Dissolved organic matter decreases the interaction between polystyrene nanoplastics and magnetic biochar in multi-solute systems

Nanoplastics (NPs) are emerging pollutants that are effectively adsorbed by magnetic biochar (MBC). However, in complex aquatic environments, other carbon substances such as dissolved organic matter (DOM) considerably affect the microinterface interactions between NPs and MBC, but the interaction mechanism remain unclear. This research investigates the effects of different DOM types-fulvic acid (FA) and humic acid (HA)-on the adsorption behavior of polystyrene NPs (PSNPs) by MBC. Both FA and HA were found to decrease the adsorption affinity of MBC for PSNPs, with reductions of 80.3 % and 53.2 %, respectively, compared to systems without DOM. It was inferred that MBC preferentially complexes and forms ligands with the aromatic and hydrophobic substances in the FA structure, inhibiting the attachment of PSNPs. Environmental factors, such as ionic strength and high-valence cations could reduce the adverse effects of DOM on MBC-PSNP interaction via ion bridging in multi-solute systems. The type of DOM also influences the sequential arrangement of functional groups during the adsorption of PSNPs by MBC. In different water media, seawater exhibited minimal impact on the interactions among PSNPs, MBC and DOM. Overall, these findings provide new insights into the fate and transport of PSNPs in multi-solute systems.