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Microplastics (MPs), as a common "vector" of pollutants in the aquatic environment, have a significant impact on the migration and transformation of heavy metals. In order to explore the mechanism and the influencing factors of the adsorption behavior of microplastics (MPs) on selenium (Se) in aqueous solution under the coexistence of nanoparticles, polystyrene microplastics (PS), nano-titanium dioxide particles (TiO2) and their coexisting compounds (PS + TiO2) were used as adsorbents to investigate the adsorption kinetics, isotherms and thermodynamic processes of Se. The effects of pH, humic acid concentration and coexisting ions on the ad-sorption behavior of Se(VI) were also analyzed. The results showed that the adsorption process of Se(VI) by PS and PS + TiO2 could be well fitted by pseudo-second-order kinetic model and Freundlich isotherm model, and it was an endothermic reaction with increased entropy. The adsorption capacity of Se(VI) by PS, TiO2, and PS + TiO2 were decreased with the increase of solution pH. Humic acid and Ca2+ promoted the adsorption of Se (VI), while PO43- significantly inhibited the adsorption of Se(VI) in the above three systems. The main adsorption mechanism of PS on Se(VI) was electrostatic adsorption and hydrogen bonding. The TiO2 adsorbed on the surface of PS mainly affected the adsorption behavior of PS on Se(VI) through hydrogen bonding. [ABSTRACT FROM AUTHOR]