Quantitative relations between exposure to respirable quartz and risk of silicosis

Abstract

Aims: To reanalyse exposure-response data from a Scottish colliery to gain a more detailed knowledge of the relations between exposure to quartz and risks of silicosis in coal miners, and hence inform the debate on an appropriate occupational standard for respirable quartz. Methods: Detailed data on working times at different quartz concentrations were combined to produce exposure profiles for miners who had provided a full chest radiograph at a follow up survey. Logistic regression methods were used to model profusion of radiographic abnormalities category 2/1+, and a general exposure index was used to compare different quartz exposure measures in these models. Results: Results in 371 men aged 50-74 indicated that cumulative quartz exposure at higher concentrations resulted in proportionally greater risks of abnormalities. One g.h.m −3 of cumulative exposure at quartz concentrations greater than 2 mg.m −3 was estimated to have equivalent risks to 3 g.h.m −3 at lower concentrations. The timing of exposure relative to follow up appeared less important, although the study had limited power to compare different lag periods between exposure and effect. Conclusions: Quantification of the risks of silicosis should take account of variations in quartz exposure intensity, particularly for exposure to concentrations of greater than 1 or 2 mg.m, even if exposure is for relatively short periods. The risks of silicosis over a working lifetime can rise dramatically with even brief exposure to such high quartz concentrations. Risk estimates are given, to inform choice of control limits.T he British coal industry's Pneumoconiosis Field Research (PFR) was an extensive programme, over more than 30 years, of research into coal workers' lung disease. In general, early reports established relations with exposures to respirable coalmine dust, but did not show any consistent evidence that the quartz component of the dust was an important determinant of risk. 1-3Coal workers' pneumoconiosis (CWP) was historically relatively rare at Scottish pits in comparison with pits in other areas of Britain. However, in one Scottish colliery, exposure to unusually high levels of quartz occurred in the 1970s, due to the incursion of coal getting machinery into the sandstone seam roof and floor. Rapid radiological changes were observed in some men within several years. Access to the detailed exposure data from the PFR showed a clear relation between this progression and exposure to quartz.4 5 The colliery closed in 1981.In 1990-91, a follow up study of these miners was carried out.6 7 Logistic regression analyses of the relation between cumulative exposure to dust and the prevalence of radiographic abnormality at follow up showed that the association was strongest for exposures during the period 1970 to 1978, followed by the period from 1964 to 1970, and was stronger in relation to estimated quartz exposure than to the non-quartz component. The association with quartz exposures during the 1970s was most marked for the prevalence of more serious abno...

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