In the first study of its kind, researchers from the University of Southern California’s (USC’s) Keck School of Medicine analyzed large population-level datasets to identify patterns of exposure to per- and polyfluoroalkyl substances (PFAS) and determine risks. The findings showed that communities exposed to PFAS-contaminated drinking water experience up to 33 percent higher incidence of certain cancers.

The new study adds to a mounting body of evidence pointing to the health harms of dietary exposure to PFAS. Also known as “forever chemicals” due to their inability to break down in the environment or the human body, PFAS are used in consumer products like food packaging and nonstick pans, and have been linked to cancers, liver and heart damage, immune and developmental damage to infants and children, and other effects. Their presence in the environment, foods, water, and humans have been observed. Notably, in April 2024, the U.S. Environmental Protection Agency (EPA) finalized drinking water standards for certain PFAS.

Published in the Journal of Exposure Science and Environmental Epidemiology, the USC study involved an analysis of county-level, age-adjusted cancer incidence (2016–2021) from the U.S. National Cancer Institute’s (NCI’s) Surveillance, Epidemiology, and End Results (SEER) Program. Cancer incidence data was controlled for a number of factors that could influence cancer risk. The SEER data was compared against data on PFAS levels in public drinking water systems from the Third and Fifth Unregulated Contaminant Monitoring Rule (UCMR 3 and UCMR 5), through which EPA collects data on drinking water contaminants that do not yet have health-based standards set under the Safe Drinking Water Act. Covering 2013–2015, UCMR 3 measured PFOS, PFOA, PFNA, PFHxS, PFHpA, and PFBS. Data for UCMR 5 was collected from 2023–2025 and expanded measurements to include PFBA, PFHxA, PFPeA, and PFPeS.

The USC researchers estimated that PFAS-contaminated drinking water may contribute to nearly 6,900 cancer cases per year nationwide. Increased rates of digestive, endocrine, respiratory, and mouth and throat cancers, ranging from 2–33 percent, were observed in communities where drinking water surpassed recommended maximum levels of PFAS. The strongest association was observed between PFBS and mouth and throat cancers.

Additionally, males in communities with PFAS-contaminated water systems had a higher incidence of leukemia, as well as cancers of the urinary system, brain, and soft tissues. Females exposed to the chemicals through their drinking water had higher incidence of cancers in the thyroid, mouth and throat, and soft tissues.

The researchers call for further, individual-level studies to determine whether the link they identified in their research is causal, and to explore what biological mechanisms are involved.

Shiwen (Sherlock) Li, Ph.D., Postdoctoral Researcher in the USC Keck School of Medicine’s Department of Population and Public Health Sciences, is the first author on the study. The research was supported by a pilot grant from the Southern California Environmental Health Sciences Center and NCI.