Leukemia risk associated with benzene exposure in the pliofilm cohort: I. Mortality update and exposure distribution

The National Institute of Occupational Safety and Health (NIOSH) recently completed a vital status update adding 6 years of observation on the rubber workers known as the Pliofilm cohort. Using traditional standardized mortality ratio (SMR) analysis, we investigate the impact of the additional information gathered in the NIOSH update. We also compare the effect of using three sets of job-, plant-, and year-specific exposure estimates on the evaluation of benzene's leukemogenicity. The lack of any additional cases of multiple myeloma does not support trends toward elevated risks for this endpoint (as had been observed earlier), and there is no indication of increased incidences of solid tumors (as predicted by animal studies). Qualitatively, which exposure estimates are used does not alter the conclusions. The data added in the update did not greatly modify the estimated relative risk of leukemia associated with benzene exposure, but did confirm previous findings that occupational exposure to high concentrations had leukemogenic potential. The fact that leukemia has not been observed in any individual who started employment in Pliofilm production after 1950 suggests that the observed leukemia cases could be a response to very high levels of benzene exposure that occurred during the early years of this manufacturing process.