Sorption And Immobilization Of Polycyclic Aromatic Hydrocarbons By Microplastics In Soil

Microplastics（MPs）as an emerging class of pollutants that have received much attention from researchers in recent years.MPs are small in size,easily migrated,strongly adsorbed and widely distributed in the soil environment.It is of great importance to study the effects of MPs on the migration,distribution and biological effectiveness of organic contaminants（OCs）in soil.This paper systematically investigate the sorption and mechanism of PAHs by MPs,to analyse the influence of the presence of MPs on the sorption and distribution of PAHs in soil,to explore the influence of the type,quantity and size of MPs,soil properties and environmental conditions on the sorption and fixation of PAHs in soil,and the results of the study will The results of this study will provide a theoretical basis for further understanding of the ecological risks of MPs in soil.The main findings are as follows:（1）Both the polyethylene（PE）microplastic and the polyvinyl chloride（PVC）microplastic showed visible sorption capacity for the PAHs,reaching sorption equilibrium within 24 h.Moreover,the sorption process was a physical sorption process dominated by hydrophobic partitioning.The equilibrium partition coefficient Log K_d for PE to PAHs is significantly greater than that for PVC.For example,the Log K_d for PE to Phenanthrene is 3.82 L kg^-1 compared to 2.70 L kg^-1 for PVC.（2）The presence of MPs enhances the sorption and immobilisation of PAHs in soil.The type of MPs and the amount of MPs added affected the relative distribution of PAHs on the soil and MPs to varying degrees.When 1%of PE were added to the soil,the sorption capacity for PAHs was 4-6 times higher,with MPs accounting for approximately 30%of the total sorption of PAHs.In addition,the presence of MPs inhibited the desorption of PAHs from the soil,for example,1%PE reduced the equilibrium desorption of Phenanthrene from 6.31 mg kg^-1 to 4.42 mg kg^-1.（3）The physical and chemical properties of the soil solution significantly influence the sorption and immobilisation of PAHs by MPs.High salinity and low dissolved organic matter（DOM）content contributed to the sorption of PAHs by MPs,and conversely PAHs were more easily desorbed.When the concentration of DOM was 100 mg L^-1,the sorption capacity of the MPs for Phenanthrene decreased by30%.As the DOM content increased,the desorption rate of Phenanthrene in the Soil-MPs system increased from 1.46%to 4.90%.At the salinity of 3.5%,the sorption capacity of MPs for Phenanthrene was enhanced by a maximum of 13.5%and the desorption rate was reduced from 1.46%to 1.10%.