Elevated cancer mortality in a German cohort of bitumen workers: extended follow-up through 2004

The mortality follow-up in a cohort of German asphalt workers covered an additional 6 years. Male workers (N = 7919) were classified into four exposure categories: (1) exposure to bitumen only, (2) to bitumen and coal tar, (3) neither to tar nor to bitumen, and (4) unknown exposure. Exposure-specific standardized mortality ratios (SMR) and associated 95% confidence intervals (CI) based on age- and calendar period-specific national mortality rates were calculated. To compare exposed and unexposed workers, relative risks were estimated by Poisson regression. By the end of 2004, 835 workers had died. The SMR for lung cancer was 1.77 (95% CI 1.46-2.16). Head and neck cancer showed an SMR of 2.36 (95% CI 1.78-3.07). Bladder cancer mortality was elevated threefold. Significantly elevated cancer-related SMRs were also found for all malignant tumors. In addition, elevated mortality rates of nonmalignant causes such as alcoholism, liver cirrhosis, and unnatural causes of deaths including accidents were observed. After stratification by exposure group, cancer mortality was elevated among bitumen-exposed and unexposed subjects. In the internal analysis, the association between lung cancer and bitumen exposure was weakened as compared with the previous follow-up (relative risk [RR] = 1.15; 95% CI 0.72-1.84). The follow-up demonstrated an excess of cancer in this cohort of asphalt workers. However, the observed mortality patterns were not clear. Although exposure to bitumen cannot be ruled out as being responsible for the observed results, a higher prevalence of alcohol and tobacco consumption may partially explain the observed risk increases. Exposure assessment in future studies should account for multiple occupational agents and nonoccupational factors to rule out that the observed differences in SMR are not due simply to random variation.