Anaerobic Microbial Defluorination of Polyfluoroalkylether Substances (Ether PFAS): Transformation Pathways and Roles of Different Microorganisms

Polyfluoroalkylether substances (ether PFAS) are widely detected in the environment, yet their environmental fate and biotransformation pathways remain sparsely documented. This study reports the microbial transformation of environmentally relevant ether PFAS and the key microbial groups involved under anaerobic conditions. The compounds examined include mono- and dichlorinated ether PFAS such as 6:2 chlorinated polyfluorooctane ether sulfonate (F53-B) and 6,7-dichloroperfluoro-5-oxaheptanoic acid, as well as unsaturated structures such as sodium <i>p</i>-perfluorous nonenoxybenzenesulfonate (OBS), Nafion Byproduct 1 (NBP1), and its analogues. Chlorine substitutions and unsaturated carbons facilitated biotransformation and defluorination. For fully halogenated ether PFAS, biotransformation only occurred under anaerobic conditions via dechlorination (reductive, eliminative, and hydrolytic), hydrolytic O-dealkylation (especially at the fluorovinyl ether moiety), and reductive defluorination, forming less fluorinated and shorter-chain products. Inhibition and pure-culture experiments suggested that cobalt-enzyme-dependent microorganisms contributed to the initial dechlorination of chlorinated ether PFAS, and transformation in a vitamin B₁₂/Ti(III) abiotic system further supported the role of cobalt enzymes. In contrast, cobalt-independent microorganisms predominantly transformed nonchlorinated unsaturated ether PFAS (e.g., NBP1) via hydrolytic O-dealkylation. These findings clarify how different microbial groups cooperate to drive anaerobic biotransformation of ether PFAS and provide important insight into their environmental fate and defluorination potential.