Biodegradable PBAT-derived microplastics induce metabolic and ultrastructural alterations in Gloeocystis ampla (Kützing) Rabenhorst

The increasing use of biodegradable plastics, such as polybutylene adipate- co -terephthalate (PBAT), raises concerns about their degradation products particularly microplastics (P-MPs) and ecological impacts. This study evaluated the physicochemical properties of PBAT-derived microplastics and their toxicological effects on the freshwater microalga Gloeocystis ampla . PBAT microplastics were produced via alkali degradation and characterized by SEM, TEM, DLS, and FTIR, revealing irregular shapes, particle sizes of 200–300 nm, and a zeta potential of −25.1 mV. G. ampla cultures were exposed to PBAT microplastics at 1–20 mg L −1 for 96 h during the logarithmic growth phase. Growth inhibition was dose-dependent, ranging from 7.3 % at 1 mg L −1 to 36.5 % at 20 mg L −1 , with a slight stimulatory effect at 2.5 mg L −1 . Chlorophyll a and b decreased significantly, while carotenoids initially increased, indicating photoprotective responses. Carbohydrate content dropped from 363.2 to 209.9 mg L −1 , while protein levels increased from 103.5 to 415.8 mg L −1 . Lipid content declined to 5 g at moderate doses but rose to 11 g at the highest concentration, with lipid yield increasing from 13.3 % to 18.3 %. FTIR analyses revealed PBAT-induced macromolecular shifts in lipid and polysaccharide-associated bands. Confocal microscopy and TEM demonstrated chloroplast degradation, lipid droplet accumulation, and intracellular localization of PBAT particles. These results suggest that even biodegradable PBAT microplastics can induce significant physiological and biochemical stress in freshwater microalgae, potentially impairing primary production and disrupting aquatic ecosystems. This study highlights the need to reassess the environmental risks posed by biodegradable plastics in natural waters. • PBAT microplastics were characterized before biological exposure experiments. • PBAT microplastics induced growth inhibition in Gloeocystis ampla cells. • Pigment, carbohydrate, and protein contents decreased under PBAT exposure. • PBAT exposure altered thylakoid structure and increased lipid accumulation. • Confocal imaging showed enhanced lipid accumulation inside algal cells.