Environmental Reactivity of PET Microplastics as Vectors for Toxic Metals in Aquatic Systems

This study investigates the adsorption behaviour of toxic metals (Pb, Cr, Zn, Cu, Cd, Hg) onto polyethylene terephthalate (PET) microplastics under various aquatic conditions. Two PET particle size fractions (<0.63 µm and 0.63–1 mm) were examined in both freshwater and simulated seawater environments. The adsorption mechanisms were assessed using Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models. The results indicate that adsorption capacity is significantly affected by particle size and water chemistry, with a higher metal uptake observed in freshwater. Adsorption energies (0.68–2.95 kJ/mol) suggest physical adsorption. FTIR analysis revealed structural changes in PET, including degradation at 1560, 1540, and 1520 cm⁻¹, particularly following the adsorption of Cu, Zn, Cd, and Hg. These findings demonstrate that PET microplastics function as chemically active carriers of heavy metals, enhancing their mobility and bioavailability in aquatic ecosystems. Even weak non-covalent interactions can induce polymer degradation, increasing environmental reactivity and ecological risk.