Effects of Aging Microplastics and Embedded Light Stabilizers on Extracellular Substances Secreted by Chlorella...

The environmental release of chemical additives from aging microplastics (MPs) and the associated ecological risks have attracted increasing research attention. Nevertheless, systematic investigations on the biological impacts of light stabilizers leached from aging MPs remain limited. In particular, the divergent toxic impacts of leachates derived from pristine versus aged stabilizer-modified MPs remain poorly elucidated. Herein, a multi-dimensional toxicological evaluation integrating physiological responses, extracellular polymeric substances (EPS) secretion, and transcriptomic profiling was conducted. Four typical light stabilizers (TiO₂, HS-944, BP-3, NBC) were compounded with polyethylene (PE) microspheres to construct composite MPs, and Chlorella vulgaris (C. vulgaris) was employed as the model aquatic microalgae to explore algal response to leachates from both pristine and aged composite systems, focusing on extracellular secretion and underlying molecular regulatory mechanisms. Results revealed that light stabilizers synchronously released during MPs aging significantly interfered with photosynthetic performance and energy metabolism of C. vulgaris, and profoundly reshaped algal extracellular secretion profiles of proteins, polysaccharides, and their subsequent assembly into transparent exopolymer particles (TEPs). Such toxic disturbances mainly stem from impaired light absorption and transduction by photosynthetic pigments, disordered cell cycle, and oxidative stress-mediated modulation of intracellular signaling cascades and gene expression. As the most toxic agent among the four tested stabilizers, BP-3 exposure exhibited unique dual effects. Pristine BP-3/PE significantly elevated algal mortality and overproduction of extracellular proteins and polysaccharides, whereas aged BP-3/PE composites strongly suppressed TEP formation as a stress-adaptive extracellular response. These findings elucidate the toxicological characteristics and underlying molecular mechanisms of microalgal responses to aging-derived light stabilizer contamination, providing fundamental scientific evidence for the ecological risk management and pollution control of aquatic MPs contaminants.