The use of aqueous film-forming foam (AFFF) at military, industrial, and municipal sites has resulted in widespread contamination with per- and polyfluoroalkyl substances (PFAS). A commonly reported ingredient, as well as one of the major transformation products of other ingredients in AFFF formulations, is 6:2 fluorotelomer sulfonate (6:2 FTS). Although 6:2 FTS has been widely detected in soil and groundwater samples at AFFF-impacted sites, little is known about its biotransformation. For the first time, the biotransformation of 6:2 FTS was investigated in AFFF-impacted soil under oxic and anoxic conditions. Surface soils collected from two locations, Robins Air Force Base (AFB) and the former Loring AFB, were used in this study. After a 154-day incubation, 6:2 FTS was readily biotransformed in Loring AFB microcosms with only ~0.2 mol% remaining. Stable transformation products including 5:3 fluorotelomer carboxylic acid (5:3 acid, 8.9 mol%), perfluoropentanoic acid (PFPeA, 0.7 mol%), and perfluorohexanoic acid (PFHxA, 3.1 mol%), and intermediates including 6:2 fluorotelomer α,β-unsaturated carboxylic acid (6:2 FTUA, 2.1 mol%) and 5:2 fluorotelomer secondary alcohol (5:2 sFTOH, 11.5 mol%) were detected. In contrast, 6:2 FTS aerobic biotransformation has not been detected in Robins AFB microcosms after a 98-day incubation. Additional microcosms constructed with Loring AFB soil are currently underway to investigate 6:2 FTS biotransformation under nitrate-, sulfate-, and iron-reducing conditions, respectively. Subsequent studies will focus on measuring 6:2 FTS biotransformation kinetics in biologically-active columns packed with Loring AFB soil under dynamic flow conditions. This work sheds light on the fate of AFFF-related products and their major transformation products under various redox conditions.

Biotransformation of 6:2 fluorotelomer sulfonate in AFFF-impacted soil under oxic and anoxic conditions

ACS Fall 2021

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