Synthetic chemicals called per- and polyfluoroalkyl substances (PFAS) have been accumulating in the environment since their introduction in the 1940s, as they are highly resistant to degradation. The general population is exposed to PFAS via drinking water in many parts of the US, and these chemicals have been linked to many health outcomes, including various cancers. PFAS disrupt the endocrine system and lipid metabolism and are listed as Group 1 carcinogens (possibly carcinogenic to humans) by the International Agency for Research on Cancers. A recent study published in the Nature Journal of Exposure Science and Environmental Epidemiology in 2025 investigated the association between the incidence of new cancers between 2016 and 2021 and PFAS detected in drinking water.
Li and colleagues used county-level cancer incidence data from the US National Cancer Institute’s Surveillance, Epidemiology and End Results database and PFAS levels in drinking water published by the US Environmental Protection Agency (EPA) to determine if there was an association between PFAS detected in drinking water and cancers in specific organ systems. PFAS in drinking water was defined as a level detected above the maximum containment levels of PFAS, which are legally enforceable limits for contaminants in drinking water. The study included approximately half of the US population across 1,080 counties and found that four types of cancer were positively associated with the detection of PFAS in drinking water. Higher incidence of cancers of the digestive system, endocrine system, oral cavity and pharynx, and respiratory system were all found to be associated with PFAS detected in drinking water.
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Leading data and analytics company GlobalData epidemiologists forecast that the number of diagnosed incident cases across many types of cancer will increase over the next several years. Diagnosed incident cases of gastric cancer are forecast to increase from approximately 28,000 cases in 2019 to 33,500 cases in 2029 at an annual growth rate (AGR) of approximately 2.0%. GlobalData epidemiologists expect diagnosed incident cases of colorectal cancer to increase from 142,000 cases in 2021 to 161,000 cases in 2031. Diagnosed incident cases of thyroid cancer were also forecast to grow to approximately 81,000 cases in 2024 at an AGR of over 5.0% from 2014. Additionally, diagnosed incident cases of oropharyngeal cancer are forecast to increase from 1,700 cases in 2016 to 2,200 cases in 2026 at an AGR of approximately 3.0%. GlobalData epidemiologists do not predict significant change in the diagnosed incident cases of non-small cell lung cancer from 2021-2031 but diagnosed incident cases of small cell lung cancer are expected to increase at an AGR of approximately 2.0% from 33,000 cases across the same forecast period. PFAS levels in drinking water in the US are monitored by the EPA as legislated in the National Primary Drinking Water Regulation. Currently, this sets the maximum containment level from PFAS at four nanograms per litre (parts per trillion) for two types of PFAS, and ten parts per trillion for the other four PFAS included. Some PFAS currently have a designation as hazardous substances in the US. These regulations may change under the Trump administration as there have been signals that the EPA strategy will change course.
PFAS in drinking water and its association with incident cancer cases is cause for concern because this exposure pathway puts large populations at risk, even in areas far from direct sources of contamination. Li and colleagues caution that their study may in fact underestimate the association between PFAS exposure in drinking water and cancer, as data in many parts of the US was limited or missing. Additionally, more study is needed to fully understand the mechanism by which PFAS cause cancer and how best to mitigate their impact on humans. As PFAS do not degrade in the environment, it is possible that their effects on cancer incidence will become more pronounced as exposure increases. Regardless, this study is an important signal that PFAS and other environmental hazards in drinking water may pose a threat to the general population and suggests that urgent study is needed to better understand them.
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