Aerobic biodegradation of 8:2 fluorotelomer stearate monoester and 8:2 fluorotelomer citrate triester in forest soil

Aerobic biodegradation of 8:2 fluorotelomer stearate (FTS) and 8:2 fluorotelomer citrate triester (TBC) was evaluated in a forest soil in closed bottle microcosms. Loss of parent, production of 8:2 fluorotelomer alcohol (8:2 FTOH), which is released along with stearic acid (SA) by microbial ester linkage, and subsequent metabolites from FTOH degradation were monitored for up to 7 months. Soil microcosms were extracted with ethyl acetate followed by two heated 90/10 v/v acetonitrile/200 mM NaOH extractions. Cleavage of the ester linkage in the 8:2 FTS occurred (t1/2 ∼ 28 d), producing 8:2 FTOH and various levels of subsequent metabolites. Quantifying the generation of SA from ester cleavage in FTS was complicated by the natural production and degradation of SA in soil, which was probed in an additional FTS and SA study with the same soil that had been stored at 4 °C for 12 months. In the latter study, FTS degraded faster (t1/2 ∼ 5 d) such that SA production well above soil background levels was clearly observed along with rapid subsequent SA degradation. Cold storage was hypothesized to enrich fungal enzymes, which are known to be effective at hydrolytic cleavage. 8:2 TBC biotransformation was slow, but evident with the production of PFOA well above levels expected from known FTOH residuals. Slower degradation of TBC compared to FTS is likely due to steric hindrances arising from the close proximity of three 8:2 FT chains on the citrate backbone limiting the enzyme access.

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► The half-life of fluorotelomer stearate, FTS, is <1 month in an aerobic soil.
► Cleavage of the ester bond was evident by release of 8:2 FTOH and stearic acid.
► Production of PFOA resulted from the biotransformation of both FTS and TBC.
► Degradation of fluorotelomer citrate tri-ester (TBC) was slow.
► Prolonged cold storage of the forest soil, increased hydrolysis rates.