Study On The Occurrence Characteristics Of Microplastics In The Surface Water Of The Yellow River Estuary

Microplastics refer to tiny plastics with a particle size of less than 5 mm.As a new type of persistent organic pollutant,microplastics are divided into primary microplastics and secondary microplastics according to their sources.Based on the severe microplastic pollution status in various regions and the important environmental significance of the Yellow River,research on microplastics pollution in the lower Yellow River and the estuary is urgently needed.In this paper,we analyzed microplastic pollution data by analyzing surface water samples from the lower Yellow River and the estuary,further analyzed the microplastic occurrence characteristics of the samples,and analyzed the sources and affecting factors of microplastic pollution.The research results provide data and theoretical support for the prevention and control of microplastic pollution in the Yellow River,and further enrich the data of microplastic pollution in rivers.This study collected surface water samples at different points on the main channel of the lower Yellow River and main channel of the estuary in July 2018 and March 2019 with the help of pontoons and ships.When sampling,5 L water samples were collected at each point through a stainless steel bucket(three times at each sampling point).Sample processing firstly validates the extraction method through pre-experiment,quality control and quality experiment(QC / QA).Then obtain microplastics through the steps of static sedimentation,centrifugal separation,density flotation,sieving and digestion.Furthermore,the microplastics of the sample are characterized by microscopic examination,and the representative microplastics are characterized and analyzed by means of scanning electron microscopy(SEM)and infrared spectroscopy(ATR-FTIR).Finally,combined with experimental data and statistical analysis of the study of regional microplastic pollution characteristics and laws,to further infer pollution sources and influencing factors.The results show that:(1)the extraction of the experimental method for polyethylene(PE),polypropylene(PP),and polystyrene(PS)with a lower density is 90.94%.The collection effect of high-density microplastics such as polyethylene terephthalate(PET)in the surface water sample is not ideal.(2)The microplastics in the water sample are in the form of fibers,flocs,debris,pellets,films,etc.Among them,microplastic fibers account for more than 90%.Most of the microplastics in the study are primary microplastics,and microscopic examination has also repeatedly found the status of microplastic fibers entangled into flocs.The types of microplastics in the lower Yellow River are more abundant than those in the Yellow River estuary,and the proportion of microplastics in the study area is relatively stable.(3)The particle size of the microplastics in the water sample is mainly 50-200 ?m,and the proportions of the lower Yellow River and the estuary during the dry season are 77.66% and 67.95%,respectively.The proportion of 50-200 ?m microplastics in the Yellow River estuary during the wet season was 92.95%.The microplastic particle size distribution of sampling points in the lower reaches of the Yellow River during low-water periods did not fluctuate significantly.(4)In the SEM analysis,the micro-plastic surface has different degrees of environmental erosion.Most microplastic surfaces are smooth with sharp edges.The results prove that the microplastics in the samples are mostly primary microplastics.Qualitative analysis of infrared spectroscopy found four plastic materials of PE,PP,PS,PET and mixed fibers of fishing nets.(5)The abundances of microplastics in the estuary of the Yellow River during high and low water periods were 654 items / L and 930.2 items / L,respectively.The abundance of microplastics in the lower Yellow River during dry season was 595.27 items / L.It can be seen that the abundance of microplastics in the Yellow River estuary is greater than in the lower Yellow River.The abundance of microplastics during the dry season is greater than that during the wet season.At the same time,compared with other rivers,the Yellow River is a river with heavy microplastic pollution.(6)The abundance of microplastics in the surface water of the Yellow River estuary has a significant linear correlation with the distance from the estuary,and this fate is common in both the dry and wet seasons.Research and analysis of this law is related to changes and interactions of various hydrological conditions in the Yellow River Estuary.(7)Based on the occurrence characteristics of microplastics in different periods and regions,such as morphology,particle size,surface characteristics and materials,it is inferred that microplastics mainly come from domestic washing wastewater and sewage treatment plant wastewater in the upper and middle reaches.In summary,the results of the study have reached the expected goal,which provides data support for further assessment of the current status of marine microplastic pollution and calculation of the fluxes of global microplastics into the sea.In addition,it is also important for improving the calculation model of river microplastic flux.In the future,we will continue to conduct more indepth research on the pollution of the Yellow River microplastics.