Dissolved organic matter derived by microplastic: The release patterns, structure properties, composition, and the impact on rice

The agricultural ecosystem, particularly the paddy field, is a notable sink for microplastics (MPs) due to the widespread application of plastics. MPs often contain some additives (bisphenol A, phthalates, etc.) and these toxic substances are released by dissolved organic matter (DOM). However, the interference behavior of MPs- derived DOM on the crop is still unclear. This study employed traditional MPs (polystyrene, PS; polyethylene terephthalate, PET) and biodegradable MPs (polylactic acid, PLA) to indicate the structural properties and composition of MP-derived DOM on the rice. PLA-MPs had the maximum potential for DOM release, which was significantly higher than the other MP types (P < 0.05). Furthermore, the PLA-DOM was easily degraded, because it contained an amount of lower molecular weight compounds (e.g., 2-hydroxy-1-propionic acid). All MP-derived DOM had an inhibitory effect on rice seed germination. These DOM also affected the biosynthesis of rice pigments and reduced stomatal conductance (7.48 %-19.8 %), because MP-derived DOM caused oxidative stress to damage cell structures and affect the synthesis of related proteins. Additionally, DOM derived from PET and PLA increased catalase enzyme activity (12.07 %-15.56 %) to scavenge reactive oxygen species. This study provides new insights into the ecological toxicity of MPs in the agricultural ecosystem.