Study On The Migration Of Microplastics In Sediment And Surfacewater Under Different Environmental Media Conditions

As a typical representative of microplastics(d<5mm),polystyrene microplastic particles are widely used in all aspects of people’s lives.Microplastics are aged through various physical and chemical effects in the natural environment,the physical and chemical properties of the surface are changed,and their migration laws in the water environment are also changed.However,people pay more attention to the transportation and migration of microplastics in the water environment,and not enough attention has been paid to the migration rules between water bodies and sediments.In this study,indoor simulated ultraviolet light irradiation was used to accelerate the aging process of polystyrene microplastics,and the migration of newly made polystyrene microplastics and aging microplastics between the two phases of mud and water was systematically studied.FTIR,SEM-EDS,Zeta potential and other characterization methods were used to analyze the changes of polystyrene microplastics before and after aging.Utilizing the thermal expansion and contraction properties of microplastics,Nile red dye is used to mark microplastics,and the quantitative and qualitative analysis of polystyrene microplastics between two phases of mud and water is quick and convenient.The beaker test was used to explore the migration efficiency of microplastics in the suspended particulate matter-water-microplastic system under different conditions(disturbance intensity,pH,HA,suspended matter concentration,organic matter);according to the beaker experiment,a disturbance test was designed to simulate different depositions.In the suspended state,the polystyrene microplastics move vertically in the overlying water and bottom mud.Using Pelect constant,DLVO theory,and sedimentation velocity theory to analyze the migration of polystyrene microplastics in water.The results of this study are as follows:(1)The migration efficiency results show that the migration efficiency of the microplastics increases with the increase of the disturbance intensity,and the aged polystyrene microplastics migrate more easily than the new ones.When the disturbance intensity reaches 220r/min,the migration efficiencies of the new and aged polystyrene microplastics reach 98.21% and 100.00%,respectively.The disturbance promotes the microplastics deposited in the bottom mud into the overlying water.Medium-speed disturbance and high-speed disturbance caused the abundance of microplastics in the overlying water to increase by 269.74% and 648.96%,respectively.The abundances in the bottom mud are140n/kg and 210n/kg,respectively.(2)As the temperature of the water increases,the pH value decreases,and the absolute value of the Zeta potential on the surface of the polystyrene microplastic decreases,which affects the agglomeration between particles and increases the migration efficiency.When the water temperature reaches 35°C,the migration efficiency of the newly prepared polystyrene microplastics increases from 80.71% to 100%;the aging polystyrene microplastics increases from 77.14% to 99.29%.In the disturbance test,the abundance in the overlying water was 53.33±7.16n/m L;the abundance in the bottom mud reached330n/kg.(3)As the HA concentration increases,the migration efficiency decreases.When the HA concentration reaches 30 mg/L,the migration efficiencies of the newly prepared and aged polystyrene microplastics are 63.05% and 70.98%,respectively.HA is adsorbed to polyphenylene through π-π interactions.On the vinyl surface,electrostatic repulsion and steric hindrance increase,which inhibits the downward migration trend of microplastics.However,in the presence of organic matter in suspended solids,the migration efficiency of newly made and aged polystyrene microplastics reached 65% and 94.28%,respectively.This may be due to the complex composition of organic matter in the water.In addition to humus,there are other organic matter,such as carbohydrates and analogs.Fatty compounds and other organic matter promote the sedimentation of microplastics.(4)Water worms have a certain effect on the migration of microplastics between mud and water.Before and after the disturbance,the abundances of microplastics in the overlying water were 245.00±8.74n/m L and 909.83%±79.39n/m L,respectively;the abundances of the control group were 261.17±16.22n/m L and 965.67±83.17n/m L,and the abundant of the sediment was 110n/kg.