Heavy metal adsorption by pristine and aged microplastics: A focused evidence synthesis

This focused evidence synthesis comparatively examined how aging alters heavy-metal adsorption by pristine and aged microplastic based on quantitative results reported in published studies. Across the selected evidence base, aging generally increased the adsorption capacities of polypropylene, polyethylene, polystyrene, and poly(butylene adipate-co-terephthalate), although the extent of enhancement varies with polymer type, metal species, and aging conditions. For example, the adsorption capacities of aged polyethylen for Pb and Cu showed a significantly increased, rising from 1.913 to 5.807 mg/g and from 1.960 to 4.299 mg/g, respectively, whereas UV-aged polypropylen and polystyren also exhibited consistent enhancement. Evidence from ultraviolet aging in different media shows that the enhancement ratio followed air > seawater > pure water for multiple metals, indicating strong pathway dependence. The enhanced adsorption of aged microplastics was mainly associated with the formation of oxygen-containing functional groups, larger specific surface area, greater surface roughness, and altered hydrophilicity. These findings suggest that environmentally aged microplastics should be explicitly considered when assessing heavy-metal ecological risk.