Mortality experience of employees exposed to 2-mercaptobenzothiazole at a chemical plant in Nitro, West Virginia.

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Abstract
Mortality trends for 1059 production workers at a rubber chemicals plant in Nitro, West Virginia were examined to find whether they had increased mortality from cancer associated with exposure to 2-mercaptobenzothiazole (MBT). This chemical and its derivatives are vulcanising agents that have been manufactured at the plant since 1935. Analyses were conducted on MBT exposed employees by cumulative exposure and time since first exposure, and were also stratified by past assignment to p-aminobiphenyl (PAB) related departments; PAB is a potent bladder carcinogen that was used at the plant between 1935 and 1955. There was an excess of bladder cancer in MBT workers who had PAB related assignments (standardised mortality ratio (SMR) = 3200, 95% confidence interval (95% CI) 1286-6593). In employees without a job assignment with exposure to PAB, there were no associations between exposure to MBT and increased rates of most malignant neoplasms. The SMR for bladder cancer was increased based on three deaths (SMR = 455, 95% CI 94-1328), although these results were too few to evaluate trends by cumulative exposure category. The possibility of confounding by PAB for exposures for jobs that covered all areas of the plant for these three cases must be considered in the light of the potency of PAB as a bladder carcinogen. There were no deaths from bladder cancer among MBT workers hired after the end of manufacture and use of PAB, but the expected number of deaths was only 0.03.