Chlorinated drinking water and micronuclei in urinary bladder epithelial cells

Background: Evidence for a causal relationship between disinfection byproducts in chlorinated water and cancer is not conclusive. This study investigates the association between disinfection byproducts in chlorinated water, as measured by trihalomethane concentration, and the frequency of micronuclei in urinary bladder epithelial cells, thereby assessing the carcinogenic potential of disinfection byproducts. Methods: A cohort study was undertaken in 1997 in 3 Australian communities with varying levels of disinfection byproducts in the water supply. Exposure was assessed using both available dose (total trihalomethane concentration in the water supply) and intake dose (calculated by adjusting for individual variations in ingestion, inhalation, and dermal absorption). Micronuclei in urinary bladder epithelial cells were used as a preclinical biomarker of genotoxicity. Results: Cells were scored for micronuclei for 228 participants, of whom 63% were exposed to disinfection by products and 37% were unexposed. Available dose of total trihalomethane for the exposed group ranged from 38 to 157 μg/L, whereas intake dose ranged from 3 to 469 μg/kg per day. Relative risk for DNA damage to bladder cells, per 10 μg/L of available dose total trihalomethane, was 1.01 (95% confidence interval [CI] = 0.97-1.06) for smokers and 0.996 (CI = 0.961-1.032) for nonsmokers. Relative risk, per 10 μg/kg per day of intake dose of total trihalomethane, was 0.99 (CI = 0.96-1.03) for smokers and 1.003 (CI = 0.984-1.023) for nonsmokers. Conclusion: This study provides no evidence that trihalomethane concentrations, at the levels we investigated, are associated with DNA damage to bladder cells.