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Congressional Testimony
ATSDR: Applied Research

Testimony by Barry L. Johnson, Ph.D.
Assistant Surgeon General
Assistant Administrator
Agency for Toxic Substances and Disease Registry
Public Health Service
U. S. Department of Health and Human Services

Before the
Subcommittee on Technology, Environment, and Aviation
Committee on Science, Space, and Technology
United States House of Representatives

November 9, 1993

I will endeavor to respond to three of the four questions in your letter of invitation. I will describe ATSDR's long-term Superfund applied research, how we are coordinating that research with other agencies, and how additional resources from the Superfund Trust Fund would be useful to that research. Because ATSDR is not involved with research on innovative technologies, that issue will not be addressed in my testimony. I should observe, however, that any remedial technology must be based on the goal of protecting public health and the environment. Therefore, scientific data are essential to establishing health-based clean-up levels at waste sites and to developing the technologies to achieve those levels.

Mr. Chairman, ATSDR is one of the eight agencies of the Public Health Service; we are the principal federal public health agency involved with hazardous waste issues. As background, ATSDR was created by the CERCLA legislation in 1980. We draw our budget and principal authorities from CERCLA [§104 (i)].

CERCLA, as amended, mandates of ATSDR a broad, national program of Superfund site public health assessments, health investigations, surveillance and registries, applied research, emergency response, health education, and toxicological database development. I have stressed the number and breadth of our CERCLA mandates in order to make a point: Our public health actions will only be as good as the scientific data on which we predicate those actions.

I believe the Congress understood the importance of research and development programs when CERCLA was reauthorized in 1986. EPA, the National Institute of Environmental Sciences (NIEHS), and ATSDR were all given the task of conducting basic or applied research in support of Superfund's purposes: protecting public health and natural resources, remediating waste sites, and removing toxic hazards from the environment.

The applied research program that is established, expanded, or continued under a title in the Superfund program should be focused and directed at the hazardous substances and related public health problems identified by the Superfund program. Applying scarce research dollars to the substances and problems of greatest priority is essential.

This testimony will describe ATSDR's current applied research responsibilities under CERCLA. Basic research, such as that conducted by NIEHS and EPA, develops new scientific information that can be used during health investigations and risk assessments, and for other purposes. ATSDR's applied research program makes use of this basic scientific knowledge in real-life situations to assess the health effects of toxic substances, and to address the health concerns of persons exposed to hazardous substances. Participants benefit from the conduct of such studies, and the knowledge gained from the studies can be applied to other known sites during the conduct of public health assessments and health intervention programs, such as health education.

ATSDR's applied research serves two major functions:

1. to respond to the public's concern: "Has human exposure to hazardous substances occurred and resulted in adverse health effects?" and

2. to provide EPA with critical health-based information so that clean-up decisions that are effective and protective of public health can be made.

HazDat: Hazardous Substances Database

The American public remains very concerned about the health implications of hazardous substances in the environment. In order for ATSDR to best respond to these concerns, we need to know what the priority toxic substances are and what adverse health conditions we should be most concerned about. In other words, our limited resources should be directed to the highest priority health problems. That requires knowing what toxic substances are released from waste sites and from unplanned releases. ATSDR has established a unique comprehensive database, called HazDat, that is used to set priorities for applied research.

At the heart of our HazDat database are the data and findings from more than 1,600 public health assessments and consultations of hazardous waste sites on the National Priorities List (NPL) or from sites for which we've received petitions, from individuals or members of Congress, for public health assessments. In conducting these assessments of how releases from sites may be affecting a community's health, ATSDR has accrued a significant amount of experience and scientific data. That experience and those data have significantly shaped what has developed into an important Superfund program of applied research.

In other words, by conducting public health assessments, we have learned much about the limits to what we as scientists and health officials really know about the toxic effects of specific hazardous substances on human health, singly and in combination. In ATSDR's view, improving our scientific database is vital to improving site risk assessments and human health assessments. In particular, we must continue to conduct studies of past exposure so that we can target resources to mitigate or prevent future exposures of public health significance. Failure to identify increases in adverse health effects will result in increased numbers of affected people and increased health care expenditures.

Key Findings from ATSDR's Applied Research

Applied research by ATSDR and others has been successful in helping us as health officials to more knowledgeably respond to the question of where there are linkages between exposure to hazardous substances and adverse human health effects. Following are key findings from ATSDR's work and others:

• Although epidemiologic findings are still unfolding, when evaluated in aggregate (i.e., by combining health data from many Superfund sites), proximity to hazardous waste sites seems to be associated with a small to moderate increased risk of some kinds of birth defects and, less well documented, with some specific cancers.

• Although environmental epidemiologists often have great difficulty designing them, health investigations of communities around some individual hazardous waste sites have found increases in the risk of birth defects, neurotoxic disorders, leukemia, cardiovascular abnormalities, respiratory and sensory irritation, and dermatitis. However, many of these studies report no adverse health findings. These apparent discrepancies may be a result of factors such as limitations inherent to epidemiologic methods, differences in environmental conditions in the communities investigated, and the small number of persons evaluated at some sites.

• lead exposure studies conducted from 1986 through 1988 in Montana and Idaho documented unacceptably high blood lead levels in young children living in communities with varying high levels of lead-contaminated soil. These studies provided the basis for soil clean-up decisions made by EPA;

• more recent studies at sites with high levels of lead- contaminated soil in Bunker Hill, Idaho, and Smuggler's Mountain, Colorado, showed very different blood lead levels in children. One study documented that children had blood lead levels of concern, the other did not. This leads to the further research question of what is the relationship between lead in soil and lead in people. ATSDR hopes to answer that question with a current study of 2,500 people potentially exposed to lead in soil.

The 1986 CERCLA amendments [§104(i)(2)] require ATSDR and EPA to jointly rank, in order of priority of health importance, hazardous substances released from NPL sites. The two agencies have worked very closely since 1987 to compile a list of 275 Superfund Priority Hazardous Substances. The first 10 substances on the list are lead, arsenic, mercury, vinyl chloride, benzene, cadmium, PCBs, chloroform, benzo(a)pyrene, and trichloroethylene. Each of these substances, depending on level of exposure and other factors, can cause adverse human health effects. The complete list of 275 priority hazardous substances was published in the Federal Register (57 FR 48801).

ATSDR also is directed by CERCLA [§104(i)(3)] to prepare a toxicological profile for each priority hazardous substance on the list. Each profile is an up-to-date compilation of information about the health effects of these substances. More than 1 million of these profiles have been distributed, and a recent evaluation found the Toxicological Profiles are extremely useful to government agencies, private industry, and concerned community groups. We have developed 176 profiles to date.

ATSDR strongly believes that continuing development of these key resource documents is important. In addition to being central sources of information on individual toxic substances, the ATSDR Toxicological Profiles identify key data gaps in scientific knowledge about these substances.

As directed by CERCLA [§104(i)(5)], ATSDR, in cooperation with EPA and the National Toxicology Program (which is administered by NIEHS) must evaluate the adequacy of scientific data for each of the 275 priority substances. Key gaps in scientific knowledge are to be filled through referral to EPA's Toxic Substances Control Act (TSCA) and Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) authorities and other mechanisms. The 117 key data gaps for the first 38 substances on the Priority List of Hazardous Substances were published in the Federal Register in 1992, and are attached to my testimony. The attached table indicates that key data gaps exist, even for some "well known" toxicants.

EPA, NTP, and ATSDR work through a committee, the TriAgency Superfund Applied Research Committee, that reviews the relevant scientific data that in turn lead to identifying key data gaps for priority hazardous substances. Recommendations from this committee are placed in the Federal Register for review and comment from the public. In ATSDR's view, this committee structure has worked very well.

As an example, our HazDat database shows us that trichloroethylene is the organic solvent most often released into groundwater. ATSDR has identified key data gaps in ascertaining the effects of trichloroethylene on the nervous system, immune function, and reproductive outcomes. We have also identified as a data gap the need for human data on trichloroethylene exposure. Having these data gaps filled through research would materially assist ATSDR in assessing the impact of trichloroethylene on communities and would be very important data for use in site risk assessments.

After key data gaps, such as the one for trichloroethylene, have been identified, CERCLA directs that ATSDR work with EPA and the National Toxicology Program to initiate applied research to fill them. In 1992, ATSDR referred 60 key data gaps on the first 38 substances from the Agency's Priority List of Hazardous Substances to EPA for handling under TSCA and FIFRA. EPA has indicated to ATSDR its potential interest in placing many of the 60 data gaps on its Master Testing List. Such an action by EPA could result in private industry conducting the research to fill specific data gaps.

A review of the key data needs for the first 38 substances from the Priority List of Hazardous Substances reveals some interesting patterns. For example, for many of the substances we lack fundamental data on potential toxic effects (noncancer endpoints). Specifically, we lack scientific data on the reproductive, neurologic, and immunologic toxicities of many of these substances that we know are being released from Superfund sites. Two other areas of need include, for most substances, more data on the levels of substances to which humans are exposed and better information about bioavailability.

Because not all key data gaps shown in the attachment are appropriate for handling under TSCA or FIFRA, some data gaps are being filled by funds from ATSDR's budget. In particular, ATSDR is filling data gaps that involve epidemiologic investigations. In addition, as directed by Congress, some data gaps are being filled through research grants to academic institutions in the Association of Minority Health Professions Schools (AMHPS). Attached are the titles of applied research projects that fall under this program between ATSDR and AMHPS. ATSDR considers this to be a particularly important applied research effort, given the evidence that large numbers of minority communities and persons of color are impacted by hazardous waste sites and other forms of environmental pollution.

ATSDR also is communicating with private industry about their ability to fill some data gaps; though results have yet to be realized.

ATSDR's experience in conducting public health assessments and epidemiologic investigations of communities around hazardous waste sites convinces us of the importance of filling key data gaps for priority hazardous substances. The program of identifying data gaps and filling them through applied research is working per CERCLA mandate, and will provide vital new scientific data for use in improving decisions on assessing public health, risk assessments, and site remediations.

Developing Critical Health-based Information

Besides the mandate to identify priority health substances, CERCLA also requires that ATSDR conduct studies of the adverse health effects of exposure to hazardous substances from waste sites. Information from these studies is provided to EPA to assist in making environmental clean-up decisions that are also protective of public health.

Epidemiologic studies by ATSDR, state health departments, and academic institutions can be classified as a) studies that combine data from populations around several sites for aggregate analysis, and b) studies of the health of persons around individual sites. Health investigations are important in a public health sense for identifying persons for whom exposure to hazardous substances must be interdicted and for assessing adverse health conditions.

Aggregate Site Studies

Investigating the broad picture of the association between hazardous waste sites and public health impact requires that we combine site populations with common environmental characteristics, thereby increasing the size of the human populations investigated. This aggregating of sites has been used by ATSDR and others as an investigative method by researchers to examine the association of cancer and birth defects rates in areas around hazardous waste sites.

Two sets of investigators have reported an increased frequency of cancers in people living in counties surrounding hazardous waste sites. A 1983 study reported that age-adjusted gastrointestinal (GI) cancer mortality rates (all sites combined) were higher in 20 of New Jersey's 21 counties than national rates. Within specific sex and race groups, mortality rates in New Jersey for cancers of the esophagus, stomach, colon, and rectum during the period 1968- 1977 significantly1 exceeded national rates. The environmental variables most frequently associated with GI cancer mortality were population density, degree of urbanization, and presence of toxic waste disposal sites (Najem et al. 1983).2 Similarly, an EPA study of 593 hazardous waste sites in 339 U.S. counties of 49 states produced analytic evidence that contaminated groundwater was the sole source of water supply (Griffith et al. 1989). Significant associations between excess deaths and all counties with hazardous waste sites, when compared with all counties without hazardous waste sites, were shown for cancers of the lung, bladder, esophagus, stomach, large intestine, and rectum in white men; and for cancers of the lung, breast, bladder, stomach, large intestine, and rectum in white women. These ecologic-epidemiologic studies of specific cancer rates need confirmation and elaboration.

Turning to birth defects studies, a study in the state of New York examined the association between congenital malformations in children and maternal proximity to hazardous waste sites (Geschwind et al. 1992). The study investigated 9,313 newborns with congenital malformations, as recorded in the New York State Congenital Malformations Registry, and 17,802 healthy comparison children. A total of 590 hazardous waste sites in 20 New York counties were selected for analysis of the incidence of malformations. (Waste sites in New York City were excluded, given what were presumed to be unique sociodemographic and geographic characteristics compared with the rest of the state.) A coordinate mapping procedure was used to match all case and comparison geographic coordinates to the hazardous waste coordinates. An "exposure risk index" was created for each respondent within a 1- mile radius of the birth residence. Results indicated that maternal proximity to hazardous waste sites may carry an additional risk of approximately 12% of bearing children with congenital malformations. Greater rates of malformation were associated with both a greater exposure risk (63% increase in risk) and documentation of off-site chemical leaks (17% increased risk).

ATSDR funded a study conducted by the New Jersey Department of Health of reproductive outcomes associated with contaminated drinking water (Bove 1992). Public drinking water systems serving 75 towns in northern New Jersey were evaluated. Hazardous waste sites were believed to have been among several sources of contaminants in the water supplies. Data pertaining to all live births and stillbirths (excluding chromosomal defects and plural births) born during the period 1985 through 1988 to residents of the 75 towns were included in the study. Significant associations were found between specific contaminants (trihalomethanes, carbon tetrachloride, tetrachloroethylene, and dichloroethylene) and various birth defects (cardiac, nervous system, neural tube, and oral cleft defects) and adverse reproductive outcomes (lower birthweight, intrauterine growth retardation).

ATSDR supported another birth defects study by the California Department of Health Services. They conducted a study to investigate the relationship between maternal residence and the presence of hazardous waste sites and the risk of congenital malformations. The study evaluated births between 1983 and 1985.

During this study, 5,617 births involving congenital malformations were evaluated. The study concluded that maternal residence in a census tract with a hazardous waste site at the time of the child's birth significantly increased the risk of giving birth to infants with malformations of the heart and circulatory system.

Studies by both ATSDR and other institutions indicate that adverse reproductive outcomes may be related to consumption of contaminated drinking water or living in proximity to hazardous waste sites. For example, birth defects were evaluated by ATSDR-funded surveillance systems in Iowa, New Jersey, and Washington. These states used birth defects registries and birth records to assess populations in geographic areas where they were potentially exposed to hazardous substances. Excess rates of stillbirth, prematurity, low birth weight, cardiac defects, urogenital defects, limb reductions, oral clefts, and central nervous system defects may be related to exposures to hazardous substances through drinking contaminated water. Birth defects data from these state surveillance systems will be used during additional epidemiologic studies by ATSDR to clarify any associations with hazardous waste sites.

Latent adverse health effects in persons who were exposed in the past to hazardous substances are suggested by findings from ATSDR's National Exposure Registry. Included in the registry are approximately 5,000 persons with documented exposure to trichlorethylene. The 5,000 registrants come from 14 sites in Michigan, Indiana, Illinois, and Pennsylvania; 10 of the sites are on the NPL. Trichloroethylene levels in drinking water ranged from 1 part per billion (ppb) to 19,380 parts per million (ppm). (The Maximum Contaminant Level for trichloroethylene is 5 ppb.) Exposure durations were for as along as 18 years. For essentially all persons on the registry, trichloroethylene exposure has ceased with provision of uncontaminated water. The health problems reported to be in excess of those reported by the general population included anemia and other blood disorders, diabetes, hearing impairment, heart disease, hypertension, kidney disease, skin rashes, speech impairment, stroke, and urinary tract disorders. Some of the health problems reported by registrants seem consistent with the toxicology of trichloroethylene. However, caution must be exercised when interpreting these health findings until ATSDR conducts medical validation studies of a sample of the 5,000-member registry cohort.

Health Studies at Individual Sites

Several investigators have reported adverse health effects associated with specific hazardous waste sites. The principal health findings include these: a) significantly shorter height by age in children at a waste site than in comparison children (Paigen et al. 1987); b) a higher prevalence of birth defects and liver disease in persons living near a thorium waste disposal site compared with persons living a greater distance from the waste site (Najem and Voyce 1990); c) lower birthweight and more birth defects in census tracts where exposure to a waste site occurs (ATSDR 1990); d) hepatomegaly and abnormal liver function tests in residents exposed to leachate from a toxic waste dump (Meyer 1983); e) dermatitis, respiratory irritation, neurologic symptoms, and pancreatic cancer at seven sites (ATSDR, 1992); and f) in residents around a Superfund mining site, significant elevations of illness rates for chronic kidney disease, stroke, hypertension, heart disease, skin cancer, and anemia (Neuberger et al. 1990). Though none of these studies measured levels of exposure to hazardous substances, they add to the scientific database on waste sites and public health and provide valuable information that will be useful in designing more definitive studies.

A considerable number of studies have been conducted to investigate health effects in communities around hazardous waste sites. Many of these studies are negative in the sense that statistically significant increases in adverse health effects were not found (Grisham 1986; Upton 1989). Although such findings may represent the true health status of the communities, negative results may also occur for the following reasons: inadequate sample sizes, inadequate information about exposure to hazardous substances, poor selection of study sites, or study of adverse health effects not associated with the specific substances found at a given waste site.

Priority Health Conditions

As research proceeds, it is prudent to consider each waste site as a potential source of the release into environmental media of substances that can adversely affect human health. Because of this concern, ATSDR has developed a list of seven priority health conditions to 1) assist in evaluating potential health risks to persons living near these sites and 2) determine program and applied human health research involving hazardous substances identified at the sites (MMWR 1992). To arrive at the priority health conditions shown in Table 1, ATSDR evaluated the toxicologic and human health effects data for the top 50 of the 275 priority hazardous substances identified as being released from Superfund sites.

About two-thirds of the health studies listed in the attachment under Priority Health Conditions research are being conducted by state health departments, using fully peer reviewed study protocols. This arrangement provides states with valuable technical and financial resources to investigate the health problems of their citizens who may be impacted by Superfund sites within their borders.

Listing of the Superfund Priority Health Conditions provides ATSDR and others with a framework for conducting health investigations around aggregate waste sites. Attached is a list of human health investigations undertaken in support of each ATSDR Priority Health Condition. It should be emphasized that these health investigations are site-specific; that is, they focus on communities believed to be at risk of adverse health effects resulting from releases from specific Superfund sites.

Exposure Studies

Concern about the public health effects of hazardous substances occurs when humans are exposed to levels believed to exceed safe levels. A series of studies conducted by ATSDR has documented exposure at some Superfund sites to heavy metals, volatile organic chemicals, PCBs, or combinations of those substances that could put affected residents at increased risk of developmental disabilities; growth retardation; kidney, liver, and blood disorders; hypertension; or birth defects. For example, the mean blood lead level of children living near the California Gulch site in Colorado was almost twice that predicted by a biokinetics uptake model (CHD 1990).

In addition, increased exposure to lead and arsenic has been reported in children living near waste sites in Montana, Washington, and Utah (ATSDR 1986; ATSDR 1987; ATSDR 1988b; Binder et al. 1987); elevated serum levels of PCBs were found in some people at two waste sites (Stehr-Green et al. 1988), although not at most sites surveyed; and 1,1,2,2-tetrachloroethylene was measured in the breath of persons whose homes were situated near a former chemical waste dump (Monster and Smolders 1984). Twelve exposure studies out of 45 conducted by ATSDR found elevated biological levels of hazardous substances, including lead, mercury, PCBs, chlordane, arsenic, and an herbicide.

The importance, and difficulty, of relating environmental contamination levels with human exposure levels is exemplified by the work ATSDR has conducted on persons exposed to lead. In one long-term investigation, ATSDR has worked with the Centers for Disease Control and Prevention (CDC) and the Panhandle Health District in Idaho to conduct blood lead surveillance of children exposed to lead from a smelter. The smelter closed operations in 1982, and the area surrounding it is an NPL site. Lead in soil and dust were the principal exposure routes. Through surveillance and intervention, children's mean blood levels have declined steadily since 1974. However, in 1993, blood lead levels of about 18% of the children still exceeded the current CDC action level for children (10 mg/dL). Efforts are ongoing to reduce all children's blood lead levels to below 10 mg/dl. The reduction of blood lead levels in this community has been accomplished through the application of environmental and health education strategies developed during studies of risk factors for lead exposure in children; some of those studies were conducted by ATSDR at other sites.

Other studies of blood lead and soil lead associations have shown quite differing results. In studies at the Smugglers' Mountain NPL site in Colorado, quite high soil lead levels did not result in children's blood lead levels of health concern. ATSDR is currently concluding the data analysis of a study of 2,500 persons potentially exposed to lead in soil. From this study should come a better understanding of the relationship between lead in soil and lead in people.

Because of the critical importance of being able to measure actual levels of exposure to hazardous substances released from Superfund sites, ATSDR has funded two significant efforts to enhance scientific knowledge of biological markers. Our first effort has been with CDC's National Center for Environmental Health, which has developed biological markers to measure dioxin in adipose tissue and blood sera. Additionally, the same CDC laboratory, under funding from ATSDR, has developed baseline levels of exposure for a representative sample of the U.S. population exposed to 37 priority hazardous substances. These baseline exposure data can be used by health investigators to against which to compare exposure levels in a community around a Superfund site.

ATSDR has also commissioned the National Academy of Sciences (NAS) to conduct studies since 1987 that have evaluated biological markers to assess exposure and toxicity for substances affecting reproductive function, immunological function, neurological health, and respiratory illness. This has resulted in a series of important recommendations for specific biological markers to use in conducting health investigations of populations exposed to hazardous substances. These NAS recommendations have been incorporated into ATSDR's Priority Health Conditions and are being used by Agency investigators in their site-specific health investigations.

Great Lakes Applied Research

I turn now to an example of one of our most successful applied research efforts. The Great Lakes Critical Programs Act of 1990 mandates that EPA, in consultation with ATSDR and the Great Lakes States, submit to Congress by September 30, 1994, a research report assessing the adverse effects of water pollutants in the Great Lakes system on the health of persons in the Great Lakes States. Since 1992, ATSDR has received $2-3 million to conduct a study of the human health effects of contaminated fish in the Great Lakes.

I should note that there are a variety of persistent toxic substances prevalent in the Great Lakes, including PCBs, DDT and its metabolites, dieldrin, toxaphene, mirex, mercury, benzo[a]pyrene, hexachlorobenzene, furans, dioxins, and lead.

This research is unique to ATSDR because 1) it involves substances identified on ATSDR's Priority List of Hazardous Substances, 2) it will serve to fill many of the data gaps discussed earlier, 3) it fulfills ATSDR's mandate to study combinations of hazardous substances commonly found at waste sites, and 4) it involves surveillance activities, the initiation of exposure and health effects studies, and establishment of subregistries of exposed persons.

Research undertaken through this program will build upon and amplify the results of past and ongoing research into fish consumption in the Great Lakes Basin, thereby utilizing structures and institutions already involved in human health research. Information gained from these efforts can then be related to national research efforts and used to develop resources that will provide long-term benefits to the human health research effort.

These studies include investigations of presumed susceptible populations who consume contaminated Great Lakes fish. It has been demonstrated that certain populations, i.e., Native Americans and the fetuses and nursing infants of women who consume contaminated Great Lakes fish, have a potentially higher risk of long-term adverse health effects resulting from exposure to these contaminants. We anticipate that research proposals will focus on these high-risk populations in an effort to further define the human health consequences of exposure to these substances.

Ultimately, information gained from these research efforts will benefit the communities by 1) providing answers to health-related questions that have persisted for many years; and 2) providing assistance to others in making better-informed decisions regarding consumption of fish from the Great Lakes Basin.

ATSDR Applied Research Addresses Public Concerns

This whole discussion of the types of public health studies and research being conducted by ATSDR makes a point that I believe is worth emphasizing. The basic function of ATSDR is not to deal with hypothetical populations experiencing hypothetical health problems based on a scientific model. On a daily basis, we deal with real people, with real health problems and concerns. For example, during this month of November, ATSDR staff are meeting one-on-one, sometimes in private homes, with people in Houston, Texas, living around a former chemical processing facility; with residents of a neighborhood in Grand Island, Nebraska, that is adjacent to a former ammunition manufacturing plant, and with citizens in Piketon, Ohio, whose homes are in the area of a gaseous diffusion plant. These are people who are asking difficult questions of public health officials-questions for which we do not always have the answers-but questions that we are addressing through applied research.

Future Research Needs

Mr. Chairman, in response to your question about how any additional research resources would be used, ATSDR has the following recommendations, based on our experience since 1987, regarding applied research:

• A relatively small number of contaminants are involved in a large percentage of the exposures that occur. There is reason to believe that we do not know all of the adverse human health effects that could result from exposure to many of those contaminants. Key data gaps for this select subset of high-priority hazardous substances must be filled in order to improve site-specific risk assessments and public health assessments for communities.

• Because releases from hazardous waste sites typically involve multiple chemicals and chemical mixtures, research is needed to characterize the toxicity of these kinds of releases.

• Additional effort must be exerted in developing human exposure data, including more specific biological markers of exposure and national population-based levels of baseline exposure, for persons believed to be at greatest health risk.

• Further research is necessary to identify additional health effects of hazardous substances on susceptible populations, including minorities and children.

• Efforts must be focused on the diagnosis of identified diseases resulting from exposure to key environmental toxicants. On the basis of previous analyses of the expected adverse health outcomes expected from exposure to hazardous substances, ATSDR has defined seven priority health conditions to serve as a framework for continuing efforts, and progress is occurring in examining the association between environmental toxicants and each priority health condition.

In summary, Mr. Chairman, ATSDR has learned a great deal from its applied research efforts since Superfund was reauthorized. However, we need to know a great deal more to improve prevention of adverse health effects in affected communities. Although a link between the release of substances into the environment and health effects in humans can be described, significant gaps exist both in our understanding of the scope of the health effects, and in our knowledge of the specific hazardous substance-related health effects that may now exist in the nation.

Human exposure assessment is a major part of the quantitative risk assessment used to make clean-up decisions. The available data are weak; thus public health professionals are forced to make conservative recommendations that could result in increased costs. The National Academy of Sciences' (NAS) report Environmental Epidemiology: Public Health and Hazardous Waste recommended that a number of research strategies and techniques be applied to the study of health effects linked with hazardous waste, including the use of "sentinel health events" as indicators of contamination and exposure. The report concludes with the exhortation that a window of opportunity exists to initiate studies in areas of contamination, and that emphasizing prevention now could forestall major public health problems in the future. ATSDR concurs with this NAS recommendation and we consider it sound advice.

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¹The word significantly is used to mean statistical significance, according to some test used by the investigator whose results are being described.

²References are available on request.

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Mr. Chairman, this concludes my testimony. I will be pleased to answer questions.

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