Cancer risks in chemical production workers exposed to 2-mercaptobenzothiazole

Objectives: To investigate cancer risks in chemical production workers exposed to 2-mercaptobenzothiazole (MBT). Methods: The mortality (1955-2005) and cancer morbidity experience (1971-2005) of a cohort of 363 male production workers exposed to MBT while employed at a chemical factory in north Wales were investigated. Two analytical approaches were used, indirect standardisation and Poisson regression. Results: Based on national mortality rates, significant excess mortality was found for cancers of the large intestine (observed; Obs 8, standardised mortality ratio (SMR) 232, 95% CI 100 to 457) and bladder (Obs 8, SMR 374, 95% CI 162 to 737). Non-significant excesses were shown for lung cancer (Obs 27, SMR 138, 95% CI 91 to 201) and multiple myeloma (Obs 3, SMR 440, 95% CI 91 to 1287). Based on national cancer incidence rates, significant excess morbidity was found for cancer of the bladder (Obs 12, standardised registration ratio (SRR) 253, 95% CI 131 to 441) and multiple myeloma (Obs 4, SRR 465, 95% CI 127 to 1191). Non-significant excesses were shown for cancers of the large intestine (Obs 9, SRR 181, 95% CI 83 to 344) and lung (Obs 26, SRR 152, 95% CI 99 to 223). In analyses that included follow-up information on an additional 1797 plant employees not exposed to MBT, Poisson regression showed significant positive trends both for risks of cancer of the large intestine and for risks of multiple myeloma in relation to estimated cumulative exposure to MBT. Conclusions: MBT may be a human carcinogen; confident evaluation awaits findings from other studies.