Microbial and Enzymatic Transformation of Per- and Polyfluoroalkyl Substances (PFAS): From Defluorination and Biological Partitioning to a Separation-First Biological Treatment Framework

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental pollutants. Conventional destructive technologies, such as advanced oxidation and electrochemical processes, can achieve partial or complete defluorination. However, their high energy demand, chemical inputs, and operational complexity limit widespread implementation. Increasing evidence indicates that biological systems provide complementary mechanisms for PFAS management through partial biotransformation, defluorination of selected structurally susceptible compounds, and biomass-driven partitioning. This review evaluates the evidence for partial, largely precursor-directed PFAS biotransformation and biocatalytic defluorination through reductive, oxidative, and hydrolytic pathways. It also examines enzymatic carbon–fluorine bond cleavage by fluoroacetate dehalogenases, haloacid dehalogenases, and reductive systems, while recognizing that their demonstrated activity is generally limited to monofluorinated, activated, or polyfluorinated substrates rather than conventional fully perfluorinated PFAS. Laboratory and field observations demonstrate substantial PFAS enrichment within aquatic biomass, including intracellular compartments and extracellular polymeric substances (EPS), indicating that living systems can function as dynamic concentrators that partition PFAS from the aqueous phase. Building on these findings, this review advances a separation-first framework in which PFAS are initially captured and concentrated within biological matrices before the application of targeted destruction, regeneration, or residual-management technologies. By decoupling concentration from transformation, this approach enables independent optimization of each step, potentially reducing treatment volumes and improving overall process sustainability.