Temperature Dominance in Governing Nanoplastic Release and Leachate Composition from Polylactic Acid–Based Disposable Plastics

Nanoplastics released from biodegradable plastics have raised concern, yet their composition and release behavior remain largely unclear. Using polylactic acid (PLA)–based disposable containers, a common alternative to conventional plastics, we developed a quantitative analytical workflow to differentiate and characterize PLA-leached chemicals (PLCs), including PLA nanoparticles (NPs), PLA oligomers (OLAs), and lactic acid (LA). Simulated use of disposable cups (DCs) showed that PLA-DCs released ~6 million particles mL-1 NPs into water, substantially higher than conventional polypropylene (PP) DCs. More interestingly, up to 55% of detected NPs were OLA self-assembled aggregates rather than PLA NPs. Across use scenarios, water temperature was the dominant determinant: PLC concentrations increased nearly two orders of magnitude from 50 to 70 °C, accompanied by a shift from particulate to dissolved OLAs. Integrating national use behaviors with release parameters, global annual PLC exposure from PLA-DCs is projected to increase by 2 folds from 2021 to 2030. Although U.S. coffee cups account for 49% of PLA-DCs, hot coffee consumption contributed >99% of exposure, whereas in China, despite coffee cup consumption being only 20% of the U.S., hot water use in PLA-DCs still resulted in ~80% of the U.S. exposure. These findings highlight the need to establish NP and oligomer release as a new benchmark for evaluating biodegradable disposable plastics and to redefine safe-use temperature thresholds.