Issues in conducting a cancer risk assessment using epidemiologic data: arsenic as a case study.

Using human data to extrapolate cancer risks at ambient levels of airborne pollutants avoids the uncertainty due to interspecies differences, but introduces other uncertainties. The unusually extensive data relating lung cancer to occupational inhalation of arsenic provide examples of 3 uncertainties: the extrapolation from partial to full lifetime risks, from high to low doses, and between populations with differing smoking habits.