Biotransformation of 8:2 FTOH in AFFF-impacted soils under different redox conditions

Biotransformation of fluorotelomer-based compounds has been documented mainly under oxic conditions in various environmental matrices such as activated sludge, landfill leachate, and pristine soils. However, there remains a knowledge gap in the understanding of fluorotelomer fate in aqueous film-forming foam (AFFF)-impacted soils and aquifer materials. This is the first study to report the comprehensive biotransformation of 8:2 fluorotelomer-alcohol (8:2 FTOH) under oxic and anoxic (nitrate-, sulfate- and iron-reducing) conditions in microcosms using microbial communities stemming from AFFF-impacted sites. Under oxic conditions, ~90 mol% of spiked 8:2 FTOH was biotransformed after 14 days, and resulted in the formation of transformation products including 8:2 fluorotelomer carboxylic acid (8:2 FTCA), 8:2 fluorotelomer α,β-unsaturated carboxylic acid (8:2 FTUA), 2H-pentadecafluoro-2-nonanol (7:2 sFTOH), 2H,2H,3H,3H-pentadecafluorodecanoic acid (7:3 acid) and perfluorooctanoic acid (PFOA). Non-targeted high resolution mass spectrometry is currently being performed to identify additional transformation products and to further delineate aerobic transformation pathways. Effects of 8:2 FTOH on the shifts in microbial communities during aerobic biotransformation were evaluated using 16Sv4 rRNA gene sequencing. It was found that 8:2 FTOH and its biotransformation products impose selective pressure on AFFF-impacted microbial communities, and Afipia sp. has biotransformation and tolerance potential. Under nitrate-reducing conditions, ~90 mol% of spiked 8:2 FTOH was biotransformed after 56 days. Similar to the oxic condition, transformation products including 8:2 FTCA, 8:2 FTUA, 7:2 sFTOH, and PFOA were detected. In contrast, after a 154-day incubation, 8:2 FTOH biotransformation was relatively slow with < 5.0 mol% of initial spiked 8:2 FTOH transformed under sulfate-reducing conditions, while the biotransformation has not been detected under iron-reducing conditions. These results suggest that the bioavailable electron acceptors in natural environments play an important role in 8:2 FTOH biotransformation. Overall, this study demonstrates the potential for microbial species to degrade 8:2 FTOH and advances our understanding of PFAS fate at AFFF-impacted sites.