Biotransformation of 6:2 fluorotelomer sulfonate and microbial community dynamics in water-saturated one-dimensional flow-through columns.

ABSTRACT

Nearly all per- and polyfluoroalkyl substances (PFAS) biotransformation studies reported to date have been limited to laboratory-scale batch reactors. The fate and transport of PFAS in systems that more closely represent field conditions, i.e., in saturated porous media under flowing conditions, remain largely unexplored. This study investigated the biotransformation of 62 fluorotelomer sulfonate (62 FTS), a representative PFAS of widespread environmental occurrence, in one-dimensional water-saturated flow-through columns packed with soil obtained from a PFAS-contaminated site. The 305-day column experiments demonstrated that 62 FTS biotransformation was rate-limited, where a decrease in pore-water velocity from 3.7 to 2.4 cm/day, resulted in a 21.7-26.1 % decrease in effluent concentrations of 62 FTS and higher yields (1.0-1.4 mol% vs. 0.3 mol%) of late-stage biotransformation products (C4C7 perfluoroalkyl carboxylates). Flow interruptions (2 and 7 days) were found to enhance 62 FTS biotransformation during the 6-7 pore volumes following flow resumption. Model-fitted 62 FTS column biotransformation rates (0.039-0.041 cmw3/gs/d) were ∼3.5 times smaller than those observed in microcosms (0.137 cmw3/gs/d). Additionally, during column experiments, planktonic microbial communities remained relatively stable, whereas the composition of the attached microbial communities shifted along the flow path, which may have been attributed to oxygen availability and the toxicity of 62 FTS and associated biotransformation products. Genus Pseudomonas dominated in planktonic microbial communities, while in the attached microbial communities, Rhodococcus decreased and Pelotomaculum increased along the flow path, suggesting their potential involvement in early- and late-stage 62 FTS biotransformation, respectively. Overall, this study highlights the importance of incorporating realistic environmental conditions into experimental systems to obtain a more representative assessment of in-situ PFAS biotransformation.