A Quantitative Estimate of Leukemia Mortality Associated with Occupational Exposure to Benzene

The risk of developing leukemia from occupational exposure to benzene at the current, 8-hr time-weighted average (TWA), permissible exposure level of 10 parts per million (ppm) ⁽¹⁾ has been vigorously debated since the mid-1970s, when epidemiologic evidence conclusively demonstrated benzene's leukemogenic potential in humans. In 1978, the Occupational Safety and Health Administration (OSHA) promulgated a revised standard of 1 ppm TWA for occupational exposure to benzene. ⁽²⁾ OSHA took the position that "once the carcinogenicity of a substance has been established qualitatively, any exposure must be considered to be attended by risk when considering any given population." OSHA concluded that it was not possible to demonstrate a threshold level for benzene-induced carcinogenicity, or to establish a safe level for benzene exposure, and therefore decided that the permissible exposure level to benzene should be reduced to the lowest feasible level.