Microplastics And Its Ecological Risk On Estuarine Tidal Flat

Microplastics are generally defined as small plastics whose sizes are less than 5mm.As an emerging pollutant,it has attracted international attention in recent years.Countries have begun to conduct research on the analysis methods,distribution characteristics,fate mechanism,and biological toxicity of microplastics.As a major country of plastic production and consumption,China has attracted much attention from international public opinion.At present,research on microplastics is mainly concentrated in the marine environment,and a large number of studies have been carried out on sea water,marine sediments,beaches,etc.Estuarine tidal flat wetland,as an interface of land and water exchange,is relatively less studied at present.However,it has important functions such as material exchange and energy flow,and is an important place for animal and plant conservation.Chongxi wetland has a unique geographical location.It is located in the first branch of the third-level branch of the Yangtze River,and it is the first wetland system of the Yangtze River Estuary.It includes six main wetland types of the Yangtze River Estuary:lake wetland,channel wetland,low-lying wetland,intertidal zone wetland,subtidal zone wetland and sandbank wetland.It is unique among the wetlands of the Yangtze River Estuary.Therefore,this paper takes Chongxi Wetland as an example,investigates environmental samples in four seasons,and conducts a preliminary study on ecological risk assessment of Chongxi wetland,so as to provide basic data and decision-making basis for the control of plastic waste in China.The main conclusions of this paper are as follows:1.The methods of quality assurance and quality control in laboratory are studied.The removal of potential microplastic stains from glassware by washing method and ashing method was compared.The influence of air background during the experiment was also studied.It was found that the removal rate of microplastics by ashing method was slightly higher than that by washing method,but there was no statistically significant difference.Therefore,it is recommended to thoroughly clean and then ash if possible to ensure the removal of plastic contamination.The study also found that even if strict quality assurance measures were taken,the background plastic fiber pollution was still found.Therefore,it is recommended that:1.Procedure blanks should be set up for each batch of samples.2.Develop and adopt common standard thresholds for background contamination.3.The background contamination should be reducing according to laboratory conditions(e.g.pretreat and analyze microplastic samples in an ultra-clean room;work on an ultra-clean table).2.The environmental samples of Chongxi wetland were collected in four seasons and the changes of microplastics abundance were analyzed.It was found that the seasonal variation of microplastics abundance was obvious,and the size distribution and polymer compositions of microplastics of different shapes were different.Among them,the water sample is about 0.5 m deep surface water collected with a submersible pump.The results show that the water body has the highest abundance in summer,which is 13.53±9.07 n/m~3,and the lowest in autumn,which is 1.90±1.36n/m~3.The overall average is 6.38±7.53 n/m~3.The sediment samples were taken from the surface with a depth of about 5 cm by using sample boxes and stainless steel shovels.The results showed that the highest value was 3.79±2.78 n/kg(30.48±21.47 n/m~2)in autumn,and the lowest value was0.64±1.20 n/kg(3.56±6.65 n/m~2)in spring,and the annual average value was2.59±3.76 n/kg(16.39±25.08 n/m~2).Taking the digestive tracts of 95 biological samples in the first season as an example,three blue plastic fragments were detected in only one Hemiculter bleekeri,and no microplastics were detected in the remaining samples.3.The adjusted Risk Characterization Ratio(RCR_Z)was used to evaluate the ecological risks of each section of Chongxi wetland in four seasons.The results showed that only the risk value of section 5 sediments in summer is high-risk,4values were low-risk,and the rest were risk-free.Generally speaking,the risk of microplastics in Chongxi Wetland is relatively low.