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Byproducts of Water Chlorination and the Risk of Bladder Cancer

Chlorine used to disinfect tap water reacts with naturally occurring organic matter already present in treated water to form disinfection byproducts (DBPs). Trihalomethanes (THMs) are a group of chemicals among more than 600 disinfection byproducts currently identified and the only ones regulated in France (100 μg/L). Santé publique France has just published two reports examining the link between trihalomethanes (THMs) and bladder cancer in France.The first is a quantitative health impact assessment (QHIA) designed to determine the proportion of bladder cancers attributable to water chlorination byproducts. It used an exposure-risk relationship published in 2011 for humans. Current exposure was estimated based on THM analyses from health monitoring (2005–2011), and past exposure (1960–2000) was modeled. The French population supplied with surface water is half as exposed as in the past, but remains twice as exposed as the population supplied with groundwater. A total of 18% of bladder cancer cases are estimated to be attributable to chlorination byproducts (1,600 [500, 2,700] cases per year). The second is an ecological study cross-referencing data from cancer registries and THM exposure data across the 11 departments covered by a general cancer registry between 1998 and 2011. It analyzes the relationship between the incidence of bladder cancer and exposure to chlorination byproducts (CBPs) present in tap water. Adjustments were made for smoking and recognized risk factors for this cancer. The analysis shows a positive association for THMs in surface water, bordering on statistical significance. The observed risk is approximately four times lower than previously published individual risks, but the failure to account for residential history may underestimate it. These results are consistent with data in the literature documenting an association between THM concentrations in drinking water and the risk of bladder cancer. Chlorine disinfection of water helps prevent diseases, some of which can be serious or even fatal: 361,000 children under the age of five die each year from diarrhea, according to the WHO and UNICEF. The microbiological risk caused by inadequate disinfection is greater than the chronic risk from disinfection byproducts—whose assessment is imperfect using current methods—but should serve as an incentive to limit exposure to disinfection byproducts.