AMERICAN JOURNAL OF INDUSTRIAL MEDICINE 30~529-539 ( 1 996) Risk of Silicosis in a Colorado Mining Community

We investigated exposure-response relations for silicosis among 134 men over age 40 who had been identified in a previous community-based random sample study in a mining town. Thirty-two percent of the 100 dust-exposed subjects had radiologic profusions of small opacities of 1/0 or greater at a mean time since first silica exposure of 36.1 years. Of miners with cumulative silica exposures of 2 mg/m3-years or less, 20 % had silicosis; of miners accumulating> 2 mg/m3-years, 63 % had silicosis. Average silica exposure was also strongly associated with silicosis prevalence rates, with 13 % silicotics among those with average exposure of 0.025-0.05 mg/m3, 34 % among those with exposures of>0.05-0.I mg/m3, and 75 % among those with average exposures>O. 1 mg/m3. Logistic regression models demon-strated that time since last silica exposure and either cumulative silica exposure or a combination of average silica exposure and duration of exposure predicted silicosis risk. Exposure-response relations were substantially higher using measured silica exposures than using estimated silica exposures based on measured dust exposures assuming a constant silica proportion of dust, consistent with less exposure rnisclassification. The risk of silicosis found in this study is higher than has been found in workforce studies having no follow-up of those leaving the mining industry and in studies without job title-specific silica measure-ments, but comparable to several recent studies of dust exposure-response relationships which suggest that a permissible exposure limit of 0.1 mg/m3 for silica does not protect against radiologic silicosis. @ 1996 Wiley-Liss, Inc