Impact of pristine and UV-aged conventional and compostable plastic bags on water quality: Physicochemical alterations, additive leaching, and ecotoxicological effects

Leaching of chemicals from plastics is an emerging concern, yet its ecological implications remain unclear. Here, we investigated the changes induced by plastic leachates on water quality and ecotoxicity. We compared bags made of conventional low-density polyethylene (i.e., LDPE) with compostable polybutylene adipate-co-terephthalate and thermoplastic starch (i.e., PBAT/TPS) alternatives. Pristine and abiotically aged (by ultraviolet light (UV)) bags were incubated in synthetic freshwater over an 11-week period, during which changes in physicochemical parameters and metal(loid) concentrations in the medium were monitored. Finally, leachates were tested for their effects on different endpoints on the duckweed Lemna minor. Leachates from PBAT/TPS and LDPE showed markedly different chemical and biological effects. PBAT/TPS, especially after UV aging, induced the most pronounced alterations in water chemistry. These included increased pH (from 5.9 in the control to 7.7), elevated dissolved organic carbon (up to 249.8 mg L−1), and enhanced release of several metal(loid)s. These changes were accompanied by nutrient depletion and stronger ecotoxicological responses in Lemna minor, including growth inhibition and root elongation. Pristine PBAT/TPS triggered more significant shifts than LDPE, which exhibited lower environmental reactivity overall. Principal component analysis clearly separated leachates by polymer type and aging conditions, reinforcing the combined influence of material composition and degradation on leachate chemistry. This study indicates that compostable plastics may negatively affect aquatic ecosystems, especially after aging. Our findings highlight the need for integrative risk assessments that account for both polymer composition, chemical characterization, and degradation behavior when evaluating the safety of plastic products.