Per-and polyfluoroalkyl substances (PFASs) are widely used anthropogenic chemicals. The PFAS class includes almost 5000 registered compounds, but analytical methods are lacking for most PFASs. The total oxidizable precursor (TOP) assay was developed to indirectly quantify unknown PFASs that are precursors to commonly measured perfluoroalkyl acids. To understand the behavior of recently identified per-and polyfluoroalkyl ether acids (PFEAs), including fluorinated replacements and manufacturing byproducts, we determined the fate of 15 PFEAs in the TOP assay. Ten perfluoroalkyl ether acids and a chlorinated polyfluoroalkyl ether acid (F-53B) were stable in the TOP assay and represent terminal products that are likely as persistent as historically used PFASs. Adding perfluoroalkyl ether acids and F-53B to the target analyte list for the TOP assay is recommended to capture a higher percentage of the total PFAS concentration in environmental samples. In contrast, polyfluoroalkyl ether acids with a -O-CFH-moiety were oxidized, typically to products that could not be identified by liquid chromatography and highresolution mass spectrometry. Application of the TOP assay in its proposed enhanced form revealed high levels of PFEAs, the presence of precursors that form perfluoroalkyl carboxylic acids, and the absence of precursors that form PFEAs in surface water impacted by PFAScontaining wastewater discharges.

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Per- and polyfluoroalkyl substances (PFASs) are widely used anthropogenic chemicals. For environmental and toxicological analysis, it is important to understand the stability of PFASs, including novel per- and polyfluoroalkyl ether acids (PFEAs), in commonly used solvents. In this study, we investigated the effects of PFAS characteristics, solvent type, water-to-organic solvent ratio, and temperature on the stability of 21 PFASs including 18 PFEAs. None of the studied PFASs showed measurable degradation in deionized water, methanol, or isopropyl alcohol over 30 days; however, nine PFEAs degraded in the polar aprotic solvents acetonitrile, acetone, and dimethyl sulfoxide (DMSO). PFEA degradation followed first-order kinetics, and first-order rate constants increased with increasing temperature and with decreasing water-to-organic solvent ratio. Monoethers with a carboxylic acid functional group adjacent to a tertiary carbon (>CF-COOH) degraded more rapidly than multiethers in which the carboxylic acid moiety was adjacent to repeating −CF2O– groups. In contrast, monoethers with a carboxylic acid moiety adjacent to a secondary carbon (−CF2-COOH) were stable in all tested solvents. Using high-resolution mass spectrometry, we determined that PFEAs with a >CF-COOH group were stoichiometrically decarboxylated in aprotic solvents and formed products with a >CFH group; e.g., hexafluoropropylene oxide-dimer acid (HFPO–DA or GenX), HFPO-trimer acid, and HFPO-tetramer acid were stoichiometrically converted to Fluoroethers E-1, E-2, and E-3, respectively. PFEA degradation results highlight the importance of solvent choice when preparing dosing solutions and performing extractions for environmental and toxicological assessments of PFEAs.

Per- and polyfluoroalkyl substances (PFAS) are widely used anthropogenic chemicals. Because of the strength of the carbon–fluorine bond, PFAS are not destroyed in typical water treatment processes. Sulfate (SO4 •–) and hydroxyl (•OH) radicals can oxidize some PFAS, but the behavior of per- and polyfluoroalkyl ether acids (PFEAs) in processes involving SO4 •– and •OH is poorly understood. In this study, we determined second-order rate constants (k) describing the oxidation of 18 PFAS, including 15 novel PFEAs, by SO4 •– and •OH. Among the studied PFAS, 6:2 fluorotelomer sulfonate reacted most readily with •OH [k •OH = (1.1–1.2) × 107 M–1 s–1], while polyfluoroalkyl ether acids containing an -O-CFH- moiety reacted more slowly [k •OH = (0.5–1.0) × 106 M–1 s–1]. In the presence of SO4 •–, polyfluoroalkyl ether acids with an -O-CFH- moiety reacted more rapidly [k SO4 •– = (0.89–4.6) × 106 M–1 s–1] than perfluoroalkyl ether carboxylic acids (PFECAs) and a chloro-perfluoro-polyether carboxylic acid (ClPFPECA) [k SO4 •– = (0.85–9.5) × 104 M–1 s–1]. For homologous series of perfluoroalkyl carboxylic acids, linear and branched monoether PFECAs, and multiether PFECAs, PFAS chain length had little impact on second-order rate constants. SO4 •– reacted with the carboxylic acid headgroup of perfluoroalkyl carboxylic acids and PFECAs. In contrast, for polyfluoroalkyl ether carboxylic and sulfonic acids with an -O-CFH- moiety, the site of SO4 •– attack was the -O-CFH- moiety. Perfluoroalkyl ether sulfonic acids were not oxidized by SO4 •– and •OH under the conditions evaluated in this study.

Granular activated carbon effectively controlled disinfection byproduct formation and calculated toxicity, especially at high influent bromide levels.