Molecular fingerprinting of biodegradable poly(butylene adipate-co-terephthalate) leaching and toxic effects on coastal phytoplankton.

Biodegradable plastics are increasingly replacing conventional polymers, yet their environmental fate and ecotoxicological impacts in marine systems remain poorly defined, particularly for poly(butylene adipate‑co‑terephthalate) (PBAT), one of the fastest‑growing biodegradable polyesters. Here we present an integrated framework linking the chemical characterization of PBAT-derived dissolved organic matter (DOM) with its physiological effects on marine phytoplankton. Using controlled kinetic leaching experiments with virgin PBAT pellets, coupled with ultrahigh‑resolution mass spectrometry and optical spectroscopy, we found that PBAT exhibited substantially higher DOM leaching rates in seawater than polyethylene, polystyrene, and poly(lactic acid). Leaching accelerated with elevated temperature, salinity, and UV radiation but was suppressed by surface biofilms. Molecular analysis revealed that PBAT‑derived DOM was enriched in aromatic and aliphatic CHO‑type compounds, distinct from natural organic matter. Laboratory assays with two diatom species showed dose‑dependent physiological stress, characterized by impaired photosynthetic efficiency, elevated reactive oxygen species, and compromised membrane integrity. Field dilution experiments further demonstrated that PBAT leachates significantly suppressed micro‑phytoplankton (20-200 μm) growth, whereas pico‑phytoplankton (<2 μm) remained resilient. These findings identify the leachate-associated hazard potential of virgin PBAT under controlled, localized high-exposure conditions, while further studies are needed to evaluate the environmental relevance of these responses under realistic marine conditions.