Dual Role of Microbe–FexSy Interaction to Drive Perfluorooctanoic Acid Multipath Chain Reaction Decay Cycles and Secondary Minerals-Ions (Fe²⁺/Fe³⁺) Transformation Cycles

The coexistence of iron–sulfur minerals (FexSy) and microorganisms is a common phenomenon, often leading to intricate interactions. Perfluorooctanoic acid (PFOA) presents extensive spatial–temporal attenuation characteristics. However, the mechanism governing PFOA in relevant diverse PFOA-ion occurrence environments remains unclear. In this study, the effects difference between microbe/FexSy and microbe–FexSy, and specific effects of four PFOA-ions environments on PFOA were investigated. Results showed a remarkable 277% increase in PFOA attenuation rate (λ) in microbe–FexSy media (0.343 h–1) than in FexSy (0.091 h–1) alone. The ion inhibiting effect on PFOA attenuation was demonstrated (λ from 0.343 to 0.159 h–1), with the maximum effect in HCO3–. It can be attributed to the occupation of sites by HCO3– which led to a greater repulsion. More PFOA was dispersed into distant regions (low reaction zone). Moreover, SO42– or NO3– with microbe–FexSy interaction exhibited pronounced retardation effects (on PFOA). Notably, enhanced formations of β-Fe2O3·H2O and α-Fe2O3·H2O regulated PFOA transport in PFOA-SO42– and PFOA-NO3– environments. Pseudomonas reduced Fe3+ to Fe2+, and Rhizobiales contributed to producing 3 Fe2+ after consuming 2 Fe2+. Fe2+ and Pseudomonas combined to drive PFOA multipath chain reaction. This provided a theoretical basis for understanding PFOA cross-media transport and fate in microbe–mineral–ions interaction environments.