A recent study has raised concerns that current regulatory limits for chlorine byproducts in drinking water may not be sufficient to protect the general population from the increased risk of bladder and colorectal cancers. Chlorine, a widely used disinfectant since the early 20th century, reacts with natural organic matter in water, forming a group of chemical compounds known as trihalomethanes (THMs). These include chloroform, bromoform, bromodichloromethane, and chlorodibromomethane, which have been found to potentially damage DNA and increase the risk of cancer.
The study indicates that THM concentrations above 41 micrograms per liter could increase the risk of bladder cancer, a level lower than the current regulatory limits set in the US (80 μg/L) and the EU (100 μg/L). In India, the acceptable levels for individual THMs are higher, with limits ranging from 60 μg/L to 200 μg/L, depending on the specific compound. The researchers argue that these limits may fail to adequately protect the population from cancer risk.
The concerns surrounding THMs are not new. In 1974, scientists first noticed the formation of THMs during the disinfection process using chlorine in drinking water. The International Agency for Research on Cancer (IARC), a branch of the World Health Organization (WHO), classified chloroform as a possible human carcinogen in 1991, based on evidence of its carcinogenicity in experimental animals and its characteristics as a human carcinogen.
Prior studies have shown that chloroform can induce liver and kidney tumors in animals, while other THMs like bromoform and bromodichloromethane are linked to rare large intestine tumors in rats. These findings have raised alarm about the potential long-term health effects of exposure to THMs, especially in the general population.
The Swedish researchers behind the recent study conducted a meta-analysis of 29 papers examining the relationship between THM exposure and various cancers. Their analysis included data on bladder cancer, colorectal cancer, pancreatic cancer, kidney cancer, and several other types of cancer. Specifically, they found a statistically significant 33% increased risk of bladder cancer and a 15% increased risk of colorectal cancer for individuals with the highest levels of THM exposure, compared to those with the lowest.
The analysis also revealed a statistically significant risk of colon cancer at THM concentrations greater than 19 μg/L up to 47 μg/L. However, no significant link was found between THMs and rectal cancer. The researchers noted that the evidence for other cancers was not strong enough to draw firm conclusions. The increased risk of bladder and colorectal cancer was more pronounced in men, suggesting a potential sex difference in how THMs affect cancer risk.
The study’s findings are considered suggestive, as they are primarily based on observational data. This means the study highlights a potential association between THM exposure and cancer but does not definitively prove a causal relationship. The researchers also pointed out that there is insufficient experimental data and inconsistent results in studies on THMs, making further research necessary to better understand the health risks associated with these chemicals.
The researchers emphasized the need for more studies on disinfection byproducts, particularly for cancers that are less studied, such as hormone-related cancers in women and malignant melanoma. Given the potential risks highlighted by this study, there is a growing call for reevaluating the current limits on THM concentrations in drinking water and for stronger protective measures to reduce exposure to these carcinogenic compounds.
