A cohort mortality study of workers exposed to chlorinated organic solvents in Taiwan

Abstract

Purpose

A retrospective cohort mortality study based on standardized mortality ratios (SMRs) was conducted to investigate the possible association between exposure to chlorinated organic solvents and various types of cancer deaths.

Methods

Vital status and causes of death of study subjects were determined from January 1, 1985 to December 31, 1997 by linking cohort data with the National Mortality Database. Person-year accumulation began on the date of entry to the cohort, or January 1, 1985 (whichever came later), and ended on the closing date of the study (December 31, 1997), if alive; or the date of death.

Results

This retrospective cohort study examined cancer mortality among 86,868 workers at an electronics factory in the northern Taiwan. Using various durations of employment and latency and adjusting for age and calendar year, no significantly elevated SMR was found for any cancer in either male or female exposed workers when compared with the general Taiwanese population. In particular, the risk of female breast cancer was not found to be increased. Although ovarian cancer suggested an upward trend when analyzed by length of employment, ovarian cancer risk for the entire female cohort was not elevated.

Conclusions

It is concluded that this study provided no evidence that exposure to chlorinated organic solvents was associated with human cancer risk.

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.