Pyrite-Mediated Typical Antibiotics Degradation in Estuarine Sediments: The Role of Sulfur Species under Aerobic and Anaerobic Conditions

The redox dynamics of estuarine sediments critically influence the environmental fate of antibiotics, yet the mechanistic pathways under oxygen-fluctuating conditions have been insufficiently elucidated. This study elucidates the dual-function role of pyrite in mediating the oxidative and reductive degradation of three model antibiotics (sulfamethoxazole, SMX; norfloxacin, NOR; and chlortetracycline, CTC) under aerobic and anaerobic conditions. Systematic batch experiments coupled with reactive oxygen species analysis reveal a dual-function mechanism for pyrite involving oxidative degradation via ^•OH under aerobic conditions and reductive transformation under anaerobic conditions. Notably, sulfur species in pyrite serve as key electron donors, driving the defluorination and dechlorination reactions of NOR and CTC in the absence of molecular oxygen. X-ray absorption fine structure along with density functional theory simulations further demonstrate an S-Fe-antibiotic electron transfer pathway, wherein sulfide donates electrons via Fe(II) coordination sites. Field validation using natural estuary sediments corroborates the laboratory findings, highlighting the substantial contribution of pyrite-mediated reductive pathways to antibiotic attenuation. These findings advance the mechanistic insight into pyrite-driven redox processes in estuarine environments and underscore the overlooked role of sulfur species in mediating nonradical antibiotic degradation, with implications for natural attenuation and remediation strategies in sulfur-rich coastal systems.