Mechanisms of Natural Organic Matter in Regulating Microplastic Aggregation and Transport in Soil-Groundwater Systems: A Review

• • NOM type dictates aggregation: humic substances enhance electrostatic repulsion, while proteins and EPS can induce bridging flocculation, with EPS from marine diatom showing significant aggregation of nanoplastics (reference [34]). • • Ionic strength and ion type critically modulate NOM effects: for example, NO3− and SO4^2− influence aggregation kinetics of CeO2 nanoparticles (reference [30]), and specific ion effects alter colloidal stability, impacting MP transport in porous media. • • NOM accelerates photochemical aging of MPs, increasing surface oxidation and hydrophilicity, as demonstrated by enhanced aggregation and oxidation of nanoplastics under simulated sunlight (reference [36]). • • Protein corona formation on nanoplastics significantly alters their transport in seawater-saturated porous media (reference [31]), indicating that NOM components can either enhance or inhibit mobility depending on surface interactions.