Nearly half of U.S. drinking water supplies likely contain at least one form of per- and poly-fluoroalkyl substances (PFAS), according to a recently published study conducted by the U.S. Geological Survey (USGS). 

Commonly known as “forever chemicals” because of their persistence in the environment, PFAS comprise a class of thousands of synthetic compounds that are frequently found in many different consumer, commercial, and industrial products. In recent years, PFAS have been detected at varying levels in a growing number of water supplies across the United States.

Exposure to certain levels of some PFAS could lead to adverse health outcomes in humans and animals, according to the U.S. Environmental Protection Agency (EPA), though additional research is needed to understand such outcomes in more detail.

A focus on tap water

For its study, the USGS collected tap water samples from 716 locations across the United States between 2016 and 2021, according to the article titled “Per- and polyfluoroalkyl substances (PFAS) in United States tapwater: Comparison of underserved private-well and public-supply exposures and associated health implications,” which was made available June 17 on the website of the journal Environment International. Of the samples, 269 came from private wells and 447 came from public water supplies.

Sampling water directly from the taps of consumers is part of what makes the recent study unique, says Kelly Smalling, a research hydrologist for the USGS and the lead author of the article. 

“Most state and federal monitoring programs typically measure exposure to PFAS and other pollutants at water treatment plants or in the surface water or groundwater wells that supply them,” Smalling says. “The USGS study specifically focused on collecting water directly from a homeowner’s tap where exposure actually occurs. This study also emphasized the importance of collecting data on PFAS from private wells which are not regulated by the EPA and monitored at the discretion of homeowners.”

Results vary

Tap water samples were collected from a range of areas that have experienced low, medium, and high levels of human impacts. “The low category includes protected lands; medium includes residential and rural areas with no known PFAS sources; and high includes urban areas and locations with reported PFAS sources such as industry or waste sites,” according to a July 5 news release from the USGS announcing the results of the study.

Three laboratories were used to assess the concentrations of 32 PFAS in the samples. At least one PFAS was detected in 20 percent of samples from private wells and 40 percent of samples from public water supplies, according to the article. 

In samples containing PFAS, the number of individual PFAS compounds ranged from 1 to 9, though the median was 2. Seventeen different types of PFAS were observed in the samples. The most frequent of these were perfluorobutane sulfonic acid (PFBS), at 16 percent; perfluorohexane sulfonic acid (PFHxS), at 15 percent; and perfluorooctanoic acid (PFOA), at 14 percent.

Detected concentrations for individual PFAS ranged from 0.025 to 319 ng/L, while the median was 2.88 ng/L. Cumulative PFAS concentrations in samples ranged from 0.348 to 346 ng/L, with a median of 7.00 ng/L.

This past March the EPA proposed maximum contaminant limits of 4.0 ng/L for PFOA and 4.0 ng/L for perfluorooctanesulfonic acid (PFOS). These proposed limits for PFOA and PFOS were exceeded in 6.7 percent and 4.2 percent, respectively, of all tap water samples collected, according to the article. However, the PFOA and PFOS limits were exceeded in 48 percent and 70 percent, respectively, of tap water samples when detected. 

PFAS in 45 percent of U.S. drinking water

The USGS used its data to model and estimate PFAS contamination nationwide. “Modeled results indicate that on average at least one PFAS is detected in about 45% of U.S. drinking-water samples,” according to the article. 

“Most of the exposure was observed near urban areas and potential PFAS sources,” according to the July 5 news release. “This included the Great Plains, Great Lakes, Eastern Seaboard, and Central/Southern California regions. The study’s results are in line with previous research concluding that people in urban areas have a higher likelihood of PFAS exposure. USGS scientists estimate that the probability of PFAS not being observed in tap water is about 75% in rural areas and around 25% in urban areas.”  

“We were not especially surprised by any of the findings,” Smalling says. “This study is important because not only does it provide information on exposure to PFAS broadly across the U.S. in tap water, but it also gives private well users information that they did not have previously. What we did find interesting is that exposure to PFAS was similar in samples collected from unregulated private wells and regulated public supply.”

The study “can help members of the public to understand their risk of exposure and inform policy and management decisions regarding testing and treatment options for drinking water, including drinking water providers,” Smalling says. “Results further indicate potential hotspots for PFAS exposure, which should provide drinking water providers with more information in their respective areas.”