Bladder cancer among chemical workers exposed to nitrogen products and other substances

To investigate further bladder cancer mortality excess based on four deaths observed among the internal comparison population of a previous historical cohort study of workers from a chemical plant in Lima, Ohio. The internal population mainly comprised workers from the Nitrogen Products (NP) Division.

The original Lima cohort was expanded to include all workers (n = 1,841) employed between 1955 and 1996. A subcohort of workers employed mainly in the NP Division (NP Subcohort) was identified and used as the primary study population and as the source of cases and controls for a matched case-control study of bladder cancer. All death records were reviewed for any mention of bladder cancer; all available personnel, medical, and insurance files were reviewed to identify any current or former employees with an existing diagnosis of bladder cancer. A qualitative exposure assessment of all cases and controls was performed to evaluate an exploratory hypothesis that the bladder cancer excess may be associated with work histories involving both NP and urea, specifically, nitric acid and urea.

We identified 96 new deaths among the expanded Lima cohort and obtained cause of death for 90. One additional bladder cancer death and one living case were identified and these were members of the original Lima cohort. The bladder cancer standardized mortality ratio (SMR) for the NP Subcohort (SMR = 3.31, 95%CI = 0.90-8.47) fell between the SMRs observed for all workers in the original and expanded Lima cohort (SMR = 3.93, 95%CI = 1.07-10.06 and 3.10, 95%CI = 1.01-7.24, respectively), but was markedly less than the SMR observed for corresponding subcohort of AN-unexposed workers in the original Lima cohort (SMR = 7.01, 95%CI = 1.91-17.96). Sparse data and a high prevalence of exposure among controls precluded an informative statistical analysis of the possible association between work histories involving both nitric acid and urea and bladder cancer risk.

This study confirms that bladder cancer mortality is elevated among persons who worked mainly in the NP Division of the Lima plant, but at a lower, less statistically significant level than indicated by the original cohort study. No occupational risk factors considered to be causally related to the bladder cancer excess could be identified by this intensive investigation; other possible reasons for the excess are suggested by the descriptive data.