Microplastic-Derived Dissolved Organic Matter: Environmental Chemistry and Ecological Consequences

Microplastics (MPs) are widely recognized as particulate hazards, yet environmental aging releases a time-evolving pool of MP-derived dissolved organic matter (MP-DOM) that engages in photochemical and redox reactions. This work provides a critical overview of the aging mechanisms of MPs and the release characteristics of MP-DOM, with emphasis on its molecular properties and the intrinsic and extrinsic factors driving DOM release. Particular attention is given to the strong polymer dependence of MP-DOM, as different plastic classes can generate dissolved mixtures with distinct release kinetics, chemical profiles, and environmental reactivities. Insights into the unstable characteristics of MP-DOM are translated into measurable physicochemical reactions by evaluating its photochemical reactivity and interactions with natural minerals. Importantly, high methodological heterogeneity in experimental protocols hampers reliable comparisons across studies, underscoring the need for standardized leaching procedures in MP-DOM quantification and characterization. The role of MP-DOM in influencing the behavior of environmental pollutants, such as organic contaminants, metals, and antibiotic resistance genes, is critically assessed, particularly its contribution to disinfection byproduct formation, an ongoing concern in water quality management. Recent advances in understanding the ecological and biogeochemical impacts of MP-DOM are synthesized, highlighting its effects on cellular toxicity, microbial responses, and disruptions in element cycling and greenhouse gas emissions. Future directions include standardized aging protocols, rapid source attribution methods, and transferable models for predicting MP-DOM fate and ecological consequences under multistressor conditions. This review provides an updated synthesis of MP-DOM by linking its environmental behavior to ecological fate, advancing our understanding of the long-term ecological impacts and toxicity of plastics.