 2006; Xing et al., 2010).

The Volume 11 committee considered three new studies in its assessment of possible reproductive effects that may be associated with benzene exposure. The three studies (Ji et al., 2012; Marchetti et al., 2012; Xing et al., 2010) reported on results of the China Benzene and Sperm Study, a cross-sectional study of chromosomal aberrations in 33 male workers who used benzene-containing glues in manufacturing, compared with 33 unexposed workers (from a meat packing plant) in Tianjin, China; all the men had worked in the plants for at least 1 year. Personal passive air sampling was conducted, and urine, blood, and sperm samples were collected from the subjects. Benzene concentrations in the workplace air ranged from below a detection limit of 0.2 ppm to 24 ppm (median, 2.9 ppm), with 27% of the men (n=9) being exposed to concentrations of ≤1 ppm. Xing et al. (2010) found, when compared with the unexposed workers, there was an increased frequency of aneuploid sperm in the low-exposed (1 ppm mean concentration) and high-exposed (7.7 ppm mean concentration) groups for disomy X, with an incidence rate ratio (IRR) of 2.0 (95% CI 1.1–3.4) and 2.8 (95% CI 1.5–4.9), respectively; there was also an increased risk for overall hyperhaploidy for chromosomes X, Y, and 21 (IRR=1.6, 95% CI 1.0–2.4 for low exposure, and IRR=2.3, 95% CI 1.5–3.6 for high exposure). The frequencies of disomy 21 were also significantly increased in the low-exposure men (IRR=2.1, 95% CI 1.0–4.7), and the frequency of disomy Y was increased in the high-exposure men (IRR=2.6, 95% CI 1.4–4.8). Ji et al. (2012) found that the sperm of these workers showed an increase in sex chromosome disomy but not chromosome 21. A significant correlation in frequency of sex chromosome disomy was observed between blood lymphocytes and sperm for the unexposed workers but not for exposed workers. Structural but not numerical chromosomal aberrations were increased in 30 of the exposed men (low exposure IRR=1.42, 95% CI 1.10–1.83; moderate exposure IRR=1.44, 95% CI 1.12–1.85; and high exposure IRR=1.75, 95% CI 1.36–2.24) compared with 11 unexposed men (Marchetti et al., 2012).

Adverse Pregnancy Outcomes

The Volume 2 committee (IOM, 2003) identified one study that reported an association between low birth weight and benzene exposure during pregnancy in female workers at a petrochemical facility in China. The effect was increased when benzene exposure was combined with work stress (Chen et al., 2000).

The 2015 ATSDR review Addendum to the Toxicological Profile for Benzene reported on one study (Zahran et al., 2012) that found a significantly increased risk of low birth weight with increasing benzene levels in ambient air in a study of resident births in the United States. No other relevant studies were discussed (ATSDR, 2015a).

The Volume 11 committee evaluated six studies that reported on fetal outcomes for women with prenatal exposures to benzene, four of which assessed benzene as a component of ambient air pollution (Estarlich et al., 2011; Ghosh et al., 2013; Llop et al., 2010; Zahran et al., 2012). In an assessment of 785 pregnant women with residential exposure to benzene in ambient outdoor air in Valencia, Spain, Llop et al. (2010) found an increased risk of preterm birth for women exposed throughout their entire pregnancies to estimated benzene levels of >2.7 μg/m³ (OR=6.46, 95% CI 1.58–26.35). In a further study of a larger cohort of 2,337 pregnant women in four regions of Spain, Estarlich et al. (2011) found that exposure to ambient benzene (mean=1.6 μg/m³), as estimated for the residence of each woman for each trimester and for the entire pregnancy, was not associated with reduced birth weight (OR=16.2, 95% CI –24.6–56.9), birth length (OR=0.16, 95% CI –0.03–0.35), or head circumference (OR=0.04, 95% CI –0.09–0.17) for any trimester or across the entire pregnancy. Ghosh et al. (2013) assessed the effects of air pollution, including benzene concentrations (mean=1.1 ppb), on the risk of having an infant with term low-birth weight. For third-trimester exposures, there was a slight but significant increase in the risk of a term low-birth weight infant (OR=1.03, 95% CI 1.00–1.05) among births to women living within 5 miles (8 km) of an air toxics monitoring station in Los Angeles, California, in 1995–2006.

Zahran et al. (2012), also cited in ATSDR (2015a), conducted a study of birth weights in 1.6 million singleton births in 422 U.S. counties across the nation. The researchers assessed maternal exposure to benzene on the basis of county-level ambient concentrations in 1996 and 1999, during which period benzene levels in gasoline dropped from 5% to 1%. A decrease in birth weight of 16.5 g (95% CI –17.6––15.4 g) was found for each unit increase in benzene concentration. Furthermore, a 1 mg/m³ increase in exposure significantly increased the risk of a low-birth-weight infant (OR=1.07, 95% CI 1.06–1.08).

In 2005–2006, Slama et al. (2009) recruited 271 nonsmoking pregnant French women to participate in the EDEN mother–infant cohort. Women wore a passive air sampler for a week during the 27th gestational week to measure ambient benzene levels. The median benzene exposure was 1.8 μg/m³ (5th percentile=0.5 μg/m³ and 95th percentile=7.5 μg/m³). Benzene exposure was associated with a 68 g mean decrease in birth weight and a 1.9 mm decrease in mean head circumference at birth (95% CI –3.8–0.0 mm), and there was an estimated 1.5 mm decrease in fetal head circumference (95% CI –3.1–0 mm) at the end of the second trimester.

Ruckart et al. (2014) conducted a cross-sectional study of 11,896 births at the U.S. Marine Corps base Camp Lejeune, North Carolina, during 1968–1985. During this period the groundwater on the base was contaminated with benzene and other solvents. The authors used birth certificate information to identify mothers at delivery and groundwater modeling to estimate solvent concentrations. The researchers found no association between residential prenatal exposure to any concentration of benzene during the entire pregnancy and the risk of a small for gestational age infant, preterm birth, reduced mean birth weight, or full-term low birth weight. A nonsignificant monotonic exposure–response relationship was also observed for benzene exposure throughout pregnancy and term low birth weight (highest exposure level OR=1.5, 85% CI 0.9–2.3). However, a significant association was shown between benzene and adjusted mean birth weight difference compared with unexposed births (mean difference= −36.2 g, 95% CI −72.3− –0.1).

Animal Studies

Animal studies have been conducted to evaluate the reproductive effects of both inhalation and oral exposures of benzene in male animals. Although Volume 2 did not include any animal studies on benzene, ATSDR thoroughly reviewed the animal literature concerning the reproductive effects of benzene via inhalation or oral exposure (ATSDR, 2007a, 2015a). ATSDR reported that although benzene does not appear to be teratogenic in animal studies, it may be fetotoxic (able to cause harm to the fetus) at concentrations that also cause maternal toxicity. ATSDR concluded that there was limited evidence from animal studies that oral exposure to benzene affects reproductive organs and that there was no information on the reproductive effects from inhalation exposure.

The Volume 11 committee identified one new animal study on the reproductive effects of benzene exposure that had not been reviewed by the IOM or ATSDR. Singh and Bansode (2011) fed male rats 0.5 mL or 1 mL benzene/kg (440 or 880 mg/kg) for 14 and 9 days, respectively. At autopsy, 1 day after exposure ended, the high-dose group exhibited a significantly decreased mean seminal vesicle weight (approximately 40% less than that of controls), with degenerative changes in the testes, such as giant cell formation, cytoplasmic vacuolization, pyknosis, chromatolysis, and the desquamation and dissolution of germ cells in the tubular lumen. The low-dose group (440 mg/kg) also had significantly decreased numbers of non-pachytene and pachytene spermatocytes, round and elongated spermatids, and decreased diameters of seminiferous tubules and Leydig cell nuclei. There was no loss in other reproductive organ weights; all animals given the high dose died.

Developmental Effects

The Volume 2 committee did not consider any studies of benzene exposure and developmental effects in humans or animals, but ATSDR did review numerous studies on the developmental effects of benzene in humans (ATSDR, 2007a, 2015a). The resulting review concluded that the epidemiological studies focused on developmental endpoints had considerable limitations, and ATSDR drew no conclusions on the possible effects of benzene in humans. The 2015 addendum reported on several epidemiological studies published since the toxicological profile that provided more information on potential developmental effects resulting from maternal inhalation exposure to benzene in ambient air. In a population-based study in Texas, Lupo et al. (2011) assessed the risk for neural tube defects, expressed in the form of spina bifida or anencephaly, as a result of prenatal exposure to ambient air pollutants. The estimated benzene levels were categorized as low (0.12–0.45 μg/m³; referent), medium-low (>0.45–0.98 μg/m³), medium (>0.98–1.52 μg/m³), medium-high (>1.52–2.86 μg/m³), and high (>2.86–7.44 μg/m³). There were increased risks of spina bifida at ambient benzene concentrations compared to low levels (medium-low OR=1.77, 95% CI 1.04–3.00; medium OR=1.90, 95% CI 1.11–3.24; medium high OR=1.40, 95% CI 0.82–2.38; and high concentration OR=2.30, 95% CI 1.22–4.33). Anencephaly was not significantly associated with any benzene concentration. Ramakrishnan et al. (2013) estimated ambient air benzene levels near mothers’ residences in Texas and compared those with the risk of having an oral cleft among offspring born between 1999 and 2008. No significant associations were found between benzene exposure and a cleft lip with and without cleft palate (OR=0.95, 95% CI 0.81–1.12) or between benzene exposure and a cleft palate without a cleft lip (OR=0.85, 95% CI 0.67–1.09).

The Volume 11 committee considered three meta-analyses that looked at the relationship between prenatal exposure to benzene and the risk of childhood leukemia: Zhou et al. (2014), Carlos-Wallace et al. (2016), and Filippini et al. (2015). In the Zhou et al. (2014) meta-analysis exposure to benzene was categorized for solvents (n=7), petroleum (n=7), or paint (n=7). For those three exposures, derived from 28 case-control studies and a cohort study, the pooled ORs for acute lymphoblastic leukemia (ALL) were

1.25 (95% CI 1.09–1.45) for solvents, 1.23 (95% CI 1.02–1.47) for paint, and 1.42 (95% CI 1.10–1.84) for petroleum; there was significant heterogeneity across the studies for paint, but not for solvents or petroleum. The authors concluded that childhood ALL was associated with maternal benzene exposure during pregnancy.

Carlos-Wallace et al. (2016) reviewed 20 studies of the association between occupational (n=17) or household product exposure (n=3) and childhood leukemia. The summary relative risk (sRR) for any childhood leukemia for the 20 studies combined was 1.96 (95% CI 1.60–2.41). Six of the studies provided data on acute myeloid leukemia (AML), giving a sRR of 2.34 (95% CI 1.72–3.18), and 14 studies reported on ALL for a sRR of 1.57 (95% CI 1.30–1.90). The risk of childhood leukemia was greater when the mother had been exposed to benzene (sRR=1.96, 95% CI 1.52–2.55; 13 studies) than when the father had been exposed (sRR=1.23, 95% CI 1.08–1.39; 14 studies). Maternal and paternal occupational exposure to benzene were both significantly associated with an increased risk (sRR=1.71, 95% CI 1.14–2.58; 7 studies, and sRR=1.18, 95% CI 1.00–1.41; 6 studies, respectively), as was household product use (sRR=1.67, 95% CI 1.24–2.26; 6 studies). Maternal exposure during gestation posed the greatest risk of childhood leukemia (sRR=2.06, 95% CI 1.51–2.81; 9 studies). Preconception (≥2 years before birth) exposure to benzene did not increase the risk when it was the mothers who were exposed (sRR=1.32, 95% CI 0.92–1.89; 6 studies), but it did when fathers were exposed (sRR=1.31, 95% CI 1.11–1.54; 8 studies), whereas neither maternal nor paternal periconception (approximately 1 year before birth) exposure was significantly associated with an increase in risk of childhood leukemia (sRR=1.29, 95% CI 0.97–1.71; 3 studies, and sRR=1.13, 95% CI 0.94–1.37; 4 studies, respectively). The authors concluded that there were associations between childhood leukemia and some benzene exposures.

Filippini et al. (2015) conducted a meta-analysis of 6 ecologic and 20 case-control studies to evaluate the association between traffic-related air pollution and the risk of childhood leukemia, with an emphasis on the effects of maternal residential exposures to nitrogen dioxide (NO₂) and benzene during pregnancy. On the basis of four studies (one of which reported on both ALL and AML), benzene was found to have an OR of 1.64 (95% CI 0.91–2.95) for any childhood leukemia. When stratified by leukemia type, the two relevant studies resulted in an OR of 1.09 (95% CI 0.67–1.77) for ALL and 2.28 (95% CI 1.09–4.75) for AML. The authors concluded that their results “support a link between ambient exposure to traffic pollution and childhood leukemia risk, particularly due to benzene.”

In one of the few studies that conducted a trimester-by-trimester assessment of the risk of childhood leukemia from maternal exposure to air toxics, including benzene, Heck et al. (2014) used the California Cancer Registry to identify children under 6 years of age who had been diagnosed with either ALL (n=69) or AML (n=46) between 1990 and 2007. Both the cases and the 19,209 controls lived within either 2 km (for ALL) or 6 km (for AML) of an air toxics monitoring station. For each trimester of pregnancy, the averages of about seven air toxic measurements were used to calculate individual exposures. A single interquartile increase in benzene concentrations did not significantly increase the risk for ALL in the first trimester (OR=0.85, 95% CI 0.58–1.26) or the second trimester (OR=1.16, 95% CI 0.80–1.67), but it did increase the risk significantly in the third trimester (OR=1.50, 95% CI 1.08–2.09). Similar results were seen for the risk of AML for each trimester (ORs=1.13 [95% CI 0.64–2.01], 1.30 [95% CI 0.74–2.28], and 1.75 [95% CI 1.04–2.93], respectively). The authors concluded that ambient exposures to benzene during pregnancy may increase leukemia risk in children.

Senkayi et al. (2014) assessed the association between air pollution from airports and road traffic and childhood leukemia in Texas. They included all the airports in the state of Texas and 2,134 incidences of childhood leukemia (children age 9 and under) statewide over a 10-year period in their model. Benzene emissions from the airports were found to be a statistically significant predictor variable for the incidence of childhood leukemia (β=0.23, 95% CI 0.15–0.31).

The association between ALL in 416 Australian children under the age of 15 and parental exposure to a variety of chemical toxicants was examined by Reid et al. (2011). Parents reported relevant information about their potential exposures, including their occupations, and an expert reviewed the likelihood of their exposure to exhausts, solvents (including benzene specifically), glues, and paints up to 2 years prior to the birth of the child and 1 year afterward. Neither maternal nor paternal exposure to low or moderate/substantial levels of benzene at any time prior to or during pregnancy was associated with a significant increase in the risk of childhood ALL.

Childhood brain cancers and their association with ambient air toxics were studied by von Ehrenstein et al. (2016) for children under 6 years of age diagnosed in 1990–2007. Exposure was based on measurements of ambient air toxics within a 5-mile radius of a monitor. The study included 43 cases of central nervous system (CNS) primitive neuroectodermal tumor (PNET), 34 cases of medulloblastoma, and 106 cases of astrocytoma from the California Cancer Registry along with 30,569 controls, all of them living within 5 miles of a monitor. PNETs were positively associated with interquartile range (1.216) increases in prenatal exposure to benzene (OR=2.14, 95% CI 1.12–4.06), although medulloblastomas and astrocytomas were not (OR=0.82, 95% CI 0.36–1.87 and OR=0.83, 95% CI 0.53–1.29, respectively).

In the large registry-based case-control NORD-TEST study, the risk of testicular germ cell tumors was studied in men ages 14–49 years (n=8,112; controls=26,264) diagnosed in 1978–2012 in Finland, Norway, and Sweden (Le Cornet et al., 2017). Prenatal exposures were assessed on the basis of the men’s parents’ occupations prior to the men’s birth. The parental occupations prior to the child’s birth were based on national censuses and job codes. No significant associations were found between prenatal maternal exposure in the year prior to birth or paternal exposure and the risk of testicular germ cell tumors across all three countries (OR=1.24, 95% CI 0.83–1.85 and OR=0.99, 95% CI 0.86–1.15, respectively).

Two studies evaluated the association between birth defects and benzene exposure from ambient air during pregnancy. One was a retrospective cohort study of birth defects (critical congenital heart defects [n=2,028], orofacial clefts [n=1,299], and spina bifida [n=271]) in children born to mothers residing in Florida from 2000 to 2009 (Tanner et al., 2015). Estimates of maternal exposures to the ambient air levels of particulate matter (PM)_2.5 and benzene were derived by aggregating ambient measurement data from EPA. The mothers with the highest level of exposure to benzene were at the greatest risk of having a child with an isolated cleft palate (adjusted prevalence ratio [aPR] 4th quartile=1.52, 95% CI 1.13–2.04) or any orofacial cleft (aPR 4th quartile=1.29, 95% CI 1.08–1.56, compared with the lowest quartile). Furthermore, there was an inverse association between exposure to benzene and the heart defect described as non-isolated pulmonary atresia (aPR 4th quartile=0.19, 95% CI 0.04–0.84), but there was no such association for other heart defects. The authors found no significant associations between estimated benzene exposures and any other birth defects.

In a smaller study in Italy, Vinceti et al. (2016) compared the prenatal benzene exposures of 228 children born with birth defects and 228 children without birth defects. The ambient benzene levels from vehicle exhaust, which were estimated based on dispersion modeling, were 23.5 mg/km and 0.82 mg/km for light and heavy vehicles, respectively, in the urban areas, and 2.96 mg/km and 0.31 mg/km in the rural areas. There was no increased risk for any birth defect associated with the average or maximal levels of benzene.

Ruckart et al. (2013) conducted a case-control study to assess the frequency of birth defects and childhood cancers in children born to mothers at Camp Lejeune, North Carolina, between 1968 and 1985. Birth certificates were used to identify the 51 cases and 526 control parent–child pairs. Prenatal benzene exposure in the first trimester, dichotomized to exposed/unexposed, was not significantly associated with an increased risk of childhood leukemia or non-Hodgkin’s lymphoma or oral cleft defects. However, first-trimester exposure to benzene was strongly associated with an increased risk of neural tube defects (OR=4.1, 95% CI 1.4–12.0).

The committee identified only two studies that assessed the association between a prenatal benzene exposure and cognitive and psychomotor development in children. Lertxundi et al. (2015) studied a population-based cohort of 438 mother–child pairs in Spain, recruited in 2006–2008 during each mother’s first-trimester antenatal care visit. Air sampling was used to determine ambient levels of PM_2.5 and NO₂, and benzene concentrations were estimated using land use regression models. Children were assessed at about 15 months of age using the Bayley Scales of Infant Development. The authors concluded that there was no significant association between exposure to benzene in ambient air and development in children.

The Volume 11 committee identified one study that assessed the impact of exposure to residential benzene on the expression of microRNA (miR)-155 and miR-223 in maternal and cord blood as part of the German Lifestyle and Environmental Factors and Their Influence on Newborns Allergy Risk study in 2006–2008 (Herberth et al., 2014). miR-155 and miR-223 are known to be involved in regulatory T-cell formation or function. The median benzene concentration measured in the homes during weeks 34–36 of pregnancy was 1.01μg/m³. Higher concentrations of benzene was significantly associated increased levels of miR-223 in maternal blood (means ratio=1.18, 95% CI 1.07–1.30), but not miR-155. Benzene levels were not significantly associated with levels of miR-155 or miR-223 in cord blood (95% CIs included 1.0). High miR-223 expression was associated with lower regulatory T-cell numbers in maternal and cord blood. Toluene concentrations were also associated with miR-223 in maternal blood, but not the expression of either microribonucleic acid (miRNA) in cord blood, and xylenes were not associated with miRNA in either maternal or cord blood (see the following sections on toluene and xylenes).

Animal Studies

ATSDR (2007a) included numerous animal studies that reported that inhalation exposure to benzene produced fetotoxicity as evidenced by decreased body weight and by increased skeletal variants such as missing sternebrae and extra ribs, although ATSDR did not consider these to be malformations, but rather the result of maternal toxicity. Alterations in hematopoiesis was also observed in the fetuses and offspring of pregnant mice exposed via inhalation to low levels of benzene. The oral studies in animals cited by ATSDR did not show any developmental effects.

One animal study on the neurodevelopmental effects of benzene was identified by the Volume 11 committee. Lo Pumo et al. (2006) found that the exposure of pregnant rats to 0.1 mg/kg benzene resulted in impaired cognition and motor behavior in male offspring at 2 months of age; females were not assessed. No teratogenic effects were seen in the offspring of either sex.

The Volume 11 committee identified several studies that assessed the effects of benzene on fetal metabolism. Fetal transcription factor c-Myb gene levels were elevated 24 h after pregnant mice were given intraperitoneal injections of 800 mg/kg benzene on gestation days (GDs) 10 and 11. Benzene also caused oxidative stress, as evidenced by decreases in the ratio of reduced to oxidized glutathione in maternal and embryonic tissues at both 4 h and 24 h after exposure; however, the decreases were no longer evident at 48 hours after dosing (Wan and Winn, 2008). There was no embryo lethality.

The effect of benzene on oxidative stress was also examined by Badham and colleagues in a series of experiments with mice (Badham and Winn 2010a,b; Philbrook and Winn, 2015). Pregnant mice received intraperitoneal doses of 200 or 400 mg/kg benzene on GDs 8, 10, 12, and 14; animals were sacrificed on GD 15. Neither dose resulted in any maternal or fetal toxicity; however, at 200 mg/kg there was significantly altered erythroid and myeloid progenitor cell growth in the hematopoietic tissue of the fetuses; increases in the reactive oxygen species, but not oxidative stress markers in the fetal hematopoietic tissue; and significantly reduced fetal liver IκB-α protein levels in the fetuses (Badham and Winn, 2010a). Female offspring, but not male offspring, of dams treated with 200 mg/kg benzene

had a significant increase in the number of erythroid-colony-forming units on GD 16 (p<0.05), although a significant decrease in the numbers of hematopoietic-colony-forming units was seen at postnatal day (PND) 2 (p<0.05); these effects were not seen in the offspring of dams receiving 400 mg/kg (Badham and Winn, 2010b). Philbrook and Winn (2015) explored the effects of prenatal exposures to benzene on epigenetic modifications. Pregnant CD-1 mice were dosed on GDs 8, 10, 12, and 14 with 200 mg/kg benzene and maternal bone marrow and fetal livers assessed for global DNA methylation, promoter-specific methylation of the tumor suppressor gene p15, and levels of acetylated histones H3, H4, and H3K56 and methylated histones H3K9 and H3K27. The authors found that although there was decreased global DNA methylation in maternal bone marrow, fetal livers showed no effect on global DNA methylation, p15 promoter methylation, or any measured histone modifications and recommended further investigation of the whole genome and epigenome.

The responses of mice to benzene may vary by strain. Badham et al. (2010) found that CD-1 mice, but not C57BL/6N mice, that had been prenatally exposed to 200 mg/kg benzene on GDs 8, 10, 12, and 14 had a significant increase in the incidence of hepatic and hematopoietic tumors at 1 year of age. Male CD-1 offspring had more hepatic tumors, while female mice had predominantly hematopoietic tumors. Female CD-1 offspring exposed transplacentally also had significantly suppressed bone marrow CD11b(+) cells at 1 year after birth.

Lau et al. (2009) administered daily intraperitoneal injections of benzene (200 or 400 mg/kg) to pregnant mice on GDs 7 to 15. On PND 9, the bone marrow micronucleus frequency was significantly elevated in the offspring of the high-dose group, although neither dose significantly altered the formation of γ-H2A.X fetal liver cells or in PND 9 bone marrow cells. No recombination events were detected in the fetal liver.

Synthesis and Conclusions

Given the ubiquity of benzene in ambient air and as a component of both fuels and exhaust from the combustion of fuels and other hydrocarbons, it is not surprising that benzene is relatively well studied. However, many of the studies of benzene have focused on its carcinogenicity, particularly as a causal agent for leukemia in adults. Benzene’s potential to cause reproductive and developmental effects has been assessed in occupational studies of both male and female workers. Studies of the effects of prenatal exposure to benzene have generally been done by measuring its concentrations in ambient air—frequently by comparing maternal exposures at residences near roads versus residences further from obvious benzene sources.

Reproductive Effects

The effects of benzene exposure on male reproduction have been studied in occupational settings, primarily in China. The Volume 11 committee considered three new studies (Ji et al., 2012; Marchetti et al., 2012; Xing et al., 2010) from the cross-sectional China Benzene and Sperm Study. The researchers that found that occupational exposure to benzene even at the lowest concentration measured (1 ppm) was associated with genotoxic effects in sperm, including increases in aneuploidy, disomy, and hyperhaploidy. However, these studies reported on only one small cohort, with just 33 exposed and 33 unexposed workers. A larger study by Katukam et al. (2012) of 160 workers also with industrial exposure to benzene reported sperm DNA damage (an increase in comet tail length) in the workers and other adverse sperm effects were seen. One animal study also showed that benzene has adverse effects on sperm parameters (Singh and Bansode, 2011).

Studies from the 1990s of occupational exposure of Finnish, French, or Chinese men to benzene reported that the men’s partners were not at increased risk of spontaneous abortion (IOM, 2003). The Volume 11 committee evaluated six studies that reported on fetal outcomes for women with prenatal exposures to benzene, four of which assessed benzene as a component of ambient air pollution (Estarlich et al., 2011; Ghosh et al., 2013; Llop et al., 2010; Zahran et al., 2012); the results were mixed. Llop et al. (2010) found an increased risk of preterm births with increasing benzene exposure in women in Spain, whereas Estarlich et al. (2011) found that benzene exposure was not associated with reduced birth weight or head circumference at any time during pregnancy. In two U.S. studies (Ghosh et al., 2013; Zahran et al., 2012) and one French study (Slama et al., 2009), benzene exposure was associated with a significantly increased risk of having a low-birth-weight infant and, in the French study, with decreased head circumference. A new study of infants born to women who lived at Camp Lejeune, North Carolina, during a period when the water was contaminated with benzene and other solvents found that benzene exposure during pregnancy was not associated with an increased risk for adverse birth outcomes. Thus, the results of the studies of prenatal benzene exposure on adverse birth outcomes were mixed.

The Volume 11 committee concludes that there is limited/suggestive evidence of an association exists between exposure to benzene and reproductive effects in men.

The Volume 11 committee also concludes that there is inadequate/insufficient evidence to determine whether an association exists between exposure to benzene and reproductive effects in women, or with adverse pregnancy outcomes.

Developmental Effects

Benzene is often singled out as an air toxic and traffic pollutant, with exposures at some point between conception and diagnosis reported to increase the risk of child leukemia (Heck et al., 2014; Senkayi et al., 2014). One challenge with these reports is that the windows of relevant exposure have not been defined. As noted earlier, benzene is a known carcinogen and causes leukemia in adults, but there is no evaluation that is specific for childhood leukemia (IARC, 2012). IARC notes that studies “support the idea that genotoxic and non-genotoxic events following exposure to benzene may be initiators of childhood leukemia in utero” (IARC, 2012). The 2015 Addendum to the ATSDR Toxicological Profile, after an evaluation of numerous epidemiological studies on developmental effects following maternal exposure to benzene in ambient air, found that there was a significant increase in the risk of spina bifida but not anencephaly or cleft lip with or without cleft palate (ATSDR, 2015a).

The Volume 11 committee reviewed three meta-analyses, all of which concluded that there is an association between prenatal exposure to benzene in ambient air and an increased risk of childhood leukemia. These findings were supported by Heck et al. (2014), who assessed benzene exposure by trimester and found that exposures in the third but not first or second trimester were associated with an increased risk of both ALL and AML in children. Living near an airport was found to increase the risk of childhood leukemia, and the risk was associated with benzene emissions (Senkayi et al., 2014). These results were contradicted, however, by an Australian study that found no increase in the risk of ALL in children whose parents had any exposure to benzene prior to or during the pregnancy.

One study of brain cancers in children in relation to ambient benzene concentrations in California found a strong positive increase in the presence of PNETs with increases in benzene, but there was no increase in the risk of medulloblastomas or astrocytomas (von Ehrenstein et al., 2014).

Studies on the association between exposure to benzene and birth defects have offered mixed results. Two studies (Ramakrishnan et al., 2013; Ruckart et al., 2013) found no association between prenatal maternal exposure to benzene in, respectively, ambient air or drinking water and cleft lips in offspring; however, a study by Tanner et al. (2015) found that mothers with the highest benzene exposure were at the greatest risk of having a child with a cleft palate or any orofacial cleft, although there were no associations with other birth defects, including heart defects. The study by Ruckart et al. (2013) of children born to mothers who had resided at Camp Lejeune, North Carolina, found that first-trimester exposure to drinking water contaminated with benzene significantly increased the risk of neural tube defects.

The committee considered only one study of prenatal benzene exposure and neurodevelopment in children, which was carried out in Spain. No association was found.

The Volume 11 committee concludes that there is sufficient evidence of an association between prenatal exposure to benzene and childhood leukemia.

The Volume 11 committee also concludes that there is inadequate/insufficient evidence to determine whether an association exists between prenatal exposure to benzene and other developmental effects in children.

TABLE 7-2 Summary of Reproductive and Developmental Effects of Benzene

continued

TABLE 7-2 Continued

continued

TABLE 7-2 Continued

continued

TABLE 7-2 Continued

NOTE: ALL=acute lymphoblastic leukemia; AML=acute myeloid leukemia; aPR=adjusted prevalence ratio; BTEX=benzene, toluene, ethylbenzene, xylene; CI=confidence interval; CNS=central nervous system; DNA=deoxyribonucleic acid; EPA=U.S. Environmental Protection Agency; IRR=incidence rate ratio; md=mean difference; miR=micro-ribonucleic acid; NO₂=nitrogen dioxide; NTD=neural tube defect; OR=odds ratio; PM=particulate matter; PNET=primitive neuroectodermal tumor; PTB=preterm birth; RR=relative risk; SGA=small for gestational age; Treg=regulatory T cell.

TOLUENE

Toluene is a widely used aromatic hydrocarbon. Toluene is a component of gasoline and is also found as a combustion product of fuel. It was sent to the Gulf War as a solvent in quantities greater than 1 kiloliter. The Volume 2 committee reported that “toluene is also present in paints, thinners, cleaning agents, and glue and is widely abused as an inhalant” (IOM, 2003). It may replace benzene in some industrial applications.

Toluene is a monosubstituted benzene derivative sometimes known as methylbenzene. It is frequently considered in combination with benzene, ethylbenzene, and xylenes as a mixture called BTEX. ATSDR (2015b) reported on the toxicokinetics of toluene and stated, “In both humans and rats, up to about 75–80% of inhaled toluene that is absorbed can be accounted for as hippuric acid in the urine” (Lof et al., 1993; Ogata, 1984; Tardif et al., 1998). The report also said that most absorbed toluene is rapidly eliminated from the body.

Toluene was among the 12 most frequently detected VOCs at the three sampling locations at JBB in both 2007 and 2009 (IOM, 2011). It was detected in 63 of 66 air samples in 2007 and in 56 of 57 air samples in 2009. Air concentrations ranged from nondetectable to approximately 55, the highest concentration measured of any of the 12 VOCs, with an average concentration of 18.6 μg/m³. The committee that wrote that report considered the likely major source of the toluene to be the combustion of petroleum-based fuel.

Toluene was also detected in the contaminated water supply at Camp Lejeune, North Carolina, possibly as a degradation product of PCE (NRC, 2009). Toluene was detected in a few water samples collected in 1984 and 1985, and the maximum concentration reported in any one well was 12 μg/L, but it was not detected in the vast majority of samples.

Epidemiologic studies on the reproductive and developmental effects of toluene reviewed below are summarized in Table 7-3 at the end of this section.

Reproductive Effects

Reproductive Effects in Men

The Volume 2 committee identified several studies that examined the effects of toluene exposure on male infertility. Plenge-Böenig and Karmaus (1999) examined male and female infertility in printing-industry workers using time to pregnancy (TTP) as the effect. Workers were interviewed about their occupational and reproductive histories, and their exposure to toluene was categorized according to job descriptions and previous measurements by industrial hygienists. Toluene exposure appeared to have no effect on TTP for exposed men, regardless of the extent of their exposure (fecund-ability ratio [FR]=1.05, 95% CI 0.93–1.19).

One report on a multitude of reproductive outcomes following male exposure to toluene was identified by the Volume 11 committee. Reproductive outcomes in 398 Dutch male painters following exposure to organic solvents, using toluene as the marker of exposure, were examined by Hooiveld et al. (2006); 302 carpenters were the unexposed referents. Toluene exposure at 3 months before pregnancy for painters was estimated to range from 0.17 to 4.66 mg/m³, below the occupational exposure limit of 150 mg/m³ in the Netherlands. Compared with carpenters, painters with occupational exposure in the 3 months before pregnancy were not at increased risk of prolonged TTP (OR=1.1, 95% CI 0.7–1.9) or decreased fecundability (FR=0.9, 95% CI 0.8–1.1).

There have been several small studies on the effects of toluene on male reproductive hormones. As reported in Gulf War and Health, Volume 2, Svensson et al. (1992a,b) found that exposure to toluene was associated with lower blood concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin, and testosterone in young male rotogravure printers as compared with factory workers. The authors stated that the effects may be transitory, as the decreases in LH and FSH levels were reversed in a subset of the printers after a 4-week exposure-free period. ATSDR’s Draft Toxicological Profile for Toluene (2015b) reported on two small studies of reproductive hormones related to toluene exposure. One study in which 1,225 male printers in Germany were compared with unexposed workers found that the serum levels of FSH, LH, and testosterone were not significantly different between those exposed to median toluene concentrations of 24 ppm (printers) and those exposed to 4.5 ppm (nonprinters) for at least 20 years (Gericke et al., 2001). Luderer et al. (1999) exposed five men and five women in the follicular phase to 0 or 50 ppm toluene for 3 hours. There were no significant direct effects of exposure on LH, FSH, and testosterone levels, with the exception of a significant decline in LH in men during exposure compared with sham exposure; however, ATSDR stated that it was difficult to assess this result in terms of what it implied for reproductive function.

The Volume 11 committee identified one new study of the effects of toluene exposure on semen. A small study in China of 24 men with occupational exposure to high concentrations of benzene, toluene, and xylenes (mean concentrations in work air were 103.34, 42.73, and 8.21 mg/m³, respectively) and 37 unexposed workers found a positive correlation between semen liquefaction and the toluene concentration in the semen (β=0.2571; significant T=0.047) (Xiao et al., 2001).

Reproductive Effects in Women

The Volume 2 committee reported on two studies that assessed reproductive effects in women who had been exposed to toluene. In one of them, Plenge-Böenig and Karmaus (1999) found, in contrast to their findings on men discussed earlier, that women who were exposed to toluene in a printing facility had an increased TTP (FR=0.52, 95% CI 0.28–0.99). ATSDR did not report on any studies of female reproductive effects in humans.

The Volume 11 committee did not identify any new studies on the effects of toluene on female reproduction.

Adverse Pregnancy Outcomes

The Volume 2 committee cited one case-control study by Taskinen et al. (1994) that found that women who worked in a laboratory with exposure to toluene were at an increased risk of spontaneous abortion (OR=4.7, 95% CI 1.4–15.9). A study in Finland that included biological monitoring of 120 male workers found consistent increases in the risk of spontaneous abortion in the partners of men with high or frequent exposure to toluene (OR=2.3, 95% CI 1.1–4.7) (Taskinen et al., 1989).

The ATSDR Draft Toxicological Profile for Toluene (2015b) reviewed three studies not included in Gulf War and Health, Volume 2 on the occurrence of spontaneous abortion in women exposed to toluene (Lindbohm et al., 1991; Ng et al., 1992; Taskinen et al., 1989). All three studies found an increased risk, but the latter two studies had substantial limitations, such as a small number of cases. ATSDR concluded, “Current data do not provide convincing evidence that acute or repeated inhalation exposure to toluene may cause reproductive effects in humans.”

The Hooiveld et al. (2006) study, whose results on male reproductive effects were described earlier, also found that, when compared with unexposed carpenters, the exposure of Dutch male painters

to toluene did not significantly increase their partners’ risks of spontaneous abortion (OR=1.1, 95% CI 0.4–2.7), preterm birth (OR=1.2, 95% CI 0.7–2.2), or low-birth-weight infants (OR=1.7, 95% CI 0.9–3.2). The Volume 11 did not identify any additional studies on the effects of maternal or paternal exposure to toluene and adverse pregnancy outcomes.

Animal Studies

There were no animal studies of possible reproductive effects of toluene cited in Gulf War and Health, Volume 2 (IOM, 2003).

The ATSDR Draft Toxicological Profile for Toluene included inhalation studies in rats at toluene concentrations ≥2,000 ppm. In female animals exposed to 3,000 ppm, reproductive effects included abnormalities of the ovaries (Tap et al., 1996). In male rats, the effects included reduced sperm count, motility, and quality as well as altered reproductive organ weight and histology (Kanter, 2011; Ono et al., 1996, 1999). However, Ono et al. (1996) found that although there were changes in sperm count and epididymis weight, there was no corresponding change in reproductive performance (e.g., fertility). Studies in rats exposed repeatedly by inhalation to toluene, including a two-generation reproductive toxicity study, have shown no evidence of adverse effects on mating or fertility at concentrations as high as 1,200–2,000 ppm (API, 1981, 1985; Ono et al., 1996; Roberts et al., 2003; Thiel and Chahoud, 1997). Thus, ATSDR concluded that the majority of animal studies provided little evidence for toluene having reproductive toxicity.

The Volume 11 committee did not identify any additional animal studies on the possible reproductive effects of toluene in male or female animals.

Developmental Effects

Several developmental endpoints have been studied following parental exposure to toluene—specifically childhood cancers and several types of birth defects—and were reported in Volume 2, by ATSDR, and by the Volume 11 committee in this volume. In addition, the Volume 11 committee identified one paper that examined cancer in adult men whose parents had occupational exposure to toluene.

Volume 2 discussed only one study that examined developmental effects in children that may have resulted from maternal or paternal exposure to toluene. Shu et al. (1999) found that children born to women who had a history of exposure to toluene were not at increased risk of ALL (OR=1.5, 95% CI 0.6–3.8) and that there was also no increased risk for children whose fathers had preconception exposure to toluene.

The Volume 11 committee identified two new studies of cancer in the children of parents who had been exposed to toluene. Heck et al. (2014)—also discussed in the section on benzene—assessed the risk of childhood leukemia after maternal exposure to air toxics, including toluene, by trimester in children in California who had been diagnosed with either ALL (n=69) or AML (n=46) between 1990 and 2007. The cases, along with the 19,209 controls, lived within either 2 km (for ALL) or 6 km (for AML) of an air toxics monitoring station. For each trimester of pregnancy, averages of the measurements of about 7 air toxics were used to calculate individual exposures. A one-interquartile increase in toluene concentrations did not significantly increase the risk for ALL in the any trimester (first trimester OR=0.95, 95% CI 0.68–1.32; second trimester OR=1.02, 95% CI 0.73, 1.42; third trimester OR=1.22, 95% CI 0.90–1.65), or for the entire pregnancy (OR=1.11, 95% CI 0.71–1.74). Similar results were seen for the risk of AML for the first and second trimester (OR=1.25, 95% CI 0.83–1.88 and OR=1.31,

95% CI 0.88–1.94, respectively), but the risk of AML was significantly increased for the third trimester (OR=1.50, 95% CI 1.04–2.16) and for the entire pregnancy (OR=1.78, 95% CI 1.03–3.06).

In the large registry-based NORD-TEST study, the risk of testicular germ cell tumors was studied in men ages 14–49 years diagnosed between 1978 and 2012 in Finland, Norway, and Sweden, on the basis of the men’s parents’ occupations prior to the men’s birth (Le Cornet et al., 2017). The parents’ occupations prior to the child’s birth were determined by examining national censuses and job codes. Although the authors found no association between prenatal maternal exposure to solvents and testicular germ cell tumors across all the countries combined, they did find an association with maternal exposure to toluene in the year before birth (OR=1.67, 95% CI 1.02–2.73), but not with paternal exposure.

ATSDR (2015b) reported on several studies of fetotoxicity following the intentional inhalation of large quantities of toluene or other organic solvents by women while pregnant; however, the Volume 11 committee does not find those exposure scenarios to be representative of those likely to be experienced by women during deployment. ATSDR identified one small study of low-level occupational exposure to toluene as well as other solvents and chemicals in Finland that suggested that there was an increased risk of CNS anomalies and neural tube closure defects in children of 14 exposed women (Holmberg, 1979).

The Volume 11 committee identified one paper that examined birth defects in children born to fathers with occupational exposure to toluene. In the Hooiveld et al. (2006) study cited earlier, which used toluene as a marker of exposure to solvents, 398 Dutch male painters were compared with 302 carpenters as the unexposed referents. Toluene exposure at 3 months before pregnancy for painters was predicted to range from 0.17 to 4.66 mg/m³, which was below the occupational exposure limit of 150 mg/m³ in the Netherlands. Compared with carpenters, painters with occupational exposure in the 3 months before pregnancy did have a significantly increased risk of birth defects in offspring (OR=2.4, 95% CI 1.2–4.9), particularly congenital malformations (OR=6.2, 95% CI 1.4–27.9).

The Volume 11 committee considered several papers on birth effects in children born to mothers with environmental exposure to toluene. Lupo et al. (2011) assessed the risk for neural tube defects, expressed in the form of spina bifida or anencephaly, as a result of prenatal exposure to ambient air pollutants in a population-based study in Texas. The estimated toluene levels, using the 1999 EPA ASPEN model, were categorized as low (0.01–0.31 μg/m³ for spina bifida, 0.01–0.30 μg/m³ for anencephaly), medium-low (>0.31–1.50 μg/m³ for spina bifida, >0.30–1.53 μg/m³ for anencephaly), medium (>1.50–2.84 μg/m³ for spina bifida, >1.53–2.85 μg/m³ for anencephaly), medium-high (>2.84–5.96 μg/m³ for spina bifida, >2.85–5.90 μg/m³ for anencephaly), and high (>5.96–14.3 μg/m³ for spina bifida, >5.90–14.3 μg/m³ for anencephaly). Although the risks were increased for both spina bifida and anencephaly at all toluene concentrations, none of the increases were significant. Ramakrishnan et al. (2013) assessed the risk for oral clefts in children whose mothers gave birth in Texas between 1999 and 2008 (estimated mean concentration of toluene in ambient air was 1.70 mg/m³). Mothers with estimated high exposure to toluene were no more likely to have a child with cleft lip with or without cleft palate (OR=1.01, 95% CI 0.86–1.19) or a nonsyndromic isolated cleft palate (OR=0.91, 95% CI 0.72–1.17) than mothers with estimated low exposure.

The Volume 11 committee identified one study that assessed the impact of exposure to residential toluene on the expression of miR-155 and miR-223 in maternal and cord blood as part of the German Lifestyle and Environmental Factors and Their Influence on Newborns Allergy Risk study in 2006–2008 (Herberth et al., 2014). miR-155 and miR-223 are known to be involved in regulatory T-cell formation or function. The median toluene concentration measured in the homes during weeks 34–36 of pregnancy was 6.95 μg/m³. Higher concentrations of toluene were significantly associated with increased levels of miR-223 in maternal blood (means ratio=1.10, 95% CI 1.02–1.18), but not miR-155 levels. Cord blood miR-155 expression was related to lower S-benzylmercapturic acid concentrations, a toluene

metabolite, in maternal urine, but miR-233 was not; toluene concentrations did not affect expression of either miRNA in cord blood. miR155 expression was not associated with lower Treg numbers in maternal and cord blood. Benzene concentrations were also associated with miR-223 in maternal blood, but not the expression of either miRNA in cord blood, and xylenes were not associated with miRNA in either maternal or cord blood (see the earlier section on benzene and the next section on xylenes).

Animal Studies

There were no toxicological or animal studies of possible developmental effects of toluene exposure cited in Gulf War and Health, Volume 2.

ATSDR (2015b) reported on several developmental toxicity studies done with rats, mice, and rabbits exposed to toluene. The results of numerous studies indicate that toluene by inhalation does not cause either toxic effects in the mother or developmental effects in the offspring when animals are exposed at levels <1,000 ppm administered for 6–7 hours/day during gestation (API, 1978, 1991, 1992; Jones and Balster, 1997; Klimisch et al., 1992; Ono et al., 1995; Roberts et al., 2007; Saillenfait et al., 2007; Thiel and Chahoud, 1997; Tsukahara et al., 2009; Win-Shwe et al., 2012; Yamamoto et al., 2009). However, at doses exceeding 1,000 ppm, retarded fetal growth and skeletal development and also altered development of behavior have been observed in offspring, while maternal toxicity is also evident (API, 1991, 1992; Dalgaard et al., 2001; Hass et al., 1999; Hougaard et al., 2003; Jones and Balster, 1997; Ono et al., 1995; Roberts et al., 2007; Saillenfait et al., 2007; Thiel and Chahoud, 1997).

ATSDR also reported on two studies of the continuous exposure of rats, mice, and rabbits to 133–399 ppm toluene during gestation, which resulted in reduced maternal body weight and reduced body weight and delayed skeletal ossification in the fetuses (Hudak and Ungvary, 1978; Ungvary and Tatrai, 1985).

The Volume 11 committee considered three additional studies on potential developmental effects from prenatal exposure to toluene. Hougaard et al. (2005) assessed whether prenatal exposure to 1,500 ppm toluene, 6 h/day, on GDs 7–20 resulted in increased effects in the female offspring of pregnant rats when combined with maternal exposure to chronic mild stress on GDs 9–20. Toluene exposure resulted in a greater decrease in plasma corticosterone in the offspring after acute stress on PND 27 as compared with the unexposed control or the chronic mild-stress animals. Maternal exposure to stress combined with toluene did not appear to exacerbate any neurotoxic effects. In a similar study, Soberanes-Chavez et al. (2013) exposed pregnant mice to restraint stress, to toluene (8,000 ppm whole body, 30 minutes, twice per day from GD 7 to parturition), or to a combination of the two. Only male pups were assessed postnatally. Exposure to toluene alone or with stress did not affect the length of gestation, the number of live pups, or the sex ratio. However, exposure to toluene significantly increased the risk of neonatal death (RR=4.2, 95% CI 1.2–14.8), with an even greater increase when toluene was combined with stress (RR=7.8, 95% CI 2.4–25.3). Toluene exposure also resulted in a significantly lower body weight at weaning. The committee notes that, given the large confidence intervals, these data should be interpreted with caution.

In a study to assess whether prenatal exposure to abusive levels of toluene impaired the neurodevelopment of offspring, Callan et al. (2017) exposed pregnant rats to 8,000 or 12,000 ppm toluene for 15 minutes twice daily from GD 8 through GD 20. Male and female offspring exposed to the lower dose exhibited no differences from controls in initial acquisition in the Morris water maze on PND 28 or on PND 44; however, rats exposed to 12,000 ppm displayed performance deficits during a probe trial and in reversal learning on PND 44.

Synthesis and Conclusions

The Volume 2 committee did not reach any conclusions on the category of association between exposure to toluene and any health outcomes, including reproductive or developmental effects.

Reproductive Effects

ATSDR (2015b) found that the data did not provide convincing evidence that acute or repeated inhalation exposure to toluene caused reproductive effects in humans. ATSDR presented limited evidence in humans to indicate that occupational exposure to toluene may lead to an increased incidence of spontaneous abortion (Lindbohm et al., 1991; Ng et al., 1992; Taskinen et al., 1989) or to decreased fecundity in female workers (Plenge-Böenig and Karmaus, 1999).

The Volume 11 committee found some evidence that exposure to toluene may adversely affect the reproductive health of women, such as fertility and the risk of spontaneous abortion (Taskinen et al., 1989). There were few studies of the reproductive effects of toluene in men, and the results showed few adverse effects on reproductive hormones or time to pregnancy (Hooiveld et al., 2006), although one study in Finland did find a significant increase in the risk of spontaneous abortion with high or frequent toluene exposure (Taskinen et al., 1989). The subjects in these studies were typically exposed to other solvents in addition to toluene. The animal studies provide little evidence on the reproductive toxicity of toluene.

The Volume 11 committee notes there are many unanswered questions regarding the reproductive effects of toluene since most studies predate the development of epigenetic biomarkers, which might help identify subclinical risk, and nearly all human studies are likely underpowered and have substantial confounders since most subjects were exposed to mixtures of chemicals. There are no data on the role of toluene exposure in the transgenerational transmission of adverse health effects or in epigenetic effects in either humans or animals.

The Volume 11 committee concludes that there is inadequate/insufficient evidence to determine whether an association exists between exposure to toluene and reproductive effects in men or women, or with adverse pregnancy outcomes.

Developmental Effects

Although there are a few studies that show that addictive inhalation of solvents by mothers during pregnancy can affect the fetal brain (ATSDR, 2015b), the Volume 11 committee did not find addiction to be a relevant exposure scenario for deployed women. Studies of prenatal exposure to low levels of toluene in ambient air did not support an increased risk of birth defects (Ramakrishnan et al., 2013) or of childhood cancer (Heck et al., 2014). Again, the maternal exposures in these studies were to mixtures that contained toluene. Animal studies did not show developmental effects with exposure to low levels of toluene, although two studies showed that toluene exposure in combination with chronic mild stress did result in adverse effects on pups.

The Volume 11 committee concludes that there is inadequate/insufficient evidence to determine whether an association exists between prenatal exposure to toluene and developmental effects.

TABLE 7-3 Summary of Reproductive and Developmental Effects of Toluene

continued

TABLE 7-3 Continued

NOTE: ADHD=attention deficit hyperactivity disorder; ALL=acute lymphoblastic leukemia; AML=acute myeloid leukemia; BTEX=benzene, toluene, ethylbenzene and xylene; CI=confidence interval; EPA=U.S. Environmental Protection Agency; FR=fecundability ratio; LBW=low birth weight; miR=micro-ribonucleic acid; miRNA=micro-ribonucleic acid; OR=odds ratio; PTB=preterm birth; SD=standard deviation; Treg=regulatory T cell; TTP=time to pregnancy.

XYLENES

Xylenes, like toluene, are components of gasoline and are also found as combustion products of fuel. Xylenes are thought to have been sent to the Gulf War in quantities greater than 1 kiloliter.

Xylenes were among the 12 most frequently detected VOCs at the three sampling locations at JBB in both 2007 and 2009 (IOM, 2011), although the concentrations varied considerably depending on where the sampling was conducted on the base and the time of year. The air concentrations of total xylenes ranged from levels below the detection limit to greater than 50 μg/m³ (second only to toluene). The authoring committee considered the likely major source of the xylenes to be unspecified combustion.

Xylene, or dimethyl benzene, is an organic aromatic hydrocarbon widely used in the production of ethyl benzene, polyester, and plastic. Like benzene and toluene, xylenes are commonly used industrial solvents and are frequently considered as part of the benzene-toluene-ethylbenzene-xylene (BTEX) complex. Also, like toluene, they are methylated forms of benzene with two methyl groups; there are three isomeric forms of xylene: ortho-, meta-, and para-.

Epidemiologic studies on the reproductive and developmental effects of xylenes reviewed below are summarized in Table 7-4 at the end of this section.

Reproductive Effects

Reproductive Effects in Men and Women

The Volume 2 committee (IOM, 2003) did not discuss any studies of male or female reproductive effects following exposure to xylene. Similarly, EPA and ATSDR did not present any human studies on reproductive effects following xylene exposure in their reviews (ATSDR, 2007b; EPA, 2003).

The Volume 11 committee identified only one small study, also discussed in the sections on benzene and toluene, of the effects of xylene exposure. This was the study of 24 men in China with occupational exposure to a mixture of high concentrations of benzene, toluene, and xylenes along with 37 unexposed workers who served as controls (Xiao et al., 2001). Multiple-regression results showed that decreased seminal γ-glutamyltransferase activity (which reflects the function of the prostate) was associated with increased xylene levels in the blood of exposed men.

Among 1,408 newly wed female petrochemical workers in China, exposure to xylene—as part of a mixture that also included benzene, toluene, and styrene—was correlated with an increased risk of oligomenorrhea (menstrual cycle length >35 days) (OR=1.63, 95% CI 1.04–2.53) (Cho et al., 2001).

Adverse Pregnancy Outcomes

The Volume 2 committee (IOM, 2003) identified one case-control study by Taskinen et al. (1994) that examined the risk of spontaneous abortion among female laboratory workers potentially exposed to solvents (206 cases and 329 controls). The authors reported that exposure to xylene was associated with an increased risk of spontaneous abortion (OR=3.1, 95% CI 1.3–7.5).

EPA (2003) did not identify any studies on adverse birth outcomes in children exposed prenatally to xylenes. ATSDR (2007b) reported on two studies of birth outcomes associated with parental exposure to xylenes, one of which was Taskinen et al. (1994), which was also discussed by the Volume 2 committee. The other study—by Lindbohm et al. (1990)—found no significant increase in the risk of spontaneous abortion among Finnish workers for whom there were biomonitoring data on xylene levels. ATSDR (2007b) concluded that “the available studies of reproductive toxicity from occupational exposure to

xylenes were not definitive because of the small number of subjects and/or concurrent exposure to other chemicals.”

EPA reached similar conclusions on the potential association between spontaneous abortion and exposure to xylenes, but it also noted the lack of specificity in the exposures (EPA, 2000). Ambient solvents modelled by land use regression in a large California study were associated with an increased risk of low birth weight for gestational age with higher exposure to several solvents including xylene, however, the effect estimate was small (OR=1.03, 95% CI 1.01–1.06) (Ghosh et al., 2013).

The Volume 11 committee did not identify any new studies on birth outcomes in humans following maternal or paternal exposure to xylenes.

Animal Studies

ATSDR (2007b) found no reproductive effects in rats exposed via inhalation to 500 ppm xylene before mating and during gestation and lactation. No histopathological changes in the reproductive organs were seen in rats and mice in intermediate and chronic oral bioassays at mixed xylene concentrations of, respectively, 800 and 1,000 mg/kg/day, given 5 days/week.

The Volume 11 committee did not identify any new relevant animal studies on the reproductive effects of xylene.

Developmental Effects

The Volume 2 (IOM, 2003) committee considered several studies that looked at solvents in general and that reported results for xylenes specifically. Olshan and colleagues (1999) found an increased risk of neuroblastoma in children whose fathers were painters (OR=2.1, 95% CI 0.9–4.8); this was the most relevant of the 73 paternal occupations listed for solvent exposure. In a follow-up study, a job-exposure matrix was used to evaluate maternal and paternal occupational exposure to 65 chemical compounds or broad categories of substances (De Roos et al., 2001). Using this approach, the authors found no significant increase in the risk of neuroblastoma in children born to mothers or fathers with occupational exposure to xylene (OR for paternal exposure=1.4, 95% CI 0.5–4.3). In a study of occupational exposures among parents in the Children’s Cancer Group, there was no association found between self-reported paternal preconception exposure to xylenes and ALL in their children (OR=1.2, 95% CI 0.8–1.8) (Shu et al., 1999). Results were not reported for maternal exposure for any time prior to or during pregnancy.

EPA and ATSDR reported few data on developmental outcomes associated with prenatal xylene exposure (ATSDR, 2007b; EPA, 2003). EPA’s Toxicological Review of Xylenes (2003) did not identify any studies on the possible developmental toxicity of inhaled xylenes in humans. ATSDR (2007b) concluded that the “data are limited for assessing the relationship between inhalation of xylene and developmental effects because the available studies involved concurrent exposure to other solvents in addition to xylene in the workplace (Holmberg and Nurminen, 1980; Kucera, 1968; Taskinen et al., 1989; Windham et al., 1991), and because of the small number of subjects, ranging from 9 to 61 (Taskinen et al., 1989; Windham et al., 1991).”

The Volume 11 committee identified three new studies that reported on developmental effects in children following maternal exposure to xylenes. In a study discussed earlier in the sections on benzene and toluene, Ramakrishnan et al. (2013) estimated ambient air levels of numerous air pollutants, including xylenes, near mothers’ residences in Texas and used the Texas Birth Defects registry to examine the occurrence of oral cleft among these mothers’ children between 1999 and 2008. No significant associations were found between a mother’s exposure to xylene (high versus low exposure) and the likelihood

of having a child with cleft lip with or without cleft palate (aOR=0.93, 95% CI 0.80–1.10) or isolated cleft palate (aOR=0.85, 95% CI 0.66–1.08). In a second study—also discussed in the sections on benzene and toluene—Lupo et al. (2011) assessed the risk for neural tube defects, expressed in the form of spina bifida or anencephaly, as a result of prenatal exposure to ambient air pollutants in a population-based study in Texas. Estimated xylene levels (ranging from 0–8.84 μg/m³) were associated with increased, but not significant, risks for both spina bifida and anencephaly.

Heck et al. (2014)—also discussed earlier in the sections on benzene and toluene—used the California Cancer Registry to identify children under 6 years of age who had been diagnosed with either ALL (n=69) or AML (n=46) between 1990 and 2007. The authors then looked for a relationship between xylene exposure and leukemia in those cases along with 19,209 controls, all of whom lived within either 2 km (for ALL) or 6 km (for AML) of an air toxics monitoring station. In the each trimester of pregnancy, an average of about seven air toxic measurements were used to calculate individual exposures. A one-interquartile increase in o-xylene or m/p-xylenes concentration did not significantly increase the risk for ALL or AML at any time during pregnancy. However, when the authors assessed the relationships as a function of trimester only, they found that during the third trimester exposure to m/p-xylenes significantly increased the risk of ALL (OR=1.37, 95% CI 1.01–1.85) and exposure to o-xylene significantly increased the risk of AML (OR=1.33, 95% CI 1.05–1.69).

The Volume 11 committee identified one study that assessed the impact of exposure to residential xylenes on the expression of miR-155 and miR-223 in maternal and cord blood as part of the German Lifestyle and Environmental Factors and Their Influence on Newborns Allergy Risk study in 2006–2008 (Herberth et al., 2014). miR-155 and miR-223 are known to be involved in regulatory T-cell formation or function. The median xylenes concentrations for the m/p-isomers was 1.55 μg/m³ and for o-isomer was 0.49 μg/m³. Higher concentrations of any xylenes were not significantly associated increased levels of miR-223 or miR-155 in either maternal or cord blood (all CIs included 1.0). Benzene and toluene concentrations were both associated with miRNA-223 in maternal blood, but not the expression of either miRNA in cord blood (see earlier sections on benzene and toluene).

Animal Studies

The Volume 2 committee did not include any animal studies of the developmental toxicity of xylenes.

In its Toxicological Review of Xylenes, EPA reported on several animal studies that examined the developmental effects in offspring following maternal inhalation exposure (EPA, 2003). In one study by Hass et al. (1995), neurodevelopmental impairments (rotarod performance) were observed in the female but not male offspring of pregnant rats exposed to 500 ppm, although the impairments did not reach statistical significance. Animal studies that looked at standard developmental endpoints in rats and mice reported decreased body weights in dams at doses of 700 ppm xylene or greater as well as fetal skeletal and visceral malformations; doses as low as 230 ppm resulted in increased abortions in rabbits, and decreased fetal body weight and fetal survival were observed in rats at 350 ppm. However, EPA noted that these effects were seen at concentrations greater than those associated with neurobehavioral effects in adults.

ATSDR (2007b) reviewed the studies cited by EPA as well as new studies and found that “in general, developmental studies in animals reported adverse fetal effects only at concentrations that caused maternal toxicity.” Inhalation studies in animals exposed prenatally to ≥350 ppm xylenes resulted in a delayed ossification of the skeleton and reduced fetal body weight, but the concentrations also caused maternal toxicity. In rats, prenatal inhalation exposure to 500 ppm m-xylene has been associated with postnatal neurobehavioral deficits (decreased rotarod performance); oral exposure to 2,060 mg/kg/day

of mixed xylenes has been associated with cleft plate and decreased fetal weight; and dermal exposure to xylene has been associated with biochemical changes in fetal and maternal brain tissue.

The Volume 11 committee did not identify any relevant new animal studies on the developmental effects of xylene.

Synthesis and Conclusions

Reproductive Effects

The data on the reproductive effects of xylenes are scant. Most studies have investigated the effects of the mixture BTEX, not xylenes specifically, and nearly all occur in the context of mixed exposures. Single studies suggested that occupational exposures to xylene may be associated with oligomenorrhea in women and reduced seminal γ-glutamyltransferase activity in men, although both studies were small.

Only two studies of the effects of prenatal occupational exposure to xylenes on the risk of spontaneous abortion were identified by ATSDR (2007b), and the results were contradictory. The Volume 11 committee did not identify any new literature on the reproductive effects of xylenes.

The Volume 11 committee concludes that there is inadequate/insufficient evidence to determine whether an association exists between exposure to xylenes and reproductive effects in men or women, or with adverse pregnancy outcomes.

Developmental Effects

One study suggested that BTEX exposure may increase the risk of low birth weight for gestational age, although the effect size was small. Some data suggest that xylenes exhibit developmental neurotoxicity but primarily at very high doses, and there is some suggestive evidence of an increased risk of AML in children if mothers are exposed in the third trimester, but the results overall are not conclusive.

EPA and ATSDR reviewed several animal studies that showed various developmental effects, including skeletal malformations, decreased fetal weight and viability, and, in one study, neurologic effects associated with gestational exposure to xylenes. ATSDR cautioned that the developmental effects were generally seen at doses that caused maternal toxicity.

Therefore, the Volume 11 committee concludes that there is inadequate/insufficient evidence to determine whether an association exists between prenatal exposure to xylenes and developmental effects.

TABLE 7-4 Summary of Reproductive and Developmental Effects of Xylenes

continued

TABLE 7-4 Continued

NOTE: ALL=acute lymphoblastic leukemia; AML=acute myeloid leukemia; CI=confidence interval; EPA=U.S. Environmental Protection Agency; miR=microribonucleic acid; OR=odds ratio.

TRICHLOROETHYLENE (TCE)

TCE is a commonly used solvent and is relatively well studied with regard to its toxicity in both humans and animals. EPA considers TCE to be carcinogenic to humans by all routes of exposure and, furthermore, has identified it as a potential threat to human health through noncancer toxicity to the CNS, kidney, liver, immune system, male reproductive system, and developing embryos/fetuses (Chiu et al., 2013).

TCE was sent to the 1990–1991 Gulf War in quantities greater than 1 kiloliter (see Table 7-1). The Volume 11 committee was unable to identify any information on the amount of TCE that was sent to the Post-9/11 conflicts. However, TCE was one of 47 chemicals detected in at least 5% of the air monitoring samples collected at JBB in 2007 and 2009 (IOM, 2011).

DoD and the Department of Veterans Affairs are also concerned about TCE because it was a major contaminant of the water supply system at the U.S. Marine Corps base Camp Lejeune in North Carolina from 1957 until the contaminated wells were closed in 1985. Residents, including children and pregnant women, were exposed to TCE, PCE, benzene, toluene, and other halogenated hydrocarbons, many of them degradation products of PCE, the most commonly detected contaminant (NRC, 2009). TCE concentrations in the well water varied greatly depending on the well and date of sampling, but they ranged from undetectable to 18,900 μg/L in 1980–1985 (NRC, 2009).

TCE metabolism in humans and animals occurs by cytochrome P450 and glutathione conjugation pathways. The major urinary metabolites of TCE in humans are the oxidative metabolites trichloroacetic acid, trichloroethanol, trichloroethanol-glucuronide (ATSDR, 2014), and dichloroacetic acid (IOM, 2003). The metabolism of TCE is relatively rapid, with a renal elimination half-life of about 10 hours following inhalation exposure (ATSDR, 2014).

For its assessment of the reproductive and developmental effects of TCE, the Volume 11 committee considered four earlier, comprehensive reports—Gulf War and Health, Volume 2 (IOM, 2003), the 2009 NRC report on contaminated water at Camp Lejeune, EPA’s Toxicological Review of Trichloroethylene (EPA, 2011), and the 2014 ATSDR publication Draft Toxicological Profile for Trichloroethylene—as well as any new studies published in the years since 2014. The committee notes that many of the key studies on TCE were reviewed by more than one of those organizations. The epidemiologic studies on the reproductive and developmental effects of TCE reviewed below are summarized in Table 7-5 at the end of this section.

Reproductive Effects

The potential reproductive effects of TCE have been studied by numerous researchers and have been evaluated by several organizations, including the NRC, EPA, and ATSDR. The 2009 NRC report on PCE- and TCE-contaminated drinking water at Camp Lejeune found limited suggestive evidence of an association between TCE, PCE, or solvent mixtures and female infertility; however, there was inadequate/insufficient evidence to determine whether an association existed between exposure to TCE, PCE, or solvent mixtures and female infertility after the exposure ceased; between maternal or paternal preconception exposure and miscarriage, preterm birth, or fetal growth restriction; or between prenatal exposure and preterm birth or fetal growth restriction (NRC, 2009).

Reproductive Effects in Men and Women

The Volume 2 committee reported on only one study of male reproductive effects (Sallmén et al., 1998). In this Finnish study of self-reported paternal exposure (with biological measurements of exposure in 69% of men) to a variety of solvents, including TCE, exposure to any level of TCE did not have an

impact on TTP. Studies of exposure to TCE among 85 male workers found moderate decreases in FSH and testosterone and stronger increases in dehydroepiandrosterone sulfate with increasing duration of exposure, but these hormonal changes were not linked to reproductive effects (Chia et al., 1997; Goh et al., 1998).

In its 2006 review, NRC found no data on the effects of TCE on human male reproduction; however, animal studies suggested that TCE “is toxic to spermatogenesis and sperm fertilizing ability.” In 2009, NRC did not find any epidemiologic studies on the possible effects of TCE exposure, whether occupational or environmental, on semen quality or male fertility.

EPA (2011) reported that of the 10 studies on male reproductive effects it considered (7 populations, 1 case study; all but 1 study looked at fewer than 100 men), all but 1 found significant associations between TCE exposure and increased sperm concentration and decreased sperm quality parameters, altered sexual drive or function, or altered serum hormone levels; however, the effects on male fertility were not reported for most of the studies or were unchanged. EPA concluded that the “database as a whole suggests that TCE does induce male reproductive toxicity independent of systemic effects.”

In 2014, ATSDR cited several studies (Bardodej and Vyskocil, 1956; El Ghawabi et al., 1973) that reported reproductive effects in men occupationally exposed to TCE, such as decreased potency or sexual disturbances and changes in sperm morphology; other studies cited by ATSDR, however, found that TCE had no effect on male reproduction (Rasmussen et al., 1988; Sallmén et al., 1998). ATSDR stated, “Evidence of trichloroethylene-induced effects in occupationally-exposed men includes reports of decreased potency, altered sex drive or function, decreased sperm quality, and decreased serum levels of reproductive hormones” (ATSDR, 2014).

Regarding female reproductive effects, the Volume 2 committee identified two studies that looked at maternal exposure to TCE and reproductive effects (IOM, 2003). Sallmén et al. (1995) found that among Finnish women occupationally exposed to high levels of TCE in the 12 months before pregnancy, fecundability was reduced, but not significantly (incidence density ratio [IDR]=0.61, 95% CI 0.28–1.33).

The EPA (2011) toxicologic review of TCE included only two studies on the effects of TCE on female reproduction. One was a study in Finland (Sallmén et al., 1995; cited in IOM, 2003), and the other was carried out at Rocky Mountain Arsenal in Colorado (ATSDR, 2001), neither of which showed a significant effect on fertility.

The Volume 11 committee did not identify any new studies on possible reproductive effects in men or women following environmental or occupational exposure to TCE.

Adverse Pregnancy Outcomes

Volume 2 included a study of Finnish women with occupational exposures to TCE that showed an increased risk of spontaneous abortion (OR=2.2, 95% CI 1.2–4.1) (Lindbohm et al., 1990).

The 2006 NRC report found that women in three states (eastern North Carolina, western New York State, and New Jersey) who were exposed to TCE-contaminated drinking water while pregnant gave birth to babies with reduced birth weights. For the Camp Lejeune population in eastern North Carolina, the longer the exposure to TCE, the greater the decrease in birth weight. In 2009, an NRC committee that reviewed health effects at Camp Lejeune found some indication that solvent exposure during, but not before, pregnancy was associated with an increased risk of miscarriage, although it was not associated with preterm birth or reduced birth weight, and there was no direct evidence on perinatal mortality (NRC, 2009).

The EPA reviewed the evidence for adverse fetal outcomes from prenatal exposure to TCE, and the resulting report included many studies that were discussed in the 2006 and 2009 NRC reports (EPA,

2011). In general, the epidemiologic studies reported associations between parental exposure to TCE, both occupational and environmental, and spontaneous abortion or perinatal death and also decreased birth weight or small for gestational age, although other studies reported mixed or null findings. EPA noted that many of these studies were small in size and a number of them reported on exposures to mixtures of solvents, not TCE alone. EPA concluded on the basis of the epidemiologic and animal data that “TCE exposure poses a potential hazard for prenatal loses and decreased growth or birth weight of offspring” (EPA, 2011).

ATSDR (2014) cited several studies that reported adverse fetal outcomes following residential or occupational exposure to TCE. The results were mixed for an increased risk of spontaneous abortion, and some studies found that prenatal maternal exposures to TCE were associated with lower birth weights.

The Volume 11 committee considered two additional studies. The first study was on fetal outcomes for women exposed to TCE present in indoor air via soil-vapor intrusion in Endicott, New York (Forand et al., 2012). Among the 1,090 births to women who were exposed to TCE levels ranging from 0.18 to 140 μg/m³, the adjusted rate ratios (aRRs) versus births to unexposed women were significantly higher for low birth weight (<2,500 g; aRR=1.36; 95% CI 1.07–1.73), small for gestational age (aRR=1.23, 95% CI 1.03–1.48), and full-term low birth weight (aRR=1.68, 95% CI 1.20–2.34). RRs for other endpoints—preterm birth (<37 weeks), very preterm birth (<32 weeks), and very low birth weight (<1,500 g)—were also elevated, but not significantly. The authors noted, however, that socioeconomic factors, particularly maternal smoking, may have led to some confounding of results.

In the second study, Ruckart et al. (2014) conducted a cross-sectional study of 11,896 births at Camp Lejeune, North Carolina, during 1968–1985, the period of groundwater contamination with TCE and other solvents (including benzene, as discussed earlier), using birth certificate information and groundwater modeling. Term low birth weight was defined as full-term babies (≥37 weeks gestation) weighing <2,500 grams at birth. For small for gestation age births, three categories were evaluated: newborns weighing <5th and <10th percentiles based on sex- and race-specific weight by gestational week norms from New Jersey, and newborns weighing less <10th percentile based on sex-specific growth curves for California. Exposure to any concentration of TCE during the entire pregnancy was associated with a significantly reduced mean birth weight (β= –78.3g, 95% CI –115.0– –41.7). It was also associated with an increased risk of a small-for-gestational-age infant at any concentration during pregnancy, including at the lowest tertile of exposure (OR=1.2, 95% CI 1.1–1.5). It was not associated with preterm births or term low birth weight.

Animal Studies

Volume 2 reported that inhalation of TCE in male rats results in dose-related increases in Leydig cell tumors (IOM, 2003). NRC (2006) reported that multiple rodent studies indicate that TCE affects spermatogenesis and the fertilizing capability of sperm in males. The second NRC review (2009) reported on a few animal studies, including some with inhalation exposure that showed a potential association with male infertility, particularly decreased sperm count and motility and increased numbers of abnormal sperm.

The EPA toxicological review (2011) also found that some, but not all, animal studies reported adverse effects of TCE on male reproduction, including sperm measures, libido/copulatory behaviors, and serum hormone levels as well as histopathological lesions in the testes or epididymides and altered in vitro sperm–oocyte binding or in vivo fertilization due to TCE or metabolites.

The animal studies cited by ATSDR (2014) in the TCE profile supported the epidemiologic studies on the effects of TCE on male and female reproduction. Exposure to TCE via inhalation was a reproductive

toxicant in male rats and mice, resulting in testicular atrophy, decreased sperm count and motility, and increased abnormal sperm morphology. In one study, male rats administered TCE by gavage at 1,000 mg/kg/day, 5 days/week for 6 weeks had impaired copulatory behavior (Zenick et al., 1984).

Regarding female fertility and pregnancy outcomes, NRC (2006) found animal studies that indicate that TCE leads to decreased fertilizability of oocytes in females. The 2006 NRC committee found that animal studies also suggested that TCE may be a reproductive toxicant in rats and that its effect requires metabolic activation by cytochrome P450 2E1 (CYP2E1), but the relevance of these studies to human reproduction was not clear. In studies on female rats described in the 2009 NRC report on Camp Lejeune, exposure before mating and during pregnancy was correlated with reduced offspring survival at high concentrations that also produced maternal toxicity. Studies of mating pairs of rats or mice exposed during mating and throughout one or more pregnancies also showed reduced numbers of litters and increased perinatal mortality. NRC (2006) reported that multiple animal studies have found decreased fetal growth after maternal exposure to TCE. In animal studies, decreased intrauterine growth has been found consistently after maternal exposure to TCE (Fisher et al., 2001; Johnson et al., 1998a,b; Smith et al., 1989, 1992).

EPA (2011) found that animal studies supported the human data: decreased fetal weight, decreased live birth weights, and decreased postnatal growth were found in rats and mice, although there were species differences in the outcomes reported for Fischer 344 or Wistar rats (increased risk of adverse outcomes) versus Sprague Dawley rats (no increase in risk). It further reported that although one study in rats showed reduced in vitro oocyte fertilizability, other laboratory animal studies of oral exposure did not report adverse effects on female reproductive function.

In the 2014 ATSDR review, animal studies supported the epidemiologic findings of reduced fertility and adverse birth outcomes, although only when the animals received repeated high doses of TCE. The only study of female rats found no reproductive effects following preconception exposure. In a continuous breeding study, oral administration of 300 mg/kg/day of TCE from 7 days before mating through the birth of the F2 generation resulted in no reproductive effects in rats. A similar study in mice treated with up to 750 mg/kg/day found no treatment-related effects on mating, fertility, or reproductive performance in either the F0 or F1 mice, but sperm motility was reduced by 45% in F0 males and by 18% in F1 males, and F1 males exhibited significantly increased mean relative weights of the left testis/epididymis and right epididymis; the effects in the F2 generation were not reported by ATSDR. No treatment-related effects on fertility were seen in studies of female rats receiving TCE from the drinking water during premating or gestation at estimated doses as high as 129 mg/kg/day.

The Volume 11 committee identified only one new animal study on the effects of TCE exposure on reproduction. Wu and Berger (2007) exposed female rats to TCE in drinking water on days 1 to 5, days 6 to 10, or days 11 to 14 of the 2-week interval preceding ovulation (oocytes collected the morning of day 15). TCE-treated oocytes had a greater incidence of protein carbonyls (an indicator of oxidative damage) and were less fertilizable than controls.

Developmental Effects

Several developmental effects have been assessed in children who were exposed to TCE either via the mother during gestation or via the father prior to conception. The health outcomes that have been examined include childhood cancer, specifically leukemia, and cardiac birth defects.

The Volume 2 committee reported on three studies that evaluated the association between prenatal exposure to TCE and childhood leukemia. Paternal preconception exposure to TCE was not significantly associated with childhood leukemia (De Roos et al., 2001; Lowengart et al., 1987; Shu et al.,

1999). However, maternal prenatal exposure to any solvent was associated with an increased risk of acute lymphocytic leukemia in children, although exposure to TCE specifically was not (De Roos et al., 2001; Shu et al., 1999).

The 2006 NRC report found that prenatal exposure to TCE via drinking contaminated water was associated in several epidemiological studies with a two- to threefold increase in the risk of congenital heart defects of the interventricular septae and heart valves. The biological plausibility of this correlation was enhanced by similar defects being reported in animal studies, although the NRC committee found the animal studies to be inconsistent and noted that there were species differences in response, with avian studies being the most convincing.

The 2009 NRC report on contaminated water at Camp Lejeune concluded that although the epidemiologic evidence of an association between chronic exposure to TCE or PCE and congenital malformations was judged to be inadequate to support conclusions, the toxicologic data from several studies reviewed by the committee, particularly the inhalation exposure study conducted in rats on GDs 6–20 by Carney et al. (2006), provided strong evidence that neither solvent was associated with congenital cardiovascular malformations in rats at concentrations up to those that have minimal maternal toxicity. Many of the developmental animal studies considered by the committee exposed the dams to TCE not only during gestation but also during lactation, which is not a relevant window of exposure for this report. The 2009 NRC committee noted that there was no evidence of second-generation effects from continuous breeding experiments in rats and mice.

Epidemiologic studies on postnatal developmental effects following prenatal exposure was assessed by EPA in its extensive 2011 toxicological review of TCE (EPA, 2011). EPA found that both human and animal studies indicated that a number of congenital malformations were associated with prenatal maternal environmental and occupational exposure to TCE; these exposures were via inhalation and consumption of contaminated drinking water. Some—but not all—epidemiologic studies found increases in total birth defects, oral cleft defects, eye/ear defects, kidney/urinary tract disorders, musculoskeletal birth anomalies, lung/respiratory tract disorders, skeletal defects, and cardiac defects. For some of these outcomes, such as eye/ear defects and kidney/urinary tract disorders, there was only one positive study (e.g., Lagakos et al., 1986). Prenatal exposure to TCE in humans was also associated with neuroanatomical changes such as neural tube defects (ATSDR, 2014; Bove, 1996; Bove et al., 1995; Lagakos et al., 1986) and encephalopathy (White et al., 1997) and also with clinical neurological changes such as impaired cognition (White et al., 1997) and speech and hearing impairment (Burg and Gist, 1999; White et al., 1997). In animal studies, the administration of TCE, whether by the inhalation or oral route of exposure, was also associated with anatomical and developmental neurotoxicity.

The most studied birth defects were those of the cardiovascular system, particularly the heart. EPA (2011) found that the epidemiologic studies, when considered as a group, showed a significant increase in the incidence of cardiac defects in children with prenatal exposure to TCE, whether from maternal inhalation of contaminated air or maternal consumption of contaminated water (ATSDR, 2008; Bove et al., 1995; Goldberg et al., 1990; Yauck et al., 2004). The animal data on cardiac defects following prenatal exposure to TCE were inconsistent; several studies found cardiac defects in rat pups born to dams administered TCE in drinking water, but some well-conducted studies did not. EPA pointed out that although some animal and mechanistic studies may have had limitations, they provided a “plausible mechanistic basis for defects in septal and valvular morphogenesis observed in rodents, and consequently support the plausibility of cardiac defects induced by TCE in humans” (EPA, 2011).

Studies on the risk of childhood cancer as a result of prenatal exposure to TCE were inconclusive, and EPA cited an ongoing study by ATSDR of childhood cancer at Camp Lejeune as a potential future resource.

ATSDR (2014) reviewed two studies of maternal exposure to TCE via inhalation and several studies of maternal exposure to TCE via contaminated drinking water and concluded that it was not possible to determine on the basis of those studies if TCE caused developmental effects, including cardiac effects and hearing impairment, in prenatally exposed offspring.

The Volume 11 committee considered six studies (Brender et al., 2014; Cordier et al., 2012; Forand et al., 2012; Heck et al., 2014; Ruckart et al., 2013; Swartz et al., 2015) and one systematic review (Makris et al., 2016) that examined developmental effects in children born to women with gestational exposure to TCE; one additional study assessed both maternal and paternal exposures (Le Cornet et al., 2017). In the Forand et al. (2012) study, cited under Reproductive Effects, children born to women with inhalation exposure to TCE as a result of soil-vapor intrusion were found to be at a significantly increased risk of cardiac defects (RR=2.15, 95% CI 1.27–3.62) and conotruncal defects (RR=4.91, 95% CI 1.58–15.24); the risks were elevated for all reportable birth defects and for surveillance birth defects, but not significantly so.

The PELAGIE mother–child cohort in Brittany, France (Cordier et al., 2012), examined the association between solvent exposure (as determined by questionnaires and, in a subset, the presence of urinary metabolites of TCE) and congenital malformations in a subset of 3,421 women who returned the inclusion questionnaire before 19 weeks of gestation; pregnancy outcomes were obtained from maternity hospital records for 3,399 pregnancies, including 79 cases and 580 controls. Levels of trichloracetic acid and trichloroethanol greater than or equal to 0.01 mg/L in urine were both associated with an increased risk of limb malformations (OR=8.0, 95% CI 2.5–25.9 and OR=5.8, 05% CI 1.4–23.6, respectively); trichloroethanol was also associated with an increased risk of any malformation (OR=3.3, 95% CI 1.3–8.3).

As discussed in the section on benzene, Ruckart et al. (2013) conducted a case-control study to assess the frequency of birth defects and childhood cancers in children born to mothers at Camp Lejeune, North Carolina, between 1968 and 1985, who may have consumed drinking water contaminated with solvents, including TCE. Birth certificates were used to identify the 51 cases and 526 control parent–child pairs. Prenatal TCE exposure in the first trimester was not associated with a significantly increased risk of childhood leukemia, non-Hodgkin’s lymphoma, oral cleft defects, or neural tube defects.

Brender et al. (2014) examined the risk of birth defects in children born between 1996 and 2008 in Texas and maternal residential proximity to industrial releases of chlorinated solvents, including TCE. TCE was not significantly associated with any of the birth defects considered: any neural tube defect, anencephaly, spina bifida, conotruncal heart defects, obstructive heart defects, any oral clefts, cleft palate only, or cleft lip with or without cleft palate, or any type of limb deficit. A correlation between TCE exposure and septal heart defects was barely significant (OR=1.06, 95% CI 1.02–1.10) and showed a positive trend with TCE emissions (p-value for trend=0.002). When analyses were stratified by maternal age, infants born to exposed mothers who were 35 years of age or older had a significantly greater risk of several defects, whereas risks were less among children born to women less than 35 years of age: oral clefts (OR=1.39, 95% CI 1.06–1.83 versus OR=1.02, 95% CI 0.91–1.14) and any heart defect (OR=1.04, 95% CI 1.00–1.07 versus OR=1.13, 95% CI 1.04–1.22).

In a study of the risk of neural tube defects in children born in Texas between 1999 and 2004, Swartz et al. (2015) estimated the ambient levels of 32 hazardous air pollutants, including TCE, using the EPA 1999 Assessment System for Population Exposure Nationwide. The authors used hierarchical Bayesian modeling, which included stochastic search variable selection (SSVS). Among the 25 hazardous air pollutants used in the model, only quinolone and TCE had Bayes factors greater than 1. The OR for the medium level of TCE exposure and spina bifida was 2.00 (95% CI 1.14–3.61); the joint model without the SSVS found only the medium level of TCE to be associated with spina bifida (OR=5.72, 95% CI 1.44–24.16).

Heck et al. (2014)—also discussed in the section on benzene—assessed the risk of childhood leukemia following maternal exposure to air toxics, including TCE, by trimester, in children in California who had been diagnosed with either ALL (n=69) or AML (n=46) between 1990 and 2007. A one-interquartile increase in TCE concentrations did not increase the risk for ALL during the first, second, or third trimester or during the entire pregnancy, nor the risk of AML at any time during the pregnancy.

In the NORD-TEST study described in the benzene section, there was no increased risk of testicular germ cell tumors in men aged 14–49 years relative to their parents exposures to TCE in the year prior to their birth in Finland, Norway, and Sweden (OR=0.98, 95% CI 0.62–1.54 and OR=1.10, 95% CI 0.94–1.28, for maternal and paternal occupational exposures, respectively) (Le Cornet et al., 2017).

In a systematic review of the risk of cardiac defects following TCE exposure, Makris et al. (2016) examined seven epidemiologic studies. Most of the studies had been included in the EPA (2011) assessment cited earlier. The authors found that “TCE has the potential to cause cardiac defects in humans when exposure occurs at sufficient doses during a sensitive window of fetal development” (Makris et al., 2016).

Animal Studies

The 2006 NRC committee identified multiple mammalian and avian studies that suggested that TCE or one or more of its metabolites (trichloroacetic acid and dichloroacetic acid) can cause cardiac teratogenesis, although the committee noted that the avian studies were the most convincing, as the rodent studies had mixed results, suggesting either methodological or strain differences. The committee noted that the “low-dose studies showing a positive correlation in TCE-induced cardiac teratogenesis showed unusually flat dose–response curves and came from a single laboratory” (NRC, 2006).

The NRC committee that examined the effects of TCE and PCE in drinking water at Camp Lejeune (NRC, 2009) concluded that the toxicologic data provide strong evidence that neither solvent is associated with congenital malformations in rats, based on the then-recent studies by Carney et al. (2006) that showed no effects on the development of the heart or other organs in the rat at concentrations up to a minimal maternally toxic concentration. The committee discussed four studies in rats that suggested the existence of neurologic effects in offspring following gestational exposure via drinking water.

The EPA (2011) toxicological review of TCE concluded, based on multiple well-conducted studies in rats and mice, that exposure to TCE poses a risk for prenatal losses and decreased growth or birth weight in offspring. EPA found mixed evidence concerning the connection between TCE and cardiac defects; it reported that numerous studies had found that the oral administration of TCE in maternal drinking water during gestation induces cardiac malformations in rat fetuses, while several other well-conducted studies had not found induction of cardiac defects in rats, mice, or rabbits when TCE was administered by inhalation or gavage.

The animal studies cited by ATSDR suggest that TCE not only can cause cardiac malformations via oral exposure but also can damage the immune system in developing fetuses and produce neurologic defects (ATSDR, 2014).

The Volume 11 committee identified several new animal studies that examined the effects of TCE on fetal development. Warren et al. (2006) assessed whether the prenatal exposure of rats to TCE and its oxidative metabolites, trichloroacetate (TCA) and dichloroacetate (DCA), affects eye development. Pregnant rats received oral doses of either TCE (500 mg/kg/day), TCA (300 mg/kg/day), or DCA (300 mg/kg/day) on GDs 6–15. On GD 21, fetal eyes were measured for lens area, globe area, medial canthus distance, and interocular distance. No gross ocular malformations were seen for the TCE, TCA, and DCA treatment groups. All four ocular measures were reduced after exposure to TCA or to DCA, but the reductions were not significant for the TCA; TCE had no effect.

Palbykin et al. (2011) found that 10 ppb of TCE administered via drinking water to pregnant Sprague-Dawley rats beginning on GD 0 induced DNA hypermethylation in the reduced Serca2 promotor region of rat embryonic cardiac tissue examined on GD 10, which corresponds to the first phase of heart development. Gilbert et al. (2014) sought to determine if the timing of TCE exposure during development resulted in different immunotoxic responses. Pregnant MRL+/+ mice received oral doses of 0, 0.01, or 0.1 mg/mL TCE from GDs 0 to birth. Peripheral CD4+ T cells from the offspring of both groups had alterations in retrotransposon (intracisternal A particle and murine endogenous retrovirus) expression indicative of epigenetic alterations. Some effects, such as alterations in thymus cellularity, were found only in offspring exposed to TCE during gestation.

Synthesis and Conclusions

TCE has been studied by several governmental and other organizations. It has been identified as a contaminant in drinking water or air at several locations. It has numerous industrial applications that may result in occupational exposures.

Reproductive Effects

NRC, EPA, and ATSDR have all reviewed multiple studies that assessed the effect of occupational exposure to TCE on male reproduction. EPA reviewed 10 studies, 9 of which included fewer than 100 men and which found significant adverse effects on semen quality. However, what impact these effects had on fertility was not reported in the studies. ATSDR cited other studies which did not find any effect of TCE on male reproduction. The Volume 11 committee did not identify any new studies of TCE exposure and male reproduction. Many, but not all, of the animal studies considered by EPA indicated that TCE may have adverse effects on male reproduction, including altered hormone levels and lesions in the testes. Together these data suggest that TCE may affect semen parameters, but the studies are limited by the small numbers of subjects and need confirmation.

There is little information on the effects of occupational or environmental TCE exposure on female reproduction. Animal studies on the subject have mixed results.

Most of the studies reviewed by NRC, EPA, and ATSDR have found prenatal exposure to TCE to be associated with a number of adverse pregnancy outcomes, particularly an increased risk of spontaneous abortion and decreased birth weight. Most of the studies were small in size, and the exposures were usually to a mixture of solvents, although some studies did make efforts to isolate exposure to specific solvents, including TCE. One study reviewed by the Volume 11 committee (Forand et al., 2012) found that environmental exposure to TCE was significantly associated with several birth outcomes, such as low birth weight and small for gestational age, but not with others (e.g., preterm birth). The animal studies cited by NRC, EPA and ATSDR supported the epidemiologic studies with findings of reduced fertility and fetal loss, although two continuous breeding studies did not find any substantial reproductive effects in the F0 or F1 generations.

The Volume 11 committee concludes that there is limited/suggestive evidence of an association between exposure to TCE and reproductive effects in men.

The Volume 11 committee also concludes that there is inadequate/insufficient evidence to determine whether an association exists between exposure to TCE and reproductive effects in women.

The Volume 11 committee also concludes that there is limited/suggestive evidence of an association between exposure to TCE and adverse pregnancy outcomes.

Developmental Effects

There have been a number of studies examining possible developmental effects, particularly birth defects, following mothers’ occupational or environmental exposures to TCE. These studies have produced mixed results. Some, but not all, of the epidemiologic studies have found that prenatal exposure to TCE may result in numerous birth defects, including oral clefts, eye/ear defects, neural tube defects, and other neurological changes. However, the study of TCE-contaminated drinking water at Camp Lejeune did not find any increased risk for neural tube or oral cleft defects.

The most studied birth defects are those of the cardiovascular system. EPA (2011) concluded that the epidemiologic and animal data together supported the “plausibility of cardiac defects induced by TCE in humans.” ATSDR (2014) found that TCE caused developmental effects, including cardiac defects, in offspring following prenatal exposure to TCE. The five studies considered by the Volume 11 committee also assessed the risk of congenital malformations or cancer in children born to mothers with exposure to TCE during pregnancy. Three of the studies—Forand et al. (2012), Cordier et al. (2012), and Swartz et al. (2015)—each found increased risks of defects in children prenatally exposed to TCE via maternal inhalation, although the types of defects varied among the studies: respectively, cardiac and conotruncal defects, limb malformation, and spina bifida. On the other hand, Brender et al. (2014) found no significant associations between maternal exposures to TCE in ambient air and any birth defects, and Heck et al. (2014) found no associations between maternal exposures to TCE in ambient air and childhood leukemia. EPA was unable to explain the disparity in results among the five studies.

Animal studies were also somewhat equivocal with regard to the effects of prenatal exposure to TCE on offspring. Although EPA (2011) concluded that the animal studies supported its contention that TCE causes cardiac malformations in rat fetuses as well as other adverse birth outcomes, it acknowledged that several other well-conducted studies did not support that conclusion, and it stated that the dissection techniques used in those studies may have precluded any finding of the malformations. ATSDR (2014) stated that the epidemiological studies it reviewed indicated that exposure to TCE via air and drinking water may be associated with developmental effects, but this was not the finding of the NRC (2009) committee. The Volume 11 committee reviewed one new animal study that showed no effect of prenatal exposure to TCE on fetal eye development (Warren et al., 2006). Gilbert et al. (2014) found that prenatal TCE exposure may cause epigenetic alterations in immunologic responses in fetal mice.

Thus, several human studies indicate that some birth defects, particularly cardiac defects, might be associated with maternal inhalation exposure to TCE during pregnancy, although some studies did not find any such associations. The animal data also provide support the association between prenatal exposure to TCE and developmental effects, particularly cardiac malformation. Although both EPA and ATSDR found that prenatal TCE exposure may result in developmental effects, a 2009 NRC committee did not. Further research on the potential for developmental effects following prenatal exposure to TCE in both animals and humans is warranted.

The Volume 11 committee concludes that there is limited/suggestive evidence of an association between prenatal exposure to TCE and developmental effects.

TABLE 7-5 Summary of Reproductive and Developmental Effects of TCE

continued

TABLE 7-5 Continued

NOTE: ALL=acute lymphoblastic leukemia; AML=acute myeloid leukemia; CI=confidence interval; EPA=U.S. Environmental Protection Agency; IQR=interquartile range; LBW=low birth weight; MCL=maximum contaminant level; md=mean difference; NTD=neural tube defect; OR=odds ratio; PTB=preterm birth; RR=relative risk; SGA=small for gestational age; TCE=trichloroethylene.

TETRACHLOROETHYLENE

Tetrachloroethylene (also called perchloroethylene, PCE, or perc) is a widely used industrial solvent. PCE has been the major solvent used in dry cleaning and is used in metal degreasing as well as in numerous industrial applications.

PCE has been detected in ambient air, where it results both from industrial emissions and from the combustion of organic materials; it has also been detected in drinking water contaminated by industrial leaks into groundwater. In 2007 and 2009 PCE was measured in air samples of emissions from a large-scale burn pit at JBB in Iraq (IOM, 2011). PCE was also a major contaminant of the drinking water at Camp Lejeune, North Carolina. PCE entered the base’s drinking water through the groundwater as a result of spills and improper disposal from an off-site dry cleaner. It was estimated that the PCE contamination there began in 1957 and continued until the groundwater wells were closed in 1985. The levels of PCE in the Camp Lejeune drinking water exceeded the EPA maximum contaminant level of 5 μg/L; for example, levels of 76–104 μg/L were found in samples taken from Tawara Terrace in August 1982 (Faye and Green, 2007a,b; NRC, 2009). Groundwater contamination from PCE has also been found at other sites in the United States, including areas around Woburn, Massachusetts, and Endicott, New York.

PCE and its metabolites can be measured in humans, although the half-life of PCE is relatively short, with the chemical being mostly metabolized within days of exposure. The urinary metabolites of PCE are trichloroacetic acid and dichloroacetic acid (ATSDR, 2014).

In its assessment of the reproductive and developmental effects of PCE, the Volume 11 committee considered four earlier, comprehensive reports—Gulf War and Health, Volume 2 (IOM, 2003), the 2009 NRC report on contaminated water at Camp Lejeune, the 2012 EPA Toxicological Review of Tetrachloroethylene (Perchloroethylene), and the 2014 ATSDR Draft Toxicological Profile for Tetrachloroethylene—as well as any new studies it found that had been published in recent years. The committee notes that many of the studies on PCE have been reviewed by more than one of the above organizations. The epidemiologic studies on the reproductive and developmental effects of PCE reviewed below are summarized in Table 7-6 at the end of this section.

Reproductive Effects

Reproductive Effects in Men and Women

The Volume 2 committee (IOM, 2003) did not identify any studies of occupational or environmental exposure of men or women to PCE and its effect on semen quality or male fertility or on female reproduction.

The 2009 NRC review found only one study of men occupationally exposed to solvents (painters and millwrights), although not to PCE specifically, that found an association between the levels of exposure to chlorinated solvents and increasing levels of FSH, but not concentrations of LH or TTP (Luderer et al., 2004). The NRC committee concluded that there continued to be inadequate/insufficient evidence to determine whether an association exists between chronic exposure to TCE or PCE and male infertility.

In 2012, EPA summarized studies of PCE effects on semen quality (Eskenazi et al., 1991b) and male fertility (Eskenazi et al., 1991b; Rachootin and Olsen, 1983) as well as TTP (Sallmén et al., 1998). Most of these studies assessed effects in men who worked in dry cleaning facilities. EPA found that although there was one study (Eskenazi et al., 1991b) reporting that PCE had effects on some sperm parameters, those results, when considered against other studies finding no such adverse outcomes, were not sufficient to conclude that PCE was associated with adverse effects on male reproduction.

ATSDR (2014) reviewed many of the same studies as those cited by EPA. It included the Eskenazi et al. (1991a,b) and the Sallmén et al. (1998) studies of male reproductive effects following inhalation exposure to PCE. ATSDR also reported on the study by Sallmén et al. (1995) that examined women who had been biologically monitored for exposure to organic solvents at the Finnish Institute of Occupational Health and asked about possible solvent exposure in the 12 months before pregnancy. Using a fecundability measure termed the IDR, Sallmén et al. reported that women with exposure to PCE had reduced fecundity (IDR=0.69, 95% CI 0.31–1.52).

The Volume 11 committee did not identify any new literature on the effects of exposure to PCE on male or female reproduction.

Adverse Pregnancy Outcomes

The Volume 2 committee identified several studies, mostly of Scandinavian women or men who worked in dry cleaning facilities, of the effects of PCE exposure on fetal outcomes, particularly the occurrence of spontaneous abortion. The results of the studies were inconsistent, as noted earlier.

Olsen et al. (1990) combined data from Sweden, Denmark, and Finland and found a slight increase in the risk of spontaneous abortion for women who worked in dry cleaning with potential low exposure (OR=1.17, 95% CI 0.74–1.85), and the increase was greater for women with high exposure (OR=2.88, 95% CI 0.98–8.44). Lindbohm and colleagues studied Finnish women and men who had been occupationally exposed to organic solvents. For women who were exposed during the first trimester of their pregnancy, there was a significant association between solvent exposure and spontaneous abortion (OR=2.2, 95% CI 1.2–4.1) (Lindbohm et al., 1990); however, there was no significant association between paternal occupational exposure to PCE and spontaneous abortion (PCE=0.7, 95% CI 0.2–2.4) (Lindbohm et al., 1991). The study used the time of spermatogenesis (80 days before conception) as the relevant window of exposure.

A study of dry cleaners in the United Kingdom who were exposed to PCE (Doyle et al., 1997) found no association with spontaneous abortion (OR=1.03, 95% CI 0.48–2.21). Ahlborg (1990) found a nonsignificant increased risk of spontaneous abortion (OR=1.1, 95% CI 0.6–2.0) in a study of women working in laundry or dry cleaning facilities in Sweden who had exposures during the first trimester. By contrast, Kyyronen et al. (1989) found a significant increase in spontaneous abortion among women in Finland who reported high exposures to PCE in dry cleaning facilities (OR=3.6, 95% CI 1.3–11.2).

The 2012 EPA review included many of the same studies of the effects of PCE and other solvents on female reproduction as reviewed by the Volume 2 committee or the NRC committee on Camp Lejeune (NRC, 2009). New studies published after the 2009 NRC report included findings of associations between PCE exposure and various adverse pregnancy outcomes, including spontaneous abortion (Aschengrau et al., 2009), low birth weight, and shortened gestational duration (Aschengrau et al., 2008).

EPA (2012) found three studies of paternal occupational exposure to PCE prior to conception that did not find increases in the risk of spontaneous abortion (Eskenazi et al., 1991a; Lindbohm et al., 1991; Taskinen et al., 1989), although the exposures in the latter two studies were to a multitude of solvents. The EPA report also included new studies of two populations living in Massachusetts that had been exposed to PCE-contaminated drinking water (Aschengrau et al., 2008, 2009; Lagakos et al., 1986). No associations were found between exposure to PCE in drinking water and the incidence of spontaneous abortion in either population. EPA noted that the studies of drinking water contamination evaluated populations with much lower exposures than those experienced by the occupational cohorts.

EPA (2012) also assessed the effect of PCE exposure on other birth outcomes. Several studies suggested that prenatal PCE exposure in drinking water was associated with low birth weight (Bove et

al., 1995; Lagakos et al., 1986; Sonnenfeld et al., 2001). However, in the Cape Cod population studies done by Aschengrau et al. (2008), individuals were exposed to a wide range of PCE in drinking water, and the authors did not find an association between exposure and birth weight or gestational duration.

EPA found that “Overall, no associations were noted in several studies that assessed maternal or paternal occupational exposure to PCE and increased incidence of stillbirths, congenital anomalies, or decreased birth weight (Lindbohm, 1995; Windham et al., 1991; Olsen et al., 1990; Kyyronen et al., 1989; Taskinen et al., 1989; Bosco et al., 1987).”

The 2014 ATSDR Draft Toxicological Profile for Tetrachloroethylene also assessed many of the studies reviewed by the IOM, NRC, and EPA. It was not possible to draw any conclusions concerning the association between maternal or paternal exposure to PCE and adverse reproductive effects in men, women, or fetuses because of the limitations of the epidemiologic studies, such as confounding from multiple exposures and small numbers of study participants.

The Volume 11 committee considered two new studies that examined reproductive effects in humans following prenatal PCE exposure. In a further study of eight towns in Cape Cod, Massachusetts, that had PCE contamination in the water system between 1969 and 1990, Carwile et al. (2014) found that PCE exposure during pregnancy for 1,091 women was not significantly associated with overall ischemic placental disease, preeclampsia, placental abruption, or small-for-gestational-age infants among women with cumulative exposure levels below the median (<28 g PCE). However, women with PCE exposures greater than the sample median (>28.9 g PCE) were at a significantly increased risk for stillbirth ≥27 weeks gestation (RR=2.38, 95% CI 1.01–5.59).

Ruckart et al. (2014) conducted a cross-sectional study of 11,896 births at Camp Lejeune, North Carolina, during 1968–1985, the period of groundwater contamination with PCE and other solvents (including, as discussed earlier, benzene and TCE), using birth certificate information and groundwater modeling. There was no association found between residential prenatal exposure to any concentration of PCE (≥81.4 ppb) during the entire pregnancy and the risk of a full-term low birth weight or reduced mean birth weight. However, there was a slight but significant increase in the risk of a small-for-gestational-age infant at a PCE concentration of ≥35.8–<52.7 ppb (OR=1.2, 95% CI 1.0–1.4), although not at other concentrations, and PCE at a concentration of ≥81.4 ppb was associated with a significantly increased risk of preterm birth (OR=1.3, 95% CI 1.0–1.6).

Animal Studies

There were no animal studies of PCE’s reproductive or developmental effects discussed by the Volume 2 committee (IOM, 2003). The 2006 NRC report examined a study by Berger and Horner (2003) that found that exposure to 0.9% PCE in drinking water reduced the percentage of females ovulating (p<0.05); however, there were no effects on oocyte fertilizability or on the number of penetrated sperm per oocyte. Females who were exposed to 1,700 ppm PCE via inhalation for two 1-hour periods per day for 2 weeks experienced a slight reduction in the fertilizability of their oocytes (p<0.05), and the number of penetrated sperm per oocyte was also reduced; there were no clinical signs of toxicity.

The 2009 NRC report found that maternal exposure to PCE led to reduced fetal weight in rats and that maternal exposure to high levels of PCE via inhalation reduced intrauterine growth.

The 2012 EPA review of animal studies reported a decrease in mean testes weight in F1 males in a two-generation inhalation study of PCE (Tinston, 1994), although there were no effects on male or female fertility or other evidence of alterations in reproductive function. Beliles et al. (1980) also found no sperm abnormalities in rats following up to 10 weeks of PCE inhalation exposures at 100 or 500 ppm, although they did find an increase in abnormal sperm heads in mice after 4 weeks of exposure to 500 ppm only.

ATSDR (2014) reported that inhalation exposures of female rats and rabbits at concentrations between 300 and 1,254 ppm during gestation resulted in increased pre- and post-implantation losses, decreased litter sizes, and decreased survival during lactation; these results were not seen in mice. Decreased fetal and maternal weight were observed in rats and mice exposed to concentrations of 300–664 ppm during gestation.

The Volume 11 committee did not identify any new animal studies on the reproductive effects of PCE.

Developmental Effects

The authoritative reviews of PCE conducted by NRC, ATSDR, and EPA cited in the preceding section also examined the developmental effects of exposure to PCE on infants and children. These findings are summarized below.

The Volume 2 committee (IOM, 2003) considered a number of studies that examined maternal and paternal solvent exposure before or during pregnancy and did not find a pattern of association with any congenital malformations. However, the four key studies cited by the committee for neural tube defects, including spina bifida (Blatter et al., 1996, 1997; Shaw et al., 1999a) and gastroschisis (Torfs et al., 1996), did not show increased risks of congenital malformations that were associated specifically with paternal or prenatal maternal PCE exposure.

The Volume 2 committee identified two studies that reported on the risk of childhood cancers and prenatal PCE exposure. Shu et al. (1999), in an extensive study of ALL in children, found a nonsignificant association with the mothers’ self-reports of prenatal exposure to PCE (OR=1.4, 95% CI 0.2–8.6) but not with the fathers’ preconception exposures (OR=0.8, 95% CI 0.5–1.5). De Roos et al. (2001) found no association between the risk of childhood neuroblastoma in children and their fathers’ preconception occupational exposure to PCE (OR=0.5, 95% CI 0.1–1.7). Thus, the Volume 2 committee concluded that there was inadequate/insufficient evidence to determine whether an association exists between chronic exposure to solvents and congenital malformations or childhood cancer.

The 2009 NRC review identified three new studies that assessed the relationship between parental exposure to PCE and childhood leukemia—one cohort study with incidence data (Morgan and Cassady, 2002) and two case-control studies (Costas et al., 2002; Infante-Rivard, 2005). No significant increase in the incidence of childhood leukemia was found for residents of a California community exposed to PCE- and TCE-contaminated drinking water (standardized incidence ratio=1.09, 99% CI 0.38–2.31) (Morgan and Cassady, 2002), nor was there an association between maternal preconception and prenatal occupational exposure to PCE and leukemia in offspring (OR=0.96, 95% CI 0.41–2.25) (Infante-Rivard, 2005). The third study cited by the NRC committee, a case-control study by Costas et al.(2002), also found no significant association. Thus, the NRC committee concluded that there was inadequate/insufficient evidence to determine whether an association exists between PCE and childhood leukemia.

The NRC committee also considered a study by Janulewicz et al. (2008) that assessed prenatal exposure to PCE in contaminated water in a Cape Cod community. The researchers found that mothers’ prenatal PCE exposure was not associated with disorders of attention, learning, and behavior in their children at 5 years of age, as determined by an examination of school records.

The 2012 EPA review evaluated the epidemiologic and animal literature on PCE exposure and adverse developmental outcomes in offspring. Epidemiologic studies of PCE assessed birth anomalies, postnatal development learning and behavior, and schizophrenia in children with prenatal exposure to PCE (Aschengrau et al., 2009; Bosco et al., 1987; Janulewicz et al., 2008; Lagakos et al., 1986; McDonald et al., 1987; Olsen et al., 1990; Perrin et al., 2007). Lagakos et al. (1986), in a study of drinking water contaminated with PCE, TCE, and other chlorinated organics in Woburn, Massachusetts, found

that exposure to PCE was associated with a significantly increased risk of eye/ear anomalies (OR=14.9, p<0.0001) and CNS, chromosomal, or oral cleft abnormalities (OR=4.5, p=0.01); no other abnormalities reached significance. Aschengrau et al. (2009) reported similar results for infants born in eight towns in Cape Cod that had PCE-contaminated water, although the number of anomalies was low. PCE levels in residential areas in Falmouth, Massachusetts, ranged from undetectable to 80 μg/L in water pipes along main streets with high water flow and from 1,600 to 7,750 μg/L in water pipes along dead end streets with low water flow. The OR for all anomalies combined for children in the uppermost quartile of PCE exposure was 1.5 (95% CI 0.9–2.5); among offspring with any prenatal exposure, the OR for neural tube defects was 3.5 (95% CI 0.8–14.0) and for oral clefts was 3.2 (95% CI 0.7–15.0). The researchers reported that diagnoses of attention deficit disorder, hyperactive disorder, or educational problems, as reported by the mothers about their children, were not associated with PCE (Janulewicz et al., 2008). However, Perrin et al. (2007) reported that prenatal exposure to PCE at a dry cleaning facility was associated with a diagnosis of schizophrenia when the offspring were ages 21–33 years. EPA concluded that “the literature is insufficient to draw conclusions regarding effects of PCE exposure on development in infants and children” (EPA, 2012).

ATSDR (2014) reviewed much of the same information as EPA (2012) did and noted that in many of the epidemiologic studies subjects had multiple exposures, which made it difficult to make any conclusions as to the reproductive and developmental effects associated with PCE specifically. In a study focusing on risky behaviors, Aschengrau et al. (2011) found that at the highest tertile of prenatal PCE exposure there was a slight but significant increase in adolescent smoking (RR=1.6, 95% CI 1.1–2.3) and alcohol use (RR=1.3, 95% CI 1.0–1.7); the increase was not seen for all exposure categories or for lower exposures. For drug use, the risks were greater for teens in the highest tertile of exposure (OR=1.6, 95% CI 1.2–2.2) and for adults (OR=1.5, 95% CI 1.2–1.9). Aschengrau et al. (2012) also found a nonsignificant risk for bipolar disorder, post-traumatic stress disorder, and schizophrenia, but not for depression, among exposed subjects. In a follow-up study in the Cape Cod population, Janulewicz et al. (2012) performed neuropsychological testing in the original cohort, although only 35 prenatally exposed and 28 unexposed adults agreed to participate. No evidence was found of an association between prenatal exposure and the results of neuropsychological tests for omnibus intelligence, academic achievement, or language endpoints; however, there were suggestive, but not significant, associations between prenatal exposure and decrements in visuospatial functioning, learning and memory, motor speed, attention, and mood in the adults. The authors attributed the equivocal findings to the small sample size.

The Volume 11 committee considered eight new publications that examined developmental outcomes in children exposed prenatally to PCE. Four of the publications reported further assessments of the Cape Cod cohort described earlier, which was exposed to PCE from contaminated drinking water from 1969 to 1983 (Aschengrau et al., 2015; Gallagher et al., 2017; Janulewicz et al., 2013; Mahalingaiah et al., 2016). PCE measurements taken in 1980 from Cape Cod public drinking water supplies ranged from 1.5 μg/L to 7,750 μg/L (Janulewicz et al., 2012). Janulewicz et al. (2013) reported findings on 26 PCE-exposed and 16 unexposed adults who were examined with structural magnetic resonance imaging of the brain. No significant differences were found between the exposed and unexposed groups on most measures (e.g., white matter hypointensities, total cerebral and cerebellum white or gray matter volumes), but the parahippocampal gyrus was larger, on average, in exposed subjects (p=0.03), as was the thalamus (p=0.05). In a larger follow-up study of 831 participants with prenatal and postnatal (to 5 years of age) exposure to PCE and 547 unexposed participants, Aschengrau et al. (2015) found no associations between PCE exposure and the occurrence of obesity, diabetes, cardiovascular disease, hypertension, color blindness, near- and farsightedness, and dry eyes. However, there was an increased risk of cancer among those with early life exposure versus the unexposed (OR=1.8, 95% CI 0.8–4.0)

and an increased risk of epilepsy (OR=1.5, 95% CI 0.6–3.6), although neither increase was significant. The committee notes that interpretation is difficult because of the small number of cases and the use of self-reported outcomes that were not confirmed by medical records. Gallagher et al. (2017) assessed whether the children with prenatal exposure to PCE in the Cape Code drinking water were more likely to engage in risky behaviors, alcohol consumption, and illicit drug use as adolescents and whether alcohol use by the mother affected the child’s risk-taking behaviors. Compared with unexposed controls (n=242), adolescents with maternal exposure to only PCE (n=361) were at an increased risk of using two or more major drugs (RR=1.6, 95% CI 1.0–2.4) and of having more than five drinks of alcohol in 4 days (RR=1.3, 95% CI 1.0–1.6), and adolescents with early life exposure to both PCE and alcohol (n=302) were at even greater risk for major drug use (RR=1.9, 95% CI 1.2–3.0) and heavy alcohol consumption (RR=1.4, 95% CI 1.1–1.47). The authors note, however, that there are difficulties in conducting such a retrospective study, including poor response rate and recall bias among both adolescents and mothers. Finally, Mahalingaiah et al. (2016) looked at the reproductive health of female offspring born to women born 1969–1983 who were exposed during pregnancy to PCE in the Cape Cod drinking water. The female children were between 23 and 39 years old at the time of the survey in 2006–2008. Of the four reproductive health outcomes assessed—adult-onset polycystic ovary syndrome, endometriosis, difficulty conceiving, and miscarriage—there was no association between PCE exposure and an increased risk of any of the outcomes.

In a study of children who attended third grade in public schools in New York City, Stingone et al. (2016) found that those with higher prenatal exposure to diesel PM and PCE (average concentration=0.68 mg/m³) had a greater risk of failing to meet math, but not English language arts, test standards (OR=1.1, 95% CI 1.07–1.12) than children with lower levels of exposure. This risk associated with the combined exposure was greater than for children with exposure to greater levels of diesel PM only (RR= 1.03, 95% CI 0.99–1.06) or to PCE only (RR=1.03, 95% CI 1.00–1.06). The exposure estimates were based on EPA’s 1996 National Air Toxics Assessment for residential census tracts.

Heck et al. (2014), which was also discussed in the section on benzene, assessed the risk of childhood leukemia following maternal exposure to air toxics, including PCE, by trimester, in children in California who had been diagnosed with either ALL (n=69) or AML (n=46) between 1990 and 2007. A one-interquartile increase in PCE concentrations at any time during pregnancy did not significantly increase the risk for ALL or AML.

In the only new study to examine birth defects as well as childhood cancers, Ruckart et al. (2013) conducted a case-control study of children born to mothers at Camp Lejeune between 1968 and 1985 who may have consumed drinking water contaminated with solvents, including PCE. Birth certificates were used to identify the 51 cases and 526 control parent–child pairs. Prenatal PCE exposure in the first trimester at concentrations below the maximum contaminant level of 5 ppb was significantly associated with an increased risk of neural tube defects (OR=3.7, 95% CI 1.0–14.1); however, when the exposures were dichotomized to exposed/unexposed, there was no increased risk. Exposure to PCE at any level was not associated with a significantly increased risk of oral cleft defects or childhood leukemia or non-Hodgkin’s lymphoma.

In the NORD-TEST study—also described in the benzene section—there were no significant associations between prenatal maternal exposure or paternal exposure to TCE in the year prior to birth and the risk of testicular germ cell tumors in men ages 14–49 years in Finland, Norway, and Sweden combined. However, there was an increased risk of testicular germ cell tumors for Finnish men with prenatal paternal exposure to PCE (OR=2.42, 95% CI 1.32–4.41) (Le Cornet et al., 2017).

Animal Studies

The Volume 2 committee did not report on any studies of developmental effects in animals following prenatal exposure to PCE.

NRC (2009) concluded that animal studies supported the epidemiologic findings for the most part. The NRC committee stated that “the toxicologic data provide strong evidence that neither solvent is associated with congenital malformations in rats”; however, it continued, other animal studies in rats “exposed to PCE prenatally or postnatally suggest that there may be sensitive windows for neurobehavioral impairment during development” (NRC, 2009).

EPA (2012) reported on a two-generation inhalation study in rats conducted by Tinston (1994). Decreased pup weights and reduced postnatal survival were seen in both generations, and behavioral alterations were observed in the F1 pups. One of the indications that in utero exposure has effects on prenatal survival was an increased degree of pre- and post-implantation loss that was seen in rats, mice, and rabbits (Schwetz et al., 1975; Szakmáry et al., 1997). In rats the oral administration of 900 mg/kg/day of PCE on GDs 6–13 resulted in an increased risk of micro/anophthalmia in the offspring. Rats exposed prenatally to PCE via inhalation also exhibited altered neurological function (Nelson et al., 1980; Szakmáry et al., 1997; Tinston, 1994) and reductions in brain acetylcholine and dopamine (Nelson et al., 1980). Several of the animal studies of reproductive and developmental effects cited by EPA had substantial limitations, including a lack of a dose response because of the use of only one treatment level and also a lack of reporting details. Nevertheless, EPA found that the PCE “database included assessments of the various potential manifestations of developmental toxicity, i.e., alterations in survival, growth, morphology, and functional development” (EPA, 2012).

The animals studies cited by ATSDR (2014) had several developmental toxicity endpoints such as alterations in fetal survival, growth, morphology (skeletal ossification in mice), and functional development, which were also described in the EPA review. ATSDR reported that delayed skeletal development was observed in rats and mice exposed to concentrations of 300–664 ppm PCE during gestation. Gestational exposure to 900 ppm PCE was associated with behavioral and neurochemical alterations in some rat offspring.

The Volume 11 committee did not find any new animal studies on the developmental effects of PCE.

Synthesis and Conclusions

The reproductive and development effects of PCE, like those of TCE, have been reviewed by several governmental and other organizations, including NRC, EPA, and ATSDR. Although PCE is a widely used solvent, particularly for dry cleaning, there is a dearth of information on its reproductive and developmental effects.

Reproductive Effects

The reproductive effects of PCE on males are unclear, and there are relatively few studies on which to base conclusions, although Eskenazi et al. (1991b) found that PCE had adverse effects on sperm quality. Studies of the effects of PCE exposure on female reproduction are also scarce. The adverse pregnancy outcomes reported in several occupational studies are not consistent. Although some studies in Scandinavian populations suggest that maternal occupational exposure to PCE may increase the risk of spontaneous abortion, studies in a Massachusetts residential population found no association between PCE in drinking water and spontaneous abortion, birth weight, or gestational age. NRC and ATSDR

found that the data were insufficient to draw any conclusions on the effects of PCE on reproductive endpoints, and EPA found that there were no associations between maternal or paternal occupational exposure to PCE and an increased incidence of adverse pregnancy outcomes.

The new studies reviewed by the Volume 11 committee found no increase in adverse pregnancy outcomes, although a study of the Massachusetts population (discussed above) reported that exposures higher than the cumulative median concentration (28.9 g) increased the risk of stillbirth and placental abruption (Carwile et al., 2014). Animal studies were inconsistent concerning the effects of PCE that they reported on sperm, male or female fertility, and birth outcomes, and there were species differences.

The Volume 11 committee finds that there is inadequate/insufficient evidence to determine whether an association exists between exposure to PCE and reproductive effects in men or women, or with adverse pregnancy outcomes.

Developmental Effects

Numerous researchers have assessed the effects of prenatal exposure, primarily maternal, on developmental effects, including childhood cancers, birth defects, and neurodevelopmental deficits. Several studies looking for a link between childhood leukemia and prenatal exposure to PCE, usually from the maternal consumption of contaminated drinking water, did not find a significantly increased risk of the disease among children who had been prenatally exposed. However, prenatal exposure to PCE was associated with other developmental outcomes in children, including the risks of eye/ear anomalies and CNS/chromosomal/oral cleft abnormalities. Several studies of the Cape Cod, Massachusetts, population that consumed PCE-contaminated drinking water found that mothers’ consumption of contaminated water was associated with a slight but significant increase in risky behaviors (e.g., smoking, alcohol use) in their children. Although prenatal exposure was associated with increases in neurobehavioral outcomes, none of the associations reached significance (Aschengrau et al., 2012; Janulewicz et al., 2012), nor was there an effect on brain morphology in the exposed children (Janulewicz et al., 2013). Animal studies generally support the findings in humans of birth defects and altered neurological function in offspring who were exposed, or whose parents were exposed, to PCE.

The Volume 11 committee concludes that there is limited/suggestive evidence of an association between prenatal exposure to PCE and developmental effects.

TABLE 7-6 Summary of Reproductive and Developmental Effects of Tetrachloroethylene

continued

TABLE 7-6 Continued

continued

TABLE 7-6 Continued

NOTE: ALL=acute lymphoblastic leukemia; AML=acute myeloid leukemia; CI=confidence interval; EPA=U.S. Environmental Protection Agency; IQR=interquartile ratio; LBW=low birth weight; MCL=maximum contaminant level; md=mean difference; MRI=magnetic resonance imaging; NTD=neural tube defect; OR=odds ratio; PCE=tetrachloroethylene; PM=particulate matter; PTB=preterm birth; RR=relative risk; SD=standard deviation; SGA=small for gestational age.

GLYCOLS AND GLYCOL ETHERS

The glycol ethers are a group of solvents classified on the basis of the alkyl ethers of one of two parent alcohols: the 2-carbon chain ethylene glycol or the 3-carbon chain propylene glycol. The glycol ethers include the following: glycol ethers (unspecified), ethylene glycol ethers, diethylene glycol, propylene glycol, ethylene glycol monomethyl ether (EGME, 2-methoxyethanol), ethylene glycol monoethyl ether (EGEE, 2-ethoxythanol), ethylene glycol monobutyl ether (EGBE, 2-butoxyethanol), and propylene glycol monomethyl ether (PGME). Glycol ethers are commonly used industrially in paints and cleaners as well as in the manufacture of semiconductors; the latter source of exposure has been examined in several epidemiologic studies. Ethylene glycol monobutyl ether (EGBE, 2-butoxyethanol) is widely used as a solvent in protective surface coatings; as an ingredient in paint thinners and strippers, silicon caulks, cutting oils, hydraulic fluids; and as a degreaser (ATSDR, 1998). Propylene glycol is a colorless, odorless, water-soluble liquid used in commercial formulations of foods, drugs, and cosmetics and to generate artificial smoke. Propylene glycol is designated as a generally recognized as safe additive by the Food and Drug Administration (ATSDR, 1997). Ethylene glycol is a toxic chemical that is a component of antifreeze and hydraulic fluids (ATSDR, 2010).

Ethylene glycol monobutyl ether, diethylene glycol, diethylene glycol monobutyl ether, ethylene glycol, and propylene glycol were all sent to the Persian Gulf in quantities of greater than 1 kiloliter (see Table 7-1). The glycols and glycol ethers discussed in this chapter are listed in Table 7-7. The Volume 11 committee did not identify any information on the use of or quantities of glycols or glycol ethers that may have been sent to the Post-9/11 conflicts. The epidemiologic studies on the reproductive and developmental effects of glycols and glycol ethers reviewed below are summarized in Table 7-8 at the end of this section.

Toxic metabolites of glycols and glycol ethers are excreted in the urine (see Table 7-7). The metabolites include 2-methosxyacetic acid (2-MMA), a metabolite of EGME; ethoxyacetic acid (EAA), glycolic acid, and oxalic acid, which are metabolites of ethylene glycol; and 2-butoxyacetic acid, a metabolite of 2-butoxyethanol. Propylene glycol may be detected in serum and urine with an elimination half-life following oral exposure of about 4 hours; it degrades in the body in about 48 hours (ATSDR, 1997). The differing toxicity of the glycols and glycol ethers is thought to be due to their metabolites (IOM, 2003).

TABLE 7-7 Glycols and Glycol Ethers Discussed in the Chapter

Reproductive Effects

Reproductive Effects in Men and Women

The Volume 2 committee reported on the effects that glycols and glycol ethers had on reproduction in exposed men and women, including semen characteristics and fertility. Most of the studies of these effects were small, and the participants had concurrent exposures to other chemicals. Veulemans et al. (1993) examined semen characteristics in 1,019 men occupationally exposed to ethylene glycol ethers who had been clinically diagnosed as infertile or subfertile, with 475 male patients of the same clinic who were diagnosed as fertile serving as controls. The authors found no association between urinary EAA and abnormal semen characteristics; they suggested that the results might be due to a latent period between exposure and the time when observable effects are seen. In another occupational case-control study, Ratcliffe et al. (1989) found decreases in mean sperm count in workers exposed to EGME at a metal-casting company, but no marked changes in sperm motility, structure, or velocity or in testicular volume after adjustments had been made for many potential confounders; the study had low statistical power. Welch et al. (1988) examined exposure to the ethylene glycol ethers—EGME and EGEE—among shipyard painters and found a higher prevalence of oligospermia and azoospermia and a higher, but nonsignificant, risk of decreased sperm count per ejaculate in the exposed group (OR=1.85, 95% CI 0.6–5.6); again, no important differences were found in sperm structure, motility, or viability.

The Volume 11 committee identified two new studies on the effects of glycol ethers on male reproductive function. The committee notes that in both studies there was concurrent occupational exposure to other chemicals, thus making interpretation of the results difficult.

In a study of 109 men in Paris, France, 48 of whom had occupational exposure to glycol ethers, Multigner et al. (2007) assessed the urinary levels of glycol metabolites. The men provided semen samples 2 to 3 months after they had provided urine samples. Compared with controls, sperm concentration, total sperm count, the percentage of rapid progressive sperm, and the percentage of morphologically normal sperm were significantly lower in the exposed group (p<0.001), although there were no differences in semen pH or sperm viability. Serum testosterone, LH, and inhibin B concentrations were similar in the two groups. FSH concentration was not significantly increased in the exposed group. Exposure to high levels of glycol ethers was associated with a significantly increased risk of a low percentage of rapid progressive sperm motility (OR=10.2, 95% CI 1.3–82.5), whereas no significant associations were observed for low sperm concentration, a low percentage of morphologically normal sperm, low seminal volume, or low total progressive sperm motility.

Cherry et al. (2008) reported a case-referent study of 2,118 men attending fertility clinics in the United Kingdom. Self-reports of exposure were reviewed by an industrial hygienist who estimated the men’s level of exposure to solvents, particularly glycol ethers, in the 3 months prior to their clinic visits. Exposure to higher levels of glycol ethers was associated with an increased risk of low motile sperm concentration: low exposure (OR=0.93 95% CI 0.74–1.17); moderate exposure (OR=1.65 95% CI 1.06–2.54); and high exposure (OR=2.54 95% CI 1.23–5.27). Exposure to low or high levels of other VOCs was not significantly associated with low motile sperm concentrations, although moderate exposure was (OR=1.55, 95% CI 1.10–2.18).

Male and female workers in the semiconductor industry are known to be exposed to ethylene glycol ethers. The Volume 2 committee examined several studies of reproductive effects, primarily TTP, in these workers. Solvent-exposed male workers at an Italian mint (Figa-Talamanca et al., 2000) did not have a significantly elevated risk of a conception delay of more than 6 months (OR=1.69, 95% CI 0.62–4.62). Samuels et al. (1995) found no increases in TTP in a subset of workers (FR=1.03, 95% CI 0.70–1.51) in whom exposure to ethylene glycol ethers was of particular concern.

Correa et al. (1996) examined the extent of subfertility (defined as taking more than 1 year to conceive) in six female workers and for 561 pregnancies of wives of male workers. In the female employees, there was a significantly increased risk of subfertility (OR=4.6, 95% CI 1.6–13.3), but not in the wives of male workers (OR=1.7, 95% CI 0.7–4.3).

ATSDR (2010) did not identify any studies on reproductive effects in humans after the inhalation of or oral exposure to ethylene glycol. The ATSDR Toxicological Profile for Propylene Glycol (1997) was included in the Volume 2 deliberations, although that committee concluded that any reproductive effects reported in that profile were inconclusive. The profile did not include any human studies of reproductive effects following exposure to propylene glycol. In the 1998 report Toxicological Profile for 2-Butoxyethanol and 2-Butoxyethanol Acetate, ATSDR reported that there were no data on whether 2-butoxyethanol (EGBE) or 2-butoxyethanol acetate caused reproductive effects in humans.

The Volume 11 committee identified one new study on the association between women’s exposure to glycol ethers (primarily from cosmetics use) and TTP (Garlantezec et al., 2013). In a study on the PELAGIE cohort in France, the researchers measured glycol ether metabolites in the urine of 519 pregnant women; the samples were collected before 19 weeks of pregnancy. TTP information was collected at the beginning of the pregnancy. Both butoxyacetic and phenoxyacetic acids, which are both glycol ether metabolites, were detected in 93% of the urine samples; however, only the fourth-quartile concentration of phenoxyacetic acid (≥1.38 mg/L) was significantly associated with an increased TTP (OR=0.70, 95% CI 0.52–0.95).

Adverse Pregnancy Outcomes

The Volume 2 committee (IOM, 2003) considered two epidemiologic studies on pregnancy and birth outcomes performed with a cohort of female semiconductor workers exposed to ethylene glycol ethers (particularly in the fabrication process) and other chemicals. A study of 152 fabrication and 251 non-fabrication female workers at two semiconductor manufacturing plants found nonsignificantly reduced fecundability (longer TTP) in a subset of those with exposure to ethylene glycol ethers (FR=0.37, 95% CI 0.11–1.19) (Eskenazi et al., 1995). Women were followed for an average of five menstrual cycles, and daily urine samples were analyzed to confirm clinical spontaneous abortions and early fetal losses. In a large study by Swan et al. (1995; cited but not discussed in Volume 2), 891 women who worked in semiconductor fabrication were asked whether they had experienced a spontaneous abortion. Exposure to glycol ethers and other chemicals during the first trimester of pregnancy was assessed on the basis of job descriptions. The risk of spontaneous abortion was significantly increased for fabrication workers with the greatest predicted exposure to ethylene glycol ether (RR=2.67, 95% CI 1.33–5.36), and there was no increase associated with exposure to propylene glycol ether. Correa et al. (1996), discussed in the previous section, noted a trend for an increased risk of spontaneous abortion with higher exposures to glycol ethers.

The Volume 11 committee did not identify any new studies on adverse pregnancy outcomes in association with exposure to glycol ethers.

Animal Studies

The Volume 2 committee (IOM, 2003) noted that the evidence from animal studies indicated that exposure to ethylene glycol ethers was associated with testicular atrophy, decreased sperm motility, and abnormal sperm structure in rats, mice, and rabbits (Bruckner and Warren, 2001). It also reviewed studies of the oral toxicity of three ethylene glycol ethers—EGME, EGEE, EGBE—in rats and mice in 2-week

and 13-week drinking water studies conducted by the National Toxicology Program (Dieter, 1993). The rats were estimated to have consumed 100–400 mg/kg of EGME, 200–1,600 mg/kg of EGEE, and 70–300 mg/kg of EGBE; mice consumed 200–1,300 mg/kg of EGME, 400–2,800 mg/kg of EGEE, and 90–1,400 mg/kg of EGBE. There was testicular atrophy in the males of both species for both EGME and EGEE; no other effects on reproductive organs in either species at any dose were reported for the three solvents. In the 13-week studies, rats received 750–6,000 ppm EGME, 1,250–20,000 ppm EGEE, or 750–6,000 ppm EGBE, and mice received 2,000–10,000 ppm EGME, 2,500–40,000 ppm EGEE, or 750–6,000 ppm EGBE. Rats and mice receiving EGME or EGEE—but not EGBE—had histopathologic changes in the testes; a more severe degeneration of the germinal epithelium in the seminiferous tubules of the testes was observed with EGME exposure in both species. Some ovarian and uterine atrophy was observed in both rats and mice administered EGEE and EGME, but almost entirely at the highest dose levels tested (Dieter, 1993).

ATSDR (1998) reported on several animal studies with EGBE, none of which showed reproductive effects in male or female animals following inhalation exposure. ATSDR (2010) discussed several animal studies of reproductive effects and exposure to ethylene glycol. Testis and uterine weights and histopathology were not affected in mice treated with ethylene glycol for 4 consecutive days and evaluated 1 day later (Hong et al., 1988). However, intermediate-duration oral exposure to ethylene glycol in three multigenerational studies (one in rats and two in mice) and several shorter exposure studies (15–20 days in rats and mice) resulted in effects on fertility, fetal viability, and male reproductive organs in mice, although not in rats.

ATSDR (1997) included one long-term inhalation study of propylene glycol in rats that showed no adverse effects on the ability to produce live young or on the survival of the offspring.

The Volume 11 committee considered 13 animal studies on the male reproductive effects of a variety of ethylene glycols and glycol ethers, particularly EGME. In 2- and 13-week repeat-dose oral toxicity studies in rats, Johnson et al. (2005) found that diethylene glycol monobutyl ether (DEGBE) administered in drinking water at 0, 50, 250, or 1,000 mg/kg/day had no effect on sperm parameters or testis histopathology.

As part of an in vitro fertilization assay, Berger et al. (2000) found that 50–100 mg EGME/kg reduced the sperm fertilizing capacity for zone-free oocytes in male rats but that sperm motility was not affected. In another study of the male reproductive toxicity, Watanabe et al. (2000) administered EGME daily at 100 and 200 mg/kg/day for 2 weeks or 100 mg/kg/day for 4 weeks to 6- and 8-week-old male rats. In the 2-week, 200 mg/kg and 4-week, 100 mg/kg groups, testis and epididymis weights were decreased, and a histopathological examination showed severe degenerative changes in the testis, such as an atrophy of the seminiferous tubules and multinucleated giant cell formation in all the rats in the 2-week, 200 mg/kg group, while at 100 mg/kg/days both the 2-week and 4-week groups had a degeneration of pachytene spermatocytes which underwent apoptotic death, with a resulting decrease in the number of germ cells. EGME (200 mg/kg) administered orally to male rats for 3, 6, or 14 days resulted in the degeneration of spermatocytes in late-stage tubules and spermatocyte depletion at day 4, with the severity of effects increasing with prolonged exposure (Enright et al., 2013).

Yoon et al. (2003) found that EGEE, administered via gavage to male rats at 0, 100, 200, 400, and 800 mg/kg body weight/day for 4 weeks, was associated with decreases in the weight of the testis and epididymis and in the number of testicular cells as well as an exfoliation of germ cells into the tubular lumen at doses of ≥200 mg/kg, and with testicular degeneration at a dose of 400 mg/kg. EGEE also reduced sperm motility in both the cauda epididymis and the “spermaduct” when given to rats at 600 mg/kg for 5 weeks (Wang et al., 2006). Doses of 0, 100, 200, and 400 mg/kg EGEE administered orally by gavage to male rats for 14 consecutive days caused significant alterations in glutathione levels,

superoxide dismutase catalase activities, malondialdehyde levels, glutathione-S-transferase and lactate dehydrogenase activities in the testes and spermatozoa with severe degeneration of the testes, and a significant decrease in daily sperm production and in the number of epididymal and testicular spermatozoa and sperm. EGEE also significantly increased the total spermatozoa abnormalities without affecting the spermatozoa live-dead ratio at all dose levels when compared with the control group (Adedara and Farombi, 2010).

Mechanistic studies of EGME in male rats that were exposed to 30 or 100 mg/kg/day for 1, 4, and 14 days found that the higher dose produced testicular damage at 14 days. An analysis of the metabolites in serum, urine, liver, and testis suggested that EGME may induce toxicity via the inhibition of flavoprotein dehydrogenase-catalyzed reactions (Takei et al., 2010).

Several studies examined the effect of EGME or its metabolite 2-MMA on gene expression. Bagchi et al. (2010) assessed the effect of 2-MMA on cultured mouse testicular TM3 Leydig cells after 3, 8, and 24 hours of treatment. Progressive changes in gene expression were seen as consistent with a reproductive system disease. In another study, 6 hours after male rats received single oral doses of 50 or 2,000 mg/kg EGME, a slight degeneration of the spermatocytes was observed in rats given the high, but not the low, dose. Significant increases in three spermatogenesis-related genes—heat shock protein 70-2, insulin growth factor binding protein 3, and glutathione S transferase—were detected prior to the appearance of obvious pathological changes in the testis at the 2,000 mg/kg dose (Fukushima et al., 2005). Fukushima et al. (2011) found similar results when male rats were treated with 50 or 2,000 mg/kg EGME for 6 or 24 hours. Again, no changes in the testis were observed at 50 mg, but at 2,000 mg/kg there was a slight decrease of phacytene spermatocytes at 6 hr and a severe decrease at 24 hr. After 24 hr, significant changes in marker genes involved in spermatogenesis were observed: miR-449a and miR-92a decreased, and miR-320, miR-134 and miR-188 increased, while only miR-760-5p increased after 6 hr. Matsuyama et al. (2018) gave male rats single doses of 200, 600, or 2,000 mg/kg EGME and studied the resulting changes in the transcript levels of genes, including spermatocyte-specific genes. The two higher doses of EGME caused dose-dependent testicular toxicity, including the degeneration and necrosis of spermatocytes, and this injury correlated with decreased spermatocyte-specific gene expression. Specific gene expression changes were for Pbk (0.11- and 0.05-fold changes at 600 and 2,000 mg/kg, respectively); Phf2 (0.11- and 0.09-fold changes at 600 and 2,000 mg/kg, respectively); Prok2 (0.13- and 0.09-fold changes at 600 and 2,000 mg/kg, respectively); and Mllt10 (0.18- and 0.12-fold changes at 600 and 2,000 mg/kg, respectively). An analysis of upstream regulators suggested that oxidative stress, protein kinase activation, and histone acetylation, but not decreased testicular testosterone, were involved in the EGME-induced spermatocyte toxicity.

Sakurai et al. (2015) studied gene expression changes in the testis of cynomolgus monkeys following oral administration of EGME at 0 or 300 mg/kg for 4 days. All the monkeys given the 300 mg/kg dose had testicular toxicity, as demonstrated by decreases in pachytene spermatocytes and round spermatids. Sixteen down-regulated and 347 up-regulated miRNAs were detected in the testis. Levels of miR-1228 and miR-2861 increased in the testis of EGME-treated animals, which the authors state reflects recovery from EGME-induced testicular damages via the stimulation of cell proliferation and the differentiation of sperm.

For female reproduction, ATSDR (1997) reported that in rats exposed to propylene glycol in drinking water there were no adverse effects on any measure of reproduction, including the number of litters, litter size, pup weight, or sex ratio, even at the highest dose, nor was there any effect on the reproductive capacity of the offspring from the high-dose group. Some female rats and rabbits that breathed in large amounts of EGBE while they were pregnant delivered fewer offspring than pregnant rats or rabbits that were not exposed; the doses also produced maternal toxicity. The live offspring of these exposed mothers

did not exhibit any adverse effects. EGMBE did not produce other developmental effects in the offspring of animals exposed via inhalation at doses that did not produce maternal toxicity (ATSDR, 1998). ATSDR (2010) reported that inhaled ethylene glycol in mice and rats resulted in effects on implant viability and live fetal weight, although no dose–response relationships were provided. Nose-only studies also showed reduced live fetal body weight, although ATSDR considered the results to be inconclusive for inhalation exposure because of the confounding caused by concomitant oral exposure. ATSDR also reported that intermediate-duration oral exposure to ethylene glycol included decreased the body weights of pups.

The Volume 11 committee identified several new studies on the effects of glycol ethers or ethylene glycols on female reproduction in animal models. The reproductive toxicity of diethylene glycol (DEG) was studied in a continuous breeding study in CD-1 mice (Williams et al., 1990). The animals were administered 0, 0.35, 1.75, and 3.5% w/v DEG for 14 weeks in drinking water; the doses were such that the highest dose was estimated to reduce body weight by 10%, the middle dose would produce no or minimal toxicity, and the lowest dose was the estimated no-observed effect level. At 3.5% DEG, breeding pairs of animals had significantly decreased numbers of litters per pair, live pups per litter, the proportion of pups born alive, live pup weight, and the numbers of pairs producing third, fourth, and fifth litters; this dose also resulted in a significant increase in the cumulative days to litter.

The toxicity of EGME to the ovary was studied by Dodo et al. (2009) in rats that received 0, 30, 100, or 300 mg/kg for 2 or 4 weeks (repeated-dose toxicity studies) or the same doses for 2 weeks prior to mating, during mating, and until day 6 of pregnancy (fertility study). Continuous diestrus and alterations of ovarian morphology were observed for doses ≥100 mg/kg at both 2 and 4 weeks regardless of period of administration. In the fertility study, doses ≥100 mg/kg resulted in irregular estrous cycles, prolonged mating periods, lower pregnancy rates, and decreased corpora lutea of pregnancy.

Weng et al. (2010) administered via gavage approximately 0 mg/kg/day, 80 mg/kg/day, 118 mg/kg/day, or 310 mg/kg/day of EGME to 6-week-old female Swiss CD-1 mice for 7 days. The mice were then induced to ovulate and mated with nonexposed males. There were no significant differences among the dose groups in terms of the number of pups per litter, oocyte apoptosis ratios, or the number of retrieved oocytes following the induction of ovulation, although there was greater variance in the number of pups per litter in the highest-dose group. The cumulus-oocyte complex apoptosis ratios were significantly different across the groups (p≤0.001), although the response was not dose-dependent. Berger et al. (2000) reported that EGME (0.15–0.25% in drinking water) administered to female rats for 14 days reduced the number of ovulated oocytes in an in vitro fertilization study.

Ballantyne and Snellings (2005) studied the reproductive toxicity of DEG in CD-1 mice and CD rats. Pregnant mice received 0 (distilled water), 559, 2,795, or 11,180 mg/kg/day, and pregnant rats received 0, 1,118, 4,472, and 8,944 mg/kg/day on GDs 6–15. At the highest doses in both species there was no effect on implantations, although there was maternal toxicity and reduced fetal body weights.

Developmental Effects

The Volume 2 committee also reviewed studies on parental exposure to glycols and the risk of childhood cancer. Feingold et al. (1992) found that paternal exposure to DEG in the year before birth was associated with a nonsignificant increase in the risk of ALL (OR=1.4, 95% CI 0.4–4.5) and of childhood brain cancer (OR=1.3, 95% CI 0.3–5.2).

Volume 2 (IOM, 2003) included a study of the occupational and hobby-related exposures experienced from 3 months before to 3 months after conception (periconception) by mothers of children with neural tube defects and controls in selected California counties (Shaw et al., 1999b). Periconceptional maternal exposure, based on mothers’ reports of activities, to glycol ethers was associated with a nonsignificant

OR of 0.93 (95% CI 0.66–1.3). Other congenital malformations were studied by Cordier et al. (1997) and Lorente et al. (2000). Cordier et al. (1997) examined maternal exposure to glycol ethers during the first trimester of pregnancy using a job-exposure matrix. There was a significantly increased risk for congenital malformations (OR=1.44, 95% CI 1.10–1.90), particularly for first-trimester exposures and neural tube defects (OR=1.94, 95% CI 1.16–3.24), spina bifida (OR=2.37, 95% CI 1.22–4.62), cleft lip (OR=2.03, 95% CI 1.11–3.73), and multiple anomalies (OR=2.00, 95% CI 1.24–3.23). Similarly increased risks were seen in a study of first-trimester maternal occupational exposure to glycol ethers and cleft lip with or without cleft palate (OR=2.10, 95% CI 1.14–3.88), although the risk for cleft palate alone was not significant (OR=1.82, 95% CI 0.82–4.03) (Lorente et al., 2000).

ATSDR (2010) found that there were no additional studies on the developmental toxicity of ethylene glycol in humans.

The Volume 11 committee found one new study of the PELAGIE mother–child cohort in Brittany, France (Cordier et al., 2012). The association between solvent exposure (as determined by the presence of urinary metabolites of glycol ethers) and congenital malformations was assessed among a subset of 3,421 women who returned the inclusion questionnaire before 19 weeks of gestation; pregnancy outcomes were obtained from the maternity hospital records for 3,399 pregnancies (n=79 cases, 580 controls). Although several of the metabolites were associated with an increased risk of some form of congenital malformation, none of the increases were significant except for the metabolite EAA, which was associated with an increased risk of oral clefts (OR=10.9, 95% CI 2.4–50) and major limb malformation (OR=3.1, 95% CI 1.1–8.2), and 2-methoxypropionic acid, which was associated with a significantly increased risk of any malformation (OR=2.9, 95% CI 1.2–6.8) and of urinary tract malformations (OR=5.3, 95% CI 1.0–27.2). The committee notes that the number of cases for many of the malformations was small, making it difficult to generalize to a larger population.

In another analysis of the PELAGIE cohort, Béranger et al. (2017) measured urinary concentrations of glycol ethers metabolites in 204 women in the first 19 weeks of pregnancy and assessed neurocognitive abilities in their children at 6 years of age using the Wechsler Intelligence Scale for Children (WISC) Verbal Comprehension Index and Developmental Neuropsychological Assessment (NEPSY) battery (Design Copying and Arrows). Of the five glycol ether metabolites measured in maternal urine (2-butoxyacetic acid, EAA, EEAA, MAA, and phenoxyacetic acid), only two of them were associated with any differences in WISC or NEPSY scores: children of mothers in the highest tertile of urinary phenoxyacetic acid scored significantly lower on the WISC Verbal Comprehension test (β [third versus first tertile]= –6.53, 95% CI –11.44– –1.62) and children of mothers with higher concentrations of EAA scored lower on the NEPSY Design Copying subtest (β [third versus first tertile]= –0.11, 95% CI –0.21– –0.00).

Animal Studies

The Volume 2 committee did not report on animal studies of glycol ethers and ethylene glycols.

ATSDR (2010) reviewed several animal studies on the developmental toxicity of ethylene glycol via inhalation, oral, and dermal exposures in acute-duration studies and by oral exposure in intermediate-duration studies. The acute oral studies indicated that developmental effects—skeletal variation and total malformations—may occur in mice and rats. Ethylene glycol did not appear to be teratogenic in rabbits at maternally lethal doses or to be a developmental toxicant via dermal exposure. ATSDR reported that inhaled ethylene glycol in mice and rats produced effects similar to those seen with oral dosing but noted that all the studies were confounded by the concurrent ingestion of ethylene glycol deposited on the fur. Whole-body inhalation studies resulted in visceral and skeletal malformations in both rats and

mice, although dose–response relationships were lacking. Nose-only studies also showed a significant increase in fused ribs, but confounding factors rendered the studies inconclusive. ATSDR found that the developmental effects of intermediate-duration oral exposure to ethylene glycol included kidney effects in offspring.

The Volume 11 committee reviewed the findings of developmental toxicity studies of several ethylene glycols and glycol ethers not cited by ATSDR. The exposure of pregnant rats and rabbits to EGEE, but not to PGME, caused fetal cardiovascular and skeletal abnormalities in both species at levels that did not result in maternal toxicity (Bruckner and Warren, 2001).

Ballantyne and Snellings (2005) studied the developmental toxicity of DEG in CD-1 mice and CD rats to determine the no-observed effect level. Pregnant mice received 0 (distilled water), 559, 2,795, and 11,180 mg/kg/day, and pregnant rats received 0, 1,118, 4,472, and 8,944 mg/kg/day on GDs 6–15. There was maternal toxicity at the highest doses in both species. There were no increases in fetal variations or malformations at any dose in mice. The highest dose in rats results in reduced fetal body weights. DEG did not affect fetal external or visceral variations; however, at the two highest doses there were significantly increased skeletal variations. There were no indications of embryotoxicity or teratogenic effects at any dose in either species.

In the Weng et al. (2010) study of the generational effects of EGME, 4- to 6-week-old female Swiss CD-1 mice were administered via gavage approximately 0 mg/kg/day, 80 mg/kg/day, 118 mg/kg/day, and 310 mg/kg/day of EGME for 7 days. Mice were induced to ovulate and then mated with nonexposed males. Female F1 offspring were induced to ovulate, and their oocytes were evaluated. EGME has no effect on the number of retrieved oocytes following the induction of ovulation effects or on the oocyte apoptosis ratio, but there was a dose-dependent increase in the cumulus-oocyte complex apoptosis ratios in the female offspring who were not directly exposed to EGME. In an in vitro study, Dayan and Hales (2012) compared the teratogenic effects of EGME (3, 10, or 30 mM) and its metabolite 2-MMA on limb development in embryos on GD 12. Only the highest dose of EGME significantly decreased limb development (14% at 30mM), whereas all the concentrations of 2-MMA significantly decreased limb development in a dose-dependent manner (12% at 3 mM; 40% at 10 mM; 64% at 30 mM).

The reproductive effects of ethylene glycol were assessed in a three-generation study in rats. Dietary doses of 1.0, 0.2, and 0.04 g/kg/day were given over three generations of reproduction. Each generation was bred once, and the F2 males from the reproduction study were bred to three consecutive lots of untreated females at weekly intervals. Doses of up to 1.0 mg/kg/day did not produce any reproductive or dominant lethal effects (DePass et al., 1986). Carney et al. (2008) reported that although ethylene glycol is teratogenic in rats, it is not teratogenic in rabbits, possibly due to rabbits’ slower metabolism of ethylene glycol to its teratogenic metabolite, glycolic acid.

Synthesis and Conclusions

Several glycols and glycol ethers were sent to the Persian Gulf, although neither the Volume 2 nor the Volume 11 committee had information on their specific uses in theater. Although there have been studies examining the reproductive and developmental effects of many of these chemicals, they tend to have limitations. In the case of epidemiologic studies, for example, the fact that occupational exposures were rarely to a single glycol or glycol ether makes it difficult to attribute any observed effects to a specific chemical. For many of the glycol ethers, there may be only a single study for any given agent, which makes it difficult to generalize effects to the class of chemicals.

Reproductive Effects

The Volume 11 committee considered two new studies of the effects of exposure to glycol ethers on sperm quality (Cherry et al., 2008; Multigner et al., 2007). These two studies, along with earlier studies cited in Volume 2, indicated that exposure to glycol ethers is associated with the impairment of at least one sperm parameter. Exposure to ethylene glycol was found not to affect sperm quality, although this was attributed to the lag between exposure and measurement. A number of animal studies have shown that oral and inhalation exposure of male animals to glycol ethers adversely affects semen quality and increases testicular atrophy.

Other studies of occupational exposure to glycol ethers reported that exposure to glycol ethers was not associated with increased TTP in male workers (Correa et al., 1996; Figa-Talamanca et al., 2000; Samuels et al., 1995) but was in female workers (Correa et al., 1996). One study in France of the effects in women also found an increased TTP, although only at the highest concentrations (Garlantezec et al., 2013). Animal studies indicated that exposure to glycol ethers could result in uterine and ovarian atrophy.

Studies of female workers in the semiconductor industry (Eskenazi et al., 1995; Swan et al., 1995) have indicated that exposure to ethylene glycol ethers may increase the risk of spontaneous abortion. ATSDR reported on several studies in both rats and mice that showed adverse pregnancy outcomes, such as reduced pup body weight, after exposure to ethylene glycol via inhalation. The animal studies identified by the Volume 11 committee also show that high exposure to glycol ethers may have adverse effects on several pregnancy outcomes, particularly birth weights.

The Volume 11 committee concludes that there is limited/suggestive evidence of an association between exposure to glycols and glycol ethers and reproductive effects in men.

The Volume 11 committee also concludes that there is inadequate/insufficient evidence to determine whether an association exists between exposure to glycols and glycol ethers and reproductive effects in women, or with adverse pregnancy outcomes.

Developmental Effects

The Volume 11 committee considered four studies that evaluated congenital malformations associated with preconception or periconception exposure to glycol ethers, with inconsistent results. Two studies found that maternal exposure to glycol ethers in the first trimester of pregnancy significantly increased the risk of having a child with a neural tube defect, spina bifida, or other birth defects such as cleft palate (Cordier et al., 1997; Lorente et al., 2000). However, Shaw et al. (1999b) did not find an increased risk of neural tube defects when mothers were exposed for 3 months before or 3 months after conception. The fourth study, by Cordier et al. (2012), examined a different cohort of mother–infant pairs and found no significant associations between exposure to glycol ethers in early pregnancy and congenital malformations, with the exception of exposure to two metabolites: exposure to EAA at the highest level was significantly associated with oral clefts and major limb malformations, and any level of exposure to 2-methoxypropionic acid was associated with all malformations and urinary tract malformations specifically. Women in the last study also had exposure to other solvents, such as TCE and PCE. A study of children in this French cohort at 6 years of age indicated that prenatal exposure to some glycol ether metabolites (e.g., EAA) may affect neurodevelopment (Béranger et al., 2017). These studies indicated that glycol ethers may be associated with birth defects, but further study is needed.

Animal studies have not supported an association between ethylene glycols and developmental effects, and they suggest that prenatal exposure to glycol ethers does not cause malformations in offspring except at very high doses. The studies were inconsistent with regard to the developmental toxicity of ethylene glycol in animals, and propylene glycol had no adverse effects on development in animal studies. A review of the toxicity of ethylene glycols indicated that they are unlikely to be reproductive toxicants or to be embryotoxic in humans at “environmentally relevant doses” and that they do not cause developmental effects at doses that do not cause significant maternal toxicity (Fowles et al., 2017).

The Volume 11 committee concludes that there is limited/suggestive evidence of an association between prenatal exposure to glycols or glycol ethers and birth defects.

The Volume 11 committee also concludes that there is inadequate/insufficient evidence to determine whether an association exists between prenatal exposure to glycols or glycol ethers and any other developmental effects.

TABLE 7-8 Summary of Reproductive and Developmental Effects of Ethylene Glycols and Glycol Ethers

continued

TABLE 7-8 Continued

NOTE: BAA=butoxyacetic acid; CI=confidence interval; EAA=ethoxyacetic acid; EEAA=ethoxy ethoxyacetic acid; EGME=ethylene glycol monomethyl ether (2-methoxyethanol); FSH=follicle-stimulating hormone; GE=glycol ether; FSH=follicle-stimulating hormone; LH=luteninizing hormone; MAA=methoxyacetic acid; md=mean difference; MEAA=methoxy ethoxyacetic acid; 2-MPA=2-methoxypropionic acid; OR=odds ratio; PAA=n-propoxyacetic acid; PhAA=phenoxyacetic acid; SE=standard error; TTP=time to pregnancy.

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