Per- and polyfluoroalkyl substances (PFASs) are important environmental contaminants, yet relatively few analytical reference standards exist for this class. Nontarget analyses performed by means of high-resolution mass spectrometry (HRMS) are increasingly common for the discovery and identification of PFASs in environmental and biological samples. The certainty of PFAS identifications made via HRMS must be communicated through a reliable and harmonized approach. Here, we present a confidence scale along with identification criteria specific to suspect or nontarget analysis of PFASs by means of nontarget HRMS. Confidence levels range from level 1a—“Confirmed by Reference Standard,” and level 1b—“Indistinguishable from Reference Standard,” to level 5—“Exact Masses of Interest,” which are identified by suspect screening or data filtering, two common forms of feature prioritization. This confidence scale is consistent with general criteria for communicating confidence in the identification of small organic molecules by HRMS (e.g., through a match to analytical reference standards, library MS/MS, and/or retention times) but incorporates the specific conventions and tools used in PFAS classification and analysis (e.g., detection of homologous series and specific ranges of mass defects). Our scale clarifies the level of certainty in PFAS identification and, in doing so, facilitates more efficient identification.

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Safe drinking water at the point-of-use (tapwater, TW) is a United States public health priority. Multiple lines of evidence were used to evaluate potential human health concerns of 482 organics and 19 inorganics in TW from 13 (7 public supply, 6 private well self-supply) home and 12 (public supply) workplace locations in 11 states. Only uranium (61.9 μg L−1, private well) exceeded a National Primary Drinking Water Regulation maximum contaminant level (MCL: 30 μg L−1). Lead was detected in 23 samples (MCL goal: zero). Seventy-five organics were detected at least once, with median detections of 5 and 17 compounds in self-supply and public supply samples, respectively (corresponding maxima: 12 and 29). Disinfection byproducts predominated in public supply samples, comprising 21% of all detected and 6 of the 10 most frequently detected. Chemicals designed to be bioactive (26 pesticides, 10 pharmaceuticals) comprised 48% of detected organics. Site-specific cumulative exposure−activity ratios (ΣEAR) were calculated for the 36 detected organics with ToxCast data. Because these detections are fractional indicators of a largely uncharacterized contaminant space,ΣEAR in excess of 0.001 and 0.01 in 74 and 26% of public supply samples, respectively, provide an argument for prioritized assessment of cumulative effects to vulnerable populations from trace-level TW exposures.

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Understanding how exposure to aqueous filmforming foam (AFFF)-impacted drinking water translates to bioaccumulation of per-and polyfluoroalkyl substances (PFASs) is essential to assess health risks. To investigate spatial variability of PFAS exposure in communities near an AFFF source zone, blood serum was collected in 2018 from 220 adult residents of El Paso County (Colorado), as were raw water samples from several wells. C6 and C8 perfluoroalkyl sulfonates (PFSAs) were predominant in serum and water. PFASs were most elevated in the water district nearest the source zone (median ∑PFSA of 618 ng/L in water and 33 ng/mL in serum). A novel PFAS, unsaturated perfluorooctane sulfonate, was detected in >80% of water and serum samples at low concentrations (≤1.9 ng/mL in serum). Drinking water wells nearest the source zone displayed increased prevalence of perfluoroalkyl sulfonamide precursors not detected in serum. Serum-towater ratios were the greatest for long-chain PFASs and were elevated in the least impacted water district. Additional serum samples collected from a subset of study participants in June 2019 showed that PFAS concentrations in serum declined after exposure ceased, although declines for perfluoropentane sulfonate were minimal. Our findings demonstrate that AFFF-impacted communities are exposed to complex, spatially variable mixtures of PFASs.