Bladder cancer risks in workers manufacturing chemicals for the rubber industry

Aim To investigate bladder cancer risks in workers from a factory manufacturing chemicals for the rubber industry. Methods The mortality (1955-2005) and cancer morbidity experience (1971-2005) of a cohort of 2160 male production workers from a chemical factory in north Wales were investigated. Exposure estimates (or surrogates) were developed for four chemicals: 2-mercaptobenzothiazole (MBT), aniline, phenyl-beta-naphthylamine (PBN) and ortho-toluidine. Two analytical approaches were used, indirect standardization and Poisson regression. Results Based on mortality rates for the general population, there was a statistically significant (P < 0.01) excess mortality from bladder cancer in the 611 study subjects potentially exposed to one or more of the four chemicals being investigated (observed 11, standardized mortality ratio 278, 95% confidence interval 139-497). There was no excess bladder cancer mortality in the remaining 1555 workers. A similar contrast was also shown for bladder cancer incidence. There were 56 study subjects who had suffered from bladder cancer (malignant or benign). In simultaneous analyses of the four exposure history variables, Poisson regression showed a significant positive trend for bladder cancer risk in relation to cumulative duration of employment in the ortho-toluidine department (P < 0.05) and non-significant positive trends in relation to cumulative duration of employment in the PBN department and to cumulative exposure to MBT. Conclusions Some members of this cohort have suffered from occupational bladder cancer. Exposure to ortho-toluidine appears to be responsible for part of this excess and the manufacture of PBN and exposure to MBT may also have been involved.