Enhanced copper adsorption by polyamide and polylactic acid microplastics: The role of biofilm development and chemical aging

Plastics undergo a range of physical, chemical, and biological changes in natural aquatic environments, which profoundly affect their environmental fate and bioavailability. This study investigates the effects of potassium persulfate (K₂S₂O₈) oxidation and biofilm attachment on the surface p'roperties and Cu(II) adsorption behavior of polyamide (PA) and polylactic acid (PLA) microplastics. Both chemical aging and biofilm formation significantly increase the specific surface area, crystallinity, and oxygen-containing functional groups of these microplastics. Specifically, the specific surface area of K₂S₂O₈-aged PA and PLA microplastics increased to 3.546 m² g^-1 and 2.930 m² g^-1, respectively. 16S rDNA analysis revealed distinct bacterial communities on PA and PLA-MPs, reflecting different microbial attachment due to polymer types. Compared to pristine microplastics, K₂S₂O₈-aged PA and biofilm-covered PA had Cu(II) adsorption capacities of 1.536 mg g^-1 and 0.946 mg g^-1, respectively, while K₂S₂O₈-aged PLA and biofilm-covered PLA capacities increased to 1.163 mg g^-1 and 0.812 mg g^-1. Cu(II) adsorption onto aged microplastics followed the Freundlich model, indicating a multilayer adsorption mechanism. The pH significantly impacted Cu(II) adsorption efficiency, with the best performance observed under near-neutral conditions. Fulvic acid inhibited Cu(II) adsorption by competing for adsorption sites and forming complexes with Cu(II). These findings highlight the transformation mechanisms of microplastics within natural settings and their potential as heavy metal carriers, providing vital insights for assessing the environmental impact of microplastic pollution.