Magnetite-mediated microbial functional restructuring and electron transfer pathways for enhanced PAHs degradation in contaminated sediments.

Polycyclic aromatic hydrocarbons (PAHs) in sediments threaten aquatic ecosystems and human health due to their persistence and toxicity. This study investigated the effects of nano-Fe₃O₄ (magnetite) on PAHs biodegradation in contaminated river sediments under simulated aquatic conditions over 210 days. Sediments amended with 0.5-5 % nano-Fe₃O₄ (by dry weight) exhibited enhanced degradation efficiencies for both low-molecular-weight (LMW) and high-molecular-weight (HMW) PAHs. Specifically, 3.5 % and 5 % Fe₃O₄ achieved rapid HMW-PAHs reduction (39.77 % by day 100) and sustained LMW-PAHs removal (53-57 % by day 210). Nano-Fe₃O₄ significantly boosted microbial electron transfer system (ETS) activity (up to 398.75 % at 1 % dosage), indicating improved energy metabolism. Microbial community analysis revealed enrichment of sulfate- and iron-reducing taxa (e.g., Geobacter, Desulfobulbaceae (f)) in high-dosage groups (3.5 % and 5 %), driving sulfate and iron reduction processes. Nano-Fe₃O₄-mediated conductivity facilitated synergistic interactions among electroactive bacteria, enhancing extracellular electron transfer and functional restructuring of microbial consortia. Bioavailability assays showed nano-Fe₃O₄ promoted PAHs desorption from sediment matrices, further accelerating microbial degradation. Redundancy analysis identified conductivity, Fe(II), and sulfate as key drivers of microbial community shifts. These findings demonstrate that nano-Fe₃O₄ fosters microbial cooperation and metabolic efficiency, offering a sustainable strategy for remediating PAH-contaminated sediments.