Study on the effects of benzethonium chloride and other factors on the adsorption and migration of polystyrene microplastics in saturated porous media.

A large number of disposable plastic products and quaternary ammonium salt disinfectants have been widely used due to health events around the world. Improper disposal of plastic products and disinfectants can lead to serious compound pollution and pose a potential threat to the environment. This study intends to explore the migration and mass distribution of Polystyrene in a sand medium under the pure Polystyrene system and the Polystyrene-benzethonium chloride composite system respectively. The batch experiment focuses on investigating the effects of various benzethonium chloride dosages, Polystyrene concentrations and chloride ion strengths on the adsorption of sand media. The sand column experiment focuses on studying the migration behavior of Polystyrene in a composite system under different injection flow rates (1, 3, and 5 mL/min), benzethonium chloride dosages (0.9, 4.5, and 9 mL), Polystyrene concentrations (10, 20, and 30 mg/L), and the ionic strength of sodium chloride solution (0, 0.001, 0.01, and 0.1 mol/L). Under the composite system with a flow rate of 3 mL/min, Polystyrene at 20 mg/L, 0 mol/L NaCl, and 4.5 mL benzethonium chloride (10 mg/L), column dissection and mass balance analysis showed the PS spatial distribution, achieving a 98.94 % recovery rate. The migration behavior of Polystyrene-benzethonium chloride in a composite porous medium is simulated by Hydrus-1D under different conditions. The model simulation value is close to the experimental observation value and the correlation coefficient R is greater than 0.9. Mechanistic studies were carried out using a Fourier Transform Infrared Spectrometer (FTIR) and zeta potential analysis. The results showed that hydrogen bonds were formed between polystyrene and benzethonium chloride, and factors such as ionic strength, the dosage of benzethonium chloride, and microplastic concentration jointly influenced the adsorption and migration behaviors of polystyrene in sandy media by changing the potential of the system. This study specifically provides a theoretical and methodological basis for the adsorption and migration of Polystyrene in groundwater composite pollution.