A cohort mortality study of workers exposed to chlorinated organic solvents in Taiwan
Introduction
In June 1998 the press in Taiwan revealed that an electronics factory located in the northern part of island improperly disposed of waste materials including chlorinated organic solvents. The dumping site has been found to result in organic solvent contamination of the underground water. This electronics factory began operations in May 1968 and was shut down in 1992. The products of this factory included various parts, main board, and integrated circuits for black-and-white and color television sets. The Environmental Protection Agency (EPA) in Taiwan verified that the water in some wells nearby had been polluted by trichloroethylene (TCE) and tetrachloroethylene (PCE). The water quality was below the standard established for drinking water by the World Health Organization (WHO). TCE and PCE are the main chlorinated hydrocarbon solvents used in dry cleaning, machine cleaning, and metal degreasing (1). Animal experiments showed that TCE and PCE cause liver carcinoma and lung carcinoma in mice, as well as renal cell carcinoma in rats 2., 3., 4., 5.. Epidemiological research has focused on the risk of cancer (including liver 6., 7., 8., 9., cervical 6., 9., 10., bladder 9., 10., 11., 12., 13., lung cancers 6., 10., 14., leukemia 6., 11. and Hodgkin's disease (10)) among workers employed by industries using these two chemicals. However, most of the results obtained from such studies were largely inconclusive. Based on the evidence in experimental animals and humans, TCE and PCE are considered “probable carcinogens” to humans (Group 2A) by the International Agency for Cancer Research (15).
The Institute of Occupational Safety and Health in Taiwan conducted an epidemiological study to investigate the association between cancer risk of workers and chemical exposures in their working environment. Initially, a proportionate cancer morbidity study was conducted in the first year. The results of the first year study showed a slightly and marginally significant proportionate cancer morbidity ratio (PCMR) for breast cancer (PCMR = 1.2, 95% CI: 1.0–4.4) among female workers in the exposed group when compared with either textile or electronics control groups. Because of the well-known methodological problems of PCMRs and to confirm the association, a retrospective cohort mortality study based on standardized mortality ratios (SMRs) was conducted to further analyze the relationship between various types of cancer and workplace exposures among the employees at this electronics factory.
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Description and ascertainment of the study cohort
Cohort of the exposed group was retrieved from the Bureau of Labor Insurance (BLI) computer database from 1978 through December 31, 1997. Data provided by BLI included employment histories at different factories and the changes of insurance status from 1978 through December 31, 1997. To ensure complete recruitment of the exposed cohort, BLI also provided hard copies of insurance records of the exposed group who had their first employment from 1973 to 1978 (since no computerized records were
Description of the study cohort members
The total number of workers in the exposed group was 86,868. Most of the cohort members were females (80%). The distribution of individual members and person-years stratified by gender, current age, duration of employment, calendar year and age at start of work is shown in Table 1. The male cohort contributed 182,847 person-years and the female cohort contributed 839,247 person-years during the 13-year observation period. Most of the workers' current age was between 30 and 50 years, and these
Discussion
Epidemiological studies of TCE and PCE exposed workers have shown an excess of several cancers, including liver 6., 7., 8., 9., cervical 6., 9., 10., bladder 9., 10., 11., 12., 13. and lung cancers 6., 10., 14., as well as leukemia 6., 11. and Hodgkin's disease (10). The results obtained in the present study do not seem to indicate any increased cancer risk from exposure to TCE and PCE. Hence, these findings do not support a causal link between cancer risk and TCE or PCE exposure. In addition
Acknowledgments
This study was supported by a grant from the Council of Labor Affairs, the Executive Yuan, Republic of China (ISOH89-M302).
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