• National Exposure Registry
• Benzene
• Dioxin
• Journal Articles
• Trichloroethylene(TCE)
• Trichloroethane(TCA)
• Registry Data

SECTION 5

Conclusions

At Followup 1, as at Baseline, the Trichloroethylene (TCE) Subregistry population reported more adverse health outcomes than a national sample population. It should be noted that the respondents at Followup 1 were not aware of the results of the analyses of the Baseline data. For Followup 1, the adverse health outcomes reported by Subregistry participants in excess of those reported by the national sample participants, for all or specific age groups, were liver problems; anemia or other blood disorders; diabetes; urinary tract disorders, including prostate trouble; arthritis, rheumatism, or other joint disorders; skin rashes, eczema, or other skin allergies; respiratory allergies or problems such as hay fever; and all cancers.

At Baseline, several of the findings were of particular note, including excess numbers of speech and hearing disorders reported in children. The Agency for Toxic Substance and Disease Registry (ATSDR) has initiated research into exploring other possible factors contributing to this excess, such as concurrent or contributing diseases or specific community activities such as aggressive hearing conservation programs. The results of these investigations, along with the results of the TCE Subregistry Followup 1 data, will be used to clarify and evaluate the Baseline information. Increased reporting was found at Followup 1 for this health condition, but not a statistically significant increase such as was found at Baseline.

Of equal concern is the continued excess reporting of stroke and anemia or other blood disorders. These conditions continue to contribute to disease and death in the United States, yet many of the underlying factors that contribute to the health outcomes stroke and anemia have yet to be identified. In the past, nonoccupational exposures to TCE have not been considered to contribute to either stroke or blood disorders. However, the findings of the Subregistry, both at Baseline and Followup 1, suggest that further study is needed to determine if exposure to TCE might contribute to the development of these conditions. More information from registrants on potentially confounding factors--diet, specific health risk behaviors (such as smoking and alcohol consumption), and other lifestyle factors--combined with the analyses of the Followup data for the TCE Subregistry population will help identify contributing factors. In addition, future studies of this population should focus on the validation of these findings and exploration of a possible TCE exposure-health outcome linkage.

Many of the conditions reported in excess of the National Health Interview Survey (NHIS) rates by the TCE Subregistry population, such as diabetes, are typically underdiagnosed in the general population. As discussed at Baseline, it is possible that the excess reporting of health conditions in the TCE Subregistry population was related to a heightened awareness of the potential for illness that led to either an increased use of health care services or a false increase in reporting.

As stated at Baseline and reiterated in this report, limitations of the comparison of the TCE Subregistry data with NHIS data must be kept in mind when interpreting the results; recent research, however, indicates that the impact on reporting rates is minimal. The comparability of the questions (some questions were very closely worded, others were similar), recall bias (exposed persons were perhaps more aware of health problems and remembered events in greater detail), frequency of health care utilization (exposed persons were perhaps more aware of health problems and sought health care more often), and underrepresentation of children younger than 5 years of age in the TCE Subregistry population must be considered when interpreting the results in light of reported national norms. Also, because of the many comparisons carried out, some of the positive results might have been chance occurrences or might have occurred because the true causal factors (confounders) were not identified.

The limitations of the environmental data for the TCE Subregistry have rendered the dose-response calculations inconclusive. Recently, several computer models have been used at ATSDR to simulate exposure patterns using the minimum amount of information available. These models, used in conjunction with statistical models, were used to develop a best estimate of actual environmental levels for exposure periods and sites. However, the paucity of historical information remains a very limiting reality in the individual dose reconstruction (for all routes of exposure) needed for further dose-response evaluations.

RECOMMENDATIONS

Cause and effect relationships cannot be determined from simple analyses of the subregistry-based information. Information obtained from this database, in conjunction with the Baseline and the additional Followup data to be collected in future followups, can and will be used to determine appropriate future activities and research. Ongoing research using these databases and the Baseline database include modification of the current data collection procedures and methods; exploration of recognized sources of bias and reduction or elimination of these biases; acquisition of additional definitive information on and confirmation of selected outcomes that appear to be in excess (validation of reporting results); and substance-specific research with specific hypotheses clearly identified.

It is unclear whether either wording differences between TCE Subregistry and NHIS questions or recall bias might have generated different response rates. In order to better understand the excess reporting of some of the health conditions, ATSDR is completing an evaluation of how these wording differences could have created differences in responses and will modify the questions appropriately for future National Exposure Registry (NER) activities. New methods will be considered that could aid in assessing the potential impact of exposure awareness on both the recall of health conditions and health care utilization by registrants. It should be noted that even if a determination is made that exposed people sought health care more often--which does not appear to be the case--it will not be possible to separate whether the increase in the number of visits was due to an awareness of exposure or to an actual increase in health problems.

Improvement of individual exposure estimates for the TCE Subregistry population and other environmentally exposed populations continues to be a priority for ATSDR. Better exposure characterization of registrants would allow improved assessment of the relationship between exposure and health outcomes.

Preliminary findings from the completed analyses leave many questions unanswered; it is hoped that additional information and further investigations will help answer these questions. Following the TCE registrants longitudinally on a routine basis will continue. The additional information collected will be used to assess trends in reporting and to assist in answering some of the questions, or clarifying some of the issues, previously discussed.

As was noted at Baseline, all of the health conditions that were reported in excess by the TCE Subregistry population are preventable or treatable, if not curable. Early detection frequently plays a role in whether a health condition can be arrested or reversed by existing medical technologies. Given the results of the Baseline analyses for this population, it was imperative that this information be shared with TCE-exposed persons in a responsible manner.

A summary version of the TCE Subregistry Baseline Technical Report was written in nontechnical language. Information packets, containing the registrant report, fact sheet, and cover letter, were mailed to all TCE Subregistry members. Similar information was furnished to appropriate federal, state and local health officials, as well as the media. Those registrants expressing specific health concerns were encouraged to see their personal physicians. A concerted effort was made by ATSDR to share all findings of the NER analyses with the appropriate health care providers in each area. In addition, specific information and education about TCE has been made available to them.

Although no definitive Conclusions can be made from the information contained in this report, it is hoped that researchers will use the information to better assess the potential for adverse health outcomes following exposure to substances in the environment. As pointed out, additional studies of the TCE Subregistry data are warranted and encouraged by ATSDR. The data files used in this report will be made available on CD-ROM (the Baseline files are already available).