Chemicals created during the treatment of public drinking water may be linked to a higher risk of uterine cancer, according to a large new study.
The research, published in JAMA Network Open, followed more than 53,000 women in California for almost 20 years and found that long-term exposure to certain disinfection byproducts was associated with a greater chance of developing the disease.
Although the study does not prove these chemicals cause cancer, it raises important questions about drinking water safety.
Uterine cancer, also called endometrial cancer in most cases, is the most common gynecological cancer in the United States.
Cases have been increasing for many years, and experts expect that trend to continue.
More than 69,000 women are expected to be diagnosed in the United States during 2025, and worldwide numbers could increase by nearly half over the next two decades.
The researchers wanted to know whether long-term exposure to common drinking water contaminants might contribute to this growing health problem. They focused on women from the California Teachers Study who had lived at the same address for at least 10 years, used public water systems, and had no previous cancer or hysterectomy.
Instead of collecting water samples from every home, the scientists linked each participant’s address to the local public water system. Government water quality records collected between 1990 and 2020 allowed them to estimate each woman’s average exposure over 15 years. They examined nitrate, arsenic, uranium, trihalomethanes, known as THMs, and haloacetic acids, called HAAs.
THMs and HAAs are created when chlorine reacts with natural organic material in water. Chlorine is essential because it kills dangerous bacteria and viruses that can spread serious disease. However, the treatment process can also create these unwanted byproducts.
During the study, 1,038 women developed uterine cancer. Women living in areas with the highest THM exposure had an 18% higher risk of uterine cancer than those with lower exposure. Chloroform, one type of THM, showed the strongest link with the most common form of uterine cancer, while higher HAA exposure was linked with almost twice the risk of rarer but more aggressive tumors.
Importantly, these associations were seen even when THM levels met current government safety standards. In contrast, the researchers found no clear link between uterine cancer and nitrate, arsenic, or uranium.
The scientists adjusted their analysis for factors including age, body weight, and smoking history. Even after accounting for these influences, the relationship between disinfectant byproducts and uterine cancer remained.
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Source: University of Maine.
