Cohort study of silicon carbide production workers

Silicon carbide is produced by a chemical reaction at high temperature between free crystalline silica and petroleum coke. The process generates airborne fibers and fibrogenic dusts such as alpha-quartz and cristobalite, which are also potentially carcinogenic. The authors report that this is the first cohort study in this industry. The study was carried out among 585 Québec silicon carbide production workers who had worked at any time from 1950 to 1980. Follow-up was to December 31, 1989, and 167 deaths were observed. The standardized mortality ratio (SMR) for all causes of death was 1.05 (95% confidence interval (CI) 0.90-1.23); for nonmalignant respiratory diseases it was 2.03 (95% CI 1.21-3.22); and for lung cancer it was 1.69 (95% CI 1.09-2.52). Controlling for smoking status using a Cox regression analysis, the risk for nonmalignant respiratory diseases and for lung cancer increased with exposure to total dust; in the highest exposure category, rate ratios (RR) were 4.08 (95% CI 1.11-14.96) for nonmalignant respiratory diseases and 1.67 (95% CI 0.57-4.83) for lung cancer. Results were in the expected direction, but the power of the study was low, because of small sample size and use of cumulative total dust as the exposure variable, which may be a poor indicator of lung irritants and other potential carcinogens in this industry, notably silicon carbide ceramic fibers.