Occupational risk factors for mortality from stomach and lung cancer amongrubber workers: an analysis using internal controls and refined exposure assessment

Objectives To determine occupational risk factors for stomach and lung canc er among workers in the German rubber industry. Methods A cohort of all male German rubber workers (n = 11 633) who had bee n employed for at least one year in one of five study plants and who were a live and actively employed or retired on 1 January 1981 was followed for mo rtality from 1 January 1981 through December 1991. A subcohort of n = 8933 workers who were hired after 1 January 1950 was defined to focus on working conditions in the more recent rubber industry. Work histories were reconst ructed using routinely documented 'cost centre codes' and classified into s ix work areas as well as subgroups of some work areas. The work areas are: 1. preparation of materials, 2. production of technical rubber goods, 3. pr oduction of tyres, 4. storage and dispatch, 5. maintenance, 6. others. Stan dardized mortality ratios (SMR) and Cox proportional hazards models were ca lculated for each of the work areas (>1 year of employment in the respectiv e work area). Hazard rate ratios were adjusted for age (time marker) and st ratified for year of hire (1950-1959, greater than or equal to 1960) and ye ars of employment in the respective work area (1-9 years, greater than or e qual to 10 years); years of employment were lagged 10 years to account for latency. Results Compared to the national reference population mortality from cancer of stomach (observed 44, SMR = 117; 95% CI : 85-157) and lung (observed 15 4, SMR = 123; 95% CI : 104-144) was slightly increased. Using internal cont rols we observed excess deaths from stomach cancer in work area 1 (relative risk [RR] = 2.3; 95% CI: 1.2-4.2) and from lung cancer in work areas 1 (RR = 1.7; 95% CI: 1.2-2.3), 2 (RR = 1.5; 95% CI : 1.1-2.1), and 3 (RR = 1.3; 95% CI : 0.9-1.8). On the basis of cumulative years of employment an exposu re response relationship was observed for mortality from both cancer sites among a subcategory of work area I: weighing and mixing. Increased risks we re also seen for lung cancer among workers employed in production of techni cal rubber goods. Conclusion Our results support an association between an excess mortality f rom stomach and lung cancer and employment in early production stages of ru bber manufacturing, especially weighing and mixing. This may point to an ae tiologic role of asbestos or carbon black. For stomach cancer additional ri sk factors, e.g. exposure to dust and talc, deserve further investigation. The results of the present study do not support a causal role of nitrosamin es for stomach or lung cancer.