The interfacial behaviors of different arsenic species on polyethylene mulching film microplastics: Roles of the plastic additives

Plastic additives widely existed in plastic mulching films, but their roles in microplastics (MPs) derived from these plastics as vectors of pollutants were not clear. This work clarified the role of plastic additives on the sorption-desorption behaviors of four arsenic species (arsenite (As(Ⅲ)), arsenate (As(Ⅴ)), roxarsone (ROX), and p-arsanilic acid (p-ASA)) on/from virgin polyethylene (V-PE), white PE mulching film (W-PE, with Si-containing additives), and black PE mulching film (B-PE, with CaCO₃ and TiO₂ additives) MPs. The maximum sorption amounts of arsenic species on V-PE (3.33–20.10 mg/kg) and W-PE MPs (4.78–21.93 mg/kg) had no significant difference, while those on B-PE (43.02–252.19 mg/kg) facilitated by its additives were up to one order of magnitude greater than V-PE or W-PE (p < 0.05). Desorption hysteresis index (HI) indicated the irreversible arsenic sorption on three PE MPs, especially for B-PE containing additives that can co-precipitate and complex with arsenicals. The effects of pH, humic substances, and coexisting anions on arsenic sorption by B-PE were more obvious than that by V-PE or W-PE MPs, attributing to electrostatic interaction enhanced by CaCO₃ and TiO₂ additives. This work provides theoretical basis for migration of arsenic species on MPs containing plastic additives and their potential environmental risk assessment.