SILICOSIS AMONG GOLD MINERS - EXPOSURE - RESPONSE ANALYSES AND RISK ASSESSMENT

Objectives. This study sought to estimate the risk of silicosis by cum ulative exposure-years in a cohort of miners exposed to silica, as wel l as the lifetime risk of silicosis under the current Occupational Saf ety and Health Administration (OSHA) standard (0.09 mg/m(3)). Methods. In a cohort study of 3330 gold miners who worked at least 1 year unde rground from 1940 to 1965 (average 9 years) and were exposed to a medi an silica level of 0.05 mg/m(3) (0.15 mg/m(3) for those hired before 1 930), 170 cases of silicosis were determined from either death certifi cates or two cross-sectional radiographic surveys. Results. The risk o f silicosis was less than 1% with a cumulative exposure under 0.5 mg/m (3)-years, increasing to 68% to 84% for the highest cumulative exposur e category of more than 4 mg/m(3)-years. Cumulative exposure was the b est predictor of disease, followed by duration of exposure and average exposure. After adjustment for competing risks of death, a 45-year ex posure under the current OSHA standard would lead to a lifetime risk o f silicosis of 35% to 47%. Conclusions. Almost 2 million US workers ar e currently exposed to silica. Our results add to a small but increasi ng body of literature that suggests that the current OSHA silica expos ure level is unacceptably high.