Drinking water contaminated with ‘forever chemicals’ may be tied to increased cancer risks

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The risk of developing certain cancers may be higher for people exposed to per- and polyfluoroalkyl substances (PFAS) — also known as “forever chemicals” — in U.S. drinking water, according to a first-of-its-kind ecological study led by researchers at the University of Southern California’s Keck School of Medicine.

PFAS are endocrine disruptors widely used in consumer products that persist in the environment and human body. While these manufactured chemicals have been linked to serious health issues including cancer, the researchers say this is the first study to examine the potential association between cancer and public water systems. Drinking water is a significant way people are exposed to PFAS, recent research has shown, based on comparisons of tap water and human blood samples.

The findings, published today [Jan. 9, 2025] in the Journal of Exposure Science and Environmental Epidemiology, suggest—albeit cautiously—that PFAS contamination of drinking water could contribute to nearly 7,000 incidences of cancer cases in the U.S. per year, based on the most recent EPA list of unregulated contaminants that are required to be monitored. 

The study also comes nine months after the federal agency announced a final National Primary Drinking Water Regulation, which sets legally enforceable Maximum Contaminant Levels (MCL) for six PFAS.

“The significant associations identified between PFAS in drinking water and various cancers, including those of the endocrine, digestive, oral cavity, pharynx, skin, and respiratory systems, underscore the urgent need for more comprehensive research,” the researchers say. “Given the recent regulation of PFAS in drinking water by the US EPA, our findings highlight the critical importance of developing effective strategies to mitigate cancer risks from exposure to PFAS through drinking water.”

Researchers looked at PFAS in drinking water measured in two waves (2013–2015 and 2023–2024) and county-level cancer incidence between 2016 and 2021. Cancer data came from the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) Program, which includes cancer registries covering about half of the U.S. population. Information about PFAS levels in public drinking water was obtained from the EPA.

According to the study, the increase in cancer risk (incidence rate ratio, or IRR) ranged from 1.02 to 1.33. The strongest link was between perfluorobutane sulfonic acid (PFBS) and mouth and throat cancers, with an IRR of 1.33—meaning the risk was 33% higher.

That was followed by an association between perfluorononanoic acid (PFNA) and perfluoroheptanoic acid (PFHpA) to cancers in the endocrine system, mostly thyroid cancers. 

While more research is needed, the study suggests drinking water contaminated by various PFAS may lead to an increased risk of leukemia and cancers of:

Researchers also found that different cancers appeared to be associated with PFAS based on sex. For men, PFAS was linked to cancers in the urinary system, brain, leukemia, and soft tissues. For women, the chemicals were linked to cancers in the thyroid, mouth/throat, and soft tissues.

The study accounted for air pollution, obesity prevalence, smoking rates, and urbanicity (how urban an area is). However, researchers say they could not control for individual-level variables except for age and sex or for potential confounders specific to each cancer type, among other factors.

The researchers say several states were not included in the SEER database, which may not adequately capture areas with the highest levels of PFAS contamination in drinking water.

“This limitation might partly explain the lack of observed associations in our study for cancers such as kidney and testicular cancers found in previous studies, as areas with the most severe contamination, such as Michigan, and potential health effects could be underrepresented,” they say, adding that people may not drink tap water “in regions where PFAS contamination or water contamination is prevalent.”

Reference

Li S, Oliva P, Zhang L, et al. Associations between per-and polyfluoroalkyl substances (PFAS) and county-level cancer incidence between 2016 and 2021 and incident cancer burden attributable to PFAS in drinking water in the United States. Nature News. January 9, 2025.