Research links PFAS contamination of drinking water to a range of rare cancers

Communities exposed to drinking water contaminated with manufactured chemicals known as per- and polyfluoroalkyl substances (PFAS) experience up to a 33% higher incidence of certain cancers, according to new research from the Keck School of Medicine of USC .

The study, published in the Journal of Exposure Science & Environmental Epidemiologyis the first to investigate cancer and PFAS contamination of drinking water in the US

PFAS, which are used in consumer products such as furniture and food packaging, have been found in about 45% of the drinking water supply in the United States. Previous research has linked the chemicals, which break down slowly and build up in the body over time, to a range of health problems, including kidney, breast and testicular cancer.

To paint a more comprehensive picture of PFAS and cancer risk, researchers at the Keck School of Medicine conducted an ecological study, using large population-level data sets to identify exposure patterns and associated risk.

They found that between 2016 and 2021, U.S. counties with PFAS-contaminated drinking water saw higher incidences of certain types of cancer, which varied by gender. In total, PFAS in drinking water is estimated to contribute to more than 6,800 cases of cancer annually, based on the most recent data from the U.S. Environmental Protection Agency (EPA).

“These findings allow us to draw an initial conclusion about the link between certain rare cancers and PFAS,” said Shiwen (Sherlock) Li, Ph.D., a postdoctoral researcher in the Department of Population and Public Health Sciences at Keck School of Medicine and first author of the study. “This suggests that it is worthwhile to investigate each of these connections in a more individualized and precise manner.”

The findings not only provide a roadmap for researchers, but also underscore the importance of regulating PFAS. Starting in 2029, the EPA will monitor levels of six types of PFAS in drinking water, but stricter limits may ultimately be necessary to protect public health, Li said.

The toll of PFAS

To understand how PFAS contamination is linked to cancer incidence, the researchers compared two comprehensive data sets: one covering all reported cancer cases and the other containing all data on PFAS in drinking water data across the country.

Data on cancer cases between 2016 and 2021 were obtained from the National Cancer Institute Surveillance, Epidemiology and End Results Programwhile data on PFAS levels in public drinking water (2013-2024) came from the EPAs Unregulated regulatory programs for monitoring contaminants.

Li and his colleagues checked a number of factors that could influence cancer risk. At the individual level these include age and gender; at the provincial level, they excluded changes in cancer incidence due to socioeconomic status, number of smokers, prevalence of obesity, urbanicity (how urban or rural an area is), and the presence of other pollutants.

The researchers then compared cancer incidence in each county with PFAS contamination in drinking water, using the EPA’s recommended limits for each type of PFAS.

Counties where drinking water exceeded recommended maximum levels of PFAS had higher incidences of digestive, endocrine, respiratory, and mouth and throat cancers. The increase in incidence ranged from slightly increased in 2% to substantially increased in 33% (the increased incidence of mouth and throat cancer linked to perfluorobutane sulfonic acid, or PFBS).

Men in counties with contaminated drinking water had a higher incidence of leukemia, as well as cancers of the urinary system, brain and soft tissues, compared to men living in areas with unpolluted water.

Females had a higher incidence of cancer in the thyroid, mouth and throat, and soft tissues. Based on the latest available EPA data, the researchers estimate that PFAS contamination of drinking water contributes to 6,864 cases of cancer per year.

“When people hear that PFAS has been linked to cancer, it is difficult to know how relevant this is. By calculating the number of attributable cancer cases, we can estimate how many people may be affected,” Li said, including distracting from the personal and financial toll of these cases year after year.

Protection of public health

These population-level findings reveal associations between PFAS and rare cancers that would otherwise go unnoticed. Subsequently, studies at the individual level are needed to determine whether the association is causal and to investigate which biological mechanisms are involved.

On the regulatory side, the results add to mounting evidence that PFAS levels should be limited, and suggest that the proposed changes may not go far enough.

“Certain PFAS that are less studied should be monitored more, and regulators should consider other PFAS that may not yet be strictly regulated,” Li said.

The work is part of a collaboration between the Southern California Environmental Health Sciences Center and the USC Norris Comprehensive Cancer Center at the Keck School of Medicine.