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Biosolids Applied to Land: Advancing Standards and Practices 3 Epidemiological Evidence of Health Effects Associated with Biosolids Production and Application This chapter reviews the epidemiological literature concerning workers and community residents potentially exposed to biosolids during production and application. This literature is valuable for four reasons: (1) it may provide documentation of human-health consequences of exposure to biosolids under the circumstances of their production, application, and use; (2) it may provide information on routes of exposure, such as airborne transmission or ingestion; (3) it may provide information on a dose-response relationship; and (4) it may identify gaps in the literature. Recognition of gaps is essential to distinguish between no evidence of effect and evidence of no effect. Finally, even though all prediction is based on logical extension from available information, an epidemiological review can provide an assessment of the strength of the knowledge foundation from which predictions are made. The committee was apprised of various human-health allegations associated with biosolids exposure from news articles, written submissions from the public, and citizens who attended its public meetings. It was beyond the committee’s charge to investigate or verify these allegations. Thus, the committee limited review to studies published in the peer-reviewed literature and reports from government agencies. The review included studies that investigated health effects or provided biomonitoring data (evidence of biological absorption [i.e., chemical absorption into the body]) and excluded studies limited to human exposure without evidence of biological absorption or human health effects. Although the committee was asked to focus on public health, the review includes epidemiological studies involving production and application
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Biosolids Applied to Land: Advancing Standards and Practices of biosolids by workers, in addition to assessments of health effects in community residents. The rationale for inclusion of information on worker exposure is that occupational exposure, which for many toxicants is usually higher in exposed workers than in residents exposed from the general environment, often provides a substantial basis for extrapolating risk assessment from higher occupational concentrations to lower environmental concentrations. The committee also considered potential risks from odors and disease vectors, but did not find any epidemiological studies of these types of risks related to biosolids. Odors and disease vectors have often been categorized as nuisance or aesthetic issues, but odors can have adverse physiological and psychological effects (see Chapter 5) and vectors can transmit disease (see Chapter 6). These are issues that need careful consideration, as there appears to be a fine line between when odors or disease vectors are merely nuisance issues and when they are health issues. DESCRIPTION OF THE LITERATURE The committee evaluated 23 studies relevant to the assessment of human health effects associated with biosolids exposure and divided them into six major focus populations: (1) biosolids users (e.g., farmers and home gardeners), (2) populations near agricultural application sites, (3) workers involved in biosolids production and application, (4) populations near sewage treatment plants, (5) workers in sewage treatment plants, and (6) compost workers. Few epidemiological studies were conducted specifically for biosolids exposure. There are substantially more studies of workers in sewage treatment plants and populations living near them. Although those studies do not involve exposure to biosolids per se, they were included because they provide valuable information about hazards to sewer workers and others exposed to raw sewage that could be used to identify potential hazards from biosolids. However, an exhaustive review of the literature on exposures from sewage treatment plants was not conducted. Table 3–1 provides the details of the studies that the committee evaluated. A summary of the populations studied, the observed outcomes, and the committee’s assessment is provided below. Exposed Populations Biosolids users. One study documents chemical exposure from avocational gardening use of biosolids (Baker et al. 1980). This single investi-
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Biosolids Applied to Land: Advancing Standards and Practices TABLE 3–1 Summary of Human Health Studies on Biosolids and Biosolids-related Exposures Study Type End Points Evaluated Findings References Biosolids Users Cross-sectional Evaluation of PCB exposure and health effects in (1) biosolids users (n=89) in Bloomington, Indiana, exposed to biosolids directly from application to gardens or indirectly from foods grown in biosolids-amended soils; (2) workers occupationally exposed to PCBs (n=18, only 1 exposed via biosolids); (3) family members of workers occupational exposed to biosolids (n=19), and (4) individuals with no known exposure to PCBs (n=22). (PCBs were discharged into the municipal sewage system by a electrical capacitor manufacturing plant.) Mean serum concentrations of PCBs were 17.4 ppb in biosolids users; 75.1 ppb in PCB-exposed workers; 33.6 ppb in worker family members; and 24.4 ppb in nonexposed individuals. For biosolids users, PCB serum concentrations were associated positively with the percentage of garden care (p=0.035) and negatively with wearing gloves while gardening (p=0.021) but were not significantly associated with the amount of biosolids used or the duration of exposure. No overt symptoms of PCB toxicity were observed, and no correlations were found between PCB exposure and tests of hematological, hepatic, or renal function. Plasma triglyceride concentrations were found to increase with serum PCB concentrations, suggesting that PCBs might alter lipid metabolism. Baker et al. 1980 Populations Near Agricultural Application Sites Prospective Three-year health survey of farm residents (n=164) and domestic animals at farm application sites in Ohio. Residents also under No significant differences in the following parameters were found between residents at land-application sites and control sites: respiratory illness, gastrointestinal illness, or general symptoms; disease Dorn et al. 1985
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Biosolids Applied to Land: Advancing Standards and Practices went tuberculin and serological testing. Results were compared with residents of farms that do not apply biosolids (n=130). occurrence in domestic animals; and serological conversions to 23 viruses and the frequency of associated illnesses. No conversions from positive to negative tine test results were found after sewage sludge application. Workers in Biosolids Production and/or Application Industry Cross-sectional Interviews with employees (n=5) loading, unloading, and applying Class B biosolids and environmental monitoring, including breathing-zone air samples for bacteria, endotoxins, VOCs, and trace metals. History of gastrointestinal illness among workers. Enteric bacteria were detected in the air and bulk samples. Endotoxin levels at or below levels found in wastewater treatment facilities. Various metals and VOCs were low. After this study was issued, it was reported that the biosolids to which the workers were exposed did not meet Class B requirements. Burton and Trout 1999; Lodor 2001 Populations Near Sewage Treatment Plants Retrospective Acute illnesses and symptoms reported between 1965 and 1971 by community in Tecumseh, MI (n=4,889). Community was divided into concentric rings radiating out in multiples of 600 m from an activated sewage sludge treatment plant. Greater than expected occurrence of respiratory and gastrointestinal illnesses in community living within 600 m of the plant. Limitations in interpreting the results were identified by the investigators as confounding by a demographically heterogeneous population (low socioeconomic population), lack of exposure and meteorological data, and relatively low volume of the exposure source. Fannin et al. 1980; Jakubowski 1986 Retrospective Monitoring of microorganisms in the air upwind and downwind of Absenteeism at the school decreased during the 2 y after the plant began operations compared with Camann et al. 1980;
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Biosolids Applied to Land: Advancing Standards and Practices Study Type End Points Evaluated Findings References a plant in Tigard, OR, and comparison of absenteeism rates in a nearby school before and after the plant opened. attendance data collected over 7 y before the plant opened. Jakubowski 1986 Prospective Health survey of community (n=4,300) in Schaumburg, IL, between 1974 and 1976, which covered a period before and after an activated sewage sludge treatment plant was operational. Serological tests and isolation of pathogens from clinical specimens were also performed on a subset of the community (n=226). Significant (p<0.01) increases were found in the reported incidence of skin disease, chest pain, diarrhea, weakness, nausea, and vomiting in the population living within 2 m of the plant. Diarrhea was the only symptom for which there were uniform reports throughout the reporting period, increasing from 4.1% before the plant opened to 7.6% after the plant opened. There were no increases in the isolation of Pseudomonas, Salmonella, or parasites in fecal samples after the plant opened, and a significant decrease in Proteus isolations were observed during the operational period. Increases in Streptococcus and Staphylococcus isolates in throat swabs were observed after plant opening, but regression analyses found no relationship with exposure to the plant. Similarly, there were increases in virus isolates in fecal samples during the operational period, but those increases were not found to be related to the plant. Antibody tests for enteric viruses found no evidence of increased exposure from the plant, and aerosol monitoring results indicated that levels Johnson et al. 1980; Jakubowski 1986
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Biosolids Applied to Land: Advancing Standards and Practices of microorganisms in the air in the residential areas in the vicinity of the plant were similar to background concentrations. Prospective Eight-month health survey of a population (n=2,378) living in the vicinity of a plant in Skokie, IL. Analyses of blood, throat, and fecal specimens were tested in subsets of the population. Microbial aerosol monitoring and meteorological data were also collected. Regression analyses performed between total particle exposure indices and self-reported illness rates, pathogenic bacteria isolation rates, prevalence rates of virus antibody, and virus antibody titers were negative. Regression analyses were also negative when illness rates and exposure indices were run with reference to length of residence, age, smoking, presence of young children, chronic respiratory disease, and chronic gastrointestinal illness. Northrop et al. 1980; Jakubowski 1986 Sewage Treatment Plant Workers Cross-sectional Health survey of workers at a sewage treatment plant in Toronto, Canada (n=50). Lung function tests and analyses of PCBs in blood samples were also conducted. (The plant received controlled discharges of PCBs from an electrical manufacturing company.) The most common symptoms reported by workers included cough, sputum production, wheezing, sore throat, and skin complaints. Workers tended to have slightly reduced lung function. Serum concentrations of PCBs could not be related to symptoms or clinical findings. Nethercott and Holness 1988 Cross-sectional A saliva test was used to detect antibodies to hepatitis A virus (anti-HAV) in workers at wastewater plants serving Columbus, OH (n=163). Results were Forty-two wastewater workers and 17 control workers tested positively for anti-HAV. After controlling for confounding effects of age and race, no association was found between wastewater work and an increased prevalence of anti-HAV (preva Trout et al. 2000
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Biosolids Applied to Land: Advancing Standards and Practices Study Type End Points Evaluated Findings References compared with those from workers not exposed to wastewater (n=139). lence ratio=1.3; 95% confidence interval 0.7 to 2.4). In an evaluation of wastewater workers alone, no statistically significant occupational risk factors for anti-HAV was found. Cross-sectional Workers (n=34) from eight sewage treatment plants in Sweden completed health questionnaires and underwent spirometry and airway tests. Results were compared with those of nonsewage workers (n=35). Reports of nasal irritation, tiredness, and diarrhea were significantly higher in sewage workers compared with controls. Airway responsiveness was increased among sewage workers, but there were no differences in spirometry results. The authors suggested that the symptoms were likely caused by endotoxin, which was detected between 3.8 and 32,170ng/m3. Rylander 1999 Cross-sectional Workers (n=189) from 16 sewage treatment plants in New York were surveyed for working habits, life style, and symptoms of illness. Results were compared with workers at a water treatment plant (n=82). The frequency of headache, dizziness, sore throat, skin irritation, and diarrhea was significantly higher among the sewage workers. Scarlett-Kranz et al. 1987 Cross-sectional Patients (n=5) repairing a decanter for sewage sludge concentration developed illnesses consistent with Pontiac fever. Serological confirmation of Pontiac fever in all five workers and recovery of Legionella pneumophila from sewage sludge. Gregersen et al. 1999
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Biosolids Applied to Land: Advancing Standards and Practices Cross-sectional Wastewater workers (n=359) and drinking-water workers (n=89) were examined for anti-HAV. Anti-HAV was detected in 28.4% of wastewater workers and in 23.6% of drinking-water workers. After adjustment for age and other variables, the odds ratio for anti-HAV was 2 (CI: 1–3.8). Additional risk factors included years in industry, never wearing face protection, and skin contact. Weldon et al. 2000 Cross-sectional Study of employees in water and sewage company (n=241). Exposure to raw sewage was a risk factor for HAV infection (odds ratio 3.7 (CI: 1.5–9.4); 60% of workers reporting exposure to raw sewage had HAV infection. Brugha et al. 1998 Cross-sectional Urine assay for pesticide among wastewater treatment workers processing effluent from pesticide plant and among comparison workers in water system. 69% of exposed workers exceeded urine cut-off value compared with 10% in comparison plant. Shift changes were consistent with occupational exposure. Elia et al. 1983 Cross-sectional Examination of sewage treatment plant workers (n=145) after hexachlorocyclo-pentadiene was dumped into a municipal sewage system. Examination of 41 employees showed proteinuria and increased serum lactic dehydogenase levels 3 d after the plant was closed. These findings were not found 3 wk later. Morse et al. 1979 Prospective Twelve-month study of infection rates in experienced and inexperienced workers (n=336) exposed to wastewater and nonexposed workers in Cincinnati, Chicago, and Memphis. No significant differences were found in illness rates by worker category or city, in virus or bacterial isolation rates, or in serological analyses. Higher rates of gastrointestinal illness were reported by inexperienced workers but could not be related to a specific agent or exposure. Clark et al. 1980; Jakubowski 1986
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Biosolids Applied to Land: Advancing Standards and Practices Study Type End Points Evaluated Findings References Serological analysis for rotavirus, Norwalk agent, and Prototheca wickerhamii from serum archived from the worker population above. No association between wastewater exposure and antibodies to either rotavirus or Prototheca. Inexperienced workers had higher levels of antibodies to Norwalk agent. Evaluation of 815 death certificates from former wastewater workers in Chicago. Deaths from leukemia (p=0.04) and pneumonia (p=0.02) were greater than expected. Cross-sectional Comparison of protozoan parasitic infection among sewer workers (n=126) in France compared with 363 food handlers (n=363). Rates of infection were higher among sewer workers for all 6 yr. Foreign travel was considered but no other possible differences were found among exposed and comparison groups. Schlosser et al. 1999 Retrospective Historical cohort study of wastewater treatment workers (n=242) and comparison group of college maintenance workers (n=54) followed for 12 mo. Significantly higher prevalence of gastroenteritis and gastrointestinal symptoms (p<0.05) and headaches (p<0.05) but not respiratory symptoms. No difference was found between high and low exposure categories. Khuder et al. 1998 Cross-sectional Health survey and clinical tests of workers at six sewage treatment plants (n=199) in Sweden compared with control workers at a drinking water plant (n=41). Reports of skin disorders, diarrhea, and other gastrointestinal symptoms were significantly greater among the sewage-treatment workers. No differences were found in white-blood-cell count or serum Ig concentrations between the groups, except for slightly increased IgM concentrations among Lundholm and Rylander 1983
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Biosolids Applied to Land: Advancing Standards and Practices sewage workers. The most likely cause of symptoms was toxins from gram-negative bacteria. Cross-sectional Workers in sewage treatment plant (n=30) compared with age-matched blood donors. Environmental measurement of dust and airborne bacteria conducted. Elevations in IgA, thrombocytes, leukocytes, endotoxin antibodies, c-reactive proteins considered consistent with endotoxin exposure. Rylander et al. 1977 Compost Workers Cross-sectional Heath complaints and diseases of compost workers (n=58) in Hamburg, Germany compared with control subjects (n=40). Significantly more symptoms and diseases of the airways (p=0.003) and skin (p=0.02) were reported by compost workers than controls. Antibody concentrations to fungi and actinomycetes were significantly increased in compost workers. Bünger et al. 2000 Prospective Infection rates among compost workers in Camden, NJ, Philadelphia, PA, Beltsville, MD, and Washington, DC, with high exposure (n=98) and intermediate exposure (n=157) and workers not involved in composting (n=133). Study period was between 1979 and 1981. Eye and skin irritation was reported more frequently among compost-exposed groups. Aspergillus fumigatus was detected in nasal and throat swabs (70% in high-exposure group, 20% in intermediate-exposure group, and 5% in low-exposure group), but there was no consistent increase in antibodies to the fungal spores. There were no differences in levels of antibodies to Legionella pneumophila between exposure groups, and no antibodies to Histoplasma capsulatum were detected. Compost workers had greater IgG antibody levels against compost-derived endotoxin, elevated C3 and hemolytic complement levels, and higher white- Clark et al. 1984
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Biosolids Applied to Land: Advancing Standards and Practices Study Type End Points Evaluated Findings References blood-cell and eosinophilic counts. In pulmonary function tests, vital forced capacity was greater at the end of the week than at the beginning of the week for compost workers. Abbreviations: CI, confidence interval; PCBs, polychlorinated biphenyls; VOCs, volatile organic compounds; ppb, parts per billion; m, meter; ng, nanogram; HAV, hepatitis A virus; Ig, immunoglobulin.
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Biosolids Applied to Land: Advancing Standards and Practices gation, conducted before current regulatory requirements for biosolids were initiated, demonstrates the possibility of chemical contamination from biosolids. No other studies of farm or nonfarm biosolids users were found. Populations near agricultural application sites. One study of a population near a biosolids land-application site was found (Dorn et al. 1985). That study reported no differences in symptoms or serological conversion between farm residents living near the application site and a comparison group. Workers in biosolids production and/or application industry. One study by the National Institute for Occupational Safety and Health (NIOSH) reported a history of gastrointestinal illness in workers handling Class B biosolids (Burton and Trout 1999). Environmental assessment found potential worker exposure to enteric bacteria. After the study was issued, Lodor (2001) reported that the biosolids to which the workers were exposed did not meet Class B requirements. NIOSH (2002) subsequently released a guidance document for controlling potential risks to workers exposed to Class B biosolids that supercedes its earlier Hazard ID document on Class B biosolids. Populations near sewage treatment plants. The committee evaluated four studies of populations living near sewage treatment plants. These studies cover a wide spectrum of outcomes and exposures and include one to a few studies of any particular area. Increases in gastrointestinal and respiratory illnesses (Fannin et al. 1980), an increase in diarrhea (Camann et al. 1980), and decrease in school absenteeism (Camann et al. 1980) were reported. However, these studies are not sufficient to evaluate the safety of populations near sewage treatment plants. Sewage treatment plant workers. Fourteen studies of sewage treatment plant workers were evaluated. These studies reported both increases (Brugha et al. 1998; Weldon et al. 2000) and no increases (Trout et al. 2000) in hepatitis A infection; increased complaints of nasal irritation, tiredness, and diarrhea, which were considered compatible with exposure to endotoxin (Rylander et al. 1977); increased prevalence of gastroenteritis (Khuder et al. 1998); a confirmed outbreak of Pontiac fever (Gregersen et al. 1999); evidence of pesticide absorption (Elia et al. 1983); no differences in illnesses rates, nor isolation of virus or bacteria (Clark et al. 1984); increased rates of protozoan infection (Scholsser et al. 1999); and increased rates of reports of skin disorders, diarrhea, and gastrointestinal symptoms (Lundholm and Rylander 1983). These studies are sufficient to suggest transmission of specific infectious diseases to sewage treatment plant workers (e.g., Pontiac Fever). However, no firm conclusions can be drawn at this time. Compost workers. Studies of compost workers have reported significant increases in diseases of the airways and skin and evidence of increased
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Biosolids Applied to Land: Advancing Standards and Practices exposure to fungi and actinomycetes (Bünger et al. 2000) and eye and skin irritation and fungal colonization but no serological evidence of infection (Clark et al. 1984). These two studies provide suggestive evidence of colonization of compost workers with fungi. Observed Health Outcomes Toxic exposures. Two studies (Baker et al. 1980; Morse et al. 1979) documented the potential for industrial chemicals to be present in wastewater. Sewage workers can be exposed, as can those who use biosolids for agriculture or other land-application purposes. Morse et al. (1979) investigated occupational exposure resulting from a one-time contamination of the wastewater, and Baker et al. (1980) studied occupational and residential exposure resulting from an ongoing contamination of wastewater. These two studies demonstrate that workers and community residents can be exposed to chemical hazards that enter into the municipal waste stream. The epidemiological literature on exposure to toxic substances in biosolids provides no information by which to gauge two issues. The first issue concerns the adequacy of routine monitoring of wastewater in order to capture common toxicants and toxicants that might be idiosyncratic to the industrial processes in a particular locale. Although wastewater is periodically examined for chemical contamination, the number of chemicals sought is much less compared with the number of chemicals used commercially. Second, the periodicity of testing and the periodicity of discharge will determine the probability of identification of a hazardous chemical in a sample of effluent. Viral infection. The potential for viral infection of wastewater workers was documented in several studies (Brugha et al. 1998; Weldon et al. 2000) and not in others (Clark et al. 1980; Northrop et al. 1980). One study documented the absence of serological evidence of viral infection among populations near application sites (Dorn et al. 1985). No study examined viral infection among workers in biosolids production or application sites. The epidemiological literature provides no evidence for or against the potential for biosolids to serve as a vehicle for viral infection. The probability that biosolids are a potential vector for infection might be revealed by other lines of research, such as environmental viral studies. Bacterial and protozoan infection. Some studies have documented complaints of gastrointestinal illness related to sewage sludge (Fannin et al. 1980; Johnson et al. 1980; Burton and Trout 1999) and others have not (Dorn et al. 1985). Similarly, some studies have detected enteric bacteria in air and
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Biosolids Applied to Land: Advancing Standards and Practices bulk samples (Burton and Trout 1999), and others have not (Johnson et al. 1980). One study found evidence of protozoan infection among sewer workers (Schlosser et al. 1999). For bacterial and protozoan infection, there is neither evidence of infection nor evidence of no infection. Evidence of viable organisms in biosolids would strengthen the biological plausibility of a causal association, as would demonstration of the potential for exposure during specific aspects of production and application of biosolids. Irritation and allergic reaction. Several studies reported allergy or irritation among sewer workers (Rylander 1999) and workers in compost production (Clark et al. 1984; Bünger et al. 2000). The role of endotoxin in these observations is strengthened by demonstration of endotoxin content of biosolids but is weakened by lack of evidence showing a relationship between level of exposure and effect. Assessment of Causality Assessment of causality requires judgment of epidemiological and other information. Conclusions that an association is causal rest on demonstration of such factors as consistency of findings in independent studies, strength of association, temporal sequence, and biological plausibility (demonstration of dose-response relationships) (Bradford-Hill 1966). There is a small body of epidemiological literature on the potential adverse health effects of biosolids. The literature is even more sparse considering the varying populations that are potentially exposed to biosolids via wastewater treatment, biosolids production, occupational exposure during application, and community exposure. For some exposures, such as chemical exposure, it is fairly clear that chemical contamination of sewage with industrial chemicals can result in product contamination leading to exposure of workers and community residents. It is unclear whether the system for preventing chemical contamination of sewage and monitoring sewage is sufficient to ensure protection from chemical exposures. Although there is evidence of infection of sewage workers, it is unclear, based on design criteria for production of biosolids or based on sampling for detection of viable organisms, whether viral, bacterial, or protozoal infection of workers or community residents exposed to biosolids is plausible. There is a relative absence of evidence documenting infection, and limited evidence documenting the lack of infection from biosolids. A similar assessment can be made for the evidence of a causal relationship of symptoms of irritation and allergy and exposure to endotoxins.
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Biosolids Applied to Land: Advancing Standards and Practices Some have contended that there is evidence of lack of health hazard from occupational exposure in wastewater treatment plants and that by extrapolation, risk from biosolids must be negligible. This reasoning is problematic for several reasons. First, as described earlier in this chapter, the knowledge base regarding wastewater treatment workers is thin and contradictory. Second, the exposure characteristics will be quite different in the wastewater treatment industry compared with biosolids land-application. For example, potential exposures to airborne contaminants from wet sewage sludge are quite different from those from dried biosolids. Third, the routes of exposure may be different between populations exposed to raw sewage sludge compared with those exposed to biosolids. Fourth, the populations exposed to biosolids may not be equivalent to the occupational population exposed to sewage sludge. Farm families and community residents will include subpopulations unlikely to be found in the workplace, such as children and individuals with respiratory diseases. Thus, lack of compelling evidence of adverse health effects among wastewater treatment workers should not be used to infer that there will be a lack of adverse health effects from exposure to biosolids. There are two types of health studies that will reduce uncertainty regarding health effects of biosolids exposure—response studies and preplanned studies. Response studies are initiated rapidly on notification that there has been either an unusual exposure or occurrence of disease among workers or community residents exposed to biosolids. Such studies are intended to assess and attempt to relate measures of exposure with measures of disease. Response studies should be conducted in a short time frame (weeks to months). Whether response studies are conducted by state or federal agencies or academia on behalf of EPA, a priority setting mechanism must be established so that limited resources are used to maximize the probability that the response studies will effectively contribute to the sparse information on the health consequences of exposure of workers and/or residents to biosolids during production and manufacture. Preplanned studies, on the other hand, are conducted to test a specific hypothesis. The hypothesis might be generated by researchers who compete for research funding, or more specific questions may be formed by EPA or other agencies. Preplanned studies must be well designed and conducted to reduce uncertainty concerning issues of importance. For example, a preplanned epidemiological study must be sufficiently large, characterize exposure, include an adequate interval between exposure and observation to allow for occurrence of disease if it were to occur, measure confounders, and be able to delineate adverse outcomes and evidence of their occurrence. There are two types of preplanned studies—exposure assessment and complete epidemiological studies. In exposure assessment studies, the goal is
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Biosolids Applied to Land: Advancing Standards and Practices to define the distribution and determinants of exposure to an agent or chemical of interest. This information may then be used in formal risk assessments. The second type of preplanned study is the complete epidemiological study. The goal of this study is to assess the association of the occurrence and distribution of disease with measurement of prior exposure (provided through a concurrent or prior exposure assessment). The purpose of preplanned studies is to determine if exposure is related to increased occurrence of disease, or its corollary. In contrast with response studies, preplanned studies are more expensive because they are larger, require more effort in planning, and involve more extensive data analysis and more effort in assessment of exposure. Consequently, more effort will be expended in setting priorities in preplanned studies. Priorities should include probability of the study reducing uncertainty, seriousness of the disease outcome, incidences of the disease outcome, a priori level of uncertainty, and importance of the results in protecting against adverse health consequences. It is also important to recognize that worker populations and communities are not homogenous in their susceptibility to disease or subsequent adverse consequences. Thus, in response and preplanned studies, it is important to include all or a sample of the potentially susceptible subpopulations. Examples of susceptible subpopulations include children, the elderly, pregnant women, and individuals with chronic disease. In addition, stakeholders should be involved in review of the design, conduct, and interpretation of studies. Stakeholders may include representatives of workers and management, community representatives, health care providers, and victims of disease. FINDINGS AND RECOMMENDATIONS The committee concludes that because of the lack of epidemiological study and the need to address the public’s concerns about potential adverse health effects, EPA should conduct studies that examine exposure and potential health risks to worker and community populations. Studies of wastewater treatment workers should not be used as substitutes for studies of actual biosolids exposure. While routine human health surveillance of all populations exposed to biosolids is impractical, the committee recommends that EPA promote and support a research effort to reduce uncertainty about the possible health consequences of exposure to biosolids. Stakeholders should be involved in review of the design, conduct, and interpretation of studies. The committee recommends the following types of study.
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Biosolids Applied to Land: Advancing Standards and Practices Response Studies Studies in response to unusual exposure and unusual occurrence of disease. On occasion, unplanned events occur that can provide information on the agents of disease. An example might be an outbreak or a symptom of disease following a known exposure or an unusual exposure scenario. In both instances, exposure and health outcomes should be determined. Preplanned Studies Biosolids exposure-assessment studies. Such studies should characterize the exposures of workers, such as biosolids appliers and farmers, and the general public who come into contact with constituents of biosolids either directly or indirectly. The studies would require identification of microorganisms and chemicals to be measured, selection of measurement methods for field samples, and collection of adequate samples in appropriate scenarios. A possible exposure-assessment study would be to measure endotoxin exposure of workers at biosolids production and application sites and of communities nearby. Complete epidemiological studies of routine biosolids use. These studies should be conducted to provide evidence of a causal association, or a lack thereof, between biosolids exposure and adverse human health effects. They should include an assessment of the occurrence of disease and an assessment or measurement of potential exposures. An example of a longitudinal epidemiological study would be an evaluation of health effects in a cohort of biosolids appliers; these workers should be characterized by duration and level of exposure, with appropriate follow-up. REFERENCES Baker Jr., E.L., P.J.Landrigan, C.J.Glueck, M.M.Zack, Jr., J.A.Liddle, V.W.Burse, W.J.Housworth, and L.L.Needham. 1980. Metabolic consequences of exposure to polychlorinated biphenyls (PCB) in sewage sludge. Am. J. Epidemiol. 112(4):553–563. Bradford-Hill, A. 1966. The environment and disease: Association or causation? Proc. Royal Soc. Med. 58:295–300. Brugha, R., J.Heptonstall, P.Farrington, S.Andren, K.Perry, and J.Parry. 1998. Risk of hepatits A infection in sewage workers. Occup. Environ. Med. 55(8):567–569. Bünger, J., M.Antlauf-Lammers, T.G.Schulz, G.A.Westphal, M.M.Müller, P. Ruhnau, and E.Hallier. 2000. Health complaints and immunological markers
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Representative terms from entire chapter: