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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 Summary PART OF OUR MODERN HERITAGE is the increasing volume of waste created by all industrial societies. Today, there also is unprecedented concern over the potential consequences for public health and the environment of exposure to wastes that are deemed hazardous under a variety of regulatory regimes. According to recent opinion polls, the American public believes that hazardous wastes constitute a serious threat to public health. In contrast, many scientists and administrators in the field do not share this belief. On the basis of its best efforts to evaluate the published literature relevant to this subject, the committee cannot confirm or refute either view. A decade after implementation of Superfund, and despite congressional efforts to redirect the program, substantial public health concerns remain, and critical information on the distribution of exposures and health effects associated with hazardous-waste sites is still lacking. Without doubt, however, substances toxic to humans and several animal species abound in hazardous-waste sites. Human health studies have shown that serious health effects cannot be ruled out. Indeed, they have occurred at a few hazardous-waste sites. Since the earliest days of industrialization, substantial volumes of waste have been produced and sometimes disposed of both at specific sites and through broader distribution in ways that could create problems for later generations. In the U.S. more than 6 billion tons of waste is produced
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 annually—nearly 50,000 pounds per person. One recent EPA survey found that more than 40 million people live within four miles and about 4 million within one mile of a Superfund site. Residential proximity itself, however, does not mean that exposures and health risks are occurring, only that the potential for exposure is increased. At the request of the Agency for Toxic Substances and Disease Registry (ATSDR), the National Research Council (NRC) convened the Committee on Environmental Epidemiology to review current knowledge of the human health effects caused by exposure to substances emanating from hazardous-waste sites and to clarify and suggest how to improve the scientific bases for evaluating the effects of environmental pollution on public health, including specifically the conduct of health assessments at hazardous-waste sites. With additional support from the Environmental Protection Agency, the committee is preparing a second volume that will examine relevant information from state health departments, and selected unpublished studies from other sources that are relevant to this field. This first report of the committee reviews and assesses the published scientific literature on health effects that could be linked with exposure to substances from hazardous-waste disposal sites and makes recommendations about major data gaps that need to be filled as scientists go on to answer important questions in the field. A second volume will review state-generated reports and studies emerging from other countries and will recommend research opportunities for the field of environmental epidemiology. ORGANIZATION OF THE REPORT This report is organized into two broad sections; it contains eight chapters overall. The first section— Chapter 1, Chapter 2, and Chapter 3 —introduces the study of the public health impact of exposure to hazardous-waste sites; discusses the role of state, local, and federal regulations in shaping the development of studies in this area; and sets forth the complexity of assessing exposures to hazardous materials. The introductory chapter defines environmental epidemiology and discusses conventional views of statistical significance and guidelines for inferring causation based on epidemiologic evidence. After that, the principles of statistical inference are evaluated in the context of constraints associated with the litigious and controversial world of hazardous-waste sites and toxic torts. Toxic torts is a rapidly growing field of litigation that involves legal claims of injuries allegedly caused by exposure to toxic chemicals. The relatively small number
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 of studies published reflects the difficulties of conducting valid studies of this complex issue, the tendency of courts to seal records of resolved disputes on these matters, and the meager resources committed to such studies. In recognition of the role of government agencies in generating information, Chapter 2 discusses relevant federal and state laws, regulations, and programs for assessing and remediating hazardous-waste sites. Chapter 3 discusses available data on materials commonly found at listed hazardous-waste sites and notes some problems in estimating human exposures to these agents. The remainder of the report reviews the published literature and considers the problems of obtaining epidemiologic information about specific routes of exposure to hazardous wastes. Chapter 4, Chapter 5, and Chapter 6 review evidence on health effects associated with toxic pollution of air, water, and soil and food, respectively, noting those few studies on hazardous-waste sites and other relevant studies of adverse health effects of materials found at such sites. Chapter 7 describes important developments in the study of biologic markers as they relate directly to the environmental epidemiology of hazardous-waste sites. Chapter 8 identifies data gaps in the areas discussed in preceding chapters, summarizes the literature reviewed in this report, and recommends that a six-part program in environmental epidemiology be developed to inform policy decisions about risks to public health presented by hazardous-waste sites. SECTION ONE: PUBLIC HEALTH AND HAZARDOUS WASTES: THE CONTEXT Chapter 1: Introduction In recent years the term “environmental epidemiology” has seen extensive use, although it has not been well defined. In Chapter 1, the Committee on Environmental Epidemiology therefore adopts the following definition: Environmental epidemiology is the study of the effect on human health of physical, biologic, and chemical factors in the external environment, broadly conceived. By examining specific populations or communities exposed to different ambient environments, it seeks to clarify the relationship between physical, biologic or chemical factors and human health. Real world constraints impede the ability to estimate health effects associated with exposures to hazardous wastes. The committee relies on a combination of evidence from different sources to reach
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 conclusions in accordance with its mandate to estimate health effects associated with hazardous wastes. Knowledge of potential exposures is derived from studies that characterize the substances found at hazardous-waste sites. Knowledge of health risks to humans from potential exposures can be obtained from a variety of sources. For some chemicals such knowledge will be available from published studies of occupational risks, usually involving higher exposures than those in the general environment. For others, especially for airborne and waterborne exposures, knowledge of health risks will come from studies of the general effects of the pollutants and from clinical reports, case-comparison studies, and animal studies, and it can be extended to circumstances where such pollutants are emitted from hazardous-waste sites. Knowledge of symptomatology or disease occurrence has in some instances been derived from studies of populations exposed to hazardous-waste sites. Often, these reports have not described exposures accurately, or they have failed completely to identify a specific causal factor. Nevertheless, with the knowledge that is available about exposure elsewhere, and from the knowledge that some of these exposures can result in the observed symptomatology or diseases found in excess in those exposed to hazardous-waste sites, sufficient indirect evidence of causality can sometimes be inferred. The world of epidemiology, like that of any human science, seldom permits elegant inferences to be drawn about causation. The object domain of epidemiology consists of numerous uncontrollable aspects, with considerable variations. To make a reasonable inference of causation in environmental epidemiology, eight basic characteristics of the findings should be considered: the strength, specificity, and consistency of the association, the period of exposure, the relationship between the dose and the response, the effects of the removal of the suggested cause, the biologic plausibility of the association, and the overall coherence of the findings. The advent of meta-analysis as a technique that pools related studies offers an important opportunity to strengthen the inferences that can be drawn from epidemiologic research. Potentially misleading conclusions can be drawn from single studies because of insufficient sample size, inadequacies of exposure determination, or publication and other biases. Meta-analysis reduces these problems and can lessen the danger of misinterpretation because it allows for combining relevant studies. Meta-analysis is limited by lack of routine publication of negative findings, and interpretation must be tempered by the
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 awareness that reporting and publication biases can distort the sample of studies available for pooling. Chapter 2: State and Federal Context for Environmental Epidemiology of Hazardous Wastes Chapter 2 discusses how federal and state environmental policies have largely shaped the development of environmental epidemiology as it pertains to the study of hazardous-waste sites in the U.S. First, scientists working for state and federal agencies perform most of such studies. Second, federal and state regulations determine the nature and limitations of available data on environmental contamination related to hazardous-waste sites. Third, federal and state agencies are continuously involved in the process of defining which chemicals found in the environment are of concern for human health and the levels at which action should be taken to protect human health. The legislation that produced these state and federal programs was clearly intended to protect human health. Congress and the states enacted the legislation which created Superfund in the early 1980s in response to public concern about the effect of hazardous-waste sites on the health of nearby communities—concerns that persisted and escalated through the decade as the dimensions of the problem continued to expand. ATSDR was also established by this legislation to provide health assessments and other relevant information on hazardous-waste sites. These programs have not allayed public concerns. Public opinion surveys consistently rank hazardous-waste sites among the most serious environmental risks and the environment as an issue of great public concern. Hazardous-waste sites are a major public health management issue in every state. Half of the U.S. population and 95 percent of the rural population relies on ground-water as the main source of drinking water. Each year thousands of wells are closed because of hazardous-waste contamination. According to a number of polls, the public fears hazardous waste, wants it cleaned up, and is willing to pay the enormous sums currently spent on Superfund because of the belief that this program will protect public health. Chapter 2 questions how so much effort and money could have been spent with such a moderate yield in knowledge. It reviews federal and state legislation, policies, and programs that determine how hazardous-waste sites are evaluated; what information on exposure and health effects is collected; how the data are analyzed and used in setting priorities and planning remediation programs; and what proportion of hazardous-waste-control budgets is spent on as-
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 sessing population exposures and risks. It also discusses the nature and extent of environmental epidemiology carried out by federal and state agencies, and recommends a program for the field that will generate needed information. The intent of Congress in enacting legislation on hazardous-waste sites was clear. As set forth in the legislative history of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), passed in 1980 and generally known as Superfund, the goals of the bill included [establishment of] an inventory of inactive hazardous-waste sites in a systematic manner, establishment of priorities among the sites based on relative danger, a response program to contain dangerous releases from inactive hazardous-waste sites, acceleration of the elimination of unsafe hazardous-waste sites, and a systematic program of funding to identify, evaluate and take responsive actions at inactive hazardous-waste sites to assure protection of public health and the environment in a cost-effective manner. In essence, Congress wanted to know how much environmental contamination has been caused by hazardous-waste sites and how serious a threat this is to human health. It also wanted to ensure that the sites that presented the worst problems would be dealt with first. The actual health risks to communities living around specific hazardous-waste sites were to be identified, so that the information could be used in making decisions about remediation. Finally, Congress's intent was that the remediation programs would do the most possible, with limited resources, to protect the health of the public. These objectives are in fact the traditional elements of a public health strategy: The discovery and preliminary assessment of as many sites as possible to describe the universe of potential exposures; the priority ranking of sites by a defined protocol, to identify and act on those most urgently requiring attention; the collection and use of data on current human exposures and health effects early in the triage and evaluation processes; and the development of remediation programs with direct and continuous attention to the public health effects of releases from the sites. Analyses of the limited federal and state regulatory support for environmental epidemiology reveal, however, that the intent of Congress in creating Superfund has not been realized, in that the public health consequences of exposures to substances from hazardous-waste sites have not been adequately assessed. Moreover, there is little reason to believe that current procedures identify the most important abandoned hazardous-waste sites, from
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 the point of view of public health. Decisions have been made not to list some sites on the National Priority List (NPL) of Superfund even though those sites have never been fully characterized. The congressional Office of Technology Assessment (OTA) notes that efforts to assess candidate NPL sites typically relegate public health concerns to a minor role; the process as a whole is directed at remediation, rather than at the assessment of public health risks. The absence of a comprehensive national program to identify and evaluate hazardous-waste sites makes it difficult to assess fully the nature and magnitude of the problem for the health of the public. Similar difficulties attend efforts to estimate the public health effects of exposures to other potentially hazardous materials, such as unregulated nonconventional pollutants that can result from agricultural practices and industrial processes. The current regulatory system has failed to devise a protocol for managing hazardous-waste sites that incorporates the essential components of public health policy. Not only is it possible that the public residing in some of these neighborhoods is imperiled, but the conditions for development of environmental epidemiology programs and methods are so adverse as to impede useful scientific investigations of many important questions. As the committee's review of federal programs concludes, there is no comprehensive national inventory of hazardous-waste sites, no site discovery program, no minimum data set on potential human exposures, no adequate system for the early identification of sites for which immediate action to protect public health or continued surveillance of health effects could be necessary, and no validation or evaluation of the components of the site assessment process. The Environmental Protection Agency (EPA) and the ATSDR are instituting some improvements in each of these areas, but these improvements are largely limited to sites proposed for or already on the NPL. A six-part environmental epidemiology program needs to be developed to improve the bases for policy decisions about hazardouswaste sites. Establish an active and coordinated system of site discovery for hazardous-waste sites, based in EPA and providing technical assistance to other federal and state programs. An aggressive site discovery program, in combination with improved assessments and triage of sites for interim and final remediation, will restore the original congressional intent to protect the health of the public from exposure to hazardous-waste sites. Define a revised approach to site assessments that integrates epidemiologic determinations of population exposures, health effects,
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 and the necessity of interim and final remediation or other actions into a continuum of site evaluation. Establish protocols and criteria for the revised preliminary assessment of all sites, with triggers for interim remediation or other action, such as relocation, and require that all sites undergo a revised preliminary assessment within one year of discovery. Establish a comprehensive national inventory of hazardous-waste sites that will track the status of all sites through assessment and remediation or closure and include health hazard assessments. Use the inventory to ensure that sites are not deferred or placed in closure status without a revised preliminary assessment as described above. Rigorously evaluate the data and methodologies used in site assessment, including the characterization of potential and actual releases of contaminants to groundwater, surface water, air, and soil that result in human exposure. Evaluate the methodologies for estimating which populations are exposed to hazardous-waste-site emissions, and use this information in preliminary assessments and in deciding how to protect the public health. Evaluate compliance with public health recommendations for the protection of exposed populations and site remediation. Improve and expand research in environmental epidemiology to illuminate the distribution and severity of exposures, risks, and health effects associated with hazardous-waste sites. Authorize ATSDR to direct responsible parties to conduct research to fill data gaps on critical substances. Expand the ATSDR mandate to establish an extensive program of applied research, including exposure registries linked to priority substances, and further the development of surveillance methods such as community health data bases, biologic monitoring, and sentinel events, that is, events that may signal environmental health problems. ATSDR, the National Institute of Environmental Health Sciences (NIEHS), and other relevant agencies should expand cooperative agreements with states and develop a comprehensive program of technical assistance for state and local agencies. They also should provide funding for competitive research grants and contracts in environmental epidemiology. Chapter 3: Dimensions of the Problem: Exposure Assessment Chapter 3 notes that exposure assessment is a crucial, and often inadequate, component of studies in environmental epidemiology. In order to establish causal relationships between exposure to chemi-
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 cal and physical agents from hazardous-waste sites and adverse consequences to human health, obtaining valid measures or estimates of exposure is essential. The field of exposure assessment entails numerous techniques to measure or estimate the contaminant, its source, the environmental media of exposure, avenues of transport through each medium, chemical and physical transformations, routes of entry to the body, intensity and frequency of contact, and its spatial and temporal concentration patterns. It also includes estimations of total exposure to different compounds and mixtures. Exposure assessment has proved difficult, because epidemiologic research typically involves retrospective studies. Records of ambient pollutant concentrations can sometimes provide a surrogate for exposure, but these surrogates are not always available, and direct measures of past exposures have not usually been recorded and must be estimated with models. Within the past decade, estimates of the number of potential NPL sites have grown dramatically. OTA concludes that there could be as many as 439,000 candidate sites. These sites include mining waste sites, leaking underground storage tanks, pesticide-contaminated sites, federal facilities, radioactive release sites, underground injection wells, municipal gas facilities, and wood-preserving plants, among others. As of December 1988, one ATSDR report concluded, 109 NPL sites (11 percent of the total) were associated with a risk to human health because of actual exposure (11 sites) or probable exposure (98 sites) to hazardous chemical agents that could cause harm to human health. Chiefly on the basis of exposure assessments, these sites were placed in the categories of “urgent public health concern ” or “public health concern.” Repositories of potentially dangerous substances can be found at a number of hazardous-waste sites that have been generated by a wide range of activities. Information about the materials generally reflects the data requirements of environmental engineering and site remediation, rather than public health considerations. Accordingly, whether the materials pose a risk to public health cannot readily be determined in the absence of more detailed information about potential human exposures. The focus of many studies has been on site-specific characterization, even though pollutants do not respect such boundaries. Given the potential for movement of materials in groundwater and air and the importance of multiple routes of exposure, efforts need to proceed to estimate plume characteristics and groundwater staging to improve the ability to anticipate the movement of pollutants and ultimately to prevent greater exposures. Similarly, exposure from domestic water is not limited to ingestion, but includes airborne ex-
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 posures from materials released during showering, bathing, or cooking. Therefore, estimates of exposure from domestic water need to be expanded to take into account the role of airborne exposures. The best estimates are that groundwater is the major source of drinking water for about 50 percent of the U.S. population. In California, groundwater provides drinking water to nearly 70 percent of the population. Millions of tons of hazardous materials are slowly migrating into groundwater in areas where they could pose problems in the future, even though current risks could be negligible. For instance, plumes of chemicals, including many nonconventional pollutants (NCPs) that are not currently regulated, are moving down the canyon from the Superfund site at Stringfellow Pits in California and may pose important problems in the future. There is evidence that NCPs are a potentially important source of hazardous exposure. Some preliminary toxicologic studies suggest that NCPs have important biologic properties, environmental persistence, and mobility. Additional studies are needed to characterize the mixture of materials deposited as hazardous wastes and to give better estimates of their potential transport and fate in the environment. In the broadest sense these unidentified, unregulated substances represent a risk of unknown magnitude. The absence of evidence of their risk is solely the result of the failure to conduct research; it should not be misconstrued as demonstrating that NCPs and “inert” pesticide components are without risk. SECTION TWO: HAZARDOUS WASTES IN AIR, WATER, SOIL, AND FOOD; BIOLOGIC MARKERS Chapter 4: Air Exposures Chapter 4 notes that although there is an extensive body of literature on the epidemiology of air pollution, there is little information about airborne exposures from hazardous-waste sites. To improve the scientific basis for studying those potential effects, methodological approaches to the study of air pollution are reviewed and discussed in terms of their applicability to the study of hazardous wastes. Also, relevant studies on airborne exposure to materials similar to those found at hazardous-waste sites are assessed, along with some evidence of exposures from hazardous-waste sites or other related exposures, such as might occur with the sick building syndrome. Many approaches have been taken to the study of air pollution epidemiology. The methods can be used in the study of hazardous
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 wastes, but their successful application will vary. Thus, studies of trends over time in air pollution and disease patterns have produced a growing body of literature that has associated day-to-day fluctuations in air pollution with daily fluctuations in mortality across a wide range of exposures with no evidence of thresholds. It is not likely to be worthwhile to conduct such studies at hazardous-waste sites, especially because the pollutants are complex and because there are no long-term records, such as exist for a number of monitored air pollutants. Cross-sectional studies provide epidemiologic snapshots of a given area at one point in time. Recent computer technology has permitted maps to be drawn that show comparative mortality data from different regions of the U.S., Canada, and other industrial countries. Such maps can show county-wide cancer and other mortality data by decade, for example, as a hypothesis-generating tool to detect geographic variations in these diseases and to infer possible causes. Of more relevance to hazardous-waste studies are small-scale comparisons of adjacent counties or ZIP codes, where differences could be better highlighted. The study of health effects that have shorter latency than most cancers—such as birth defects, neurologic effects, and other acute and chronic effects—increases the likelihood that a connection can be drawn between environmental exposures and disease. Cross-sectional community studies typically compare communities with different levels of air pollution or populations that live different distances from a hazardous-waste site. All such studies have several problems: Measurement error occurs because of the assumption of the same exposure for every subject within a group. There can be undetected differences between communities for risk factors, such as illness, tobacco use, or occupational exposures. There can be “recall bias ” if one group knows it is in the high-exposure category. There is little standardization of the equipment used to measure exposure in different locations. In spite of these difficulties, successful community studies have been done on air pollution patterns. In contrast to purely descriptive studies, which lack information on potential confounders, community studies generally contain data on nonpollution risk factors. A few studies have involved materials like those which occur at hazardous-waste sites. Excesses of the rare cancer angiosarcoma occurred in residents near a vinyl chloride manufacturing plant. Another study found increased rates of birth defects in children whose parents lived near such plants. Longitudinal analyses also have been developed for the epidemiologic study of air pollution. These have some direct bearing on the study
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 of hazardous wastes, and they include long-term studies of actively exposed persons, prospective studies of a distinct group, and followup studies of exposed children. Here, problems of execution relate to the emotional turmoil that usually surrounds suspicion of exposure to hazardous wastes, the difficulty of following residents who might have moved away, and the climate of distrust that sometimes arises after the discovery of a hazardous-waste site. In addition, because the courts often seal resolved lawsuits, potentially valuable information on long-term consequences of exposure is unavailable for scientific review and analysis. The committee's second report will discuss this further. Although few studies directly assess airborne exposures to hazardous wastes, the committee finds persuasive evidence that health effects can occur from such exposures. Review of the relevant animal literature on compounds known to occur at hazardous-waste sites, along with the few epidemiologic studies, shows that a wide range of effects may occur, including such serious diseases as cancer, birth defects, and neurologic disease. Studies of populations near hazardous-waste sites have detected complaints of neurobehavioral symptoms. Although it might be concluded that recall bias explains the differences in such subjectively reported symptoms, the real possibility nevertheless exists that the symptoms complained of are more sensitive as indicators of significant exposure than are more severe diseases that have long latencies, such as cancer and other chronic diseases. The constellation of self-reported symptoms in persons living near some hazardous-waste sites shows remarkable consistency in populations with similar exposures in different countries. These symptoms have recently been provoked in double blinded tests using subjects who might or might not have previously reported symptoms. Those exposed to odorless test agents developed neurobehavioral symptoms, further strengthening the argument that there is a physiologic basis to some of the complaints. Symptom reports appear to be sensitive indicators of adverse health effects. Simultaneous use of air monitoring and diary records could reduce the problem of recall bias, which is especially troubling in situations where people suspect ill effects could be produced by their exposures. These methods are particularly valuable when small changes in pollutant levels cannot be detected by the subjects in a study. The committee believes that further studies of acute symptoms linked to monitoring data, based on concurrent exposure measurements, are likely to reveal that reported symptoms are not completely explained by recall bias. The current data base clearly indicates the importance of continued use of these techniques.
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 Chapter 5: Domestic Water Consumption Water is the key medium of concern in most hazardous-waste sites. Chapter 5 reviews evidence on the possible impact on health of waterborne exposures that could emanate from hazardous-waste sites, and it discusses several abandoned hazardous-waste sites in the U.S., such as Love Canal, New York, and Woburn, Massachusetts. Contamination of groundwater and aquifers occurs where the waste dumps are poorly constructed or managed, or where wastes have been disposed of improperly, sometimes over long periods. Few studies have been conducted directly on populations exposed to water contaminated with hazardous wastes. Accordingly, this chapter reviews evidence about some compounds commonly found at hazardous-waste sites that have been shown to cause adverse effects in humans exposed to these materials through the use of domestic water. Epidemiologic evidence on the risk to health from contaminated water from hazardous-waste sites or from other sources of contamination, such as pesticide runoff, has largely been derived from ecologic (descriptive) studies, and therefore is seldom conclusive as to cause. The ecologic studies that involve broad-scale comparisons of available data are unable to control for important confounding variables such as smoking, occupational exposures, dietary factors, or other relevant exposures. A number of descriptive and case-control studies indicate that drinking water can include by-products of domestic water chlorination that pose increased risks of cancer. Some chlorination by-products, particularly halogenated hydrocarbons or trihalomethanes (THMs), occur in greater quantities in drinking water if large amounts of organic matter are present. Two THMs, chloroform and carbon tetrachloride, have been commonly found in the chemical mixtures at some toxic dump sites at levels above those permitted in drinking water. The by-products of chlorination can include dichloroacetic acid and trichloroacetic acid, which are metabolites of trichloroethylene (TCE), one of the most common contaminants at Superfund sites. Of course, chlorinated water and its by-products do not come from hazardous-waste sites. Still, studies of the impact of these materials on public health are relevant to this report, insofar as exposures can occur in connection with hazardous-waste sites. The largest individual- and population-based case-control study of cancer and exposure to contaminated drinking water was performed in 1978 in 10 areas of the U.S. by researchers from the National Cancer Institute. Their results showed the risk of bladder cancer increased with intake of beverages made with tap water. In particular,
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 women and nonsmokers of both sexes who consumed chlorinated surface water at rates above the median for 60 or more years had rates of bladder cancer that were more than three times the rates of those who had not consumed surface water. The gender difference could be due to the fact that men are subject to other, more important risk factors for bladder cancer. In New Jersey, descriptive studies have linked exposures to hazardous-waste sites to increased cancer risks. These studies have related cancer mortality at the county and municipal levels to environmental variables, including the location of chemical toxic-waste-disposal sites, and presumed contamination of water and air. One analysis of age-adjusted female reproductive organ and breast cancer mortality showed significant positive associations between breast cancer mortality and proximity to toxic disposal sites among whites in 21 New Jersey counties. The clusters of excess cancer mortality were confined for the most part to the highly urban and industrial northeastern part of the state. Such descriptive investigations provide, at best, suggestive evidence. Other evidence linking consumption of industrially polluted, domestic water use with cancer is provided by an unusually strong cohort study of residents of North Carolina, who consumed raw, industrially polluted river water from 1947 to 1976. Residents had rates of all forms of cancer that were more than twice those expected, at times corresponding to the expected latency for cancer. Moreover, once exposure ceased, rates returned to the expected level, adjusting for latency. The study of adverse reproductive effects on males and females exposed to hazardous-waste sites remains surprisingly sparse. Nonetheless, several important reports have found adverse reproductive effects associated with use of contaminated domestic water. In a case-control study it was found that women in the Mount Gambier area of South Australia who consumed principally groundwater had nearly a threefold increase in the risk of bearing malformed children who had defects of the central nervous system compared with women who drank only rainwater. The children of parents who regularly used water that contained nitrate at more than 15 parts per million had four times more central nervous system defects. It was recognized, however, that other, as-yet-undetected chemicals could have been responsible for the excess. Despite the serious problems that must be overcome in developing reliable data on the connection between birth defects and environmental contamination, several lines of evidence point to a causal nexus between exposure to TCE and cardiac congenital anomalies. Both animal and human studies have found that exposure to TCE increases
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 the risk of some cardiac anomalies. Persons living in a small valley of Tucson, Arizona, who consumed contaminated water were three times more likely to produce offspring with congenital heart disease. A limited number of reports in the peer-reviewed scientific literature have linked spontaneous abortion, low birth weight, and birth defects to the consumption of domestic water or to other environmental exposures. A variety of other health effects, including liver and neurologic disease, have also been associated with waterborne exposure to substances from hazardous-waste sites. Some studies have detected increased rates of neurologic deficits in persons with chronic exposures to contaminants such as TCE. Several factors lead us to conclude that contamination of domestic water supplies with a number of hazardous chemicals, such as those that could be encountered at hazardous-waste sites, is injurious to human health, although the magnitude of the risk cannot be determined. Some of the common by-products of chlorination also occur as contaminants at Superfund sites, such as dichloroacetic and trichloroacetic acid, metabolites of TCE. Moreover, exposures are not limited to ingestion, but include those due to volatization of hazardous gases and dermal absorption. There is also evidence from epidemiologic studies that neurologic, hepatic, and immunologic function can be damaged by exposure to domestic water contaminated with some toxic chemicals. The long-term consequences of the abnormalities detected, however, are largely unknown and must be the subject of further research, on which the committee will comment in more detail in its next report. Chapter 6: Soil and Food as Potential Sources of Exposure at Hazardous-Waste Sites Soil provides a usually unrecognized source of exposure to contaminants. Models indicate that adults can be exposed directly or indirectly, through the food chain, and that children incur greater exposures per unit of body weight. Home gardening and ingestion of subsistence or recreational fish can be important sources of these contaminants. In addition, commercial shellfish and finfish may also be contaminated. Epidemiologic studies of hazardous-waste sites need to incorporate broader consideration of soil and food as routes of exposure. It is difficult to identify completely the routes of exposure when ill health effects are suspected from hazardous-waste sites, as Chapter 5 notes. The same problem of determining precisely who is exposed exists for exposure through ingestion of soil as it does for exposure
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 through domestic water use, in that direct ingestion does not constitute the sole route. Soil ingestion suffers from an additional complexity. Except among small children, it is unusual for soil to be ingested directly, although adults do ingest small amounts of soil nonetheless. Unless a chemical is extremely potent, the exposure is particularly direct (as with certain occupations), or there is extensive dust contamination of food and residences, exposure due chiefly to contaminated soil is unusual. However, contaminated soil and domestic water can act as vehicles for contamination of plant or animal foods that are subsequently ingested—as is the case for mercury and pesticide contamination of fish and heavy metal or pesticide contamination of fruits and vegetables. The questions of the effects of pesticide residues on foods and the subsequent health risks for children are the subject of study for another NRC committee, and are not considered here. A recent report from the Institute of Medicine documents the extent to which fish may bioconcentrate lipophilic pollutants from the surrounding water. Persons that consume fish taken from contaminated waters have average blood levels of polychlorinated biphenyls (PCBs) that are several times those found in other general population groups, in ranges that extend into concentrations typically found in industrially exposed workers. In the U.S., mercury contamination of fish is especially prevalent in the Great Lakes region. Although advisories have been issued to pregnant women, nursing mothers, and women who intend to have children, no such advisory has been developed for men who may wish to reproduce, despite evidence that sperm are also vulnerable to subtle toxic effects. The routes of exposure to PCBs are not well characterized, despite the ubiquity of this compound and its occurrence at some level in most persons tested in the U.S. PCBs also occur at many Superfund sites. Studies from a number of research institutions confirm that exposure to background levels of PCB below both the relevant standards for occupational exposure and those for food contamination produces developmental deficits in children. In addition, studies of Japanese children exposed to higher levels of PCBs prenatally and through lactation indicate higher rates of abnormalities of lungs, skin, nails, teeth, and gums, low birthweight, and reduced growth. In investigations of a number of species, perinatal exposure to PCBs causes similar effects. However, humans appear to be particularly sensitive. Other studies have indicated that exposure to PCBs occupationally or through transformer fires is linked to a range of neurobehavioral and functional problems, including muscle pain, skin color changes, nervousness, or sleep problems.
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 Because of the difficulties of determining relevant exposures and health outcomes, studies of sentinel animals can provide some hypothesis-generating results. Wild mice trapped in Love Canal, New York, showed weight loss and impeded development associated with areas of the greatest contamination. Similar studies of wildlife and of domestic animals could provide useful indicators of, or sentinels for, potential exposure at hazardous-waste sites, especially for playgrounds or other sites that have been used for recreation that involves frequent contact with soil. Chapter 7: Biologic Markers in Studies of Hazardous-Waste Sites Chapter 7 draws on emerging developments in molecular biology to describe a conceptual framework for using biologic markers in the study of hazardous-waste sites. This chapter reviews studies of biologic markers in persons exposed to materials such as those commonly encountered at hazardous-waste sites, along with the few studies of persons directly exposed at sites. Examples of markers of exposure, effect, and susceptibility are provided and methodologic or other important considerations in their use are presented. Important ethical and legal issues are involved in the use of biologic markers in studies at hazardous-waste sites. As defined by the NRC Committee on Biologic Markers, a biologic marker is any cellular or molecular indicator of toxic exposure, adverse health effects, or susceptibility. It is useful to classify biologic markers into three types—exposure, effect, and susceptibility—and to describe the conditions (normal exposure, disease, or susceptibility) that each kind of marker represents. A biologic marker of exposure is an exogenous substance or its metabolites or the product of an interaction between a xenobiotic agent and some target molecule or cell that is measured in a compartment within an organism. A biologic marker of effect is a measurable biochemical, physiologic, or other alteration within an organism that, depending on magnitude, can be recognized as an established or potential health impairment or disease. A biologic marker of susceptibility is an indicator of an inherent or acquired limitation of an organism's ability to respond to the challenge of exposure to a specific xenobiotic substance. Biologic markers have been used occasionally in epidemiologic studies of hazardous-waste sites, predominantly as indicators of effect. An array of dermatologic, behavioral, and neurological symptoms have been identified that might provide markers of exposure to toxic chemicals, or early indicators of effect. Not counting symptoms or frank signs of morbidity, changes in liver enzymes, which indicate liver function,
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 are among the most commonly used, presumably because of their nonspecificity and ease of analysis. Sometimes these effects are transitory, as was shown in a study of persons with increases in the liver enzyme alkaline phosphatase who had been exposed to chlorinated chemicals in domestic water in Hardeman County, Tennessee. Other multiphasic tests to find markers of exposure or effect in blood and urine also have been used, but to a lesser extent. For example, serum cholesterol, gamma-glutamyl transpeptidase (an indicator of enzyme induction in the liver), and blood pressure have been studied as markers of effect in residents of Triana, Alabama, who were exposed to PCBs chiefly from subsistence eating of contaminated fish. Eighty to 90 percent of the population in Triana had levels of PCB within the range found in other community groups. For those with elevated levels, results indicated that PCB was positively associated with measures of blood pressure and other indicators, independent of age, sex, body mass, and social class. Similar findings have been reported in studies of workers exposed to PCBs in capacitor manufacturing. Researchers also have studied markers of neurologic function in persons from Woburn, Massachusetts, some six years after exposure to TCE ceased, and in others with similar exposure. In Woburn, TCE levels in domestic water had been from 30 to 80 times higher than the recommended EPA Maximum Contamination Level of 5 parts per billion (ppb). Exposed and control subjects were studied with a neurobehavioral evaluation protocol that included clinical tests, nerve conduction studies, blink reflex measurements, and extensive neuropsychological testing. The highly significant differences in a variety of neuropsychologic tests indicate that neurotoxic effects occurred in those who had been exposed. Although they are not commonly thought of as constituting markers, the results of neurobehavioral tests can provide a diverse range of measures of toxic exposures and effects. A battery of neurobehavioral tests has been applied to the study of persons exposed to materials that occur at hazardous-waste sites. A comprehensive review of developing techniques in neurobehavioral assessment found consistent and significant neurobehavioral effects and a range of other subtle neurological alterations in persons exposed to metals, solvents, and insecticides, with some indication of greater effects in those with higher estimated exposures. These findings corroborate studies that reveal that TCE inhalation induces a range of neurotoxic effects in rodents. Although the risk of cancer provides a central focus for much research on markers, risks to human reproduction offer another focal point for which much shorter time periods between exposure and
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 evidence of a related health effect are involved. Several studies have revealed that workplace exposures to hazardous materials, as well as consumption of alcohol, drugs, and tobacco, influence both the ability of males and females to reproduce and the health of their off-spring. Whether environmental exposures could also create such effects on reproductive function needs to be studied further. A series of studies using refined and automated measures of sperm concentration and sperm head morphology has recently found significant effects on male reproductive capacity related to exposures to pesticides. Studies of Vietnam veterans noted that those who served in Vietnam were twice as likely to have lowered sperm concentrations and significantly different sperm morphology, with longer axis length and greater head circumference. The number of children fathered by both groups was comparable. Whatever the mechanism, a variety of characteristics of sperm have been detected and found to change with exposures to pesticides and other toxic chemicals, including those encountered at hazardous-waste sites or through other channels. Markers of exposure or effect can include changes in sperm shape, concentration, pH, viability, velocity, and motility. CONCLUSIONS Whether Superfund and other hazardous-waste programs actually protect human health is a critical question with respect to federal and state efforts to clean up hazardous wastes. To answer this question requires information on the scope of potential and actual human exposures to hazardous wastes and about the health effects that could be associated with these exposures. Based on its review of the published literature on the subject, the committee finds that the question cannot be answered. Although billions of dollars have been spent during the past decade to study and manage hazardous-waste sites in the U.S., an insignificant portion has been devoted to evaluate the attendant health risks. This has resulted in an inadequate amount of information about the connection between exposure and effect. A decade after implementation of Superfund, and despite congressional efforts to redirect the program, substantial public health concerns remain, and critical information on the distribution of exposures and health effects associated with hazardous-waste sites is still lacking. Whether for the purposes of environmental epidemiology or for the protection of public health, the nation is failing to adequately identify, assess, or prioritize hazardous-waste-site exposures. In spite of the complex limitations of epidemiologic studies of hazardous-waste sites, several investigations at specific sites have docu-
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 mented a variety of symptoms of ill health in exposed persons, including low birth weight, cardiac anomalies, headache, fatigue, and a constellation of neurobehavioral problems. It is less clear whether outcomes with a long delay between exposure and disease also have occurred, because of complex methodological problems in assessing these outcomes. However, some studies have detected excesses of cancer in residents exposed to compounds, such as those that occur at hazardous-waste sites. Although current public health burdens from hazardous-waste sites appear to be small, the future risk might be greater insofar as many of the substances involved are highly persistent, and other materials already in the groundwater can migrate into areas where exposure potential is greater. In some cases, unnecessary or inappropriate remediation might create more of a hazard than would be caused by leaving such materials undisturbed. Despite the lack of adequate data with which to characterize the effects of hazardous wastes on public health in general, the committee does find sufficient evidence that hazardous wastes have produced serious health effects in some populations. We are concerned that populations may be at risk that have not been adequately identified, because of the inadequate program of site identification and assessment. To improve the ability to evaluate health effects associated with exposures to hazardous-wastes sites, a number of important data gaps and resource constraints need to be remedied, as this report illustrates. There is a need to make public health assessments an early priority in the routine evaluation of hazardous-waste disposal sites and a need to create mechanisms for sharing this information and epidemiologic investigations of these sites nationwide. There must be adequate support for state and local health department investigations of hazardous-waste sites. Better measurements or estimates of human exposure are needed from a variety of sources, including abandoned hazardous-waste disposal sites, and other point sources such as leaking storage tanks, and from agricultural and industrial practices that may produce nonconventional pollutants. Monitoring of sentinel health events, and increased use of disease registries and vital statistics systems will be required to assess the public health impacts of all of these sources of exposures. Although the effect on large populations of very low levels of toxic pollutants is unknown, measures must now be taken to protect future public health. According to a number of previous assessments from the NRC, a substantial risk of contamination of the groundwater is not being averted by current remediation practices. Moreover,
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 the Institute of Medicine recently noted that pollution of lakes and rivers increases contamination in fish. It should be recognized that if exposure becomes general and almost uniform, current epidemiologic techniques will not be able to ascertain any related health effects. There is a window of opportunity to initiate studies in areas where groundwater pollution has remained high and localized. There is also an important opportunity for prevention that could forestall major public health problems in the future. The legislative mandates, policies, and programs of the federal and state agencies that currently manage hazardous-waste sites are inadequate to the task of protecting public health. The distribution and frequency of exposures of specific populations near specific hazardous-waste sites cannot be ascertained, because the needed data have not been gathered. Our report indicates that the nation is not adequately identifying, assessing, or ranking hazardous-waste site exposures and their potential effects on public health. We are currently unable to answer the question of the overall impact on public health of hazardous wastes. Until better evidence is developed, prudent public policy demands that a margin of safety be provided regarding potential health risks from exposures to substances from hazardous-waste sites. We do no less in designing bridges and buildings. We do no less in establishing criteria for scientific credibility. We must surely do no less when the health and quality of life of Americans are at stake.
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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 This page in the original is blank.
Representative terms from entire chapter: