Quantitative Relations Between Silica Exposure and Development of Radiological Small Opacities in Granite Workers

Abstract

The risks of radiological opacities in relation to cumulative silica exposure were estimated in 338 (206 current and 132 previously employed) male granite workers in two quarries. They represented 91 % of all currently employed and 61 % of surviving past workers who had worked for at least 1 year between 1967 and 1985. Cumulative silica exposure was estimated for each man based on quarry- and job-specific measures of past and recent dust concentrations and exposure years. The mean quartz content in respirable dust was 27%. Particle counts were converted to gravimetric equivalents of respirable quartz concentrations. Pneumoconiosis was defined as 1/1 or greater profusion of small rounded or irregular opacities as read by at least two of three experienced readers, using the most recent chest radiographs and ILO standard films. The observed prevalences of small opacities was significantly related to cumulative exposure, and adequately described by a logistic model, incorporating both age and cumulative exposure. A linear model, however, appeared to give a better fit to the data. Nevertheless, both models predicted similar risks of about 6% rounded opacities and 9% irregular opacities in the average 50 year old worker with a cumulative dust exposure of 2.0 mg m−3 year.