Spatial And Temporal Distribution Of Microplastics And A Preliminary Study On Ecological Risk Assessment Of Microplastics In The Changjiang Estuary And East China Sea

Microplastics have caused various environmental problems in recent years owing to the long existence time,various sources and transportation.Accumulation of microplastics and effects of pollution with other pollutants in the marine environment lead to an increasing number of marine organisms suffering the survival threat.It is significant to research temporal and spatial characteristics of microplastics in estuaries and offshore areas.China is a great country with miles of coastline,which has concerning problems at marine plastic pollution.At present the research of marine microplastics in China is just in the phase of beginning and has not formed a complete system to assess risk degree of marine microplastic pollution.In this study,we took the case of Changjiang Estuary and explored preliminarily the distribution of marine microplastics and the methods of microplastic ecological risk assessment.In Changjiang Estuary and the adjacent East China Sea,we set up monitoring sections and carried out three cruises in winter,spring and summer in 2017 to collect sediment and water samples.The surface sediments and sea water were collected respectively with a box-type mud sampler and a water pump.Then density flotation,biological digestion and filtration were conducted in laboratory analysis.Finally,morphological characteristics of microplastics were observed under Leica microscope and the chemical composition was identified by the Attenuated total reflection mode of Fourier micro-infrared spectrometer.Based on the field investigation of microplastics,an appropriate ecological risk assessment framework for marine microplastics was established.Microplastics were ubiquitous in surface sediments of Changjiang Estuary and the adjacent East China Sea.Average concentration of microplastics in flood season(200.0±17.3 particles/kg)was higher than that in dry season(111.2±10.8 particles/kg).Microplastics came in a kind of shapes with the largest number of fiber.Microplastics was the wide range of particle size and concentrated in the smaller size level(less than 1 mm).Microplastics in the sediments were colorful and difficult to be identified.The chemical composition of microplastics constituted a variety of polymers,such as polyethylene,polypropylene,polyamide,polyvinyl chloride and polystyrene.There was no direct relationship between the size of sediment and the spatial distribution of microplastics.Changjiang Estuary was the primary channel for microplastics from land entering the ocean.A total of 3225 microplastics were detected in Changjiang Estuary and East China Sea.Abundance of microplastics in July was significantly higher than that in February and May.Average particle size of microplastics in May was less than that in February and July.Microplastics with small size(less than 1 mm)accounted for more than 70% of the total.Fiber is widespread in all seasons.Comparing abundance of microplastics in the surface seawater and sediments between the Changjiang Estuary and other regions,the pollution degree of microplastics in China was at the medium level in the world.Based on safe concentration of microplastics under ideal conditions,the pollution risk of microplastics was evaluated by pollution load index and potential ecological risk index respectively.The results showed that the ecological risk of microplastics in the study areas was generally light,which Hangzhou Bay faced more serious pollution risk.Different with other microplastic polymers,polyvinyl chloride may release toxic chemicals and cause potential ecological harm.According to the comprehensive evaluation,there were factors deserving concerns including production and use of plastic products,discharge of plastic waste and measures of human beings.The study area was divided into three zones,that is Changjiang Estuary near Shanghai,Hangzhou Bay and East China Sea.In conclusion,temporal and spatial characteristics of microplastics in Changjiang Estuary presented quarterly different and the runoff could improve the distribution of microplastics in the water environment.Therefore it would lead to mistakes to calculate flux of microplastics flowing into the sea by single quarter data.It is important to strengthen regular monitoring In order to control microplastic pollution.Meanwhile all sectors of society should speed up legislation,control the use of plastic products and take measures to reduce the risk of marine microplastic pollution.