Spatial Distribution Of Microplastics In Mollisol Farmland Of Northeast China

Microplastics usually were defined as the plastic particles with diameter or length less than 5 mm,which have been widely distributed in the environment.Due to its small size,stable nature and difficulty in degradation,microplastics can exist for a long time and widely distribute in the environment.In recent years,the ecological environmental effects of microplastics have become a kind of concern in the global ecological environment.In particular,a lot of work has been done by researchers on the spatial and temporal distribution as well as the potential ecotoxicological effects of microplastics in rivers,coastal zones and oceans.While the research on the land environment,especially the cultivated soil,is insufficient,the main reason is the lack of analytical methods for the separation,extraction and identification of microplastics from soil.With the improvement of new methods for the determination of soil microplastics,some methods has realized the separation,identification and quantitative analysis of microplastics from soil,and accelerated the research progress of spatial and temporal distribution of soil microplastics and its ecological and environmental risk assessment.As the largest plastic repository on land,the spatial and temporal distribution and migration process of microplastic are related to the whole terrestrial ecosystem and even the global ecosystem,so it is very important to study the morphological characteristics,spatial and temporal distribution and the main driving mechanism.The cultivated land soil covered with plastic film in typical black soil area of Harbin was selected as the research object,and a total of 4 typical cultivated lands were studied by means of sample belt,sample plot survey and indoor simulation.Density floatation separation method and heating method were adopted to research the spatial distribution characteristics of the abundance,particle size and mass and main driving mechanism of microplastics in cultivated soil.It provides theoretical basis and technical support for revealing the distribution characteristics of plastic pollutants in black soil area and evaluating their ecological and environmental effects.The main research results and conclusions are as follows:(1)Microplastic residues were found in all four sampling areas,the abundance of microplastics was between 60-2300 μm at 0-20 cm and 90-4000 μm at 20-30 cm.The abundance of microplastics in different sampling areas is related to the macroplastic residues,the more large plastic residues in the soil,the greater the microplastic abundance would be.The abundance of microplastics in surface soil could reach 89 n/kg;(2)The main factor affecting the horizontal distribution of microplastics in soil is soil erosion.Microplastics are abundant in low-lying areas with high water content.The abundance of microplastics also varies between different layers of soil,which detected in the subsoil were up to 400 n/kg,4 timeshigher than the corresponding topsoil.The abundance of microplastics in the subsoil was determined by the presence and strength of the preferential flow.Due to the influence of weathering degree,the size distribution of environmental microplastics is not completely consistent,and there is spatial variability in the particle size and abundance of microplastics.The smaller the size of microplastics,the easier it is to migrate in the soil.(3)The migration of microplastics in soil is mainly affected by surface runoff and soil flow.Under the influence of water erosion,the number of horizontal migration was the largest,accounting for98.33 % of the total migration.The lower the surface runoff is,the more soil erosion is,and the higher the quality of horizontal migration of microplastics is.In the vertical direction,the downward migration amount of microplastics is small,but the change trend is stable,and the migration amount is between0.01-0.03 g;(4)In the horizontal direction,the smaller the soil bulk density,the more the microplastic migration.In the vertical direction,the higher the soil bulk density,the more the microplastics migrate downward.In terms of the loss of soil surface microplastics,the bulk density of 1.0 g/cm3 was 38.92 %higher than that of 1.2 g/cm3.The migration of microplastics by interflow was 6.12% and 26.7% lower in 1.0 g/cm3 treatment than in 1.2 g/cm3 treatment at the bottom two exits,;(5)In the horizontal direction,the microplastics are mainly transported by the eroded soil under the bulk density of 1.2 g/cm3.When the soil bulk density is 1.0 g/cm3,while the microplastics are carried by the eroded soil,they are more likely to migrate with the runoff compared with 1.2 g/cm3.In the vertical direction,it is mainly the downward migration with subsurface runoff,and the longer the runoff duration,especially under the influence of corredeiras,the more microplastics migrate downward;In a word,microplastics are ubiquitous in the soil covered by film of the black soil area,and their distribution is not only affected by the macroplastics and cultivation,but also mainly affected by erosion,surface runoff,interflow and other factors.In particular,water erosion changes the horizontal distribution characteristics of soil microplastics.