Distribution Characteristics And Migration Influencing Factors Of Microplastics In Drainage Ditch Of Hetao Irrigation District

Microplastics pollution in terrestrial runoff has attracted more and more attention due to its closer relationship with human beings.In this study,microplastics in the water and sediment of the drainage ditches of Hetao Irrigation District were taken as the research objects,and samples of microplastics in the water and sediment were collected in the dry season,normal season and wet season for analysis.The characteristics of the abundance,shape,particle size,color and type of microplastics in the water and sediment in the drainage ditches of Hetao Irrigation District were investigated by flotation separation method and identification techniques of type microscope,laser confocal microscope,scanning electron microscope and Fourier infrared spectroscopy.In order to further clarify the influencing factors of the migration of microplastics in water,a simulation experiment was carried out through an indoor flume,and a simulation equation of the migration of microplastics was established.The main research conclusions are as follows:（1）Microplastic particles were found in all the samples of dry ditch water in Hetao Irrigation District,and there were significant spatial differences in their abundance.The maximum abundance value at U12 is 12190 n·m^-3in low water season,11200 n·m^-3 in normal water season and 9600 n·m^-3 in wet season,respectively.The minimum abundance value of U10 was in the upstream of the total drainage,which was 3200 n·m^-3 in dry season,2880n·m^-3 in normal season and 2910 n·m^-3in wet season,respectively.In general,the abundance of microplastics increased from upstream to downstream,and the abundance of microplastics in the dry season was higher than that in the normal season and higher than that in the wet season.The microplastics were mainly fibrous,accounting for 40.95%-72.59%in dry season,39.23%-68.87%in normal season and 49.58%-70.39%in wet season,respectively.The color of microplastics was mainly transparent,black,red,blue and green,and the size of microplastic is mainly less than 1mm.（2）The maximum abundance value of microplastics in the sediment of drains in Hetao irrigation area is U8 point in the middle reaches of the seventh drains,which were 360n·kg^-1 in dry season,292 n·kg^-1 in normal season and 245 n·kg^-1 in wet season,respectively.The minimum abundance value of U10 was in the upstream of the total drainage,which was141 n·kg^-1 in dry season,100 n·kg^-1 in normal season and 85 n·kg^-1 in wet season,respectively.In the distribution of time,the average abundance value of microplastics in the dry season was higher than that in the normal season and higher than that in the wet season,which was due to the weak hydrodynamic conditions and less precipitation in the dry season,which provided good conditions for the deposition of microplastics.The shape of microplastics was also mainly fibrous,accounting for 46.55%-59.14%in dry season,42.25%-66.01%in normal season and 55.69%-62.34%in wet season,respectively.The color of microplastics was mainly transparent and black,with some red,blue and green,and the microplastic particle size was also less than 1mm as the main particle size.（3）The results of FTIR analysis showed that PE（polyethylene）was the main type in dry,normal and wet seasons,followed by PS（polystyrene）and PP（polypropylene）.The proportion of PE in water is 45%in dry season,43%in normal season and 38%in wet season.The proportion of PE in sediment is 35%in dry season,44%in normal season and 36%in wet season.The results showed that it was related to the widespread use of agricultural film in Hetao Irrigation District.SEM analysis results show that after a long time of wind erosion and hydraulic friction,the scratches and holes formed on the surface of microplastics are very likely to provide adhesion points for other pollutants in the water,thus increasing the combined pollution effect of microplastics and other pollutants.（4）In order to investigate the microplastic discharge quality of the total dry ditch drainage in Hetao Irrigation District,Inner Mongolia,the proportion flow method was used to estimate that the microplastic discharged into the Lake Ulansuhai by the total dry ditch drainage in Hetao Irrigation District was about 116.06kg per day,with an average annual discharge mass of about 42.36t.In terms of microplastic particle size,the microplastics with particle size of 2.5～5.0 mm had the highest weight.The microplastics accounted for 76.03%of the total mass,and the debris accounted for 71.27%of the total mass.（5）In order to explore the influencing factors of the migration of microplastics,the microplastic particle size,initial flow velocity and microplastic quality were considered comprehensively,and the equation y=27.303-0.022X₁+13.205X₂+1035.708X₃ was established through multiple regression fitting with SPSS 22.0 software.By investigating the occurrence of microplastics in the drains of Hetao Irrigation District,the pollution level of microplastics in Hetao Irrigation District was clarified,which has certain guidance and reference significance for the treatment of microplastics in the large and medium-sized irrigation areas of the Yellow River basin,which are mainly dominated by agricultural film mulching.The total mass of microplastics in total drainage was estimated.To provide theoretical support for the quality comparison and analysis of microplastics in different rivers;The model of microplastics migration was established to provide a reliable theoretical basis for river treatment of microplastics pollution.