Bladder Cancer and Water Disinfection By-product Exposures through Multiple Routes: A Population-Based Case–Control Study (New England, USA)

BACKGROUND: Ingestion of disinfection byproducts has been associated with bladder cancer in multiple studies. Although associations with other routes of exposure have been suggested, epidemiologic evidence is limited. OBJECTIVES: We evaluated the relationship between bladder cancer and total, chlorinated, and brominated trihalomethanes (THMs) through various exposure routes. METHODS: In a population-based case–control study in New England ([Formula: see text] cases; [Formula: see text] controls), we estimated lifetime exposure to THMs from ingestion, showering/bathing, and hours of swimming pool use. We calculated odds ratios (ORs) and 95% confidence intervals (CIs) using unconditional logistic regression adjusted for confounders. RESULTS: Adjusted ORs for bladder cancer comparing participants with exposure above the 95th percentile with those in the lowest quartile of exposure (based on the distribution in controls) were statistically significant for average daily intake mg/d of total THMs [[Formula: see text] (95% CI: 1.01, 2.32), [Formula: see text]] and brominated THMs [[Formula: see text] (95% CI: 1.19, 3.29), [Formula: see text]]. For cumulative intake mg, the OR at the 95th percentile of total THMs was 1.45 (95% CI: 0.95, 2.2), [Formula: see text]; the ORs at the 95th percentile for chlorinated and brominated THMs were 1.77 (95% CI: 1.05, 2,.99), [Formula: see text] and 1.78 (95% CI: 1.05, 3.00), [Formula: see text] , respectively. The OR in the highest category of showering/bathing for brominated THMs was 1.43 (95% CI: 0.80, 2.42), [Formula: see text]. We found no evidence of an association for bladder cancer and hours of swimming pool use. CONCLUSIONS: We observed a modest association between ingestion of water with higher THMs ([Formula: see text]) and bladder cancer. Brominated THMs have been a particular concern based on toxicologic evidence, and our suggestive findings for multiple metrics require further study in a population with higher levels of these exposures. Data from this population do not support an association between swimming pool use and bladder cancer. https://doi.org/10.1289/EHP89