Recent research from the Keck School of Medicine at the University of Southern California (USC) has revealed concerning evidence about the relationship between PFAS (per- and polyfluoroalkyl substances) contamination in drinking water and an increased incidence of certain cancers in U.S. communities. The study, which was published in the Journal of Exposure Science & Environmental Epidemiology, sheds new light on the public health risks associated with these manufactured chemicals, which are commonly found in consumer products like furniture, food packaging, and firefighting foam. This marks the first study of its kind to explore the connection between PFAS contamination in drinking water and cancer rates across the United States.
What Are PFAS?
PFAS are a group of synthetic chemicals that are resistant to heat, water, and oil, making them highly effective in a wide range of industrial and consumer applications. These substances have been used in products such as non-stick cookware, water-resistant clothing, stain-resistant fabrics, and food packaging. However, the very properties that make PFAS useful in everyday products also make them a serious environmental and health hazard. PFAS do not break down easily in the environment and can persist for years, earning them the nickname “forever chemicals.”
Due to their stability, PFAS have accumulated in drinking water supplies across the U.S. and are found in approximately 45% of public water systems, according to past research. While the chemicals are primarily associated with industrial use, they can seep into the environment through various sources, including manufacturing facilities, landfills, wastewater treatment plants, and firefighting foam. As they accumulate in the body over time, PFAS have been linked to a range of health problems, including liver damage, immune system dysfunction, developmental issues, and cancers, including kidney, breast, and testicular cancers.
A First-of-Its-Kind Study on PFAS and Cancer
In an effort to better understand the relationship between PFAS exposure and cancer, researchers at the Keck School of Medicine conducted a comprehensive ecological study using large-scale population data. The team focused on U.S. counties with known PFAS contamination in their drinking water, examining cancer incidence data from 2016 to 2021. By analyzing these datasets, they sought to identify patterns between PFAS exposure and the incidence of different types of cancer.
The study’s findings were striking: communities with higher levels of PFAS contamination in their drinking water experienced a significantly higher incidence of certain types of cancer. In fact, the research found that, on average, these communities saw up to a 33% increase in the incidence of specific cancers, depending on the type of PFAS present and the demographic characteristics of the affected populations.
The researchers discovered that PFAS exposure was linked to a higher incidence of digestive, endocrine, respiratory, and mouth and throat cancers. In some instances, the increase in cancer incidence was substantial, with some cancers showing a 33% higher rate of occurrence in areas with higher PFAS levels. For instance, exposure to perfluorobutanesulfonic acid (PFBS), a type of PFAS, was strongly associated with an elevated risk of mouth and throat cancers.
Cancer Risks Vary by Sex
One of the notable aspects of the study was the difference in cancer risk based on sex. Males living in areas with PFAS-contaminated drinking water exhibited higher incidences of leukemia, urinary system cancers, brain cancers, and soft tissue cancers compared to males in areas with uncontaminated water. On the other hand, females in PFAS-contaminated areas had a higher incidence of cancers of the thyroid, mouth and throat, and soft tissues.
These sex-specific differences highlight the need for more targeted research to better understand how PFAS exposure affects different groups of people. The researchers also noted that the association between PFAS contamination and cancer risk could vary depending on the specific type of PFAS present in the water, as different chemicals in the PFAS family may have different health impacts.
The Toll of PFAS on Public Health
Based on the study’s findings, the researchers estimate that PFAS contamination in drinking water is responsible for more than 6,800 cancer cases each year in the United States. This figure, derived from the most recent data from the U.S. Environmental Protection Agency (EPA), underscores the significant public health burden posed by these chemicals. While these numbers may seem alarming, they also serve to highlight the magnitude of the problem and the urgency of addressing PFAS contamination in drinking water.
“For many people, hearing that PFAS is linked to cancer may not seem immediately relevant. However, by estimating the number of cancer cases attributed to PFAS exposure, we can better understand the scale of the problem and the personal and financial toll these cancers take on affected individuals and their families,” said Dr. Shiwen (Sherlock) Li, the lead author of the study and a postdoctoral researcher at the Keck School of Medicine.
The study’s findings provide an important step toward understanding the scope of the cancer risks associated with PFAS contamination. However, more individual-level research is needed to establish a definitive causal relationship between PFAS exposure and cancer. Future studies should explore the biological mechanisms underlying the observed cancer risks and examine how factors such as timing and duration of exposure influence the development of disease.
The Need for Stricter Regulation of PFAS
One of the key implications of this research is the urgent need for stronger regulation of PFAS in drinking water. While the EPA has made strides in addressing the issue, particularly with the upcoming implementation of regulations to limit the levels of six types of PFAS in drinking water by 2029, researchers suggest that these measures may not go far enough to protect public health.
“Although the EPA’s regulations are a step in the right direction, certain PFAS that are less studied and not yet subject to regulation still need to be monitored more closely,” Dr. Li explained. “Regulators must also consider other forms of PFAS that may not be strictly regulated yet but still pose a significant risk to human health.”
The EPA’s current plan will set limits for six types of PFAS, but many other compounds in the PFAS family remain unregulated or inadequately studied. Dr. Li and his colleagues suggest that these less-well-known substances may also contribute to cancer risks and should be prioritized for further research and regulation.
Reference: Shiwen Li 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 (2025). DOI: 10.1038/s41370-024-00742-2