EXECUTIVE SUMMARY
This is a report on the baseline activities and results of the statistical analyses of the baseline data for the Trichloroethylene (TCE) Subregistry. The TCE Subregistry is one of the three subregistries currently contained in the National Exposure Registry. The National Exposure Registry was created in response to a mandate given in the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 to the Agency for Toxic Substances and Disease Registry (ATSDR) to create a registry of persons exposed to hazardous substances. This mandate was reiterated in the Superfund Amendments and Reauthorization Act of 1986.
The National Exposure Registry is a database composed of names of persons, along with additional information on these persons, with documented exposure to specific chemicals. The purpose of the Registry is to assess the long-term health consequences of long-term exposure to low levels of environmental contaminants. One of the goals for meeting this purpose is to establish a database that will furnish the information needed to generate appropriate and valid hypotheses for future activitiessuch as epidemiologic studies. The Registry is not a definitive study. Cause and effect relationships cannot be established using only Registry-based information. However, the results of the dat a analyses will identify reported health outcomes that should be considered for future activities; such is the case for the results of the TCE baseline data analyses.
The data collected for each member of the Registry includes environmental data, demographic information, smoking and occupational history, and self-reported responses to 25 general health status questions. The files for each chemical-specific subregistry are established at the time baseline data are collected and are updated and maintained by ATSDR on an ongoing basis (annually the first year, biennially thereafter).
The TCE Subregistry file includes information collected on 4,280 persons (4,041 living, 239 deceased) who had documented environmental exposure to TCE and had resided in 13 areas in 3 states (Illinois, Indiana, and Michigan). These registrants were exposed through drinking water from TCE-contaminated private wells. To be eligible for the subregistry, persons had to have lived for more than 30 days and used the water at an address where the water supply (private wells) was contaminated with TCE (in most cases, other contaminants were also present). For eligible persons who were deceased, death certificates were obtained and pertinent information abstracted. The participation rate for those identified as eligible exceeded 98% at each site.
The health outcome rates for the TCE Subregistry were compared with morbidity data in the 1989 National Health Interview Survey (NHIS) and with the National Cancer Institute's Surveillance, Epidemiology and End Results Program data. The mortality data were compared with the national mortality data from the National Center for Health Statistics. The analyses also included comparisons between exposure groups in the Subregistry based on levels and lengths of exposure.
When interpreting the statistical results and planning future activities based on these results, the limitations of the Subregistry data files must be kept in mind. For instance, a bias in the rate of reporting could have existed because people were aware of their TCE exposure, had been advised of the potential effect on their health, and might have sought medical care more often than the general population. To moderate this potential bias, the Subregistry data were collected with the restriction that a health care provider had to have either told the person they had or treated them for the condition. Also, some of the questions in the two data collection instruments were worded differently, making direct comparisons of the reported rates more difficult to interpret. There is the possibility that, given the large number of comparisons used in the analyses, there might be some false positive findings. These limitations and restrictions are discussed further in this report.
The morbidity data analyses indicated an increased reporting by TCE Subregistry registrants for several health outcomes. Statistically significant increases (p .01 significance level) were found in children under 10 years of age for the conditions speech impairment, and hearing impairment; anemia (males only); and urinary tract disorders (females only). The excess number of hearing impairment and speech impairment cases were unique to the 0 through 9 years of age group. Urinary tract disorders were significantly higher for the male and female 18 through 34 years of age groups and females 35 through 44 and 55 years of age or older groups. Stroke was reported in excess for the 35 through 54 years of age groups (males and females). Liver and kidney problem rates were significantly higher for females aged 55 through 64 years; diabetes rates were higher for females 18 through 24 years and 45 through 54 years. Anemia and other blood disorders were reported at a statistically higher rate for males in the 0 through 9, 35 through 44, 55 through 64, and 65 years of age and older groups and for females in the 18 through 24 and 35 through 54 years of age groups. Statistically significant deficits for the TCE population were found for the following health conditions: hearing impairment (after age 25 years); asthma, emphysema, or chronic bronchitis; arthritis, rheumatism, or other joint disorders; and other respiratory allergies or problems, such as hay fever. However, these are conditions for which the rate might have been affected by the restriction on the registrants of the required confirmation by a health care provider.
The environmental data collected on each registrant were explored for potential dose-response relationships. For most registrants, the only available environmental data were the results of one well water sample; those data documented exposure. Further information on past levels and lengths of exposure to TCE and other chemicals was not available; therefore, the results of these analyses must be interpreted with caution. The most striking finding from the limited statistical analyses that were carried out was the significant elevation in stroke risk with increased maximum TCE exposure levels. The results also suggested other associations such as respiratory diseases with cumulative exposure to TCE and other chemicals and hearing problems with length of exposure. It should be noted that the outcomes stroke and hearing impairment were significantly higher in the morbidity outcome comparisons with NHIS as well.
The findings of this report do not identify a causal relationship between TCE exposure and adverse health effects. In addition, the excess reporting of some health conditions might be explained by methodological differences in data collection. The findings of this report do, however, reinforce the need to continue the biennial followup of registrants. In addition, the findings suggest several areas that need further exploration or clarification:
New methods need to be explored to improve the environmental exposure characterization of registrants (TCE registrants, in particular). Additional environmental data and exposure modeling would be helpful in assessing exposure-outcome relationships. This project is under way within ATSDR.
Additional information is needed for those persons responding positively to questions about health outcomes that were reported at a significantly higher rate. Information on lifestyle factors (for example, alcohol consumption) and diseases potentially related to the reported outcomes would be helpful when considering what future activities and studies should be conducted. In the near future, ATSDR will contact appropriate registrants to obtain this additional information. These data, along with the data obtained from the continued followup of the registrants, will aid in further exploration of suggested linkages.
The Subregistry questionnaire will be altered to more closely align it with the appropriate NHIS questionnaire.
The data file, without personal identifiers, will be made available to the public. Other researchers are encouraged to study these reported results more extensively and to explore other analyses.
Another of the stated goals of the National Exposure Registry is to keep registrants informed of all current information related to their exposures. Prior to informing the registrants, a TCE Subregistry Technical Assistance Panel (STAP)--composed of representative membership from the states involved, other federal agencies, and other knowledgeable persons--was formed to advise ATSDR on this process and future research needs. Following the STAP meeting and immediately prior to the release of information to the registrants, a meeting with community representatives, along with interested county, state, and federal agency representatives, was held for planning any site-specific activitiesincluding public meetings. A registrant report, written for the general public and containing the findings of this technical report, was prepared and sent to each registrant. The registrant report was then released to the media. The mailing was followed by a public meeting at each site to discuss the report.
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