Occupational exposure to silica and lung cancer risk in the Netherlands

Objectives The lung cancer carcinogenicity of crystalline silica dust remains the subject of discussion. Epidemiological evidence is based on occupational cohort studies and population-based case-control studies. The aim of this study was to assess associations between male lung cancer risk and silica exposure in a population-based cohort study. Methods The study was conducted among men aged 55-69 years (n 58 279) from the Netherlands Cohort Study, which included self-reported, life-time job histories. Job titles were linked to the occupational groups of the external Finnish Job Exposure Matrix (FINJEM), including probability and level of silica exposure, each for specific time periods. 1667 incident lung cancer cases with known silica exposure status (210 exposed) were available after 11.3 years of follow-up. Risks were estimated based on a case-cohort design, and using Cox proportional hazards models. Results Adjusted for smoking and other confounders, elevated risks were observed for exposure duration (RR 1.65, 95% CI 1.14 to 2.41 for 26-51 years vs no exposure) and cumulative exposure (RR 1.47, 95% CI 0.93 to 2.33 for >= 3 vs <3 mg/m(3). year). Associations with average exposure levels were weaker. Associations were stronger for occupations with an exposure probability of >= 90%. Adjustment for asbestos exposure slightly increased the risk. Conclusions Results from this prospective population-based cohort study corroborate the classification of crystalline silica as a lung carcinogen. Associations could not be explained by smoking or by asbestos exposure.