Research On Temporal And Spatial Pollution Characteristics Of Microplastics In Urban River Water Body And Sediment After Comprehensive Treatment

Microplastics refer to plastics with a size less than 5mm,which is a new type of pollutant in the environent.Microplastics are small in size,large in specific surface area,and strong in hydrophobicity.They are ideal carriers for many hydrophobic organic pollutants and heavy metals.Microplastics existing in aquatic ecosystems can enter the food chain through direct and indirect pathways,where they are transferred and enriched.Which poses a potential threat to organisms.In order to fully evaluate the ecological and environmental risks of microplastics,it is necessary to characterize their abundance,distribution and potential sources.Rivers are the key path for the transmission of microplastics from land to the sea.In recent years,comprehensive renovation projects to improve the water environment may have an impact on the occurrence characteristics of microplastics pollution in rivers.This article takes the Fenhe River Taiyuan city section,which has undergone three phases of comprehensive improvement projects,as the research object,and collects water and sediment samples for analysis during the wet season（June）and the dry season（December）.The microplastics are separated by a combination of sieving,flotation separation,static sedimentation,H₂O₂digestion,etc.,and then the microplastics in the samples are counted by microscopic examination,and finally the microplastics are identified by Fourier infrared spectroscopy identification technology Composition,the characteristics of the abundance,color,shape,size and composition of the microplastics in the water and sediments of the study area were studied.It reveals the temporal and spatial distribution characteristics of microplastics in the water and sediments of the Taiyuan section of the Fenhe River,and further clarifies the influence of different economic development levels,industrial divisions and river governance models on the distribution of microplastics,as well as the abundance of microplastics in the water and sediments.relationship.The main findings are as follows:（1）A study on microplastics in the water bodies of the Taiyuan section of the Fenhe River during wet and dry periods showed that the abundance of microplastics in the wet period varied from 0.8 n/L to 11.7 n/L,with an average value of 7.59 n/L;in dry periods The abundance of microplastics ranged from 5.7±1.39 n/L to 34.8±3.58 n/L,with an average of 13.89±1.97 n/L.The abundance of microplastics has decreased significantly due to river improvement projects such as comprehensive interception pipes and revetment treatment.The increase in the flow of people brought by landscape improvement projects in the improvement projects may increase the abundance of microplastics.The microplastics in the water body are mainly fibrous,and the size is mostly small particles（<1mm）,75.75%in wet periods and 61.00%in dry periods;the largest proportion of microplastics is rayon（31.25%）and poly Ester fiber（25.00%）.Compared with other areas,the pollution degree of microplastics in water bodies is at a medium level.（2）The study of microplastics in the sediments of the Taiyuan section of the Fenhe River during wet and dry periods showed that the abundance of microplastics ranged from108.00 to 732.00 n/kg,with an average of 333.40 n/kg.The abundance of microplastics in the dry season ranged from 168±86.11 n/kg to 1145±186.11 n/kg,with an average of 530±108.2 n/kg,which was a moderately low level.Among them,the abundance of fibrous microplastics is much higher than that of other shapes,exceeding 50%of the total.Microplastics<500μm（45.96%）in the wet season dominate.Among various types of microplastics,the largest proportion of components is Rayon（25.14%）,PES（22.95%）and PE（15.85%）.Compared with water bodies,the composition of microplastics in sediments is more abundant.（3）The comprehensive treatment measures of the Fenhe River in Taiyuan City section have a certain impact on the distribution characteristics of the abundance of microplastics.The sewage interception pipes and revetment from the south of Chaicun Bridge to the south of Jinyang Bridge are conducive to reducing the abundance of microplastics,and the impact of the surrounding direct current and sewage plant drainage on the microplastics in the Taiyuan section of the Fen River is reduced.Small;in the renovation project,the increase in the flow of people caused by the landscape treatment project around the north of Shengli Bridge and the south of Jinyang Bridge may have a negative impact on the microplastic pollution;through the analysis of the abundance and color of the microplastics at the S3 sampling point,it is found that the table In the wetland with relatively high temperature,the wetland can have a certain retention effect on the microplastics,and at the same time,the retention effect makes the proportion of yellow microplastics in the microplastics increase significantly.（4）Correlation analysis of the abundance of microplastics in water and sediments during wet and dry periods revealed that there is no significant correlation between the abundance of microplastics in water and sediments during dry and wet periods（R²<0.1,P>0.05）,This may be due to the fact that the upper reaches of the Taiyuan section of the Fenhe River accepts microplastics in rivers and reservoirs,the middle reaches are affected by the comprehensive treatment of urban rivers,and there are tributaries and sewage treatment plants in the downstream..（5）In this study,the abundance of microplastics in the Taiyuan section of the Fenhe River was combined with distance to conduct a quantitative analysis.The results showed that the abundance of microplastics in the water body was positively correlated with the distance from the city center,and there was a fairly high correlation coefficient（r²=0.710,p<0.05）,it is inferred that after the sewage is intercepted,the microplastics produced by people flow,traffic,and non-point source overflow in the rainy season may also be an important source of plastic in the water body and one of the reasons for microplastic pollution..（6）Through the frequency distribution of the size of microplastics in the Taiyuan section of the Fenhe River,it can be found that more than 50%of the microplastics in the water samples of the Taiyuan section of the Fenhe River are concentrated in smaller sizes（<1mm）;the sizes of water bodies and sediments are distributed in the wet period.There is a significant difference（p<0.01）,but the difference in the dry season is not obvious（P>0.05）.The reason for this phenomenon may be related to the dynamic conditions of the water.The relatively stable water environment in the dry season makes the water body and The size of the microplastics in the sediment is larger.（7）Principal component analysis（PCA）method was used to describe the distribution of microplastics at sampling points with PCAs of 4 variables.The results showed that the first component fiber contributed a lot.Microplastic pollution has a greater impact,and the distribution characteristics of microplastics are closely related to the agricultural and human activities in the region.Principal component analysis of 8 variables（KMO>0.5,sig<0.05）of the microplastics in the water and sediments of the Taiyuan section of the Fenhe River:Whether the microplastics in the water of the Taiyuan section of the Fenhe River are in dry or wet seasons Rayon accounts for a large part.Rayon is a large-scale raw material used in the textile industry.It indicates that the plastic fibers produced during the production and use of textiles may be one of the important sources of microplastics in this area.