Interaction of Dissolved Organic Matters and Microplastics Regulates the Transport of Microplastics in Saturated Porous Media

The transport behavior of microplastics in soil environments is significantly affected by dissolved organic matter (DOM). However, the regulation of different types of DOM on the transport of microplastics in media is poorly understood, especially at a quantitative level. In this study, we found that three types of DOM, humic acid (HA), bovine serum albumin (BSA), and sodium alginate (SA), promoted the transport of polystyrene microplastics (PS) in column experiments. The transport of PS was stronger with increasing DOM concentrations. Among the three types of DOM, HA promoted the mobility of PS the most due to electrostatic repulsion and steric hindrance. Through the combination of Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, isothermal titration calorimetry (ITC), and colloidal atomic force microscopy (AFM), we found that the interactions between PS and HA, as well as the BSA, were mainly van der Waals forces, hydrogen bonding, and hydrophobic forces. In contrast, the interactions between PS and SA were mostly hydrogen bonding and electrostatic forces. The results provide a deep understanding of the interfacial interaction of microplastics and DOM in the transport process, based on both experimental measurements and model predictions, and are of great significance to evaluate the fate of microplastics in soil environments.