Science CornerScience CornerThe Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA), which created the Agency for Toxic Substances and Disease Registry (ATSDR), mandated the establishment of a registry of "persons exposed to toxic substances." The National Exposure Registry was developed to address this mandate. The purpose of the Registry is to facilitate the development of new scientific knowledge on long-term health consequences of environmental exposures to specific hazardous substances, known as primary contaminants. The National Exposure Registry is made up of subregistries based on specific primary contaminants. The policies and procedures for establishing subregistries have been published (ATSDR 1988a). ATSDR has developed exposure subregistries for persons exposed to trichloroethylene (TCE), benzene, and dioxins.
Trichloroethylene
Trichloroethylene Subregistry
Selection of Trichloroethylene
The human health effects of exposure to individual hazardous substances, let alone mixtures, are not fully known or well understood. Information on long-term health effects of low-level, long-term exposures is particularly limited. Registries can be useful tools for assessing long-term effects potentially related to exposure. The first chemical selected for inclusion in the Registry was trichloroethylene (TCE). TCE was selected because of its ubiquitousness in the environment; published evidence of toxicity; and the paucity of information on the health effects of low-level, long-term exposures. These factors suggested that a TCE subregistry could contribute to the detection of any excess adverse human health effects following low-level, long-term exposure to TCE in the environment. A thorough review of the literature in 1988 (the year TCE was selected for a subregistry) on health effects related to TCE exposure can be found in the Toxicological Profile for Trichloroethylene (ATSDR 1989).
At the time of its selection, TCE was the most prevalent contaminant found at National Priorities List (NPL) sites (Figure 1). TCE was identified at 37% (n = 355) of all NPL sites and was a groundwater contaminant at 91% (322) of those sites. Local communities were using TCE-contaminated groundwater as a source of drinking water at 87% (279) of the groundwater sites. Of these sites, 33% (91) had private well systems, 33% (93) had municipal systems, and 34% (95) used both private and municipal systems to provide residents with drinking water. Furthermore, 11% (31) of TCE-contaminated groundwater sites also used TCE-contaminated surface water as a drinking water source (ATSDR 1988b).
Site selection procedure
The procedure for selecting sites for the TCE Subregistry has been described (ATSDR 1988a) and discussed elsewhere (Gist 1993). Sites included in the TCE Subregistry were implementation trichloroethylene subregistry national exposure registry selected based on the identification and documentation of the a) level(s) of TCE contamination in drinking water, b) estimated size of the exposed population, c) period of exposure, d) susceptible subpopulations, e) existing biomonitoring data, and f) number and levels of secondary contaminants.
In all, 883 households at 13 sites in 3 states were selected for inclusion in the TCE subregistry (Table 1). (Note: The total population size of the TCE Subregistry is based on preset statistical confidence levels [ = 0.10, ƒ = 0.80] for a doubling of the overall cancer rate in the general population. A sample size of approximately 5,000 was determined to be necessary to complete the TCE Subregistry.) The exposure period for each of these sites was calculated using estimated beginning dates, calculated from existing environmental data and other information obtained from local, state, or other federal agencies, and confirmed ending dates of contamination.
Eligibility requirements
Persons were eligible to participate in the TCE Subregistry if evidence existed of TCE contamination and a plausible pathway for human exposure. In addition, potential registrants had to have lived in identified households for at least 30 days during the period of contamination and had to have used well water for bathing or drinking. The data-collection phase began with public outreach. A packet of information about the chemical of concern and the Registry purposes was sent to each potential registrant. A public meeting was held to address any questions potential registrants had about the Registry. State and local officials were invited to participate in both efforts. Interviewers who participated in the data-collection phase were introduced to potential registrants at the public meeting.
Once eligibility requirements were met, residents were asked to begin participation in the Registry program by completing a questionnaire. The questionnaire addressed the following general areas: eligibility for participation in the Registry, residential history, demographic information, health information, reproductive history, smoking history, and occupational history. Proxies (usually next of kin) provided information on eligible deceased registrants, and a death certificate for each deceased registrant was requested from the appropriate state office.
Database collection effort
The TCE baseline data-collection effort was well received in the communities. High levels of participation were achieved at all sites, as shown in Table 1. Participation rates were calculated by dividing the number of registrants (living and deceased) by the number of potentially eligible persons contacted and asked to participate. At several sites, litigation was ongoing, and problems related to registry participation had to be solved; however, in most cases litigation was not a barrier to participation. The questionnaire information and death-certificate data make up the permanent files for registrants. Release of information
Registrants were informed that information from their files would not be released without their written consent, as provided in the Privacy Act (5 USC 552a[e]). Registrants were permitted to participate in the subregistry without agreeing to the release of personal identifiers or medical records. ATSDR agreed to keep each registrant informed of significant health and scientific issues and to maintain the files in a secure and confidential manner. The names and declinations of exposed persons not choosing to participate in the subregistry were recorded as part of the subregistry file. ATSDR might contact thesepersons in the future if circumstances change significantly (for example, if new evidence of adverse health effects associated with the contaminant[s] becomes available).
Termination of TCE Subregistry
Most subregistries will have a finite lifetime and definite termination rationales. The TCE Subregistry could be terminated under the following circumstances. o TCE is no longer used and manufactured, no longer found at dump sites, and all registrants are deceased; however, an exception could be made if TCE is found to have the potential for causing multigenerational effects.
o Technological advances enable the measurement of a previously immeasurable hazardous substance, such as TCE, in tissue or body fluids more than 48 hours after exposure. After applying this new technology to persons in the TCE Subregistry who were originally enrolled on the basis of less precise measures, ATSDR finds that none of the registrants has had significant exposure to TCE.
o TCE is determined through further study to cause no adverse health outcomes.
If any of these conditions are met, the TCE Subregistry, including follow-up and updates, will be terminated. When the subregistry is terminated, surviving registrants will be notified of the termination, the rationale for it, and its implications. A registrant can request to be removed from the subregistry at any time by informing ATSDR in writing of the decision.
References
Agency for Toxic Substances and Disease Registry (ATSDR). (1988a). Policies and procedures for establishing a national registry of persons exposed to hazardous substances: National Exposure Registry. Atlanta: U.S. Department of Health and Human Services, Public Health Service.
Agency for Toxic Substances and Disease Registry (ATSDR). (1988b). VIEW Database. Atlanta: U.S. Department of Health and Human Services, Public Health Service.
Agency for Toxic Substances and Disease Registry (ATSDR). (1989). Toxicological profile for trichlorethylene. Atlanta: U.S. Department of Health and Human Services, Public Health Service.
Gist GL, Burg JR, Radtke TM. (1994). The site selection process for the National Exposure Registry. J Environ Health 56:7-12.