Characterization of cancer risk from airborne benzene exposure.

Airborne benzene is a ubiquitous environmental air pollutant. However, research regarding ambient environmental benzene exposures and leukemogenesis is lacking. Alternatively, occupational exposure to significantly elevated levels of benzene is associated with acute myeloid leukemia (AML). This investigation uses ambient air monitoring data from six counties in the state of Florida to characterize the extrapolated cancer risk from airborne benzene concentrations. The study uses both a regulatory and comparative risk analysis methodology to appropriately frame "risk" for the public. Between the years 2003 and 2006, 3794 air samples were collected from 23 monitoring stations distributed in Broward, Duval, Orange, Miami-Dade, Hillsborough, and Pinellas counties. The mean benzene concentrations by site ranged from 0.18 to 3.58ppb. Extrapolated cumulative lifetime exposures ranged from 0.036 to 0.702ppm-years. Regulatory risk analysis resulted in cancer risk estimates ranging from 4.37 x10(-6) to 8.56 x 10(-5), all of which exceed the Florida Department of Environmental Protection acceptable risk of 1x10(-6). Comparative analysis with the epidemiologic literature indicates the association between benzene exposure and AML is related to cumulative exposures far in excess of 1ppm-years, with the likely threshold for benzene-induced leukemogenesis of 50ppm-years cumulative exposure. Based upon the results of this investigation, it is unreasonable to anticipate AML cases in Florida residents as a result of ambient airborne benzene concentrations.