The presence of additives dominates the metal adsorption process on plastic over polymer type and UV aging

Plastic materials have been observed to adsorb (trace) elements in water, with environmental implications. However, the underlying mechanisms and governing factors remain unclear. Recent studies have examined plastic-related factors (polymer type, additives, and aging), but a systematic comparison of their effects on the adsorption is still missing. Our study aims to test their effects on the metal adsorption, focusing on copper (Cu) and lead (Pb). We selected two polymer types (namely, a conventional polymer- low density polyethylene, and a compostable polymer- polybutylene adipate terephthalate), used as pellets and additive-containing plastics. All samples were analyzed in pristine form and after an artificial ultraviolet aging, comparing their physicochemical properties (i.e., surface morphology, functional groups) and their adsorption capacity through kinetics and isothermal experiments. The results highlight the role of additives as a primary factor influencing adsorption capacity, with values reaching hundreds of mg/mg for Cu and exceeding 700 mg/kg for Pb for the additivecontaining samples. UV aging further enhanced adsorption capacity in a sample-dependent manner, with a notable increase in Cu adsorption observed only for the PBAT sample. Importantly, the additive free pellet sample exhibited negligible depletion of the analyzed metals. Our study provides valuable insights into the behavior of plastics with metals, emphasizing the role of the final chemical composition in defining reactivity. These results emphasize the greater complexity induced by plastic formulation in evaluating their environmental implications and guiding the use of plastic materials to assess environmental risks.