Iron-oxidizing bacteria-mediated Fe(II) organo-mineralization drives arsenic and microplastics co-immobilization.

Abstract

The increasing coexistence of arsenic (As) and microplastics (MPs) in acid mine drainage (AMD) environments poses amplified ecological risks to aquatic ecosystems. However, the mechanisms underlying their co-immobilization remain poorly understood. Here, quartz crystal microbalance with dissipation monitoring, molecular dynamics simulations, and microanalytical techniques were integrated to investigate Fe(II) organo-mineralization mediated by Acidithiobacillus ferrooxidans, a typical iron-oxidizing bacterium, and its role in As-MPs co-immobilization. The results show that A. ferrooxidans promoted organo-poorly crystalline Fe-As minerals (organo-PCFAMs) formation, whose organic components including lipids, free fatty acids, and/or saccharides, facilitated their adhesion to polyethylene (PE)- and polystyrene (PS)-MPs primarily through van der Waals interactions. Meanwhile, hydroxyl radicals generated during Fe(II) bio-oxidation, continued organo-PCFAMs accumulation and transformation intensified MPs surface damage with their size reduction, and increased organo-PCFAMs loading capacity. These coupled processes enhanced As-MPs co-immobilization, achieving removal rates of 61-98% for As and 73-97% for MPs, with PS-MPs immobilized more effectively than PE-MPs owing to stronger interfacial interactions. Overall, this study elucidates molecular-to-microscale mechanisms by which A. ferrooxidans-mediated organo-mineralization generated mineral bridge to drive As-MPs co-immobilization, advances understanding of their coupled biogeochemical cycling, and provides a strategy for mitigating As-MPs co-contamination in AMD environments.

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