Impact of microplastic aging and humic acid on heavy metal adsorption onto polystyrene microplastics (PS-MPs)

This study investigates how microplastic (MP) aging and humic acid (HA) influence heavy metal (Zn, Cu, Cr) adsorption onto polystyrene microplastics (PS-MPs) in aquatic systems. Pristine and Fenton's reagent-aged PS-MPs were characterized using FTIR, Raman spectroscopy, and SEM-EDX. HA accelerated surface oxidation and increased metal binding, particularly enhancing Cr uptake via stable complexation, while Zn adsorption declined due to competitive interactions. Adsorption data fitted the Freundlich isotherm (R 2 > 0.98), with maximum adsorption capacities in the presence of HA, and followed pseudo-second-order kinetics. These results demonstrate that aged MPs act as active vectors for heavy metals, underscoring the ecological risks of organic matter–mediated adsorption in aquatic environments.