Pollution Characteristics Of Microplastics In Dongting Lake Area And A Study On Microplastics To The Contribution Of Total Organic Carbon

Plastics are polymer compounds produced by condensation or addition polymerization.Plastics have excellent properties,corrosion resistance,and does not react with acid or base.In addition,plastics also have the advantages of low manufacturing cost,durability,water resistance and light weight.Due to the lack of management of plastics,a large number of them enter the environment.The plastics distributed in the environment are easily broken into small pieces of plastics or microplastics(Microplastics,MPs)under the influence of water flow,light,sediment s and other environmental factors.Generally,the diameter of microplastics is less than5mm,which has the characteristics of small particle size,diverse forms and different types.In recent years,the pollution of microplastics to rivers and lakes has aroused wide concern.As the second largest fresh water lake in China,Dongting Lake is a key area for ecological protection.At present,there are few reports on the microplastic pollution in Dongting Lake.In this study,Dongting Lake and four major river estuaries(Xiangjiang River,Zijiang River,Yuanjiang River,and Qushui River)were selected for the investigation.A total of 15 surface water samples and 15 sediment samples were collected.The concentration,distribution,shape and size of microplastics in surface water and sediments were studied.The results showed that the concentration of microplastics in surface water in the Dongting Lake area was0.62-4.30 items/m~2.The sampling point of the highest concentration of microplastics was S6,located near Yuanjiang city,4.30 items/m~2,and the lowest concentration of S14 was 0.62 items/m~2,located near the drinking water source.The concentration of microplastics in the sediments of Dongting Lake ranged from 21-52 items/100g(dry weight).The highest concentration of microplasti cs in the sediments was W13(52items/100g dry weight).The sampling point W13 is near Yue yang tower,which is a famous tourist attraction.The lowest concentration of microplastics is located in W3(21 items/100g dry weight),near the entrance of Yuanjia ng river.This area is near wetlands with rarely population.The characteristics of microplastics in surface water and sediments were similar.In terms of shape,they were mostly fibrous,and in terms of size,they were concentrated in the small size range.The color was mainly transparent.The types of microplastics detected in the sediment s and water were mainly polypropylene(PP),polyethylene(PE)and polyethylene terephthalate(PET).The microplastic pollution in the Dongting Lake area was spatially di fferent.Microplastics were more abundant in human activity and industry and near cities than elsewhere.Microplastics were also detected at higher levels in the estuaries of the lake,which fully shows that the rivers are an important source of microplast ics in Dongting Lake.Inferred from the characteristics and types of microplastics,many of them were produced during production and enter the environment due to mismanagement.Because microplastics are organic particles,Theoretically,microplastics may contribute significantly to total organic carbon(TOC)in water.We used diluted solution of nanoscale microplastics and mixed solution of river water(nanoscale microplastics+natural river water)for TOC detection.We found that the value of TOC can be directly measured by nanoscale microplastics solution.The TOC of the natural river water was measured to be 9.78 mg/L,and the TOC of the mixed solution reached 21.21 mg/L by adding nanoscale microplastics.These results fully demonstrated that microplastics have important contributions to TOC.TOC is an important parameter to evaluate the level of environmental organic pollution,and the contribution of microplastics makes this important parameter need a new understanding.The contribution of microplastics makes this important parameter need new thinking,for example,the proportion of microplastics in natural water and soil TOC.This study is helpful to comprehensively understand the pollution characteristics of microplastics in Dongting Lake and provide data support for the evaluation and treatment of microplastics pollution in Dongting Lake.On the other hand,the contribution of microplastics to TOC enriches the meaning of TOC.