Ecological implications of biodegradable and conventional microplastics: Dissolved organic matter bioavailability and...

The increasing accumulation of microplastics (MPs) in marine environments raises concerns about their ecological impacts, particularly through the release of dissolved organic matter (DOM). However, the bioavailability and ecological effects of MPs-derived DOM (MPs-DOM) remain poorly understood. In this study, we systematically investigated the leaching characteristics and microbial bioavailability of DOM derived from three biodegradable MPs (BMPs) including polylactic acid (PLA), polycaprolactone (PCL), polybutylene adipate terephthalate (PBAT) and two conventional MPs (CMPs, PE: polyethylene, PET: polyethylene terephthalate) under simulated photoaging. Our results demonstrated that BMPs released significantly more dissolved organic carbon (DOC) than CMPs, with PBAT showing the highest yield (40.77 vs. PE: 11.63 mg-DOC g-C^-1). Optical analyses revealed that BMPs-DOM contained more protein-like fluorescent components, with higher fluorescence index and biological index, indicating greater lability. BMPs-DOM stimulated microbial growth more efficiently, with PBAT supporting the highest bacterial concentrations (∼52 ×10³ cells mL^-1) and DOC utilization (76.39 %). 16S rRNA sequencing revealed that MPs-DOM exposure reduced community richness, reshaped microbial communities through selective enrichment of copiotrophic and plastic-degrading taxa (e.g., Pseudomonas, Bacteroidota), and promoted stochastically driven assembly with specialized functional modules. Our study highlights that while BMPs may alleviate particulate plastic accumulation, their labile DOM release warrants careful evaluation for potential impacts on marine microbial ecology.