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.