Risks of silicosis in coalworkers exposed to unusual concentrations of respirable quartz.

Abstract

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 at one Scottish colliery during the 1970s were invited to a health survey. Chest radiographs were taken from 547 subjects. Classifications of these films under the International Labour Organisation (ILO) 1980 scheme were related, by logistic regression, to existing data on individual 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 on 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, and 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 experienced in the 1970s, and more strongly for quartz than for the nonquartz fraction of the dust. Estimates of risk are presented over the range of quartz exposures experienced. Conclusions-The quartz exposures experienced by some men at this colliery have caused considerable progression of radiographic abnormalities since exposure ended. The data accumulated oVer opportunities for further more detailed analyses to inform debate on occupational limits for quartz exposures, both in collieries and in other industries where there is exposure to quartz in mixed dust. (Occup Environ Med 1998;55:52-58) Keywords: silica; silicosis; coalworkers; exposureresponse; quartzThere is a shortage of reliable information on the risks of silicosis after exposure to respirable quartz, particularly as a component of respirable mixed dust. Epidemiological exposureresponse studies so far [1][2][3][4][5][6][7] give widely disparate estimates of risk, almost certainly because of deficiencies in the exposure data, 8 much of which is poorly suited, or was never intended, for the reliable estimation of risks.Some members of a colliery population were exposed, during a period in the 1970s, to unusually high concentrations of freshly cut quartz in mixed coalmine dust. The population's exposures to quartz dust had been measured in unique detail, for a substantial proportion of the men's working lives, and throughout the period when the critical exposures occurred. Health status was monitored at regular intervals while the population was exposed.We report on the results of a follow up survey of the respiratory health of survivors from this population. We describe the radiographic abnormalities which have developed, some of them severe; derive exposure-response relations for the risks of developing the silicotic abnormalities; and calculate preliminary risk predictions. THE COLLIERYIn the early 1950s the National Coal Board began the pneumoconiosis field research (PFR) programme, which has been the princ...

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