Researchers at the Keck School of Medicine of USC have discovered a link between concentrations of man-made “persistent chemicals” in drinking water and increased risks of certain types of cancer, including those affecting the digestive system, endocrine system, respiratory system, mouth and throat.
New research from the Keck School of Medicine of USC finds that communities whose drinking water is contaminated with man-made chemicals called per- and polyfluoroalkyls (PFAS) have up to a 33 percent higher risk of certain types of cancer.
Published in the Journal of Exposure Science and Environmental Epidemiology and funded by the National Institutes of Health , this is the first study in the United States to directly examine the link between PFAS contamination in drinking water and cancer.
PFAS are widely used in consumer products such as furniture and food packaging and have been detected in about 45% of drinking water supplies in the United States. These chemicals break down slowly and build up in the body over time. Previous studies have linked PFAS exposure to a range of health problems, including kidney, breast and testicular cancer.
To paint a more complete picture of PFAS and cancer risk, Keck School of Medicine researchers conducted an ecological study, using large population-level data sets to identify patterns of exposure and associated risks. They found that between 2016 and 2021, counties across the United States with PFAS-contaminated drinking water had higher rates of several types of cancer, which varied by gender. Overall, PFAS in drinking water are estimated to contribute to more than 6,800 cancer cases each year, according to the latest data from the U.S. Environmental Protection Agency (EPA).
“These findings allow us to draw initial conclusions about the association between some rare cancers and PFAS,” said Dr. Shiwen (Sherlock) Li, a postdoctoral researcher in the Department of Population and Public Health Sciences at the Keck School of Medicine and first author of the study. “This suggests that it is worth studying each of these relationships in a more personalized and precise way.”
In addition to providing a roadmap for researchers, these findings underscore the importance of PFAS management. Starting in 2029, the EPA will regulate levels of six PFAS in drinking water, but it may eventually have to impose stricter limits to protect public health, Li said.
Harmful effects of PFAS
To understand the link between PFAS contamination and cancer incidence, the researchers compared two comprehensive data sets: one that included all reported cancer cases and the other that included all data on PFAS in drinking water nationwide. Data on cancer cases from 2016 to 2021 came from the National Cancer Institute’s Surveillance, Epidemiology, and End Results Program, while data on PFAS levels in public drinking water (2013–2024) came from the EPA’s Unregulated Contaminant Monitoring Rule programs .
Li and colleagues controlled for several factors that might influence cancer risk. At the individual level, these factors included age and sex; at the county level, they excluded changes in cancer incidence due to socioeconomic status, smoking rates, obesity status, degree of urbanization (how urban or rural the area was), and the presence of other pollutants.
The researchers then compared cancer rates in each county to PFAS contamination in drinking water, using EPA-recommended thresholds for each type of PFAS. Counties with drinking water exceeding recommended maximum levels of PFAS had higher rates of gastrointestinal, endocrine, respiratory, and mouth and throat cancers. Incidence increased from a slight 2% increase to a significant 33% increase (increased incidence of oral and pharyngeal cancer associated with perfluorobutanesulfonic acid , or PFBS).
Men living in counties with contaminated drinking water had higher rates of leukemia, as well as cancers of the urinary system, brain, and soft tissue, than men living in areas with uncontaminated water. Women have higher rates of thyroid, mouth, throat, and soft tissue cancers. According to the latest EPA data, researchers estimate that PFAS contamination in drinking water contributes to 6,864 cases of cancer each year.
“When people hear that PFAS are linked to cancer, it’s hard to know what the link is. By calculating the number of attributable cancers, we can estimate how many people might be affected,” Li said, including extrapolating the personal and financial cost of these cases over the years.
Protecting public health
These population-level findings suggest links between PFAS and rare cancers that might otherwise go undetected. Individual-level studies are next needed to determine whether this association is causal and to explore what biological mechanisms are involved.
On the regulatory front, these results add to evidence that PFAS levels should be limited and suggest that the proposed changes may not be enough.
“Some less-studied PFAS need more monitoring, and regulators should consider other PFAS that may not be as well regulated,” Li said.
Reference: “Associations of perfluoroalkyl and polyfluoroalkyl substances (PFAS) with county-level cancer incidence from 2016 to 2021 and cancer burden caused by PFAS in drinking water in the United States” by Shiwen Li, Paulina Oliva, Lu Zhang, Jesse A. Goodrich, Rob McConnell, David V. Conti, Lida Chatzi, and Max Aung, January 9, 2025, Journal of Exposure Science & Environmental Epidemiology . Research paper: 10.1038/s41370-024-00742-2
The work is part of a collaboration between the Southern California Environmental Health Sciences Center, funded by the National Institute of Environmental Health Sciences, and the USC Norris Comprehensive Cancer Center at the Keck School of Medicine.
This work was supported by a pilot grant from the Southern California Environmental Health Agency.
