Environmental Epidemiology, Volume 1 Public Health and Hazardous Wastes (1991) / Chapter Skim
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3. Dimensions of the Problem: Exposure Assessment
3. Dimensions of the Problem: Exposure Assessment
Pages 101-154
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3~. In environmental epidemiology, exposure assessment has proved difficult.
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The national failure to address the many known and suspected hazards from uncontrolled hazardous waste sites led Congress to pass the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA) , generally known as the Superfund law.
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HAZARDOUS-WASTE SITES Within the past decade, estimates of the number of potential NPL sites have shifted dramatically. The Office of Technology Assessment (OTA, 1989)
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(1985) have reviewed the adverse health effects associated with specific toxicants identified at hazardous-waste sites.
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Source: U.S. Environmental Protection Agency, Office of Emergency Response, Washington, D.C.
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Hepatic, hematopoietic, renal, reproductive, and CNS effects were the most likely indicators of chronic, low-dose exposure through ingestion. UNIDENTIFIED OR UNCHARACTERIZED CONTAMINANTS To date, attention has focused on a relatively small number of chemical contaminants identified at hazardous-waste sites.
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Toxic contaminants in groundwater can be considered as "hazardous waste" in a public health or toxicologic context, in contrast to the regulatory framework for defining hazardous waste. Secondly, contaminated groundwater close to defined hazardous-waste sites may act as a confounder in environmental epidemiologic investigation.
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108 UO ._, o Ct a; Cal Q · — a' ·_.
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has been identified at only one NPL site. A1though DBCP use was suspended in California in 1979, it persists in the environment and has been detected in more than one-fifth of drinking water wells in California not related to NPL sites.
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NPL sites are included, but other sources of contamination are also important. The groundwater contamination from sources other than hazardous-waste sites is relevant to the conduct of exposure assessment in environmental epidemiology.
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51 16,400 Surface impoundments 32 191,800 Injection wells 10 280,800 Dissolved solids, iron, manganese, trace metals, acids, organic compounds, and pesticides. Brines, acidic mine wastes, feedlot wastes, trace metals, and organic compounds.
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From page 113... ...
The purpose of exposure assessment in environmental epidemiology is to facilitate investigation of and to establish cause-effect relationships between environmental exposure and adverse health outcomes. Causation may be implied in descriptive studies in which no direct determination of exposure is carried out, but well-conducted studies of population exposure enhance confidence in the interpretation of a causal relationship between exposure and health outcome.
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Within this overall context, exposure assessment strategies have several secondary objectives: 1. To facilitate identification of persons at risk for adverse health consequences from exposure to toxic chemical agents i.e., to identify with reasonable accuracy persons who are being or have been exposed to materials considered hazardous waste.
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4 ~ 584, 728 _ 130,840 ~ 98, 67880 630 5 6 1 133,896 1 _ 10* Region FIGURE 3-3c Population living within 1 mile of a Superfund site(s)
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3. To assess the nature of potentially confounding exposures, including groundwater contamination that may occur from numerous sources, such as agricultural runoff, and may increase the health risk of a study population or inhibit population identification and characterization and identification of causal factors in epidemiologic investigations.
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Exposure to toxic chemicals would most likely occur through contaminated groundwater that has leached or run off from waste sites to enter the drinking water supply. Other sources of exposure include direct contact with contaminated sediment; accidental ingestion of contaminated soil or surface water; release of volatile agents into the air; and ingestion of contaminated vegetables, fruit, meat, poultry, or fish.
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has developed an indoor air model validated by air measurements of TCE from residential bathrooms. He found that TCE inhalation exposures from a six-minute shower are comparable to ingestion of TCE in drinking water.
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They do not constitute epidemiologic investigations nor were they intended to be used for those purposes. They provide a starting point for epidemiologic investigations, insofar as they contain information about some of the chemicals identified at hazardous-waste sites.
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In development of estimates of human exposure and estimating population exposure in connection with waste sites, a hierarchy of exposure or surrogate exposure data can be useful in establishing a sampling strategy (Table 3-4~. Direct measurement of exposure assessment includes personal monitoring and use of biologic markers (see Chapter 7)
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Improved quantitative exposure data could enhance study population identification and improve ecologic studies, but that information has not been pursued, because ecologic studies have relied on surrogates of exposure. Ecologic studies are often considered hypothesis-generating, and in-depth exposure evaluations would not necessarily be considered appropriate to a design of this type.
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Absent such information, internal dose measures the contribution of exposure to a contaminant from all media. Internal dose is generally assessed by means of biologic monitoring when biological monitoring techniques are available.
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and the neurotoxicity of acrylamide (Hattie and Shapiro, 1990~; for better estimation of target-tissue dose for purposes of risk assessment for butadiene (Hattie and Wasson, 1987) and ethylene oxide (Hattie, 1987~; and for risk assessment of drinking water with particular reference to the quantitative estimation of uncertainty (NRC, 1987; Hattis and Froines, in press)
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The NRC report on estimation of human exposure described the principal advantage of models as their ability to estimate concentrations in different microenvironments or exposures on which there is little direct information. Where personal or biologic monitoring, microenvironment characterization, and modeling cannot be readily accomplished, surrogate measures of exposures are the last resort; they were the method of choice in the earlier ecologic investigations reviewed here.
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V Absorption through G I tract FIGURE 3-6 Parameters required to calculate the potential and internal dose.
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The specific aim of an environmental epidemiologic study of hazardous waste sites is to identify and establish a relationship between exposures derived from a site and adverse health outcomes. Identification and subsequent characterization of the study population represents the challenge before the investigator.
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The precision of derived risk estimates is proportional to the population size under study, and validity is improved by reducing measurement error in the actual exposure data (Checkoway et al., 1989~. Therefore, an exposure assessment strategy that gathers indepth, quantitative exposure data on individuals might reduce measurement error, but it will probably do so at the expense of study size because of resource limitations.
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Case-control approaches such as the two radon exposure studies being conducted by the New Jersey Health Department and the Argonne National Laboratories are useful examples of approaches to the in-depth estimation of exposure in a defined study population (NRC, 1991~. One useful approach for resolving the apparent contradiction between the requirements for in-depth exposure assessment and study population size is through the use of nested exposure-assessment designs in which a small number of the overall study population is subject to extensive direct and indirect measurements of exposure including personal and microenvironmental monitoring, biomarkers, and modeling.
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(1985) suggest that estimating the extent of exposures TABLE 3-6 Some Common Problems with All Types of Human Exposure Data High variability of human exposure, past and present Time to time Person to person Lead times of decades Synergy Questions of what to measure: Peak exposure vs.
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Landrigan (1983) has illustrated the problem of grouped versus individual data in comments on a study of arsenic in drinking water ~~ a ~ -r ~
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When estimates of bottled drinking water consumption were incorporated, the correlation between arsenic exposure and well water consumption strengthened the dose-response relationship. EXPOSURE ASSESSMENT IN SPECIFIC EPIDEMIOLOGIC INVESTIGATIONS The committee reviewed epidemiologic studies of hazardous-waste sites or water contamination to evaluate the exposure assessment in each.
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FRESNO COUNTY, CALIFORNIA Whorton and co-workers (Whorton et al., 1988; Wong et al., 1988, 1989) conducted an ecologic and case-control study of the relationship between drinking water contaminated with DBCP and birth rates, gastric cancer, and leukemia in Fresno County, California.
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The case-control study did not identify any relationship between gastric cancer and DBCP in drinking water. However, the variable "Hispanic surname" was a risk factor for gastric cancer; Hispanics had a relative risk of gastric cancer of 2.77, compared with non-Hispanics.
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Toxicologic investigations that evaluate the potential of the chemicals in question to produce adverse reproductive effects might be valuable in providing indirect confirmation of the epidemiologic investigations. MCCOLL SITE, FULLERTON, CALIFORNIA An interesting surrogate of exposure was used by California researchers (Lipscomb et al., in press)
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They suggest that living near a hazardous-waste site and being concerned about the environment can result in "recall bias" that could affect findings more than does the toxicity of the chemicals found in the site. Unfortunately, the report provides no environmental monitoring data.
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Baker and co-workers conducted a health survey to assess whether there were increased rates of mortality, adverse pregnancy outcomes, disease incidence, or symptom prevalence, such as blurred vision, pain in ears, daily cough for more than a month, nausea, frequent diarrhea, unsteadiness when walking, and frequent urination among individuals living near the waste site. The exposure surrogate they chose was based on "relative exposure likelihood of residents to toxic waste from the Stringfellow site" (Baker et al., 1988, p.
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That limits the confidence in a positive association between the exposed populations and subjective health outcomes. Absence of an association is equally problematic, given the lack of individual exposure data, information derived from microenvironmental monitoring, or indirect methods based on modeling.
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The authors briefly review the potential exposures to citizens in the Love Canal area and correctly point out that exposure to residents of Love Canal is not well understood, especially given the fact that more than 200 chemicals have been found in the Love Canal dump site. Selection of the study population and the exposure surrogate were based on residence in the Love Canal neighborhoods.
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did not find evidence of any serious and chronic health conditions. OTHER STUDIES OF CONTAMINATED DRINKING WATER Drinking water contaminated by hazardous wastes has served as the basis for exposure assessment in a number of studies.
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(1990) approached the problem of associating specific health end points to chemical exposure by developing an animal model to explain the cardiac malformations associated with exposure to drinking water contamination by TCE and dichloroethylene (DCE)
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which they associated with contaminated drinking water. The most common contaminant detected in private wells serving the exposed study population was carbon tetrachloride, which was identified in concentrations as high as 18,700 micrograms per liter.
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This chapter has detailed major difficulties in assessing the more than 600 chemical compounds identified at hazardous-waste sites, along with the hundreds or thousands of unidentified pollutants, in the context of environmental epidemiology. The potential for exposure is of such a magnitude that researchers who develop exposure
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Evaluations of exposure associated with hazardous-waste sites must consider all possible media as potential sources of toxic contaminants. Regarding the specific pollutants measured, evidence indicates that uncharacterized pollutants are a potentially important source of chemical exposures.
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APPENDIX 3-A Frequency of Substances Reported at Final and Proposed NPL Sites (3/91)
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anthracene Cyanide Dieldrin/ aldrin Chloroform Benzene Vinyl chloride Methylene chloride Heptachlor/heptachlor epoxide Trichloroethene
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fluoranthene Chrysene p-Dioxin Lead Nickel Arsenic Beryllium Cadmium Chromium PCB-1260,54,48,42,32,21,1016 Priority Group 2 Priority Group 3 Carbon tetrachloride Chlordane N-Nitrosodimethylamine 4,4'DDE, DDT, DDD Chloroethane Bromodichloromethane 1,1-Dichloroethene Isophorone 1,2-Dichloropropane 1,1,2,-Trichloroethane 1,1,2,2-Tetrachloroethane Pentachlorophenol 3,3'-Dichlorobenzidine Benzidine 1,2-Dichloroethane Toluene Phenol Bis (2-chloroethyl) ether 2,4,-Dinitrotoluene BHC-alpha, gamma, beta, delta Bis(chloromethyl)
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148 ENVIRONMENTAL EPIDEMIOLOGY APPENDIX 3-B Continued 88062 91203 98953 100414 107028 107131 108907 118741 122667 124481 156606 193395 606202 1330207 7221934 7440224 7440508 7664417 8001352 51285 59507 62533 65850 67721 74839 75150 75694 75718 78933 84662 85018 87683 95487 95501 105679 108101 120821 120832 123911 131113 206440 534521 541731 7440280 Priority Group 4 2,4,6-Trichlorophenol Naphthalene Nitrobenzene Ethylbenzene Acrolein Acrylonitrile Chlorobenzene Hexachlorobenzene 1,2-Diphenylhydrazine Chlorodibromomethane 1,2-Trans-dichloroethene Indeno(1,2,3-cd) pyrene 2,6-Dinitrotoluene Total xylenes Endrin aldehyde/endrin Silver Copper Ammonia Toxaphene 2,4-Diitrophenol p-Chloro-m-cresol Aniline Benzoic acid Hexachloroethane Bromomethane Carbon disulfide Fluorotrichloromethane Dichlorodifluoromethane 2-Butanone Diethyl phthalate Phenanthrene Hexachlorobutadiene Phenol,2-methyl 1,2-Dichlorobenzene 2,4-Dimethylphenol 2 - Pe n t an on e ,4 - m e thyl 1,2,4-Trichlorobenzene 2,4-Dichlorophenol 1,4-Dioxane Dimethyl phthalate Fluoranthene 4,6-Dinitro-2-methylphenol 1,3-Dichlorobenzene Thallium
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1982. An environmental health survey of drinking water contamination by leachate from a pesticide waste dump in Hardeman County, Tennessee.
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1985. Low birth weight, prematurity and birth defects in children living near the hazardous waste site, Love Canal.
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1987. Evaluating health effects of exposure at hazardous waste sites: A review of the state-of-the-art, with recommendations for future research.
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1987. Growth of children living near the hazardous waste site, Love Canal.
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1988. An epidemiologic investigation of the relationship between DBCP contamination in drinking water and birth rates in Fresno County, California.
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