Science Corner

ATSDR Biennial Report to Congress 1991 and 1992

This biennial report covers the period from January 1, 1991, through December 31, 1992, and is the third submitted by the Secretary of the Department of Health and Human Services (DHHS) to the Congress and to the Administrator of the Environmental Protection Agency (EPA). It is submitted in accordance with Section 104(i)(10) of the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA), also known as Superfund), as amended by the Superfund Amendments and Reauthorization Act (SARA) of 1986, which requires the Agency to publish a report on its programs and operations every 2 years.

EXECUTIVE STATEMENT

As part of its assigned responsibilities under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA or Superfund), as amended, the Agency for Toxic Substances and Disease Registry (ATSDR) is required to prepare a biennial report to Congress that fulfills the following objectives:

• describes the linkages between human exposure to single contaminants or contaminant combinations resulting from releases of hazardous substances and any increased incidence or prevalence of adverse health effects, and

• reports the results of activities of specified program areas.

Findings available to ATSDR subsequent to the release of the NRC report further demonstrate that, for some sites, an association exists between the release of hazardous substances and some human health effects. This conclusion is supported by data from two major sources: human health studies and analysis of ATSDR's public health assessments and toxicological profiles.

A number of health studies completed within the past few years most clearly demonstrate the association between hazardous substances and illness. In addition, analysis of public health assessments and toxicological profile data contained in ATSDR's HazDat database illustrate that 1) people are, in fact, being exposed to hazardous substances from a variety of waste sites and unplanned releases, and 2) the health effects described in toxicological profiles for the most commonly encountered hazardous waste site contaminants coincide with the increased health effects observed at elevated rates in people who live or work near hazardous waste sites.

Highlights of these analyses are discussed in this Executive Statement; a more detailed discussion follows in Chapter One.

FINDING:

Human health studies have shown that adverse health effects have occurred in persons exposed to hazardous substances released from some waste sites.

• Health investigations have reported increased rates of liver disease; birth defects; neurologic disorders; and respiratory, skin, and eye irritation in communities near some hazardous waste sites.

• Although epidemiologic findings are still unfolding, when health data from many Superfund sites are evaluated in aggregate, proximity to hazardous waste sites seems to be associated with a small to moderate increased risk of some types of birth defects and cancers.

• ATSDR has established subregistries of persons exposed to trichloroethylene (TCE), benzene, and dioxin from hazardous waste sites. Persons on the TCE subregistry reported higher rates of some health conditions compared with the rates seen in respondents to a national survey. Although this association does not mean that TCE is the cause of those conditions, it indicates that a relationship exists between the increase in the self- reported conditions (diabetes, kidney disease, skin rashes, high blood pressure, urinary tract disorders, and heart problems) and exposure to TCE in drinking water. The nature of the association requires further study.

• In most cases, the waste site source of TCE responsible for the exposures of the TCE subregistry subjects was removed by the time they were interviewed for the subregistry; therefore, one important implication of these findings is that hazardous waste site remediation does not necessarily resolve all public health concerns. An increasing body of scientific evidence indicates that past exposures to hazardous substances can cause adverse health effects with long latencies.

FINDING:

People are being exposed to hazardous substances from a variety of sites and unplanned releases.

• The National Research Council, using data supplied by the U.S. Environmental Protection Agency (EPA), has estimated that approximately 41 million people live fewer than 4 miles from one or more of the nation's 1,134 National Priorities List (NPL) sites, and that an average of 3,325 persons live within 1 mile of any given NPL site, it can be estimated that a large percentage of the U.S. population have a waste site "in their back yard."

• ATSDR's public health assessments conducted in 1991 and 1992 show that the number of people actually or potentially exposed to hazardous wastes at a site can range from zero to as many as 735,000.

• On the basis of the median number of people estimated to have been exposed at sites assessed in 1991 and 1992, 10 times more people are exposed to chemicals from former manufacturing sites than exposed from landfills or former waste treatment facilities (Approximately one third of all sites assessed by ATSDR are manufacturing facilities; half are waste storage and treatment facilities, primarily landfills).

• Analyses of blood, urine, and other tissues have documented human exposures to many hazardous substances, including arsenic, lead, mercury, dioxin, cadmium, chlordane, and polychlorinated biphenyls (PCBs), from specific waste sites. However, the extent of human exposure to these and other substances from all unplanned releases is, for the most part not known.

• For people living near some hazardous waste sites, certain activities, such as children's play and eating fish and game animals, have been associated with an increased risk of exposure to some contaminants. The results of studies investigating such activities will help ATSDR prevent or reduce exposures at other hazardous waste sites.

• Factors such as age, length of residence, and proximity to hazardous waste sites can influence the degree of exposure to hazardous substances. The results of studies investigating these factors will help ATSDR identify populations that are most likely to be affected by hazardous waste and target resources for health studies and health education to prevent or mitigate health effects.

• Some substances that persist in the environment and in the human body, for example, PCB's, are passed to offspring -- in the womb, through breast milk, and perhaps through mothers' and fathers' preconception exposures. The health consequences to children depend on the time, amount, and duration of exposure. The best way to prevent such exposure is to prevent parental exposures.

• Data from ATSDR's Hazardous Substances Emergency Events Surveillance System (based on 3,125 events in 10 states from 1990 through 1992) showed that in 54% of the unplanned releases, only one person was affected.

• Respiratory and eye irritation (37% and 23%, respectively) and nausea (10.0%) were the most frequently reported health effects associated with exposures resulting from unplanned releases of hazardous substances (e.g., emergency events).

FINDING:

By analyzing all existing data for hazardous waste sites and the most commonly encountered substances at those sites, ATSDR has determined where and how people are most likely to be exposed to substances from those sites and the adverse health effects most likely to result.

• A relatively small number of contaminants are the focus of many of the health-based decisions at Superfund sites. For example, at half of the sites for which ATSDR's public health assessments document human exposure to hazardous substances, fewer than 2% of the total substances (25 of the total 2,000 substances) were involved. It should be noted that at any single site, a seldom-used substance is sometimes the only concern, and many people can be affected by that substance.

• The types of substances most commonly found at waste sites are volatile organic compounds (VOCs) (66% of sites), inorganic compounds (65%), and halogenated pesticides and related compounds, such as polychlorinated biphenyls (PCBs) (34%).

• Certain combinations of contaminants in environmental media at hazardous waste sites are found more often than others. For example, the combination of TCE, tetrachloroethylene (PCE), and 1,1,1-trichloroethane in water was identified at 12% of the waste sites ATSDR has assessed. Cadmium, chromium, and lead also were identified together in soil at 12% of the sites.

• For this biennial report, ATSDR compared the concentrations of contaminants in completed exposure pathways at hazardous waste sites with concentrations of concern (See Footnote 1.) for health effects caused by those chemicals. The concentrations of some substances (for example, lead, TCE, and vinyl chloride) exceeded concentration of concern for health effects more than 80% of the time.

• The concentrations of other substances (for example, 1,2- dichloroethylene, zinc, toluene, and barium) in completed exposure pathways exceeded concentrations of concern for health effects less than 20% of the time.

• It is generally true that, for a given hazardous substance, the levels of exposure that pose an unacceptable risk of cancer are much lower than the exposure levels associated with noncancer effects. For this reason, more attention may be paid to the potential cancercausing effects of a substance when actions are being considered at a particular hazardous waste site. Nonetheless, at sites with hazardous substances identified in completed exposure pathways, concentrations of concern for noncancer effects are often also exceeded.

• Considerable data on health effects associated with the more than 200 hazardous substances described in ATSDR's toxicological profiles indicate that any organ system can be affected by the range of toxicants found at hazardous waste sites, provided exposure levels are great enough. However, most of these data are from reports of acute, high-level exposures (often from emergency events). There is a paucity of human data on chronic, low-level exposures found at hazardous waste sites, although epidemiologic data are beginning to accrue.

• The Superfund site remediation process focuses on the most sensitive health effects (often cancer) associated with substances at sites. Consequently, general toxicity information on noncancer effects is lacking for some of the most frequently encountered substances. Because of this lack of data, concentrations of concern for noncancer health effects at hazardous waste sites may be exceeded more often than is recognized.

• Analysis of the documented exposures to hazardous substances described in ATSDR public health assessments and of toxicity information presented in ATSDR toxicological profiles has shown that the potential noncancer health effects of waste site contamination include liver and kidney disease and developmental, lung, nervous system, and dermal effects. Some of these adverse health effects have been observed in people exposed to contaminants at hazardous waste sites. Furthermore, analysis of data from ATSDR's public health assessments and toxicological profiles suggests that adverse health effects on the reproductive, immune, and musculoskeletal systems of exposed populations may also be expected.

• Liver and lung cancers are by far the most common types of cancer reported in the literature when all waste site contaminants profiled by ATSDR are considered. However, when exposures to the 15 substances most often exceeding concentrations of concern are considered, this heavy predominance of liver and lung cancers disappears. Cancers of the skin, blood, kidney/urinary, and reproductive systems are reported almost as frequently as a result of exposure to these commonly encountered substances as are lung and liver cancers. This finding is somewhat surprising considering the predominance of lung and liver cancers when all possible causes are evaluated, but it fits well with preliminary findings by ATSDR and others suggesting that a variety of types of cancers are encountered more often than would be expected in human populations exposed to contaminants at waste sites.

FUTURE DIRECTIONS FOR ATSDR

The public health implications of this new information confirm many of the program decisions ATSDR has made for directing future health studies and substance-specific research. In addition, the findings point ATSDR in the new directions discussed in the following paragraphs.

Focus Efforts on Assessing Potential Environmental Causes of Some Chronic Diseases

On the basis of previous analyses of the adverse health outcomes expected from exposures to hazardous waste site contaminants, ATSDR has defined seven priority health conditions for additional research. Studies of exposed populations and analysis of exposures described in public health assessments clearly corroborate the priority health conditions chosen. Furthermore, these analyses indicate that environmental exposures may be linked with a number of chronic diseases that appear to be increasing.

For each priority health condition, a battery of clinical tests and biologic markers of exposure, susceptibility, and effect are being developed and will be applied to future health studies of populations exposed to hazardous waste. This will aid in the collection of consistent and appropriate health data and also allow for combining data from multiple studies.

The seven priority health conditions defined by ATSDR are these (alphabetical order):

• birth defects and reproductive disorders,
• cancer (selected anatomic sites),
• immune function disorders,
• kidney dysfunction,
• liver dysfunction,
• lung and respiratory diseases, and
• neurotoxic disorders.

Fill Data Gaps for the Most Commonly Encountered Contaminants

A small number of contaminants are involved in a large percentage of the exposures that occur, and it is likely that ATSDR does not yet know all of the adverse health effects that could be caused by these exposures. For example, a review of key data needs that have been identified for 38 of the most commonly encountered hazardous waste site contaminants revealed a lack of fundamental data on reproductive, neurologic, and immunologic toxicity. In addition, information about human exposure levels and the bioavailability of particular chemicals (e.g., how much mercuric sulfide in soil will be absorbed by the body) is also missing for these high-priority hazardous substances. For some of the most commonly encountered substances, too few studies have been conducted to allow confident derivation of the minimal risk levels (MRLs) needed to assess whether people are being exposed to levels that might cause adverse health effects.

Because of these data gaps, health effects in exposed populations may be overlooked. It is imperative that the key data gaps for these commonly encountered hazardous substances be filled.

Emphasize the Collection of Human Health Effects Data Using Persons Listed on ATSDR's Exposure Registries and Other Populations Known to Have Been Exposed to Commonly Occurring Waste Site Contaminants

Key human health effects data are lacking for virtually all of the hazardous substances found at waste sites. ATSDR exposure registries provide the raw material for generating much of this needed data.

The need to conduct health studies of these and other exposed populations will be determined using knowledge about the chemicals to which Americans are most often exposed and the adverse health effects that are most likely to result. This approach will allow ATSDR to achieve, with available resources, the greatest human health benefit in the least amount of time.

Continue Developing Essential Data for Hazardous Substances Released Infrequently

Many sites have unique contaminants that potentially affect health at only one or two sites in the country. Although the frequency of any one of these unique contaminants may be low, their frequency as a class is high, and many people may be affected. Therefore, ATSDR will continue to develop profiles that enhance assessment of the public health effects of substances that are found at few sites.

ATSDR is considering using specific analytic methods and computer models to develop essential data for these less frequently encountered substances. For example, structure activity relationship modeling can be used to predict the effects on and behavior in the environment of unstudied chemicals, using what is known about similar chemicals. Also, computer models (e.g., pharmacokinetic, pharmacodynamic, or dosimetry models) can be used to supplement and extend the usefulness of available information for a chemical.

Consider the Potential Toxic Effects of Commonly Occurring Combinations of Substances

People may be exposed to multiple substances at many waste sites, complicating diagnosis of resulting health effects. Furthermore, because of the frequency of the identification of combinations of substances at sites, the potential health effects of specific combinations may be of greater potential health concern for the nation as a whole than the effects associated with many individual substances. ATSDR will assess the health hazards of hazardous substance combinations, beginning with frequently occurring combinations.

Develop Consistent and Efficient Approaches to Hazardous Substance Releases on the Basis of Past Experience

Thousands of different hazardous substances are released under a wide variety of conditions and in a wide variety of communities, causing a vast array of different potential exposures and health effects. However, predictable patterns are associated with the types of sites involved in releases, the chemicals released, the ways the chemical move in the environment, the sizes of populations exposed to the chemicals, and the health effects that may result.

ATSDR will develop strategies that exploit these patterns to improve the efficiency and efficacy of its response to hazardous substance releases. For example, health assessors will draw upon past experience at any similar site as a starting point for new sites, thereby reducing response time and providing consistent approaches to sites across the nation.

ATSDR's HazDat database will simplify the development of such strategies and facilitate their implementation.

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Footnote 1. In this context, a concentration of concern is the concentration of a substance in air, water, or soil that corresponds to a minimal risk level (MRL) as defined by ATSDR or a reference dose (RfD), reference concentration (RfC), or a one-in-a million risk of cancer as defined by EPA. It should be noted that the MRL is defined as a level "without an appreciable risk of noncancer adverse health effects." (See the definition of MRL in the glossary for a discussion of what health effects may be expected if a concentration of concern is exceeded, as well as a discussion of the uncertainty inherent in estimating MRLs.)

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Charlie Xintaras / chx1@cdc.gov