Study On The Adsorption Behavior Of Polyethylene Microplastics On Typical Pesticides In Water Environment

Microplastics are pieces of plastic smaller than 5 mm in size.In addition to the pollutants contained in microplastics,microplastics can also enrich and migrate organic matter,heavy metal and other pollutants.In recent years,microplastics pollution has been widely concerned.Scholars from various countries have conducted a lot of research on the compound pollution of microplastics with persistent organic pollutants,heavy metals,and antibiotics,but the interaction between microplastics and pesticides has not received enough attention.China is a great agricultural country with the most output of pesticides in the world,and the pesticides are typical pollutants in farmland soil.It is of great scientific significance to study the adsorption behavior of pesticides on microplastics to understand the combined pollution of microplastics and pesticides.In this paper,polyethylene microplastics and four pesticides(Imidacloprid,Indoxacarb,Buprofezin and Difenoconazole)were selected as the research objects.Effects of the adsorption time,microplastics dosages,pH,and NaCl salinity on the adsorption behaviors were investigated.The adsorption mechanism of pesticides on microplastics was explored by the analysis methods of adsorption isotherms,adsorption kinetics,adsorption thermodynamics,microplastic characterization,and molecular dynamics simulations.The results showed that:(1)The adsorption capacity of pesticides on microplastics increased with time and finally reached dynamic equilibrium at 30 h.When the concentration of pesticides was 50 μg/L,increasing the concentration of microplastics could reduce the unit adsorption capacity of microplastics.High pH(pH was in the range of 6 to 10)and low NaCl salinity(salinity was in the range of 0.05 % to 3.5 %)were conducive to the adsorption.(2)The adsorption data were well fitted by the Freundlich isotherm model and the pseudo-first-order kinetics,indicating that it was multilayer adsorption and mainly controlled by physical function.The thermodynamic study indicated the adsorption of all pesticides as spontaneous and exothermic processes,and the elevated temperature was favorable to the adsorption.(3)SEM-EDS and FT-IR analysis verified that pesticides may be adsorbed on the microplastics with little adsorption and no response in FT-IR.The molecular dynamics simulations showed that the adsorption mechanism of pesticides on microplastics was surface adsorption,and the adsorption was mainly affected by Van Der Waals Force and electrostatic force between pesticide molecules and the PE molecule.