Cancer risk assessment for crystalline silica to implement California's hot spots act.

Crystalline silica has been identified as a probable human carcinogen. To assess the potential for adverse health effects due to environmental exposures to respirable crystalline silica, a quantitative estimate of carcinogenicity has been made using incidence data from three studies in which long-term silica inhalation caused lung tumors in rats. The uncertainties in risk assessment in general and in the risk assessment for silica in particular are discussed.