Resistance of perfluorooctanoic acid to degradation by the microbially driven Fenton reaction

Per- and polyfluoroalkyl substances (PFAS) such as perfluorooctanoic acid (PFOA) have received recent heightened attention as emerging contaminants. Due to widespread application in household products and aqueous film-forming foams, PFAS are globally distributed in the environment, and bioaccumulate in the blood and tissues of mammals including humans. The microbially driven Fenton reaction, a hybrid biotic/abiotic hydroxyl radical (HO•)-generating system, previously degraded a wide variety of persistant organic pollutants. In the present study, the microbially driven Fenton reaction was employed to attempt degradation of PFOA. Batch cultures of the facultatively anaerobic bacteria Shewanella oneidensis were amended with PFOA and Fe(III)-citrate. Under aerobic conditions, S. oneidensis reduced oxygen to hydrogen peroxide (H2O2), while under anaerobic conditions, S. oneidensis reduced Fe(III) to Fe(II). During aerobic-to-anaerobic transition periods, Fe(II) and H2O2 interacted chemically via the Fenton reaction to produce HO• radicals, which in turn interacted with PFOA. Batch reactors were cycled between aerobic and anaerobic phases for four cycles, residual PFOA was extracted via liquid-liquid extraction and analyzed by liquid chromatography combined with tandem mass spectrometry. Unlike degradation of other organic pollutants, PFOA concentrations remained unchanged, which indicated that PFOA was resistant to degradation by the microbially-driven Fenton reaction. Similar to abiotic (purely chemical) Fenton reaction systems, these results most likely reflect the inability of HO• radicals to oxidatively degrade PFOA.