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New Insights into the Long-Term Leaching Process of Dissolved Organic Matter from Microplastics: Dynamic Formation and Transformation Mechanism
Summary
This study tracked how polystyrene and a biodegradable plastic (PBAT) release dissolved organic compounds as they age under ultraviolet light over 94 days. Polystyrene released chemicals much more slowly but with steadily increasing toxicity over time, while the biodegradable plastic released compounds faster but with less overall toxic buildup. These findings are important because they show that microplastics in the environment continuously leach potentially harmful chemicals, and so-called biodegradable plastics may not be as safe an alternative as assumed.
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.