Increased bladder cancer risk among workers exposed to o-toluidine and aniline: a reanalysis

In 1991, the US National Institute for Occupational Safety and Health (NIOSH) reported an increased bladder cancer risk in a cohort of 1749 workers potentially exposed to o-toluidine and aniline at a chemical manufacturing plant. As additional information showed that workers in certain departments had been misclassified regarding o-toluidine exposure, we therefore conducted a reanalysis of the data using updated exposure categories.

We updated exposure categories based on information ascertained during a plant walkthrough, documents on file at the plant, interviews with current and former employees, and answers provided by company and union officials to specific questions. Bladder cancer incidence was determined through 31 December 1988 and mortality through 31 December 1994.

Thirteen cases of bladder cancer were observed versus 3.57 expected (New York State rates excluding New York City) (standardised incidence ratio (SIR) 3.64, 95% CI 1.94 to 6.23). Among workers classified as definitely exposed, increasing risks were observed for longer duration of employment (for > or = 10 years, standardised rate ratio (SRR) 6.07, 95% CI 0.77 to 48.17) and time since first employment in the exposed departments (for > or = 20 years, SRR 3.39, 95% CI 0.40 to 29.03). One bladder cancer death was observed among those definitely exposed.

These findings are comparable to the results reported earlier by NIOSH, and confirm that workers in this plant have an increased risk of bladder cancer.