RISKS OF SILICOSIS IN COAL-WORKERS EXPOSED TO UNUSUAL CONCENTRATIONS OF RESPIRABLE QUARTZ

Objectives-To describe the radiographic changes in coalworkers exposed to unusual concentrations of respirable quartz during the 1970s, and to relate these to exposure measurements. Methods-Men who had worked a t one Scottish colliery during the 1970s were invited to a health surv ey. Chest radiographs were taken from 547 subjects. Classifications of these films under the International Labour Organisation (ILO) 1980 sc heme were related, by logistic regression, to existing darts on indivi dual men's exposures to respirable dust and quartz. Results-Taking the median of the three readers' results on profusion of small opacities, 203 men (38%) showed progression of at least one profusion category o n the 12 point scale, from the various 1970s surveys to the follow up in 1990-1. A total of 158 men (29%) had a profusion of at least 1/0, a nd 47 (8.6%) of at least 2/1 at the follow up survey, Large opacities were recorded as present by at least two readers for 14 (2.6%) of the men. Profusion of small opacities was strongly related to exposures ex perienced in the 1970s, and more strongly for quartz than for the non- quartz fraction of the dust, Estimates of risk are presented over the range of quartz exposures experienced. Conclusions-The quartz exposure s experienced by some men at this colliery have caused considerable pr ogression of radiographic abnormalities since exposure ended, The data accumulated offer opportunities for further more detailed analyses to inform debate on occupational limits for quartz exposures, both in co llieries and in other industries where there is exposure to quartz in mixed dust.