Cohort study of workers employed in an Italian tire manufacturing plant, 1962-2004

Purpose: To investigate mortality and bladder cancer incidence among workers of a tire manufacturing plant where antioxidants severely contaminated by beta-naphthylamine were never used. Methods: Mortality follow-up was performed of 9,501 workers first hired between 1962 when the plant started operations and 2000. Person-years of observation from 1962 to 2004, expected deaths, and standardized mortality ratios (SMR) were calculated. Follow-up for bladder cancer incidence from 1988 to 2003 was carried out, and standardized incidence ratios (SIR) were calculated. Multivariable (Poisson) analyses of bladder cancer incidence and mortality by duration of employment (DOE) and time since first employment (TSFE) were performed. Results: Among men, SMRs were significantly reduced for all causes, all cancers, lung cancer, cardiovascular, and ischemic heart diseases. Bladder cancer mortality and leukemia mortality were close to expectation but increased with TSFE. Seventy-two incident cases of bladder cancer were observed (SIR = 1.15; 95 % confidence interval 0.90-1.44), and multivariable analysis suggested a possible increase in rate ratios with DOE. Among women, mortality was close to expectation, but the limited number of observed deaths prevented detailed analyses. Conclusions: No significant cancer excess was observed. A suggestion of increased risks of bladder cancer and leukemias after extended TSFE was present in men, deserving consideration as exposure to carcinogens possibly occurred early in plant operation. Furthermore, this cohort of workers is still relatively young and less than 10 % have died. There was, thus, limited power to detect small increases in risk at rare cancer sites. Further epidemiological surveillance of this cohort is planned.