The Impact of Microplastics on Adsorption of Chlorophenols by River-Suspended Sediments

Although microplastics (MPs) are widely recognized as carriers of environmental pollutants, their impact on the adsorption behavior of chlorophenols (CPs) by river-suspended sediments (SS) remains poorly understood. This study systematically investigated the effects of three common MPs (PVC, PS, and PE) on the adsorption of 4-chlorophenol (MCP), 2,4-dichlorophenol (2,4-DCP), and 2,4,6-trichlorophenol (2,4,6-TCP) by SS from the Yellow River. Adsorption isotherms revealed that PVC significantly promoted CP adsorption, fitting well with the Langmuir model (R² > 0.95), whereas PS and PE showed better agreement with the Freundlich model (R² > 0.96). The enhancement effect varied with MP type and CP species, with PVC demonstrating the most pronounced promotion (65% increase for 2,4,6-TCP). Conversely, PS and PE hindered 2,4-DCP adsorption due to its higher partition coefficient in SS (36.83 ± 6.3 L/kg) compared to MPs (1.85 ± 0.01 L/kg for PS and 2.03 ± 0.05 L/kg for PE). Environmental factor analysis revealed that ionic strength exerted dual effects by initially enhancing CP adsorption through reduced solubility and later inhibiting it via electrostatic repulsion. Humic acid (HA) promoted TCP adsorption but inhibited DCP adsorption through aggregation and dispersal mechanisms on SS surfaces. Acidic conditions (pH 2–6) significantly enhanced CP adsorption by maintaining their molecular states, while alkaline conditions reduced adsorption due to electrostatic repulsion. Mechanistically, MPs altered SS surface properties and formed aggregates that either facilitated or competed for CP adsorption sites. This study provides a theoretical basis for ecological risk assessment of combined microplastic-pollutant contamination in sediment-laden rivers.