New Insights into the Long-Term Leaching Process of Dissolved Organic Matter from Microplastics: Dynamic Formation and Transformation Mechanism

A deeper understanding of the photoaging dynamic release mechanism of microplastic-derived dissolved organic matter (MP-DOM) is crucial for revealing the behavioral patterns and ecological risks of microplastics. This study focused on the MP-DOM release process and molecular transformation mechanism of conventional polystyrene (PS) and biodegradable poly(butylene adipate-co-terephthalate) (PBAT) particles for 94 days under ultraviolet aging. Multistage kinetic simulation results indicated that the leaching rate constant and half-life of PS-DOM were approximately 10-3-10-6 and 30-300 times that of PBAT-DOM, respectively. The leaching process of PS-DOM could be categorized into three distinct stages: a rapid release period, plateau period, and slow release period, initially undergoing -C reactions of lignin-like compounds, followed by +H2O2 reactions of aromatic compounds, and finally -CH2 reactions of lignin-like compounds. PBAT-DOM displayed a rapid release period, slow release period, and degradation period, with lignin-like compounds as the main reaction components, experiencing -CH2, +O, and +H2O2 reactions, respectively. Noticeably, PS-DOM, along with its continuously increased molecular toxicity, exhibited a greater risk of toxicity relative to PBAT-DOM with a volcanic-like change of toxicity during the whole transformation process. This study reveals the staged characteristics and molecular transformation mechanisms of MP-DOM, which is beneficial for gaining a deeper understanding of their potential harm to eco-environment systems.