Breaking the Carbon-Fluorine Stronghold: Reductive Defluorination of PFASs.

Per/polyfluoroalkyl substances (PFASs), characterized by their ultrastable C-F bonds and pervasive environmental persistence, present critical remediation challenges due to their recalcitrance and bioaccumulative potential. Conventional oxidative degradation methods predominantly yield bioaccumulative short-chain fluorinated derivatives, failing to achieve molecular annihilation. We highlight reductive defluorination as a transformative strategy to directly cleave C-F bonds and mitigate toxicity through two distinct electron-transfer modalities: indirect routes mediated by reactive species (e.g., hydrated electrons/active hydrogen) contrasted with direct mechanisms employing biocatalytic or electrochemical systems for targeted electron injection. Mechanistic taxonomy and quantitative structure-reactivity analyses reveal that defluorination efficiency is governed by the molecular architecture (e.g., chain length and fluorination patterns) and operational parameters (e.g., pH, redox potentials, and solution matrices). While standalone reductive technologies face scalability constraints from energy intensity and secondary contamination risks, synergistic integration of bioremediation-electrochemical-photocatalytic systems demonstrates enhanced defluorination efficiency. By coupling molecular-level degradation mechanisms with modular engineering, we propose future directions for developing reductive defluorination, offering a sustainable pathway to eliminate environmental recalcitrance and comply with evolving global water quality mandates.