Microplastic Aging And Their Effects On The Sorption Of Phenanthrene And Atrazine In The Water Environment

Microplastics（MPs）have the characteristics of small particle size,large specific surface area,and strong adsorption capacity for organic pollutants,which are key factors affecting the environmental behavior of organic pollutants.At present,the research on the adsorption of organic pollutants by MPs has mostly focused on the effect of single water quality conditions.However,there is still a lack of research on the adsorption of organic pollutants by MPs due to the changes of multiple factors（ie,compound factors）in complex and changeable environment.Dissolved organic matter（DOM,such as humic acid）is an important water quality indicator,which can interact with organic pollutants to affect its water solubility,and it can also be adsorbed by MPs to change the surface chemical properties of MPs.Moreover,the conformation and charge of DOM are affected by other water quality conditions（such as p H and salinity）.These will affect the behavior of MPs in adsorbing organic pollutants.Therefore,this paper selects newly made and aged polyethylene（PE and APE）and polystyrene（PS and APS）MPs as adsorbents,two organic pollutants with different polarities（Phenanthrene and Atrazine）as adsorbates,to study the effects and mechanisms of single water quality conditions（p H,salinity,humic acid）and composite water quality conditions on the adsorption behavior of organic pollutants in water.The main results obtained in the thesis are as follows:（1）After aging,the surface pores and polarity of PE and PS MPs increased.The adsorption isotherms of phenanthrene and atrazine on these four MPs conform to Freundlich model（R²>0.91）;The adsorption capacity（log K_f）for phenanthrene was APE>PE>PS>APS,and the adsorption was dominated by partition.The adsorption capacity of APE and APS for atrazine was higher than that of PE and PS,and the adsorption was dominated by partition and surface adsorption.In addition,the adsorption capacity of the same kind of micro plastics for phenanthrene is stronger than that of atrazine,which is related to the hydrophobicity of the two pollutants.（2）The adsorption results of phenanthrene and atrazine by MPs under single water quality showed that the adsorption capacity of phenanthrene and atrazine by these four micro plastics increased firstly and then decreased with p H value,and the maximum adsorption capacity appeared near the isoelectric point.The adsorption of phenanthrene and atrazine on these four MPs varies with salinity(Na⁺and Ca²⁺concentrations)just opposite to p H.And the effects of salinity and p H on the adsorption of PE and APE are significantly lower than that of PS and APS.The adsorption capacity of phenanthrene on PE and APE was little affected by the concentration of humic acid,while the adsorption capacity on PS and APS increased significantly.Humic acid has little effect on the adsorption of atrazine by these four MPs.（3）The results of compound water quality conditions showed that the influence of Ca²⁺concentration on the adsorption of humic acid by these four MPs was significantly higher than that of Na⁺under the same p H condition.And the adsorption capacity of humic acid increased significantly with the increase of Ca²⁺concentration.Under the same Na⁺/Ca²⁺concentration,the lower the ion concentration,the more significant the effect of p H on the adsorption of humic acid on MPs.Under complex water conditions(different Na⁺/Ca²⁺concentrations and p H),humic acid significantly affected the adsorption of phenanthrene and atrazine on MPs.The correlation results showed that the adsorption of phenanthrene by MPs was significantly positively correlated with the adsorption of humic acid in most cases,regardless of the addition of Na⁺or Ca²⁺;on the contrary,atrazine showed a significant negative correlation.Electrostatic interaction and conformational change of humic acid are the main mechanisms affecting the adsorption of phenanthrene and atrazine by MPs in compound water quality conditions.