Reductive defluorination of PFAS in source water of the three gorges reservoir area by local microbial communities

Per- or polyfluoroalkyl substances (PFAS) are persistent organic pollutants that pose significant risks to human health and aquatic ecosystems. The Three Gorges Reservoir Area, a critical water source for approximately 400 million people, is severely affected by PFAS contamination. This study investigates the biological reductive defluorination of four typical PFAS (perfluorooctanoic acid, PFOA; perfluorohexanoic acid, PFHxA; Perfluoro (4-Methyl-2-Pentenoic Acid), PFMeUPA; and 6:2 fluorotelomer alcohol, 6:2 FTOH) using microbial communities enriched from surface sediments, deep sediments, and deep soils in the Three Gorges Reservoir Area. Differential analysis of PFAS degradation rates showed that surface sediments had the highest degradation efficiencies for three conventional PFAS: PFOA (37.85 %), PFHxA (34.58 %), and 6:2 FTOH (81.67 %), while deep sediments degrade the emerging PFMeUPA more rapidly (90.86 %). Cultivation with PFOA resulted in an increased relative abundance of Pseudomonadota (increased to 30.79 %±4.89 %), while PFHxA-based cultivation induced a marked enrichment of Thermodesulfobacteriota and Chloroflexota. Correspondingly, the abundance of dehalogenase-encoding genes (increased by 28.81 %-104.13 %) and decarboxylase-encoding genes (increased by 1.51 %-194.88 %) was found to be elevated across both PFOA and PFHxA treatment groups. Since PFAS degradation and F^- release did not reach the theoretical ratio, an analysis was conducted on the defluorinated products and possible degradation pathways were analyzed. It was found that microbial enzymes target the carboxyl groups of perfluorinated carboxylic acids (PFCA) to produce a step-by-step decarboxylation processes, while unsaturated PFAS may undergo C-H cleavage to form unstable intermediates, leading to defluorination.