Observed and predicted silicosis risks in heavy clay workers

Abstract

There is increasing pressure to tighten the regulation of workers' exposures to airborne silica, which can lead to severe and in some cases rapid development of disease. However, estimated risks from respirable silica vary greatly across industries. To clarify differences in risks between workers in the heavy clay and coal industries with documented exposures to respirable silica, in order to assist decisions on whether further investigation of possible differences might be justified. We applied a published equation for radiological risks from exposure to respirable silica, from a study of Scottish coalworkers (with unusually high exposures) to exposure estimates from an epidemiological study of heavy clay workers, by the same research team and using similar methods. The equation based on coalworkers' risks predicted in the heavy clay workers 31 cases of abnormalities at grade 2/1+ on the International Labour Organization scale, greatly in excess of the eight cases observed. Statistical variation is an implausible explanation (P < 0.0001). While there were some methodological differences between the studies, the disparity in risks provides some support for the case for further investigation of possible differences.