Coupled Reactive Regulation by Microplastic-Derived Dissolved Organic Matter Sustains Reactive Oxygen Species Cycling in Laccase-Metal Synergy for Continuous Microplastic Degradation

Microplastics (MPs) persist in the environment due to their chemical inertness and structural stability, underscoring the need for effective degradation strategies. Here, we develop a surface-confined cascade system in which laccase is coupled with metal ions (Na+, Cu2+, Fe3+) to activate reactive oxygen species (ROS) for the degradation of three representative polymers─polyethylene (PE), polyethylene terephthalate (PET), and polylactic acid (PLA). The laccase-Cu2+ system (optimal at 0.1 mM) exhibited the strongest catalytic performance, inducing substantial oxidative transformation of MPs, as reflected by pronounced increases in O/C ratios and extensive disruption of polymer surface chemistry. Among the three polymers, PLA showed the highest degradation susceptibility owing to its lower crystallinity, labile aliphatic ester linkages, and enhanced responsiveness to ROS. In situ-generated MPs-derived dissolved organic matter (MPs-DOM) further regulated interfacial redox processes by accelerating electron transfer to metals, stabilizing reduced species, and sustaining ROS cycling. XPS and solution-phase analyses corroborated the DOM-assisted metal redox cycling at polymer interfaces. Multivariate modeling identified humic-like components and oxygenated moieties as the dominant ROS predictors. These findings reveal MPs-DOM as an active redox mediator that reinforces laccase-metal synergy, enabling persistent ROS generation and progressive MPs degradation.