Cancer incidence among workers in the Norwegian silicon carbide industry

The presence of silicon carbide (SiC) fibers in the SiC smelter work environment has suggested a possible cancer hazard. The authors studied cancer incidence among 2,620 men employed for more than 6 months in three Norwegian SiC smelters. Follow-up from 1953 to 1996 revealed an overall excess risk of lung cancer (standardized incidence ratio = 1.9, 95% confidence interval (CI): 1.5, 2.3) and an elevated risk of stomach cancer (standardized incidence ratio = 1.5, 95% CI: 1.1, 2.0). Both standardized incidence ratio and Poisson regression analyses showed that lung cancer risk increased according to cumulative exposure to total dust, SiC fibers, SiC particles, and crystalline silica. The standardized incidence ratio for the upper SiC fiber exposure category was 3.5 (95% CI: 2.1, 5.6) when exposure was lagged by 20 years, while the Poisson regression analysis showed a rate ratio of 4.4 (95% CI: 2.1, 9.0). Smoking did not seem to be an important confounder. The excess risk of lung cancer may be explained by exposure to SiC fibers, but a strong correlation between the different exposures made it difficult to distinguish between them.