Pollution Characteristics And Risk Assessment Of Microplastics In Lake Ulansuhai

As an emerging organic pollutant,the concept of microplastics has been put forward since2004,and its research is in the period of ascendant.Marine and coastal sediments are the main detection locations.And the combination of microplastics and conventional pollution and its further toxic effect on aquatic organisms have gradually become the focus of academic circles.However,there are few studies on the occurrence and abundance distribution of it in inland shallow lakes.In this study,Lake Ulansuhai in Inner Mongolia,was taken as the research lake.The samples of surface water and sediment were collected and the microplastics were separated by flotation.The abundance,size,color and shape of microplastics in surface water and sediment were analyzed by stereomicroscope,laser confocal microscope,SEM and FTIR,and their micro morphology and composition were analyzed.On this basis,the risk index method and the Nemero pollution index method were used to evaluate and predict the possible risk and toxic effects of microplastics on the Lake Ulansuhai,and the main results are as follows:Microplastics were found in the surface water of Lake Ulansuhai,with obvious spatial distribution characteristics.The maximum concentration was found at U2 point located in the north of the lake,with a content of 10120±4090 n/m~3,which was close to the outlet of the backwater channel of Hetao irrigation area;the minimum concentration was found at U8 point where located in the south of the lake,with a content of 1400±390 n/m~3,this point is located in the south end of Lake Ulansuhai.The distribution of microplastics in surface water gradually decreases from north to south.Fiber,film,fragment and granular microplastics were detected,and fiber microplastics were the main samples in all sampling points,accounting for 68.18%to78.64%.Black,red,green and transparent colors are the main detected colors in each sampling point,the highest proportion of colored plastics is 94.9%,and the majority of micro plastics in each point are larger than 2 mm.Microplastics were also found in the surface sediments of the lake.The maximum content of microplastics was at U4(24±7 n/kg WW),which was located in the east side of the lake.The flow condition was weak,which was conducive to the deposition of microplastics.The minimum concentration was 14±3 n/kg WW,which was at U9,which was near the entrance of Lake Ulansuhai retreat into the Yellow River.Fiber,film,fragment and granular microplastics are also found in the sediment samples of each point,and the proportion of fiber microplastics is the largest,but compared with that of water samples,it has decreased from40.01%to 62.50%.The highest proportion of colored microplastics(black,red,green and transparent)was 93.4%,and the microplastics>2 mm were also the main size.The results of FTIR showed that polyethylene,polyethylene terephthalate,polystyrene,PVC were microplastic components,and polyethylene was the main detection category at each point,accounting for 63.7%in surface water and 39.2%in surface sediment.The results showed that there was a certain correlation with the widespread use of agricultural film in Hetao irrigation area.EDS-SEM analysis results show that microplastics after a long time of hydraulic friction and immersion show that there are etchings,holes,cracks and other morphological characteristics,which provide adsorption sites for other pollutants in the water body,and the presence of Fe,Zn,Ni and other metal elements detected on the surface can improve the risk of harm.The ecological risk index and the Nemero pollution index were used to evaluate the pollution of microcellular materials in Lake Ulansuhai.The results showed that the maximum EI of the surface water pollution risk index of Lake Ulansuhai was 21.380 at U2 point,and the risk level of the point was II,and the EI also had regional differences.The EI of sediment is significantly higher than that of surface water,the maximum appears at U4 point,which is81.142,and the risk level of all points is level II.The evaluation results of Nemero pollution index show that the P_Z of surface water is higher than that of the sediment,and the pollution degree is lighter.Considering two evaluation methods synthetically,the pollution of Microplastics in the lake is generally at a light state.