Radiographic Evidence of Silicosis in Relation to Silica Exposure

Abstract

Although the risk of silicosis has long been recognized as a consequence of exposure to crystalline silica, there are only limited data available for quantitatively estimating risk in relation to modern concentrations. Reports on three large groups of workers (Vermont granite workers, South African gold miners, and Ontario hardrock miners) form the basis for estimating silicosis risk; two other smaller studies, of British gypsum miners and North Carolina dusty trades workers, provide additional but less quantitative information. For 40 years of exposure to a respirable silica concentration of 0.1 mg/m³, the estimated cumulative risk of radiographic evidence of silicosis is approximately 1 to 3 percent based on the Ontario miners (depending on whether diagnosis requires a positive reading by a majority of five readers or by only one reader) and is 60 percent based on South African miners. Findings from Vermont granite workers and North Carolina dusty trades workers are more consistent with the lower risk estimate. Reasons for the substantial difference in risk estimates are not clear. However, underestimation of exposure in the South African study is a possibility; moreover, because of the shape of the dose-response curve, a twofold underestimation could account for more than a tenfold overestimation in risk. Data from additional studies are needed, as well as information on other related issues such as the extent to which the presence of small opacities among current workers are associated with functional impairment and/or with future risks associated with these generally low level opacities. Hughes, J.M.: Radiographic Evidence of Silicosis in Relation to Silica Exposure. Appl. Occup. Environ. Hyg. 10(12):1064–1069; 1995.