Aqueous film-forming foams (AFFFs) are water-based chemical mixtures applied to liquid-fuel fires to extinguish flames and prevent fuel re-ignition.  Poly- and perfluorinated alkyl substances (PFASs) are important AFFF constituents responsible for the surface tension reduction properties that facilitate rapid fire suppression. Because perfluorocarboxylates and perfluorosulfonates are persistent in the environment and have adverse effects on human health, particularly the C8 homologs PFOA and PFOS, their use in AFFF has been phased out. Little is known, however, about the environmental fate of AFFF PFASs that possess larger ionic alkyl groups and ethyl moieties adjacent to their perfluoroalkyl chains, such as fluorotelomer thioamidosulfonate (FtTAoS or Lodyne�), a PFAS present in several widely-used AFFF formulations.Here, the aerobic biotransformation of 6:2 FtTAoS was investigated in soil microcosms constructed with AFFF-impacted top-soil from a U.S. military base and enriched with an FtTAoS-containing AFFF formulation. 6:2 FtTAoS was biotransformed in live microcosms during two AFFF doses administered over a 60 day incubation to form 6:2 fluorotelomer sulfonate (6:2 FtS), perfluorohexanoate, perfluoropentanoate, and perfluorobutanoate. Two additional intermediate products were identified through LC-MS/MS molecular ion scans and confirmed via Orbitrap high resolution mass spectrometry (HRMS). Molecular ions 602 and 618, which contain 1 and 2 oxygen additions to the thioether functional group of 6:2 FtTAoS, respectively, were identified. Time-course LC-MS/MS analyte responses of the molecular ions in the microcosms confirmed that while the form with a single oxygen addition was present in both live and autoclaved microcosms, its production was only observed in live cultures. The double oxygen form was only present in live microcosms, and its production was observed over the incubation period. This suggests that the first two steps in the transformation of 6:2 FtTAoS were sequential oxygen additions to the thiol group, followed by dealkylation and formation of 6:2 FtS.

Aerobic biotransformation of fluorotelomer thioamidosulfonate (Lodyne�) in AFFF

248th National Meeting (2014)

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