Spatial Distribution And Migration-Sedimentation Law Of Microplastics In Ulansuhai

As a new type of pollutant with easy migration,small particle size and great harm,microplastics have received more and more attention in the research of water environment.Traces of microplastics have been found in oceans,rivers,mountain lakes,urban lakes,reservoirs and other environments.However,most of them focus on the basic investigation of microplastics,their horizontal migration and distribution affected by the external environment,and their toxicological effects in water bodies.There are few studies on the influence of the nature of microplastics on their migration distribution in different environments and the correlation between the migration distribution of different types of microplastics and wind speed.This thesis takes Ulansuhai,a typical shallow lake in northern China,as the research object.Combining similar environmental behavior of microplastics and suspended particles in water bodies then considering its differences,refer to the research method of suspended particles,a new research method for microplastics is proposed.The samples were collected using a new self-made microplastic trap to accurately quantify the vertical sedimentation process of d ifferent types of microplastics.Using a combination of laboratory experiments and microscope observations,the pollution level of microplastics in the water and sediments of Ulansuhai was investigated,the source of microplastics in Ulansuhai was explored,and the effects of various parameters on the migration of microplastics in different media were analyzed.The risk index（H）model and the pollution load index（P LI）method were used to evaluate the ecological risk of microplastics in lake water and sedi ment environment,and to determine the grade and pollution degree.To explore the effects of its own physical properties（density,size,shape）and different wind speeds on different types of microplastics when microplastics undergo vertical migration-settlement process.The main findings of this study are listed as follows:1.The abundance of microplastics in the Ulansuhai water body is in the range of（621±62.8）-（1224±185）n·L^-1,with the direction of lake water flow,it is wavy from north to south.The abundance value of mouth and scenic spot is higher.Among the three microplastics with different density ranges,the microplastics of 1.0-1.2g·（cm³）^-1 are the most abundant in the lake;among the three particle size ranges of microplastics,the abundance of microplastics between 0.5-2mm is the highest and shows a decreasing trend from north to south;in addition,among the four different shapes of microplastics,fibrous microplastics were evenly distributed and dominant.According to the results of Raman spectroscopy,there are 5 kinds of microplastics in Ulansuhai water,namely polypropylene（PP）,polyethylene（PE）,polystyrene（PS）,polyvinyl chloride（PVC）and polyethylene terephthalate（PET）,of which polypropylene（PP）and polyethylene（PE）are high in c ontent.2.The abundance of microplastics in Ulansuhai sediments ranges from（582±45）-（1013±49）n·100g^-1,and the abundance of microplastics at each sampling point is generally high.In the lake,the abundance is high in the central lake area and low at bot h ends,and the abundance near the lake entrance is the highest.The abundance of microplastics with a density range of 1.0-1.2g·（cm³）^-1 was higher in lake sediments,and the abundance of microplastics with a size of 0.05-0.5mm was higher and increased from north to south.In addition,the microplastics in the sediment are mainly in the form of films and fibers.According to the results of Raman spectroscopy,five kinds of microplastics,which are the same as those in the water,were found in the sediments of Ulansuhai.Among them,polystyrene（PS）,polyvinyl chloride（PVC）and polyethylene terephthalate（PET）,which are denser,have higher contents.3.Using risk index（H）and pollution load index（PLI）models,the overall potential ecological risks of microplastics in different environments were evaluated from the perspectives of microplastic component toxicity and abundance,respectively.The results showed that the microplastic pollution in water bodies and sediments was at moderate to severe levels,and the sediment medium was generally more ecologically risky than the water body environment.4.The vertical sedimentation flux of low-density microplastic polymers（with a density lower than water body）in the Ulansuhai increases with the increase of wind speed.Among them,the fibrous and different sizes（0.05-0.5mm,0.5-2mm,2-5mm）low-density microplastic polymer sedimentation flux have a good correlation with wind speed,and the correlation coefficient is between 0.268-0.836.In addition,according to the detection results of Fourier infrared spectroscopy,the main components of the low-density microplastic polymer are polypropylene（PP）and polyethylene（PE）.5.The vertical sedimentation flux of high-density microplastic polymer（density higher than water body）in Ulansuhai increases with the increase of wind speed,and its correlation coefficient is between 0.72-0.894.High-density microplastic polymers are more affected by wind than low-density microplastic polymers.In addition,according to the detection results of Fourier infrared spectroscopy,the main components of high-density microplastic polymers are polystyrene（PS）,polyvinyl chloride（PVC）,polyethylene terephthalate（PET）and Rayon（RAY）.6.The properties（density,size,shape）of microplastics in the Ulansuhai have important effects on the horizontal and vertical migration-settling processes in the water body.For micropla stics of different densities,the higher the density,the shorter the migration distance in the horizontal direction,and the more prone to vertical sedimentation,and the lower the density,the longer the migration distance.For different sizes,the small er the particle size of microplastics,the longer the migration distance,and the larger the particle size,the shorter the migration distance.For different shapes,fibrous and film-like microplastics tend to migrate horizontally,while fragmented and sph erical microplastics tend to settle vertically.