Long-term exposure to trihalomethanes in drinking water and risk of liver and kidney cancer: a population-based cohort study.

Chlorination of drinking water effectively prevents waterborne infections but also results in the formation of potentially carcinogenic disinfection by-products, including trihalomethanes (THMs). Experimental animal studies indicate that the liver and kidney are target organs for THM carcinogenicity, yet epidemiological evidence remains limited for these sites. In this study we assessed the association of long-term exposure to THMs in drinking water with incidence of liver and kidney cancer in two large Swedish population-based cohorts. We included 58,664 adults from the Swedish Infrastructure for Medical Population-Based Life-Course and Environmental Research (SIMPLER), who were supplied by public drinking water. Individual residential histories were linked to a national database of drinking-water monitoring results to estimate long-term exposure to total THMs. Incident liver and kidney cancer cases were ascertained through linkage to the Swedish National Cancer Register. Multivariable adjusted Cox proportional hazards regression models were fitted to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). Over 25 years of follow-up, 183 liver cancer cases and 347 kidney cancer cases were ascertained. Residential drinking water THM exposure was not associated with liver cancer. For kidney cancer, THM was dose-dependently associated with higher risk (p-trend = 0.047) among men with HR 1.54 (95% CI 1.00, 2.38) comparing ≥15 µg THM/L with no drinking water chlorination. No association was observed among women. Although based on a limited number of cases, these findings provide novel prospective cohort evidence on the potential association between long-term THM exposure and kidney cancer at exposure levels below current regulatory limits for drinking water. The observed association warrant confirmation in future independent studies.