Chlorine Disinfectant Byproducts Linked to Cancer Risks

February 26, 2025

Recent research has raised alarms about the health risks associated with trihalomethanes (THMs), a byproduct of chlorine used in drinking water disinfection. This study indicates that current regulatory limits in the United States and European Union may not adequately protect against colorectal and bladder cancer. The findings suggest a need for reassessment of these standards.

About Trihalomethanes (THMs)

THMs are formed when chlorine reacts with natural organic matter in water. The four most common THMs are chloroform, bromoform, bromodichloromethane, and chlorodibromomethane. These compounds are prevalent in chlorinated drinking water and may pose health risks.

Regulatory Limits and Health Risks

In the US, the total concentration of THMs in drinking water is limited to 80 microgrammes per litre. The EU has a slightly higher limit of 100 microgrammes per litre. In India, the acceptable limits vary by compound. Recent studies indicate that these thresholds may not sufficiently mitigate the risk of cancer, especially bladder cancer, which shows increased risk at concentrations above 41 microgrammes per litre.

Carcinogenic Properties of THMs

Previous studies have identified THMs as potential carcinogens. The World Health Organization classified chloroform as a possible human carcinogen in 1991. Research has shown that exposure to THMs can lead to tumours in animals, raising concerns about their impact on human health.

Study Overview and Findings

A comprehensive review analysed 29 studies focusing on the relationship between THM exposure and various cancers. The analysis included over 84,000 participants and brought into light a 33% increased risk of bladder cancer and a 15% increased risk of colorectal cancer associated with higher THM levels. Notably, the risk of colon cancer was at THM concentrations between 19 and 47 microgrammes per litre.

Gender Differences in Cancer Risk

The study observed differences in cancer risk between sexes. Men showed a more pronounced increase in the risk of both bladder and colorectal cancers compared to women. This may reflect biological differences in how men and women metabolise carcinogens.

Limitations of the Study

The evidence presented is classified as limited-suggestive. Most findings stem from cross-sectional studies that do not establish causality. Further experimental studies are required to confirm these associations and explore other cancers potentially linked to THM exposure.

Call for Further Research

Researchers emphasise the need for additional studies on disinfection by-products and their health implications. Specific attention is needed for cancers that are less studied, such as hormone-related female cancers and malignant melanoma.

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