Iron-Loaded Microplastics: An Unintended Legacy of Fenton Wastewater Treatment with High Affinity for Arsenic

Industries like textiles release substantial amounts of microplastics (MPs) into the environment. The Fenton process was identified in this study to enable Fe loading onto MPs in real textile wastewater, which may influence the geochemical cycling of arsenic (As) when entering the environment. Our results show that Fenton treatment can load Fe species onto various MPs with Fe content of 3318.8-4290.9 μg/g. The surface Fe species, primarily existing as amorphous Fe(OH)₃ and FeOOH, are embedded within the surface layer of ∼8 μm and exhibit high stability. The MP-Fe composites exhibited strong adsorption affinity for both As(III) and As(V), with saturated adsorption capacities of 557.2-631.8 μg/g and 304.7-572.8 μg/g, respectively, representing 5.3-26.5-fold enhancement compared to pristine MPs. Synchrotron radiation-based X-ray fluorescence (SRXRF) revealed spatial consistency between Fe and As on the MP-Fe surface (R² = 0.4938-0.8152), confirming that Fe species are critical for As adsorption. For As(III), the adsorption process is accompanied by oxidation, with the oxidation ratio reaching up to 84.1%. Temperature and pH exert a greater influence on PS-Fe and PA-Fe but have a limited effect on PLA, whereas NOM and P(V) affect all MP-Fe samples, which is mainly related to their interaction mechanisms.