Chemical byproducts produced by disinfecting drinking water with chlorine are associated with an elevated risk for both bladder and colorectal cancer, according to a new review published in Environmental Health Perspectives.
In short:
- Trihalomethane (THM), a byproduct created when chlorine reacts with organic matter in water, is linked to a 33% increased risk of bladder cancer.
- THM is also linked to a 15% increased risk of colorectal cancer.
- These risks were found at exposure levels well below the regulatory limits set in both the US and European Union.
Key quote:
“Our findings suggest that [regulatory] limits may fail to protect against cancer in the general population.”
Why this matters:
Assuring that public drinking water supplies are free from bacteria and other infectious agents is critical to maintaining public health. Chlorination has been adopted as a disinfecting method across the globe due to its low cost and accessibility, but animal studies have shown that several of the most common forms of THMs are genotoxic and carcinogenic in rodents. The authors of this study highlight the critical need to improve exposure assessment in order to better understand the potential health effects of commonly used chemicals.
Related EHN coverage:
- Wastewater treatment plants fail to remove most toxic PFAS from drinking water sources
- Disadvantaged communities in California exposed to toxic chemical mixtures in tap water
- Disinfection dangers: How to avoid viruses without exposing yourself to toxics
More resources: Environmental Working Group maintains a state-by-state database of contaminants in drinking water. For more information on THM contamination, visit Tap Water Database: trihalomethanes.
Helte, Emilie et al. for Environmental Health Perspectives vol. 133, 1. Jan. 21, 2025
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