OBJECTIVES:An update of a study of workers exposed to 2-mercaptobenzothiazole (MBT) at a rubber chemicals plant in Nitro, West Virginia is reported. The earlier study found high rates of lung cancer, prostate cancer, and bladder cancer in these workers who also had potential exposure to 4-aminobiphenyl (PAB), a potent bladder carcinogen.METHODS:This cohort mortality study examines the mortalities of 1059 full time white male production workers employed at the plant from 1955 to 1977. A detailed exposure assessment was done on the 600 workers with exposure to MBT. Nine years of additional follow up to the previous study are added.RESULTS:It was found that MBT workers have expected rates of lung (standardised mortality ratio (SMR) = 1.0 95% confidence interval (95% CI) 0.7 to 1.5) and prostate (SMR = 0.9, 95% CI 0.2 to 2.3) cancer. There was an excess of bladder cancer among MBT workers who had definite exposure to PAB (SMR = 27.1, 95% CI 11.7 to 53.4), and MBT workers with potential exposure to PAB (SMR = 4.3, 95% CI 1.4 to 10.0). However, there were no deaths from bladder cancer among workers with no exposure to PAB (SMR = 0.0, 95% CI 0.0 to 24.7), although there were only 0.2 deaths expected.CONCLUSIONS:The potential confounding of exposure to an unknown portion of PAB in the MBT workers makes it impossible to evaluate risk of bladder cancer in this population at this time. However, exposure to MBT does not seem to increase the risk of most cancers including cancers of the lung and prostate.

Epidemiologic studies on dioxin, specifically 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), have not consistently found an increased cancer risk. This study examines mortality rates for 754 employees at a chemical plant after an accident in 1949 in which 122 workers developed chloracne from high exposure to TCDD. We also examined exposure to 4-aminobiphenyl, a potential bladder carcinogen. Although the numbers are small, and confounding factors cannot be ruled out, workers exposed to 4-aminobiphenyl who developed chloracne from the accident had increased mortality rates from soft tissue sarcoma, bladder cancer, and respiratory cancer. All soft tissue sarcomas occurred among workers with potential 4-aminobiphenyl exposure, whereas no soft tissue sarcomas occurred among workers with TCDD exposure alone. In these workers, exposure to TCDD alone at levels great enough to cause chloracne was not associated with increased cancer rates.