Unraveling the role of natural and pyrogenic dissolved organic matter in photodegradation of biodegradable microplastics in freshwater

Abstract Biodegradable plastic is often perceived as a possible solution for microplastic (MP) pollution. Photodegradation is an important transformation pathway of biodegradable MPs in aquatic environments. However, the influence mechanisms of dissolved organic matter (DOM) from different sources on photodegradation of biodegradable MPs are poorly understood. This study explored the role of naturally and pyrogenically sourced DOM in the photodegradation of polylactic acid (PLA) MPs. The aromatics of natural DOM (NDOM) were higher than those of biochar-sourced DOM (BDOM) and showed a stronger improvement in PLA-MPs degradation, as evidenced by particle size reduction, crystallinity increase and polymerization decrease, breakage of surface morphology, and increase in oxygen-containing functional groups on MPs’ surface (O/C increase: 65.1% for NDOM; 34.9% for BDOM). Reactive oxygen species analysis showed that the excited triplet states of DOM ( 3 DOM * ) generated by NDOM produced more •OH and 1 O 2 than that of BDOM, accelerating PLA-MPs photodegradation. Such photodegradation processes were further enhanced through the sorption of DOM by PLA-MPs, in which non-aromatic components were preferentially sorbed, causing the enrichment of aromatics in the solution, leading to more 3 DOM * formation. This study improves the understanding of the migration and transformation of biodegradable MPs with the presence of DOM. Graphical Abstract