Butatdiene Dose Reconstruction. M. Macaluso, Department of Epidemiology and International Health, University of Alabama at Birmingham
Retrospective, quantitative estimates of exposure to 1,3-butadiene (BD), styrene and benzene were developed for a follow-up study of 16,610 subjects employed at six North American styrene-butadiene rubber (SBR) manufacturing plants (418,846 person-years, 58 leukemia deaths). The estimation procedure entailed identifying work areas within 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. Estimates were linked with the subjects’ work histories to obtain cumulative exposure indices. Elevated leukemia mortality was observed, with excess risk in subgroups of workers who had high BD exposure potential. There was dose-dependent association of BD exposure with leukemia risk, and no styrene or benzene effect. The validity and precision of the exposure estimates, however, was uncertain, and BD risk assessment based on the estimates may be inaccurate. UAB collaborated with a panel of experts to improve the quality of the estimates. The re-estimation effort included review of the methods and collection of additional data. The new estimation included a better definition of plausible ranges of BD exposure levels, and estimates of cumulative BD exposure above and below specified thresholds. Preliminary re-analyses of the study suggest that 1) the original UAB estimates underestimated historical levels of BD exposure; 2) the ranking of workers according to the two sets of estimates, however, is very similar, and the dose-dependent association between BD and leukemia is confirmed in the reanalysis; 3) exposure to peaks above 100 ppm seems to explain the association between BD and leukemia.
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