Mortality in a German Cohort of Asphalt Workers with Potential Bitumen Exposure

Abstract

Fumes from heated bitumen have been associated with various types of cancer, including cancer of the lung. However, epidemiological studies conducted so far yielded only equivocal results with respect to an increased risk of cancer. To investigate the mortality of bitumen workers, the International Agency for Research on Cancer assembled an international study group investigating a cohort of workers employed in the asphalt industry. Here we report the results of the mortality follow-up of the German cohort until December 1998. Cause of mortality was determined by death certificates. Based on company information, subjects were classified to be exposed to bitumen (N = 2,535), to bitumen and (potentially) coal tar (N = 832), and neither to tar nor to bitumen (N = 2,737). 1,873 workers were classified to have unknown exposure. Standardized mortality ratios (SMR) and 95% confidence intervals (CI) were calculated, based on age- and period-specific reference data for the West German male population. In internal comparisons bitumen exposed and unexposed subjects were compared, calculating the relative risk (RR) by Poisson regression and adjusting for age and period. The German part of the multicentric bitumen cohort study comprised approximately 10,500 subjects. Included in the follow-up were 7,919 male workers who fulfilled the inclusion criteria (employment in the asphalt industry for at least one year, German citizenship). Among the entire cohort, we observed a total of 90,890 person years. By the end of 1998, 497 cohort members had died (SMR = 1.23, 95% CI 1.12–1.34). The number of deaths from lung cancer was 63 (SMR = 1.91, 95% CI 1.49–2.44). 36 workers had died from head and neck cancer (defined as oral, pharyngeal, laryngeal, or esophageal cancer; SMR = 2.47; 95% CI 1.73–3.42). Significantly elevated SMRs were also found for all malignant tumors (SMR = 1.31; 95% CI 1.12–1.54), alcoholism (SMR = 1.97; 95% CI 1.22–3.17), and unnatural causes of death (incl. accidents, SMR = 1.32; 95% CI 1.05–1.65). When we stratified the cohort according to bitumen exposure, no clear mortality pattern emerged. Cancer mortality was significantly elevated among both, the exposed and unexposed subjects. The internal comparison between bitumen-exposed and unexposed workers revealed elevated, but non-significant associations for lung cancer (RR = 1.34; 95% CI 0.76–2.37) and head and neck cancers, respectively (RR = 1.24; 95% CI 0.57–2.78). We cannot rule out that our results may have been biased by confounders that were not collected in our study, most notably smoking and alcohol consumption, as well as other occupational exposures in- and outside the asphalt industry. Currently, a nested case-control study is under way to clarify potential reasons for the elevated SMRs, taking into account the workers' smoking history, jobs outside the asphalt industry, and use of personal protective equipment when working with asphalt.

Keywords:

• asphalt workers
• bitumen
• cancer
• cohort study
• IARC
• mortality

ACKNOWLEDGMENTS

We would like to thank the German Bitumen Forum and the European Asphalt Paving Association for their support of the study. We also thank all participating companies for technical support in data collection. We are grateful to Nikolaus Becker, German Cancer Research Center (DKFZ), who provided the reference data of the West German male population, and to Igor Burstyn for collecting and registering exposure data for exposure assessment. This study was funded by Steinbruchs-Berufsgenossenschaft (STBG), Tiefbau-Berufsgenossenschaft (TBG), Arbeitsgemeinschaft der Bitumen-Industrie e.V. (ARBIT), the German Asphalt Association (DAV), and was coordinated by Paolo Boffetta, International Agency for Research on Cancer.

Notes

^A Numbers do not add up to N of the entire cohort due to subjects changing exposure categories.