Study On Vertical Migration Characteristics Of Microplastics In Soil

As a natural resource for human survival,soil is faced with the problem of microplastic pollution.Compared with plastic fragments,microplastics are more uncertain in terms of migration,deposition and bioutilization,and are more likely to accumulate in organisms and migrate along the food chain.Understanding the transport and interaction of microplastics in various soils is very important for pollution prevention and control.In order to find out the retention and migration characteristics of microplastics in soil,the migration behavior of polystyrene microspheres(PS)in different soil media was investigated.Quartz sand medium was used to simulate soil leaching environment to explore the migration and change law of microplastic particles,and soil minerals and soil were divided into porous media to study the transport characteristics of PS particles in soil environment.The main conclusions are as follows:(1)The migration ability of PS particles strongly depends on the particle size.The mass recovery(TMR)of PS particles(PS50)with 50 nm particle size in quartz sand is more than 85%,which can be moved out more completely.PS500 showed slower migration rate and higher adhesion efficiency than PS50 and PS100(TMR ≤ 20% at10 m MNa Cl).The experimental adhesion efficiency(α)follows the law of PS50 <PS100 < PS500.In addition,the retention rate of PS particles increases with the increase of initial concentration.(2)The eluent with high ionic strength will lead to high retention rate of PS particles in porous media.Weak alkaline solution and SOM content are beneficial to the migration of PS particles in porous media.Combined with characterization and CFT colloid theory analysis,electrostatic repulsion dominates the change of migration behavior of microplastics.The hydrodynamic size of PS particles will change with the change of solution chemical conditions,and the physical strain caused by the increase of particle size is also an important factor affecting the retention of microplastics in the medium.(3)In soil mineral media,the mobility of microplastics in volcanic rocks is about0.4-0.6 times that of quartz sand under the same conditions,and that of fine river sand is about 0.7-0.8 times that of quartz sand.The TMR of PS particles in concentrated SOM is ≥ 89%,which is higher than that in quartz sand media.The mixture of humus and soil minerals can effectively reduce the retention rate of PS particles,and has a higher response intensity to change the migration capacity of microplastic particles.