Fast Generation of Perfluoroalkyl Acids from Polyfluoroalkyl Amine Oxides in Aerobic Soils

Studies of the environmental fate of polyfluoroalkyl substances have revealed a broad range of precursor degradability and yields of perfluoroalkyl acids (PFAAs). For those electrochemical fluorination-derived zwitterionic fluorosurfactants present in aqueous film-forming foams (AFFFs), environmental persistence and potential contributions to perfluorooctanesulfonate (PFOS) and carboxylate (PFOA) are significant knowledge gaps. Here, we demonstrate that perfluorooctane-amido and -sulfonamido amine oxides (PFOANO and PFOSNO) can rapidly degrade in aerobic surface soils to produce PFOA and PFOS, respectively. When incubated in soil microcosms for 90 days, the two chemicals exhibited low stability with DT50 values (disappearance time for a 50% decline) of 3-7 days for PFOANO and similar to 15 days for PFOSNO. PFOANO degraded to PFOA at a yield of 15-21 mol %, and PFOSNO produced PFOS at a yield of similar to 2 mol %. The two chemicals unexpectedly underwent extensive abiotic transformations, generating products similar to those in biotic processes except for PFOA and PFOS. This study suggested for the first time that polyfluoroalkyl amine oxides could represent important sources to PFAAs, and their low environmental stability may explain their sporadic environmental occurrence at historical AFFF-impacted sites.