Study On The Aggregation Of Nano-polystyrene In Simulated Lung Fluid And Its Adsorption Behavior In Water Environment

Microplastics is a global environmental pollutant.Due to its small particle size and resistance to degradation,it is ubiquitous in the atmosphere,water and land environment and can be used as the carrier of various pollutants in the environment.The aggregation and adsorption behavior of microplastics can affect their transport and toxicity in the natural environment.In this paper,four kinds of polystyrene microplastics PSMPs（MP500、MP100、A-MP100、C-MP100）modified with different particle sizes and surface functional groups were selected,and two simulated lung fluids（ALF pH 4.5 and GMB pH7.3）were used.The dynamic light scattering technology,atomic absorption spectroscopy,image acquisition and other methods were applied.The effects of the physical-chemical properties of PSMPs and the lung fluid components on the aggregation kinetics of PSMPs in lung fluid and the effects of PSMPs on the adsorption performance of lead ions(Pb²⁺)in aquatic environment were studied,to explore the factors that play a key role in the aggregation of PSMPs,to clarify the aggregation mechanism of PSMPs in simulated lung fluid,to analysis the influence of water environment conditions such as pH and coexisting ions on the adsorption of heavy metal lead by PSMPs,to reveal the adsorption mechanism of PSMPs to lead ions,giving basis for predicting the harm of microplastics to human exposure in the environment.The main conclusions are as follows:（1）The aggregation rate of PSMPs in lung fluid is not only related to its particle sizes,but also related to the modification of PSMPs surface by functional groups and the composition of simulated lung fluid.In simulated lung fluid ALF,the aggregation rate of PSMPs is A-MP100>C-MP100>MP100>MP500.The particle size of A-MP100 increased to 575.4 nm at 20 min.Meanwhile,in simulated lung fluid GMB,A-MP100,MP100 and MP500 did not aggregation,while C-MP100 could aggregation.（2）When the four kinds of PSMPs stay in ALF and GMB for a long time,the particle size of the four kinds of PSMPs gradually increases within 24 h（If it stayed in ALF for 6 h,the particle size of A-MP100 was 2222.33 nm）,and then reaches a certain value due to the gravity deposition.The pH changes of simulated lung fluid can affect the aggregation behavior of PSMPs.（3）The inorganic components in ALF and GMB have a significant effect on the aggregation behavior of MP100.The critical coagulation concentrations（CCC）value of monovalent salt solution was significantly higher than that of divalent salt solution,and MP100 was more stable in monovalent salt solution.In ALF,the CCC value of MP100 in sodium was about 14 times that of calcium.The aggregation rate of MP100 in organic components of ALF and GMB varies with the concentration of the components,which is determined by the type of organic components.（4）PSMPs can quickly adsorb Pb²⁺and reach equilibrium in 30 min.The adsorption process conforms to the pseudo-second-order kinetic model,and the adsorption isotherm fits the Langmuir model.The surface charge of microplastics can be changed by pH,and the equilibrium adsorption capacity of Pb²⁺by PSMPs increases with the increase of pH.With the increase of NaCl concentration,the equilibrium adsorption capacity of PSMPs for Pb²⁺decreased.However,in the presence of Mn²⁺,the promoting ability of PSMPs on the equilibrium adsorption capacity of Pb²⁺gradually weakened with the increasing of Mn²⁺concentration.