Exposure to “forever chemicals” in drinking water is significantly associated with the increased risk of multiple cancers, including some not previously linked to these toxic compounds, a first-of-its-kind study shows.

PFAS (per- and polyfluoroalkyl substances) are endocrine-disrupting chemicals widely used in consumer products, from textiles and food packaging to cleaning agents. Known for their persistence in the environment, they accumulate in humans and animals and have been linked to cancer, birth defects, liver disease, thyroid disease, decreased immunity, hormone disruption, childhood obesity, and a range of other serious health problems.

Researchers from the University of Southern California’s Keck School of Medicine estimate that PFAS-contaminated water may contribute to as many as 6,864 cancer cases per year in the U.S. Communities where drinking water surpassed recommended maximum levels of PFAS had higher rates of digestive, endocrine, respiratory, and mouth and throat cancers—ranging from 2% to 33%, they say. 

“The key takeaway is that PFAS contamination in everyday water sources is a risk factor for long-term health consequences, including cancers,” the researchers say. “[Our] findings highlight the critical importance of developing effective strategies to mitigate cancer risks from exposure to PFAS through drinking water.”

This study, published in The Journal of Exposure Science & Environmental Epidemiology [January 2025], is the first large-scale analysis examining the association between PFAS-contaminated drinking water and cancer incidence across multiple organ systems using county-level U.S. data.

It follows the EPA’s establishment last year of the first enforceable drinking water standard for six PFAS types, a regulation currently being challenged by water systems and industry groups in federal court. Meanwhile, legislators in at least five states, including Vermont and California, are pushing for stricter PFAS limits.

Key findings show elevated PFAS-related cancer risk

Researchers found strong links between PFAS exposure and cancers of the mouth, throat, digestive, respiratory, and endocrine systems. Among the most notable findings:

• Perfluorobutane sulfonic acid (PFBS) had the strongest correlation, with a 33% increased risk of mouth and throat cancers.
• Perfluorohexanesulfonic acid (PFHxS) was associated with a 12% higher risk of digestive system cancers.
• Perfluoroheptanoic acid (PFHpA) correlated with a 10% increased risk of endocrine system cancers.
• Perfluorooctanoic acid (PFOA) was linked to a 6% higher risk of lung cancer.
• PFHpA and perfluoropentanoic acid (PFPeA) were tied to 3% and 4% higher risks of respiratory system cancers, respectively.

Different cancers were also associated with PFAS by gender. The data showed:

• Females: Higher incidence of thyroid, mouth, throat, and soft tissue cancers
• Males: Increased cases of urinary system (kidney and bladder), brain, leukemia, and soft tissue cancers

“The significant associations identified between PFAS in drinking water and various cancers underscore the urgent need for more comprehensive research,” says Dr. Claudia Thompson, chief of the Population Health Branch at the National Institute of Environmental Health Studies (NIEHS), which funded the study.

Increased evidence of other PFAS-related harms

Scientists have confirmed that PFAS levels in the blood come mainly from drinking water, based on tests of both tap water and blood samples. One or more types of PFAS were detected in at least 45% of the nation’s tap water, according to a 2023 report by the U.S. Geological Survey. Other recent studies have reinforced health concerns about PFAS exposure. 

One study, scheduled for publication in The International Journal of Hygiene and Environmental Health (May 2025), found that PFAS may elevate blood pressure in pregnant women, even in those who otherwise have normal blood pressure, increasing the odds of pregnancy complications. It found higher levels of PFOS linked to increased systolic blood pressure and PFHxS linked to increased diastolic blood pressure.

“Because of their characteristics, including the propensity to propagate through the food chain, accumulate and biomagnify, and ultimately pose a threat to human life, it is crucial to replace and remove these chemicals,” that study concluded.

Study methodology and limitations

Previous studies have focused primarily on PFOS and PFOA, with limited research assessing the effects of PFAS from drinking water. In the NIEHS study, researchers analyzed PFAS in public drinking water systems over two monitoring periods (2013-2015 and 2023-2024). They also examined all cancer cases reported between 2016 and 2021 across 22 cancer registries, covering about half of the U.S. population.

To refine their analysis, researchers accounted for demographic variables, air pollution, smoking rates, obesity levels, and urbanicity (how urban an area is). They note several study limitations, including:

• Inability to control for individual-level risk factors beyond age and sex
• Missing data from certain states
• Not able to account for the delay between PFAS exposure and cancer onset
• Potential exposure misclassification due to lack of personal drinking behavior data

“While these results should be interpreted cautiously, they highlight an urgent need for further research using personal health data and molecular studies,” the researchers say.

Next, they plan to conduct more detailed investigations, including an ongoing analysis of PFAS in Los Angeles drinking water.

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. Journal of Exposure Science & Environmental Epidemiology. Published online January 9, 2025. doi:10.1038/s41370-024-00742-2