Spatial And Temporal Distribution Characteristics And Ecological Risk Assessment Of Microplastics In Danjiangkou Reservoir

As an emerging pollutant,microplastics can be found in almost any environmental medium,which has become a hot environmental issue of global concern.Many studies have shown that microplastics can cause potential ecological risks.Therefore,it is of great significance to understand the distribution characteristics and environmental behavior of microplastics in water environment.This paper takes Danjiangkou Reservoir as the research object,which is a national first-class water source protection area and studies the spatial and temporal distribution characteristics and ecological risk assessment of microplastics in it.This study is not only of great significance to ensure the sustainable utilization of water resources,but also can accumulate basic data of freshwater microplastics and provide a scientific basis for microplastics control.In this study,13 monitoring sections were set up in the reservoir area and 15 sections in tributaries.The water and sediment samples were collected in flood season and non-flood season.The spatial and temporal distribution characteristics and ecological risk assessment of microplastics in Danjiangkou Reservoir were studied.The main research contents include:(1)The spatial and temporal distribution characteristics of microplastics in water:The results indicated that the average abundance of water in flood season was 7,205±4,438 n/m~3,and that in non-flood season was 8,228±4,687 n/m~3.There was no significant difference in the abundance of microplastics between the two periods.The abundance of middle water in the reservoir area is higher than that of surface and bottom water.In flood season,fragmentary microplastics(67.9%-93.1%)were dominant,with the transparent(31.4%)and blue(32.9%)accounting for the highest proportion.In non-flood season,the fibrous(45.3%-82.2%)and fragmentary(10.1%-46.9%)were dominant,with the transparent(31.4%)and blue(32.9%)accounting for the highest proportion.Polymer of PE and PS plastics were the most frequently detected types.The flood season of microplastics in tributary water is higher than that in non-flood season.(2)The spatial and temporal distribution characteristics of microplastics in the surface sediments:The abundance of microplastics in the surface sediments of Danjiangkou Reservoir area in flood season ranged from 708-3,206 n/kg(dry weight),with an average of 1,816±684 n/kg.In non-flood season,the abundance ranged from 500-3,166 n/kg(dry weight),with an average of 1,537±851 n/kg.Compared with Dan reservoir,the abundance of microplastics in Han reservoir had a large seasonal fluctuation,and the overall abundance had no significant seasonal variation.The colors were mainly transparent and brown,and the sum of the two colors at each sampling point was more than 50%.Compared with water body,the proportion of colored microplastics and spherical microplastics increased significantly.(3)The risk assessment of microplastics pollution:The species sensitivity distribution method was adopted,and the result is the safety concentration of microplastic is 2.9×10~5n/m~3.Using the risk quotient method,the microplastics pollution in Danjiangkou reservoir area was evaluated comprehensively.The results showed that the microplastics pollution in Danjiangkou reservoir was relatively light.