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 with limited knowledge of their environmental fate via biological processes. This study reports the microbial transformation of environmentally relevant ether PFAS and similar structures and important microbial groups involved in the anaerobic biotransformation process. The investigated ether PFAS include mono- and dichlorinated ones such as 6:2 chlorinated polyfluorooctane ether sulfonate (F53-B) and 6,7-dichloroperfluoro-5-oxaheptanoic acid, as well as unsaturated ones such as sodium p-perfluorous nonenoxybenzenesulfonate (OBS) and the Nafion Byproduct 1 (NBP1). The presence of chlorine-substitution and unsaturated carbon facilitated the biotransformation and defluorination of ether PFAS under anaerobic or aerobic conditions. For fully halogenated ether PFAS, biotransformation only occurred in anaerobic conditions via dechlorination (reductive, eliminative, and hydrolytic), hydrolytic O-dealkylation, and reductive defluorination, forming less fluorinated and shorter chain products. Strong evidence was obtained from community and pure culture experiments for the involvement of cobalt-enzyme-dependent microorganisms, such as Sporomusa sphaeroides, in the initial dechlorination step during the biotransformation of chlorinated ether PFAS. Meanwhile, microorganisms independent of cobalt-enzymes, such as Desulfovibrio aminophilus, were responsible for the biotransformation of non-chlorinated unsaturated ether PFAS (e.g., NBP1), especially for the hydrolytic O-dealkylation reaction. The findings provide significant insights of the fate of ether PFAS in anaerobic environments and underscore the cooperation of different microbial groups in a community to achieve further transformation and higher defluorination.