MORTALITY EXPERIENCE OF WORKERS EXPOSED TO HALOGENATED ETHERS (EPIDEMIOLOGY, CANCER, OCCUPATION)

An industry-wide retrospective cohort mortality study was conducted on chemical workers engaged in the manufacture of chloromethyl methyl ether (CMME) at seven major U.S. companies. The study included 2460 CMME-exposed workers and 3692 nonexposed workers for follow-up from 1948 through September 1979 for companies 1-6, and from 1953 through 1980 for company 7. At the end of follow-up, 32% were employed, 56% had separated, and 12% were known dead. Death certificates were obtained for 98% of 744 known deaths. Personnel records provided information on the duration and relative magnitude of exposures based on job descriptions with allowance for temporal changes in plant processes. Selected cause-specific mortality of CMME-exposed and nonexposed workers was evaluated using U.S. general population rates specific to cause, sex, race, and quinquennia of age and calendar year. In all companies combined, a significant excess mortality occurred only in CMME-exposed workers for deaths from all malignant neoplasms and from respiratory cancer. This was attributed to excess respiratory cancer mortality at companies 2 and 7. Significant trends of increasing respiratory cancer mortality with increasing cumulative exposure were evident at both companies based on external comparisons. External comparisons examining risk in relation to time since last exposure and age at first exposure demonstrated significant trends of decreasing risk with increasing time since last exposure and suggested an increasing risk with increasing age at first exposure. Analyses based on internal comparisons of respiratory cancer risk at company 2 demonstrated significant exposure-response relationships for increasing relative risks with increasing exposure duration, cumulative exposure, and average exposure intensity. Relative risks decrased with increasing time since last exposure. An inverse relationship between life-table latency estimates and cumulative exposure was evident at companies 2 and 7. Maximum likelihood procedures using a "case-control-within-a-cohort" methodology found a significant negative interaction between age and cumulative exposure, meaning that for given cumulative exposures, younger workers are at higher risks than older workers. When the data were interpreted using predictions of the multistage model, there was strong evidence in support of CMME as a late-stage carcinogen.