Per- and poly-fluoroalkyl substances (PFAS) in United States tap water

Models suggest at least one PFAS detected in 45% of US drinking water samples

The quality of drinking water is a growing concern in the United States (US), highlighting the importance of assessing exposures and potential health effects at the point of use. Per- and poly-fluoroalkyl substances (PFAS) in drinking water are a national issue, but there is limited information about PFAS in residential tap water, especially from private wells. To address this gap, U.S. Geological Survey researchers conducted a nationwide study comparing human exposure to PFAS in unregulated private well water and regulated public supply tap water. They collected tap water samples from 716 locations (269 private wells and 447 public supply sources) across the US between 2016 and 2021, including three locations where multiple samples were taken over time.

The concentrations of PFAS were assessed by three laboratories, and the results were compared with land-use and potential-source metrics to understand the factors contributing to contamination. The number of different PFAS detected ranged from 1 to 9 (median: 2), with cumulative concentrations (total of all detected PFAS) ranging from 0.348 to 346 ng/L. Seventeen different PFAS were detected at least once, with PFBS, PFHxS, and PFOA being the most frequently observed substances in approximately 15% of the samples. Overall, the profiles of PFAS and the estimated median cumulative concentrations were similar between private wells and public supply tap water across the US. The researchers estimated that at least one PFAS could be detected in about 45% of drinking water samples in the US. The likelihood of detection varied across different regions, but there was limited variation over time in terms of concentrations and the number of PFAS detected.

Benchmark screening methods indicated that potential human exposure risk was mainly driven by PFOA and PFOS, whenever they were detected. The cumulative concentrations of PFAS and the number of PFAS detected were related to information about potential sources and land use; however, specific relationships with individual PFAS were limited, likely due to infrequent detection and higher detection limits. The information generated from this study underscores the need for further assessments of the cumulative health risks associated with PFAS as a class, as well as their interactions with other co-occurring contaminants. This is particularly important for unmonitored private wells where limited or no information is currently available.

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