Transformation of per-and polyfluoroalkyl substances from groundwater impacted by aqueous film forming foam using commonly occurring co-metabolic organisms

Per- and polyfluoroalkyl substances (PFAS) is a large (>15,000) group of fluorinated organic compounds used extensively in commercial and industrial applications including Aqueous Film Forming Foam (AFFF) for fire-fighting. Fire-fighting and fire training activities at all major airports and military bases across the US and worldwide have led to extensive groundwater (GW) contamination. There is growing concern over recalcitrance, widespread use, and deleterious health effects at low concentrations. This prompted the Environmental Protection Agency to issue stringent drinking water standards for 6 perfluorinated compounds. Previous literature established larger PFAS that are not perfluoroalkyl acids (PFAAs) can transform to terminal PFAAs, (including the regulated six) and therefore are referred to as PFAA-precursors. This transformation is suspected to be co-metabolic (fortuitous) as few, if any, bacteria have been found that can metabolically degrade perfluorinated PFAS. Most of the work up to the beginning of these studies was performed on single compounds and did not specifically address AFFF contaminated aquifers nor explored known co-metabolic bacteria from previous bioremediation work. This collection of work presents, for the first time, studies looking at transformation both with bioaugmented and naturally occurring bacteria transforming PFAS from actual site-material impacted by the historical use of AFFF. The use of high-resolution mass spectrometry was used to identify PFAS not commonly reported due to lack of analytical standards. Biotransformation pathways were proposed and follow-up studies with pure-compounds were conducted to validate results from the AFFF microcosms. The type of studies presented here can be broken into three main categories; AFFF-GW microcosms bioaugmented with known co-metabolic cultures and grown for 4 and 8 weeks, AFFF soil-GW microcosms stimulated with hydrocarbon substrates known to induce co-metabolic enzymes (oxygenase enzymes) for 8 and 16 weeks, and lastly pure-compound studies using a single PFAS and a known bacterial culture to observe transformation products in a simpler matrix for 4 and 8 weeks. PFAA-precursors were transformed across all three study designs and all bacteria used were able to transform some amount of the initial PFAA-precursor present. The most prolific transformation was observed in the mixed methanotrophic consortia and the naturally stimulated bacteria grown on octane. PFAA-precursors synthesized by both fluorotelomer and electrochemical fluorination chemistry were both observed to transform and produce intermediates as well as PFAAs. All of the regulated PFAAs were produced from larger, unregulated PFAS in this work emphasizing the importance of addressing PFAA-precursors in site assessments and of monitoring PFAS without analytical standards.