8

General Conclusions

ACCORDING TO A NUMBER OF 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 either viewpoint. Regrettably, insufficient data are available for evaluating the impact on public health of exposure to substances from hazardous-waste sites. Without doubt, substances toxic to several animal species abound in hazardous-waste sites. Many sites have not been adequately assessed for content, or for potential routes of human exposure. Human health studies, while mixed in quality and persuasiveness, provide evidence that serious health effects cannot be ruled out, and have been documented to occur at some hazardous-waste sites. More and better health studies need to be conducted.

Whether Superfund and other hazardous-waste programs actually protect human health is a critical question for environmental epidemiology, at least with respect to federal and state efforts to clean up hazardous-waste sites. To answer it would require 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,



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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 8 General Conclusions ACCORDING TO A NUMBER OF 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 either viewpoint. Regrettably, insufficient data are available for evaluating the impact on public health of exposure to substances from hazardous-waste sites. Without doubt, substances toxic to several animal species abound in hazardous-waste sites. Many sites have not been adequately assessed for content, or for potential routes of human exposure. Human health studies, while mixed in quality and persuasiveness, provide evidence that serious health effects cannot be ruled out, and have been documented to occur at some hazardous-waste sites. More and better health studies need to be conducted. Whether Superfund and other hazardous-waste programs actually protect human health is a critical question for environmental epidemiology, at least with respect to federal and state efforts to clean up hazardous-waste sites. To answer it would require 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,

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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 the committee finds that this question cannot be answered. One recent EPA survey found that more than 40 million people live within four miles of a Superfund site. Residential proximity does not per se mean that exposures and health risks are occurring, but the potential for exposure is increased. National decisions to clean up hazardous-waste sites have been made independently of studies about the overall impact such sites may have on public health. During the past 10 years, less than 1 percent of the estimated $4.2 billion spent each year on hazardous-waste sites in the U.S. has been used to evaluate health risks at listed Superfund sites. As a result, existing data on exposures and health effects are inadequate either to support decisions on the management of hazardous-waste sites or to allow the conduct of epidemiologic investigations of the health impact of these sites. However, recent efforts by the Agency for Toxic Substances and Disease Registry (ATSDR) and EPA have improved the information base and should be further extended. 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 the evaluation of attendant health risks. For that reason and because of technical obstacles, information about the connection between exposures from hazardous-waste sites and health effects remains inadequate. This chapter draws on the preceding ones and recapitulates the committee 's major findings about the epidemiologic study of hazardous-waste sites. Despite the lack of adequate data with which to characterize the effects of hazardous wastes on public health in general, the committee concludes that exposures from hazardous-waste sites have produced serious health effects in some populations. Table 1-1 summarizes the peer-reviewed literature on this subject. A limited number of epidemiologic studies indicate that increased rates of birth defects, spontaneous abortion, neurologic impairment, and cancer have occurred in some residential populations exposed to hazardous wastes. We are concerned that other populations at risk might not have been adequately identified. To improve the ability to evaluate health effects associated with exposures to hazardous wastes, a number of important data gaps need to be filled and several resource constraints need to be remedied, as this report illustrates. There is a need to make health assessments a priority in the routine evaluation of hazardous-waste sites. There is also a need to create mechanisms for sharing this information as well as information from epidemiologic investigations of these sites nationwide. Accordingly, state and local health department investigations of hazardous-waste sites must be adequately sup-

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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 ported. Better measurements or estimates are needed of human exposure from a variety of sources, including abandoned hazardous-waste sites; other point sources, such as leaking storage tanks and industrial operations; and from non-point sources, such as agriculture, all of which can produce nonconventional pollutants (NCPs). 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 exposure. STATE AND FEDERAL CONSTRAINTS There are reasons to suppose that current procedures might not be identifying the most important abandoned hazardous-waste sites, from the point of view of public health. The congressional Office of Technology Assessment (OTA) notes that efforts to assess candidate National Priority List (NPL) sites typically relegate public health concerns to a minor role and that the process as a whole is directed at engineering aspects of remediation rather than at the assessment of public health risk. Because public health concerns have been given only minor importance, many potential Superfund sites have never been considered for inclusion on the NPL or have been dropped from the list, even though their public health impacts have not been studied adequately. At NPL sites where potentially critical exposures are detected, there is no regular application of an adequate system of early assessment of the health risks involved or of the need for interim action to protect the health of exposed populations. The failure to construct a system for managing hazardous-waste sites that incorporates the early assessment of health risk means that the health of nearby residents could be imperiled. Moreover, the conditions for development of environmental epidemiology are adverse and impede the development of useful scientific investigations of many important questions. OTA recently concluded that the maximum number of potential sites from which Comprehensive Environmental Release and Compensation Liability Inventory System (CERCLIS) and NPL sites are drawn is approximately 439,000. These sites include facilities covered under the Resource Conservation and Recovery Act (RCRA) as Subtitle C and D facilities, mining waste sites, nonpetroleum leaking underground storage tanks, pesticide-contaminated sites, federal facilities, radioactive releases, underground injection wells, municipal gas facilities, and wood-preserving plants, among others. The lack of a site discovery program and of a comprehensive inventory presents a particular problem for public health. The range

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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 and distribution of human exposure to releases from hazardous-waste sites is unknown. EPA now acknowledges that undiscovered sites could well present significant health risks, even though previously the agency had announced that most sites with serious potential for harm had been detected. Reviews in several states show that the current system of CERCLIS reporting misses potential health risks. In 1984 an evaluation of 93 sites on the California Department of Health State Superfund list showed that only 19 of the sites were on the federal NPL. Forty-six of the sites showed evidence of waste release into groundwater, and in 34 of these cases the groundwater was known to be used for drinking. Extensive or systematic sampling existed for only 22 of the sites where release into groundwater had occurred, despite the evidence of potential human exposure. Moreover, in all of the sites where there was known contamination of groundwater, more than 10,000 persons were potentially exposed. PROBLEMS OF EXPOSURE ASSESSMENT Exposure assessment provides critical information about potential human contact with relevant materials. Best estimates are that groundwater provides 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. Although current risks could be negligible, studies show that millions of tons of hazardous materials are slowly migrating into groundwater in areas where they could pose problems in the future. For instance, plumes of chemicals, including many nonconventional pollutants, are moving down the canyon from the Superfund site at Stringfellow Pits in California and could pose important problems in the future. The public health component of the information base for decisions about site listing and remediation is inadequate, and there is no systematic tracking of deferred sites. The attendant cost has been confusion about the actual risks that hazardous-waste sites pose to human health. Clues to the potential scale of human exposure to toxic chemicals released from hazardous-waste sites are emerging, however. By mid-1990, ATSDR had completed 1151 health assessments at NPL sites. ATSDR determined that hazardous substances had been released at 85 percent of the sites and that about 15 percent of these sites merited further public health investigation. The committee urgently recommends the development and validation of an adequate initial health assessment methodology for hazardous-waste sites. The committee recommends that initial site characterization include at least minimal information on potential exposure.

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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 This should include sampling of tap water, estimating outgassing from showers as relevant, absorption through cooking or eating, and other residential uses, and surface soil. Epidemiology is not merely a passive science, cataloguing exposures and effects. It is an active tool for evaluating the link between potentially hazardous exposures and disease and for directing interventions to prevent further exposures. Where the evaluation of human exposures and health effects associated with hazardous-waste sites is not integrated into early site evaluation and interim remediation decisions, the real contributions of epidemiology are lost. This is of grave concern because hazardous wastes have constituted a significant public health hazard to specific populations at specific sites, summarized in Table 1-1. Further, in 1988, ATSDR reported that conditions at about 11 percent of all 951 NPL sites constituted ongoing or probable public health concerns. During 1990, 32 percent of a specially reviewed subgroup of sites were identified as requiring some kind of protective health action. The health of the public has remained in jeopardy at many sites long after the risks could have—and should have—been identified. As Chapter 3 reports, repositories of potentially dangerous substances can be found at a number of hazardous-waste sites. Dangerous substances also have been generated by leaking underground storage tanks, non-point sources such as agricultural pesticide runoff, automobile emissions, agricultural, mining, storage, and other activities. Information about these materials generally reflects the data requirements of environmental engineering and site remediation, rather than public health considerations. Accordingly, whether these materials pose a risk to public health cannot readily be determined in the absence of more detailed information about potential human exposures. Improvements must be made in the ability to assess the more than 600 chemical compounds identified at hazardous-waste sites, along with the hundreds or thousands of unidentified pollutants that could enter the groundwater. The potential for exposure is of such magnitude that researchers who develop exposure assessment strategies will have to direct their attention not solely to an analysis of the contaminants at a hazardous-waste site, but to off-site migration and public exposure as well. In this context, measures of personal exposure, including the use of biologic markers and biologic monitoring as discussed in Chapter 7, along with personal sampling, although often difficult and time consuming, must receive greater scientific attention if appropriate associations are to be made between contaminants, exposures, and health effects. Enough hazardous-waste sites have been identified where the popu-

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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 lation exposed is large and the exposures are great that it should be feasible to conduct environmental epidemiologic studies. The difficulty has been primarily with the lack of resources to conduct adequate exposure characterization or to collect sufficient outcome measures. It should be recognized, however, that for most sites the populations are too small to provide studies of sufficient power for risks to be detectable unless it is possible to combine data from a number of sites. Combining studies of small populations into meta-analyses might generate sufficient statistical power to reach conclusions, provided that the basic measures involved are comparable and that sound methods are used in all separate studies. Several chapters explain that NCPs could be an important source of hazardous exposure. Some important pollutants are not regulated under a variety of acts, including the Safe Drinking Water Act, the Clean Air Act, and the Toxic Substances Control Act. These NCPs need to be identified and placed under appropriate regulatory control. Some preliminary toxicologic studies suggest that NCPs and so-called inert pesticide ingredients have important biologic properties of environmental persistence and mobility. More studies are needed to characterize the mixture of materials deposited as hazardous wastes and to give better estimates of their transport and fate in the environment. In the broadest sense, these unidentified, unregulated substances present a risk of unknown magnitude. The absence of evidence of their effects reflects the failure to conduct research; it should not be misconstrued as demonstrating that NCPs and “inert” pesticide components are without risk. Where the potential for human exposure exists, exposure assessment should be conducted for important pollutants that can migrate from hazardous-waste sites. For the purposes of epidemiologic study, better characterizations of exposure are required than those usually available from engineering and hydrogeologic models and other estimates. Such models based on cursory local data often have been overemphasized while actual measurements or estimates of human exposure have gone undone. Models are only as valid as the assumptions and data on which they are based. Modeling needs to be improved both for health risks and for site assessment. Many studies have focused on site-specific characterizations, even though pollutants do not respect boundaries. These site-specific investigations have often not proceeded to the steps of defining the populations at risk and quantitatively evaluating exposure to toxic contaminants. The characterizations of the sites more often reflect requirements of environmental engineering and site remediation than assessment of public health considerations. Whether the toxic con-

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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 taminants pose a risk to the exposed population cannot be determined in the absence of more detailed information about human exposures. Instead of focusing on the toxic chemicals that have been identified at a site itself, it is necessary to develop estimates of exposure to define and assess the population at risk, including estimation of the population size and exposure-related characteristics. AIR POLLUTION FROM HAZARDOUS WASTES 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 those few epidemiologic studies of airborne exposures from sites, shows that a wide range of effects may occur, and they include serious diseases, such as cancer, neurobehavioral complaints, and constellations of self-reported symptoms. In addition, a few studies have explicitly linked airborne exposures from hazardous-waste sites to increased rates of birth defects, low birth weight, and chronic diseases in some small populations. Lessons that have been learned in air pollution studies are relevant to epidemiologic studies of hazardous-waste sites. As with the assessment of other health effects, a crucial lesson from the recent history of epidemiologic studies of air pollution has been the critical role played by the general availability of monitoring data for criteria air pollutants. Without the extensive network of data on those pollutants for which monitoring data are routinely acquired, such as respirable particulates, epidemiologic studies of air pollution would not have been possible. Many of the pollutants of interest at hazardous-waste sites are not routinely evaluated. Exposure to hydrocarbons in urban air has not been monitored regularly since the 1970s, and there has been little work on their direct effects except in studies of the sick building syndrome and occupational studies. The committee understands that routine monitoring of ambient air around hazardous-waste sites is not generally feasible because of the number of sites, the low likelihood of detection in most cases, and the cost of monitoring. The small populations near most sites make the sites difficult to study with standard epidemiologic techniques. Nevertheless, more systematic determinations of where such specific monitoring and studies might be appropriate need to be made early in the process of identifying and describing sites for study. The methods of meta-analysis also could prove useful to the extent that examples of similar exposures at different sites could be combined.

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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 The committee examined several cross-sectional morbidity studies of hazardous-waste sites, in which significant differences in symptoms were found between an exposed and a control population. None of these studies found differences in reproductive outcome or cancer mortality, but several documented significant self-reported symptoms including headache, irritability, and fatigue. These reports contain considerable discussion of how differences in symptom perception and recall can be avoided, but neither factor can be avoided altogether. The authors of these reports drew somewhat different conclusions from these studies, based on the degree to which they believed recall bias accounted for differences in reported symptoms. Recall bias is difficult to rule out if a community is episodically exposed to a noxious agent with a powerful odor or in other incidents of acute exposure. Although it might be concluded that recall bias explains the symptom differences in all of the studies of self-reported symptoms, it is plausible that the symptoms complained of are more sensitive indicators of significant exposure than are more severe outcomes. The fact that disparate populations in different countries experience similar symptoms indicates that a common set of exposures may be involved. Our belief that a constellation of symptoms may be associated with airborne exposures to emissions from hazardous-waste sites relies on a number of recent studies on the sick building syndrome and other studies of neurologic symptoms in solvent-exposed workers, which have found similar effects in exposed persons in different countries. The syndrome has been firmly established for several reasons. First, a remarkable concordance has been found in the kinds of complaints made by workers in different locations and in different countries: Headaches, fatigue, inability to concentrate, and mild inflammation of the eyes and pharynx were the most common complaints. The complaints were generally more common in air-conditioned buildings, and they could not be attributed to fungi (such as Aspergillus) known to be responsible for the “ humidifier fever” infection. The sick building syndrome contains important lessons for hazardous-waste-site epidemiology. In many cases involving hazardous-waste sites the complaints are subjective and similar to those associated with the sick building syndrome. Furthermore, many of the volatile organic compounds found in modern sealed buildings, including formaldehyde, toluene, and trichloroethylene, also are common constituents of waste dumps. Recent controlled exposure work from Denmark noted in Chapter 4 can play an important role in clarifying the specificity of reported

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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 symptoms. Symptom reports appear to be sensitive indicators of adverse health effects. The simultaneous use of air monitoring and diary records could reduce the problem of recall bias, and these methods are particularly valuable when small changes in pollutant levels cannot be detected by the subjects in a study. It has been suggested that airborne exposure to low levels of formaldehyde is followed by changes in cells that indicate that the immune system has been affected. Although the precise significance of such changes is unclear, the possibility must be considered that exposure to toxic substances from hazardous-waste dumps causes similar or related changes, as these involve similar exposures. It is likely that air emissions from hazardous-waste sites have caused a variety of symptoms that indicate low-level interference with normal function. Asthma and other respiratory diseases are common and well-studied disturbances of the respiratory system. During the past decade, our knowledge of factors related to airway responsiveness has expanded greatly. Exposures to a wide range of substances (more than 200 are listed in one review) can change airway responsiveness or reduce the threshold for response to a specific substance. More commonly, exposure leads to a nonspecific increase in airway responsiveness as measured by inhaled histamine or methacholine aerosols. A number of studies of hazardous-waste sites document complaints of chest tightness and shortness of breath. Therefore, the possibility must be entertained that proximity to some of these sites has induced increased airway responsiveness. To our knowledge, this has not yet been specifically sought in hazardous-waste-site studies. Although the role of ambient air pollution in asthma prevalence has not yet been determined, it seems likely that air pollution is an aggravating factor. It seems unlikely, however, that exposures from hazardous-waste sites could have played a part in the generally increased prevalence of asthma. The role of exposures from hazardous-waste sites in the development of respiratory symptoms cannot be readily evaluated. DOMESTIC WATER CONTAMINATED WITH HAZARDOUS WASTES As Chapter 5 makes clear, exposure from domestic water is not limited to ingestion, but includes airborne exposures from materials that can outgas during showering, bathing, or cooking, or can be absorbed through the skin. Therefore, estimates of exposure from domestic water need to be expanded to take into account the role of airborne exposures from volatile and nonvolatile substances.

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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 We have noted that complete accounts of the possible health effects associated with human exposure to hazardous-waste sites are not generally available, both because of legal restrictions that are often placed on findings by attorneys and because of the limited government resources applied to the study of the issue. However, several factors lead us to conclude that contamination of domestic water supplies with hazardous chemicals, such as those that can be encountered at hazardous-waste sites, is injurious to human health, even though the magnitude of the risk cannot be determined. Perhaps the most persuasive evidence now derives from studies that link an increased risk of bladder cancer to exposure to chlorinated surface water contaminated with trihalomethanes (THMs). Also, both experimental and epidemiologic studies link TCE exposure to increased rates of some cardiac congenital anomalies. One large ecologic study also associates bladder cancer with exposure to contaminated drinking water from hazardous-waste sites. Ample evidence shows an association between exposure to THMs and bladder and other cancers in test animals. Some epidemiologic studies of humans corroborate this relationship. The fact that other studies have not found an increased incidence of bladder cancer in persons exposed to toxic-waste sites could result from several factors, including the cancer's generally long latent period, the small numbers of people usually studied, the relatively pervasive exposure that occurs, and the fact that bladder cancer can have more than one cause. In a study in North Carolina strong evidence was found that increased cancer mortality rates were associated with exposure over a period of two decades to what was estimated to be a broad range of industrial by-products and hazardous substances in domestic water supplies. In a rural area, significant clusters of cancer developed about twenty years after residents had begun drinking raw, untreated river water contaminated by hazardous wastes. The timing of the appearance of the excess in all forms of cancer corresponded to the estimated time of peak exposure to contaminated domestic water, taking into account the typical latency for cancer. Increased rates of cancer might be anticipated in populations that have experienced solvent contamination of drinking water. Leukemia and lymphoma are of obvious concern, inasmuch as other studies have found increases linked to such occupational exposures to solvents. Unfortunately, the rarity of these diseases and the small populations usually exposed to solvents in drinking water have resulted in a dearth of studies with sufficient power to detect an increase in risk. Some researchers advocate restricting studies of clus-

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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 ters to those where very high rates have been found. However, the number of heavily exposed individuals that might be expected to show an increase in risk of fivefold or more is generally so small that for cancers as rare as leukemia or lymphoma such risks would be difficult to detect. Meta-analysis, which allows the appropriate pooling of relevant studies to increase the statistical power for detecting an effect, could offer some solution. This will be discussed further in the committee's next report on research opportunities in environmental epidemiology. 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 contaminated domestic water supplies. Studies in Santa Clara County, California, have been inconclusive as to the cause of a cluster of birth defects observed there. Two distinct studies in Love Canal, New York, however, link low birth weight to exposure to hazardous wastes. In Tucson, Arizona, the rate of congenital cardiac anomalies was three times higher in children of persons who consumed water contaminated with TCE. Such effects should continue to be monitored because there is far less difficulty with the latent period for reproductive effects than for cancer. Human population studies in Arizona and laboratory studies of animals provide evidence that cardiac abnormalities can develop after exposure to TCE. Recent reports of increasing trends in cardiac anomalies should be carefully evaluated, as improvements in case finding may be involved, along with real increases. There also is evidence that neurologic, hepatic, and immunologic function can be damaged by exposure to domestic water contaminated with 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. SOIL CONTAMINATED WITH HAZARDOUS WASTES Although direct ingestion of contaminated soil poses a risk chiefly to toddlers and children, as noted in Chapter 6, adults also could be at risk if they eat food grown in contaminated soil, or fish that have absorbed contaminants, or if they otherwise come into regular contact with contaminated soil through their work or personal habits. Sophisticated methods have been devised for improving assessments of soil exposures. These take into account peak, average, or cumulative exposures, to determine relationships between exposure and disease. Refined methods need to be applied in epidemiologic studies

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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 to improve the ability to estimate exposures from soil. These should include detailed metabolic studies of ingested plants, adequate characterization of chemical transformation, and better measurements of residues. One area that should not be neglected entails estimating exposures from consumption of fish that bioconcentrate lipophilic materials from sediment and water. Site assessments should use more realistic exposure measures, including direct studies of contaminants at the tap for domestic water supplies and estimates of consumption of contaminated foods and fish. In addition, efforts should be made to include relevant soil, food, and airborne measurements, so that integrated exposure assessments can be made. Current public health burdens from hazardous-waste sites appear to be small, but the future risk could be greater insofar as many of the substances involved are highly persistent and other materials already in the groundwater or soil can migrate or be transported into areas where exposure potential is greater. For instance, some of these materials in soil, such as chromium and other heavy metals, can contaminate large and populous sections of urban areas and remain persistent, as noted in Chapter 6. Similarly, lead is found at most Superfund sites and also contaminates some sections of urban areas; it is a nondegradable, persistent substance. Even for these materials, plausible routes of human exposure must be carefully assessed. Occurrence only increases the potential for risk. In some cases, unnecessary or inappropriate remediation can create more of a hazard than would be caused by leaving such materials undisturbed. CONCLUSIONS Although the effect on large populations of very low levels of toxic pollutants is unknown, action must be taken now to protect public health in the future. Threats of contamination of groundwater merit serious preventive policies. A substantial risk of contamination of groundwater is not being averted by current remediation practices, according to a number of assessments. It should be recognized that if exposure becomes general and almost uniform through contamination of groundwater, current epidemiologic techniques might not be able to ascertain any related health effects. There is now an opportunity to begin studies in areas where groundwater pollution has remained high and localized. There also is an important opportunity for prevention that could forestall major public health problems in the future. A number of research techniques should be extended to the study

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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 of health effects linked with hazardous wastes, including the use of “sentinel health events” as additional indicators of environmental contamination. Such indicators are most useful when they identify causes of morbidity and mortality that are uniquely or predominantly associated with specific and preventable exposures. Some illnesses, such as methemoglobinemia, which results from exposure to excessive amounts of nitrate in water, indicate hazardous environmental exposure, even when they occur as single cases. Other diseases indicate potential environmental exposures when they occur at elevated rates among larger populations, such as bladder cancer among non-smokers or chronic respiratory disease among children. The committee believes that further studies of acute symptoms, if combined with 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 study in this area. Surveys of the similar constellations of subjective symptoms reported by persons exposed in different countries to hazardous wastes indicate that such symptoms collectively can represent sentinel health events associated with such exposures. The further development and application of this approach to environmental surveillance holds particular promise for the epidemiologic investigation of populations exposed to hazardous wastes. A six-part environmental epidemiology program needs to be developed to inform policy decisions about risks to public health presented by hazardous-waste sites. Establish an active and coordinated system of site discovery for hazardous-waste sites, based in EPA and providing technical assistance to 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 public from hazardous-waste-site exposures. Define a revised approach to site assessments that integrates public health determinations of population exposures, health effects, 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

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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 remediation or closure. 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 to groundwater, surface water, air, and soil that result in human exposure; and the methodologies for estimating the size and make-up of populations exposed to hazardous-waste site emissions. 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 to fill data gaps in environmental epidemiology to illuminate the distribution and severity of exposures, risks, and health effects associated with hazardous-waste sites. 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. Direct ATSDR and other relevant agencies to expand cooperative agreements with states and develop a comprehensive program of technical assistance for state and local agencies. Federal and state agencies, such as ATSDR and the National Institute of Environmental Health Sciences, also should provide increased support for university-based research in environmental epidemiology. 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. Although evidence suggests that specific populations near specific hazardous-waste sites are exposed to substantial risks, the distribution and frequency of these exposures cannot be ascertained, because the needed data have not been gathered. 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 and their potential effects on public health. Our next report will contain a review of selected state health department reports on this subject and of case studies of legal decisions that have evaluated epidemiologic

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ENVIRONMENTAL EPIDEMIOLOGY: Volume 1 evidence not otherwise available in the published literature. On the basis of this review, we will recommend important research initiatives in the field. Until better evidence is developed, prudent public policy demands that a margin of safety be provided regarding potential health risks from exposures to 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.