LEUKEMIA AND CUMULATIVE EXPOSURE TO BUTADIENE, STYRENE AND BENZENE AMONG WORKERS IN THE SYNTHETIC RUBBER INDUSTRY

Retrospective, quantitative estimates of exposure to 1,3-butadiene, st yrene and benzene were developed for a follow-up study of leukemia mor tality among 16610 subjects employed at six North American styrene-but adiene rubber manufacturing plants (418846 person-years, 58 leukemia d eaths). The estimation procedure entailed identifying work areas withi n each manufacturing process, historical changes in exposure potential and specific tasks involving exposure, and using mathematical models to calculate job- and time-period-specific average exposures. The resu lting estimates were linked with the subjects' work histories to obtai n cumulative exposure estimates, which were employed in stratified and Poisson regression analyses of mortality rates. Mantel-Haenszel rate ratios adjusted by race, age, and cumulative styrene exposure increase with cumulative butadiene exposure from 1 in the nonexposed category to 4.5 in the category of 80 ppm-years or more (P = 0.01). The risk pa ttern is less clear and statistically nonsignificant for styrene expos ure. A trend of increasing risk with butadiene exposure is still prese nt after exclusion of the nonexposed category (P = 0.03). A parsimonio us interpretation of the findings presented here, in light of previous epidemiologic studies, is that exposure to butadiene in the synthetic rubber industry produces a dose-related increase in the occurrence of leukemia.