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Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are widely used in many of the products we use in everyday life. As a result, PFAS in the environment are widespread, and some PFAS are known or suspected to be associated with adverse human-health effects. Sources of water used for drinking-water supplies, particularly those sources from groundwater, are highly susceptible to contamination from PFAS. Groundwater supplies 35 percent of drinking water in the United States. Although there has been much discussion on the topic, knowledge of the factors that are related to the presence of PFAS in groundwater has been lacking. To address this need, USGS scientists analyzed more than 250 samples of groundwater used for drinking water in the eastern United States to evaluate the occurrence of PFAS in groundwater and built a model to identify potential factors related to PFAS occurrence. The data revealed that 60 percent of public-supply and 20 percent of domestic-supply wells contained PFAS. In addition, many samples with PFAS also contained tritium, chloride, sulfate, dissolved organic carbon, manganese, and iron. The interactions among these constituents and other features were examined to identify the most important factors related to PFAS occurrence in groundwater used for drinking water is described in a new report: Perfluoroalkyl and Polyfluoroalkyl Substances in Groundwater Used as a Source of Drinking Water in the Eastern United States.

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Relatively little is known about potential effects of complex PFAS mixtures in drinking-water sources on human health, but better understanding of the composition of those mixtures could help inform toxicity studies. The relatively common occurrence of multiple PFAS in the samples has implications for the sum of PFAS compounds (ΣPFAS) and the complexity of PFAS mixtures in well water. ΣPFAS strongly correlated with the number of PFAS detected in the samples (Spearman’s rho = 0.91; p < 0.001) (fig. 2C).  Networks NECBS, NECBD (both in New England), and SURF have relatively large fractions of samples containing >6 PFAS (37 to 54 percent) (fig. S2A). Not surprisingly, networks with the largest numbers of co-occurring PFAS (New England has the top two in this study) also have the largest numbers of unique PFAS mixtures relative to the number of samples in the networks (fig. S2B). In New England, in the shallow aquifer (NECBS), 68 percent of the samples contain combinations of two or more PFAS that are unique to that sample. Overall, three PFAS occur in ≥80 percent of the mixtures (perfluorooctanoate [PFOA] > perfluorobutanesulfonic acid [PFBS] > perfluorooctane sulfonate [PFOS]), but the dominant PFAS in mixtures vary between networks.

Broadly, USGS researchers found that groundwater affected by modern anthropogenic activity appears to be associated with PFAS, given significant relations between PFAS detections and variables such as tritium, urban land use, VOCs, and pharmaceuticals. Modeling indicates that it is possible to predict PFAS occurrence based on the hydrologic, geochemical, and geospatial explanatory variables investigated here.

For more information about this study or the report, contact Andrea Tokranov (atokranov@usgs.gov) or Joseph Ayotte (jayotte@usgs.gov).