In 1997 the International Agency for Research on Cancer (IARC) classified crystalline silica dust exposure as a known human carcinogen, group 1. In Western countries this change in status has not resulted in any immediate shift to reduce workplace exposure, adopt new occupa tional standards, nor to marked changes in environmen tal hazard assessments. The one place where crystalline silica has been treated as an environmental carcinogen is under California's Proposition 65, which has required quantitative risk assessment to determine if exposures to carcinogens could result in greater than 1 in 100,000 excess cancer risk. There have been several peer- reviewed cancer risk assessments for silica based on ani mal, human and threshold extrapolations. This paper reviews and contrasts those determinations, discusses the impact of IARC's reassessment on research, and sug gests where future policy may lead.
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