Carcinogenic Effects Of Benzene: An Update (Draft Report)
The major issue addressed in this document involves the nature and magnitude of the risk of cancer to humans exposed to low levels of benzene. Occupational studies continue to provide the bulk of evidence of benzenes carcinogenicity. Workers are exposed at much higher levels than is the general public. This document verifies that benzene is a known human carcinogen by all routes of exposure. This finding is supported by evidence from human epidemiologic studies, animal data, and an improvement in understanding of mechanism(s) of action. Human epidemiologic studies of highly exposed occupational cohorts have demonstrated that exposure to benzene can cause acute nonlymphocytic leukemia and other blood disorders, that is, preleukemia and aplastic anemia. Additionally, changes in blood and bone marrow consistent with hematotoxicity are recognized in humans and experimental animals. Currently, there is insufficient evidence to reject a linear dose-response curve for benzene in the low-dose region, i.e., that benzene is, in fact, nonlinear in its effects. Because this knowledge is not available at the present time, the Agencys approach of using a model with low-dose linearity is still recommended. Of the various approaches employing a linear assumption, utilizing the Pliofilm workers cohort, the risk at 1 ppm ranges from 4.7 x 10-3 to 2.5 x 10-2. This reaffirms the benzene interim unit risk estimates derived in EPAs 1985 interim risk assessment. There exists very limited data on children from environmental exposure to benzene.