Mechanistic insights into UV/H₂O₂-aged polystyrene enable an optimized protocol for fungal biodegradation

Plastic pollution poses a global environmental challenge, yet its biodegradation remains inefficient and the underlying mechanisms are still unclear. In this study, we developed a plastic degradation protocol by pretreating polystyrene (PS) films with ultraviolet (UV) irradiation and hydrogen peroxide (H₂O₂), followed by biodegradation with Phanerochaete chrysosporium ( P. chrysosporium ). The UV/H₂O₂ pretreatment exhibited the best performance, achieving a mass loss of up to 25.75% and introducing key oxygen-containing functional groups, including carbonyl, hydroxyl, and carboxyl groups. These functional groups act as electron donors, facilitating subsequent extracellular enzymatic chain-cleavage reactions. This treatment also promoted fungal colonization and enhanced the activities of extracellular enzymes, including manganese peroxidase (MnP), lignin peroxidase (LiP), and laccase (Lac). Furthermore, the pretreated PS was degraded through three main pathways before entering the tricarboxylic acid cycle: (1) direct assimilation of carboxyl-containing compounds by microorganisms; (2) cleavage of aromatic rings in PS-derived compounds mediated by homogentisic acid 1,2-dioxygenase and 4-hydroxy-2-oxoglutarate aldolase, producing metabolizable intermediates; (3) further oxidation of long-chain aromatic intermediates by cytochrome P450, producing smaller compounds that enter central metabolism. Overall, this work demonstrates that UV/H₂O₂ pretreatment enhances surface oxidation, microbial colonization, and enzymatic reactivity, providing new insight into accelerating plastic biodegradation in environmental applications.