Chlorine is used to disinfect water and is highly effective at killing bacteria and viruses. Disinfecting water is essential for preventing diseases, some of which can be serious (hepatitis A, dysentery, etc.) or even fatal: 361,000 children under the age of five die each year from diarrhea, according to the report on water recently published by the WHO and UNICEF: 30% of the world’s population lacks access to safe drinking water, and 60% do not have access to safely managed sanitation services.

Water chlorination is the most widely used method for disinfecting drinking water worldwide, including in France. The chlorine used to disinfect water reacts with naturally occurring organic matter already present in treated water to form chlorination byproducts (CBOs).

THMs are a group of chemicals that are the most prevalent among the more than 600 disinfection byproducts (DBPs) identified to date. They are the only DBPs regulated in France, with a quality limit set at 100 µg/L.

For THMs, an exposure-risk relationship published in the literature in 2011 allows for the quantification of the risk of bladder cancer associated with THM exposure in humans.

Two new studies by Santé publique France focused on THMs (an indicator of SPC contamination) and bladder cancer (a health indicator for which a relationship exists). While the first study does not provide sufficient evidence to establish a causal link between THM exposure and bladder cancer, and the ecological nature of the second study limits its scope, these results are nonetheless consistent with data in the literature documenting an association between THM concentrations in drinking water and the risk of bladder cancer.

Learn more

• Quantitative assessment of the health impact of chlorination byproducts in water intended for human consumption in France

• Relationship between the incidence of bladder cancer and exposure to chlorination byproducts in tap water in France: a geographical ecological study