Aerobic biotransformation of 8:2 FTCA in activated sludge: Carbon source dependence and multiple transformation pathways.

8:2 fluorotelomer carboxylic acid (8:2 FTCA) has been detected in environmental matrices and biota, yet its aerobic biodegradation remains poorly understood. Here, 30-day activated-sludge microcosms were used to investigate the degradation kinetics, transformation pathways, and microbial responses of 8:2 FTCA (10 μM) under carbon-limited and carbon-amended conditions. Only 38 mol% removal occurred without external carbon, whereas acetate, butanol, and octane increased removal to 85-90 mol%, with octane producing the highest fluoride release (24 μM). Target and non-target analyses identified 8:2 FTUCA and 7:3 FTCA as major intermediates and revealed the accumulation of five perfluorocarboxylic acids (PFCAs). Detection of OH-8:2 FTCA and PFNA supported a potential α-oxidation pathway. Mechanistically, 8:2 FTUCA forms via HF elimination and 7:3 FTCA via H/F exchange, while hydroxylation, α/β-oxidation, and decarboxylation may have contributed to PFCAs formation. Metagenomic analysis showed that 8:2 FTCA exposure and carbon amendments selectively enriched microorganisms, including Tepidiforma, Ectorhizobium, and Actinocorallia, which harbored genes encoding dehalogenases, monooxygenases, and fluoride exporters. Collectively, these results suggest that carbon sources availability may influence 8:2 FTCA transformation, defluorination, and microbial functional profiles in activated sludge, providing additional insights into the potential aerobic biotransformation of FTCAs in multi-contaminant environments.