Irradiation-Based Degradation of Per-and-polyfluorylalkyl substances (PFAS): Isomer-Dependence, pH, and Transformation

ABSTRACT: This study investigates degradation of fourteen different per- and polyfluoroalkyl substances (PFASs) in water following treatment with gamma irradiation. Perfluorooctanoic acid (PFOA), perfluorooctanesul-3 fonic acid (PFOS), and 6:2 fluorotelomer sulfonate (6:2 FTS) were irradiated independently to investigate overall degradation, isomer-specific degradation, and transformation into shorter-chained PFAS. Independently PFOA was decreased by 81+-5%, PFOS was decreased by 70+-8 %, and 6:2 FTS was decreased by 44+-7%. Decrease in the initial PFAS present and corresponding transformation into smaller chained carboxylates were highest at pH 11, but transformation products were higher, indicating a pH-dependent transformation mechanism into shorter-chained PFAS including C2, C3, and H/F exchanged polyfluorinated alkyl substances. Thirteen different PFAS, including C4-C12 carboxylates, C4, C6, C8 sulfonates, and C8 sulfonamide were irradiated together to investigate any synergistic/antagonistic effects. In the PFAS mixture, carboxylate degradation did not depend on chain length or pH, with average total degradations of 978+-3%. Sulfonate degradation was highly dependent on chain length, with degradation totals of 4+-1% for PFBS (C4), 49+-1% for PFHxS (C6) and 61+-1% for PFOS (C8). Degradation of PFOSA was highly dependent on pH, with a total degradation of 99+-1% at pH 7 compared to 70+-3% at pH 11. Degradation rates for most PFAS were twice as high at pH 11 compared to pH 7. PFOS and PFHxS exhibited isomer-dependent degradations, with linear isomers being more resistant to degradation than their branched counterparts. These findings provide critical information for developing PFAS remediation technologies that can be applied to a wide range of PFAS including different chain lengths, functional groups, and isomers. These findings also suggest that further development of existing analytical methods is required to provide better insight into partial defluorination products.