Beyond the surface: how dissolved organic matter recasts the biogeochemical behaviors of micro- and nanoplastics in aquatic environments

Micro- and nanoplastics (MNs) and dissolved organic matter (DOM) widely coexist in aquatic environments, and their interactions are receiving increasing attention. These interactions influence the biogeochemical behaviors of plastic particles in natural systems. However, the behavioral characteristics, fate processes, and ecotoxicological impacts of MNs under DOM involvement have not been systematically analyzed. Therefore, this review summarizes the promotion and inhibition mechanisms of DOM on MNs photoaging, in which the primary chromophore (light-absorbing entity) of DOM can induce the production of triply excited state DOM (³DOM*) and reactive oxygen species (ROS) to promote MNs photoaging, or alternatively, limit MNs photoaging by shielding light and scavenging the reactive intermediates. The effect of DOM on the stability of MNs particles is emphasized, where forces such as hydrogen bonding, coulombic forces, hydrophobic forces, and π-π bonding can help mediate the interaction between DOM and MNs, with the resulting additional electrostatic and spatial effects subsequently dominating the aggregation, deposition, and transport behaviors of the particles. The impacts of DOM on the adsorption of inorganic and organic pollutants in water by MNs and their corresponding interference mechanisms are discussed. Additionally, special attention focuses on the toxicological effects on aquatic biota of the ecological and biological corona formed by DOM with MNs, which provides a protective coating that reduces the physicochemical toxicity of particles, but in certain cases, it may exacerbate toxicity. Finally, knowledge gaps that need to be addressed for DOM-MNs interactions and related effects, as well as future research directions are presented.