Probing in-Situ Abiotic Defluorination of Perfluorooctanoate and Perfluorooctanesulfonate.

Perfluoroalkly substances (PFASs) have been widely used in industrial and commercial application for about 50 years as surfactants, emulsifiers, stain resistant coatings, fire retardants, and polymer additives. The PFASs of greatest current concern in the environment are perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA), which have been shown to be environmentally persistent, bioaccumulative and potentially toxic. PFOS and PFOA may enter the environment through direct discharges, from residuals in commercial products, or as terminal end products of the microbial degradation of other PFASs. Due to their exceptional stability, many conventional techniques including biological degradation, oxidation and reduction are not effective at destroying PFOS and PFOA in ambient environments. The objectives of this study are to evaluate the effect of temperature on persulfate activation and its effectiveness to defluorinate PFOS and PFOA. The overall goal is to find a suitable in situ chemical oxidation method for environmentally relevant concentrations. We quantified the effect of temperature 20 °C - 60 °C, persulfate concentration (1,000 to 20,000 mg/L), reaction time (up to 225 hours for lower temperatures), and the presence of other co-contaminants (e.g.,  chlorinated solvents and fuel constituents) on the efficacy of persulfate to defluorinate PFOS and PFOA. The apparent removal of PFOA increased with increasing temperature with 75% removal at 40 °C in 138 hours and complete loss of PFOA at 50 °C in 72 hours and at 60 °C in 48 hours. Increasing initial persulfate concentrations at 50 °C increased the rate of PFOA degradation. Low levels of shorter perfluorinated chained metabolites including perfluorobutanoic, perfluoropentanoic, perfluorohexanoic, and perfluoroheptanoic acids were generated and then subsequently degraded. Analysis of fluoride using both ion chromatography and an F-specific electrode was challenging due to the large amounts of sulfate present. Persulfate oxidation did not appear to impact PFOS concentrations.