Cumulative inhibitory effect of 6:2 chlorinated polyfluorooctane ether sulfonate in anaerobic digestion processes

Microbial anaerobic metabolism is crucial for biogeochemical cycles, impacting both natural and engineered ecosystems. However, the increasing emissions of 6:2 Cl-PFESA, an alternative to PFOS, pose significant risks. In this study, long-term high 6:2 Cl-PFESA concentration level of 10 µg/g TS exposure led to a substantial decrease in methane production from 204.8 ± 4.8 mL/g VS to 143.6 ± 3.5 mL/g VS, indicating a cumulative inhibitory effect on carbohydrate-related anaerobic digestion. Key processes such as polysaccharide release, hydrolysis, acetogenesis, and acetoclastic methanogenesis were contributed by 28.6 %, 9.3 %, 8.9 %, and 11.7 % of significant reduction, respectively, correlating with inhibition in relevant enzymatic activities and gene expressions. Hydrolytic bacteria such as Rectinema and Defluviitoga declined to 11.7 % from 14.3 % and 20.9 % from 23.9 %, reflecting decreased hydrolysis efficiency. Reduced transcription levels of acetogenesis- and acidogenesis-related genes further inhibited these processes. Conversely, methanogens Methanolinea and Methanothrix increased from 35.8 % to 55.7 % and 10.9–40.8 %, suggesting enzyme inhibition rather than methanogen abundance reduction. Additionally, 6:2 Cl-PFESA partially biotransformed into 6:2H-PFESA, facilitated by species like Dechloromonas, unclassified Xanthomonadales, and Betaproteobacteria. These findings confirm that the limited degradation and cumulative inhibitory effects of 6:2 Cl-PFESA during anaerobic digestion highlight its significant disruption to carbon cycling stability within ecosystems.