Radiographic Evidence of Silicosis Risk in the Diatomaceous Earth Industry

There is limited and conflicting evidence regarding the exposure–response relationship between exposure to crystalline silica and silicosis; the level of risk to current workers remains uncertain. We conducted an epidemiologic investigation of 1,809 workers in the diatomaceous earth industry, where exposures to crystalline silica are primarily to the cristobalite form. On the basis of the median of three independent readings, 81 (4.5%) workers were judged to have opacities on chest radiographs (small opacities, profusion ⩾ 1/0, and/or large opacities). Age-adjusted relative risk of opacities increased significantly with cumulative exposure to crystalline silica. The concentration of respirable crystalline silica to which workers were exposed (highly correlated with period of hire) was an important determinant of risk after accounting for cumulative exposure. For workers with an average exposure to crystalline silica of ⩽ 0.50 mg/m3 (or hired ⩾ 1950), the cumulative risk of opacities for a cumulative expos...