Beyond Particle Effects: Leachate-Induced Duckweed Toxicity from PBAT and PLA under Global Warming

Mounting evidence confirms that microplastics (MPs) pose ecological risks. Despite the environmental relevance of aged MPs under warming, little is known about their particle versus leachate toxicity. Here, we mechanistically quantify these contributions in the duckweed Spirodela polyrhiza at concentrations of 10–500 mg L–1. Our results reveal polymer- and end point-specific effects, indicating distinct modes of action. While particle effects dominated the toxicity of polyvinyl chloride (PVC, 55.2–86.2%) and polystyrene (PS, 50.5–67.1%), the toxicity of poly(butylene adipate-co-terephthalate) (PBAT) and polylactic acid (PLA) was primarily driven by their leachates (51.1–78.5% and 54.0–91.7%, respectively). High-risk chemical candidates, including docosanamide, pyrene, hexadecanamide, nonanoic acid, stearic acid, oxepanone, and adipic acid, were further identified and prioritized within the leachates from PLA and PBAT through nontarget screening via HPLC-MS and integration with the Toxicological Priority Index (ToxPi) framework. Although elevated temperatures enhanced chemical leaching, the resulting toxicity did not increase proportionally. By elucidating how particles and leachates differentially drive MP toxicity in a polymer-specific manner under warming, this work provides critical insights for developing mechanism-driven risk assessment frameworks.