Biotransformation of PFAA Precursors by Oxygenase-Expressing Bacteria in AFFF-Impacted Groundwater and in Pure-Compound Studies with 6:2 FTS and EtFOSE

Numerous US drinking water aquifers have been contaminated
with
per- and polyfluoroalkyl substances (PFAS) from fire-fighting and
fire-training activities using aqueous film-forming foam (AFFF). These
sites often contain other organic compounds, such as fuel hydrocarbons
and methane, which may serve as primary substrates for cometabolic
(i.e., nongrowth-linked) biotransformation reactions. This work investigates
the abilities of AFFF site relevant bacteria (methanotrophs, propanotrophs,
octane, pentane, isobutane, toluene, and ammonia oxidizers), known
to express oxygenase enzymes when degrading their primary substrates,
to biotransform perfluoroalkyl acid (PFAA) precursors to terminal
PFAAs. Microcosms containing AFFF-impacted groundwater, 6:2 fluorotelomer
sulfonate (6:2 FTS), or N-ethylperfluorooctane sulfonamidoethanol
(EtFOSE) were inoculated with the aerobic cultures above and incubated
for 4 and 8 weeks at 22 °C. Bottles were sacrificed, extracted,
and subjected to target, nontarget, and suspect screening for PFAS.
The PFAA precursors 6:2 FTS, N-sulfopropyldimethyl ammoniopropyl perfluorohexane
sulfonamide (SPrAmPr-FHxSA), and EtFOSE transformed up to 99, 71,
and 93%, respectively, and relevant daughter products, such as the
6:1 fluorotelomer ketone sulfonate (6:1 FTKS), were identified in
quantities previously not observed, implicating oxygenase enzymes.
This is the first report of a suite of site relevant PFAA precursors
being transformed in AFFF-impacted groundwater by bacteria grown on
substrates known to induce specific oxygenase enzymes. The data provide
crucial insights into the microbial transformation of these compounds
in the subsurface.