In this testimony, the mortality experience of a cohort with occupational exposure to benzene (71432) was updated in efforts to learn more about a possible connection to leukemia. Job/exposure matrices were used to derive cumulative exposure concentrations. These matrices were based on available air sampling data. The standardized mortality ratio (SMR) for leukemia was 328 and the SMR for multiple myeloma was 398. SMRs for leukemia increased from 105 in workers with less than 40 part per million years (ppm-y) cumulative exposure to 314 in workers with from 40 to 199.99ppm-y; to 1,757 in those with from 200 to 399.99ppm-y; and to 4,535 in those with 400 ppm-y or more. A 40 year working lifetime exposure at 10 parts per million was equivalent to a cumulative benzene exposure of 400ppm-y. When the boundaries of the exposure categories were varied, this strongly positive trend in SMRs remained evident. A conditional logistic regression was performed to examine the shape of the exposure/response relation. A log linear model best explained the association between cumulative benzene exposure and leukemia. It was calculated from this model that protection against benzene induced leukemia will be increased exponentially by any reduction in the permissible exposure limit.
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