Unraveling Complexation and Contaminant Vector Potential in Aged Polyamide-Heavy Metal Interactions

Polyamide (PA) microplastics, commonly used in aquatic activities, are ubiquitous environmental contaminants. Our research objective was to determine the potential impact of aged PA on the environment, acting not only as microplastics but also as vectors for heavy metals (such as cadmium and copper), which could release adsorbed metals back into the environment under different conditions. To mimic the natural aging of PA, tested PA samples were exposed to heat-activated persulfate and subsequently brought into contact with metal solutions. Time-dependent changes in metal concentrations were measured using ICP-OES, followed by the determination of adsorption kinetics and isotherms. The aged PA exhibited an enhanced adsorption capacity for both metals, likely due to increased surface area from the formation of cracks, increased surface roughness, and abrasion sites. Cu exhibited the highest adsorption efficiency. This is attributed to its smaller hydrated ionic radius, higher charge density, and strong ligand field stabilization energy, which promotes stronger coordination with O- and N-containing functional groups on the aged PA surface. The best fit for the adsorption process was a pseudo-second-order kinetic model and Langmuir isotherm, suggesting that electrostatic interactions are likely the dominant adsorption mechanism. Environmental factors influenced the adsorption and desorption efficiency by altering the charge interactions between PA and metal ions. This study highlights the dual role of aged PAacting not only as microplastics that persist in the environment but also as contaminant vectors, facilitating the transport and release of harmful metals into aquatic ecosystems.