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

Case Studies in Chemical and Environmental Engineering 2026

Summary

Tiny plastic particles (microplastics) that break down in water don't just pollute on their own, when combined with natural organic matter found in lakes and rivers, they become better at soaking up toxic heavy metals like chromium. This means "aged" microplastics floating in waterways could act like tiny sponges, carrying extra heavy metal contamination into the food chain, which raises concerns about the pollutants we might ultimately consume through water and seafood.

Polymers

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.

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