Research On The Pollution Of Microplastics In The Water And Sediment System Of The Ganjiang River

As a new kind of global pollutants,microplastic has been paid more and more attention by international community because of its extensive existence and difficult degradation in the environment.It's harmful to the ecological environment because it can absorb pollutants from the environment and transmit them through the food chain.The research on microplastics in China is relatively late and is still at the initial stage.The Analytical Method is not yet mature.The research on the pollution of microplastics in freshwater environmental media in China is relatively lacking,the investigation on the content of microplastics in fresh water environment has the shortage of time and environment medium,and there is no systematic research on the pollution of microplastics in Ganjiang River.We selected Ganjiang River as the study area,and collected the surface water and sediments in the beach of each sampling sites as the materials and used the sampling profiling method to analyze and identify microplastics in the surface water and sediments during wet season and dry season respectively.Flotation separation and fourier infrared spectrum identification technology were used to study the content,size,colour and types of the microplastics in the surface water and sediments of Ganjiang River.The spatial and temporal distribution of microplastics in the surface water and sediment of Ganjiang River was investigated,and the relationship of microplastic content between surface and sediment was further clarified.Relationship between microplasitc content and environmental factors in water was clarified.The main conclusions are as follows:?1?The amount of microplastics in water at sampling sites of Ganjiang River during dry season and wet season was investigated.The result showed that the range content of microplastics in the surface water was 0.5-4.95 ind/L during dry season and0.2-5.4 ind/L during wet season.Fiber-based microplastics were particularly abundant,the major size of microplastic was less than 1 mm,and the colour of microplastics were various.Chemical weathering of microplastics was also observed and confirmed by?-FTIR,and the main polymer-types of microplastics in water were polyethylene,polypropylene and polystyrene.Compared with other freshwater,the pollution of microplastics in this study was at the medium level.?2?The present study investigated the content of microplastics in sediments during dry season and wet season.The result showed that the average?range?content of microplastics in sediments was 247 ind/kg?10-1280 ind/kg?during dry season and228 ind/kg?20-1150 ind/kg?during wet season.The content of microplastics in south branch of Ganjiang River was significantly higher than that in the north branch,upper and middle reaches of Ganjiang River and lake area.The major type of microplastics among the studied sediments was fiber,with transparent being the most frequent colour.Microplasics which size less than 1 mm were dominant in dry season,while those more than 1 mm size were dominant in wet season.The main polymer-types of microplastics in sediments were polyethylene,polypropylene,polystyrene,polyethylene-polypropylene copolymer,ethylene vinyl acetate alcohol.The pollution of microplastics in this study was at the medium level.?3?Due to the influence of continuous cascade water conservancy projects,in the process of changing from river morphology to reservoir morphology,the content of microplasitcs decreased,but before reaching the downstream reservoir,the content of microplasitcs recovered,so as to keep the fluctuation range of microplastics in water and sediments in the whole reservoir group small.?4?There was no significant correlation between the content of microplastics in water and sediment and environmental factors.However,the content of microplastics in sediment was significantly correlated with TN,NH³-N,TP and PO₄^3--P,and significantly correlated with DOC and CODMn at p<0.05.The retention effect of cascade reservoirs on microplastics may also be the reason for the significant correlation between the contents of microplastics and TN,TP etc..In addition,the attachment growth of microplastics had a correlation with nitrogen and phosphorus,and the attachment growth of microorganisms was an important reason that causes microplastics with a density less than water to sink into the sediment.