RISK OF SILICOSIS IN A COLORADO MINING COMMUNITY

We investigated exposure-response relations for silicosis among 134 me n over age 40 who had been identified in a previous community-based ra ndom 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 pears. O f miners with cumulative silica exposures of 2 mg/m(3)-years or less, 20% had silicosis; of miners accumulating > 2 mg/m(3)-years, 63% had s ilicosis. Average silica exposure was also strongly associated,vith si licosis prevalence rates, with 13% silicotics among those with average exposure of 0.025-0.05 mg/m(3), 34% among those with exposures of > 0 .05-0.1 mg/m(3), and 75% among those with average exposures > 0.1 mg/m (3). Logistic regression models demonstrated that time since last sili ca exposure and either cumulative silica exposure or a combination of average silica exposure and duration of exposure predicted silicosis r isk. Exposure-response relations were substantially higher using measu red silica exposures than using estimated silica exposures based on me asured dust exposures assuming a constant silica proportion of dust, c onsistent with less exposure misclassification. 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 studi es without job title-specific silica measurements, but comparable to s everal recent studies of (lust exposure-response relationships which s uggest that a permissible exposure limit of 0.1 mg/m(3) for silica doe s not protect against radiologic silicosis. (C) 1996 Wiley-Liss, Inc.