Investigation On Distribution And Migration Of Microplastics In Tidal Flat Of Daliao River

Microplastics usually refer to microplastics with a maximum size of less than 5 mm in the environment.As a new type of pollutant widely existing in the marine environment,its pollution problem is being widely concerned by the international community.Microplastics in the environment are small in size and low in density,and can be migrated over long distances by external forces such as rivers,tides and winds,and are widely distributed in freshwater,marine and terrestrial environments.Microplastics can easily migrate with the water flow after entering the water body.The migration distance of it with a density greater than water in the water body is relatively short,and gradually settles into the sediment during the migration process.Microplastics are rich in color and small in particle size,which is extremely easy to be eaten by organisms as food,causing physical damage to organisms,such as blocking the digestive tract and causing satiety.The toxic substances carried in it and persistent pollutants adsorbed during the migration process will also enter the food chain,seriously affecting the safety of the ecosystem.In the past 10 years,there have been more and more studies on the pollution of Microplastics in marine water bodies,coastal sediments and organisms,but there are relatively few studies on the abundance,distribution,types and sources of Microplastics in river bank sediments.In this research,the bank sediments of the Daliao River are taken as the research object to quantify the abundance of Microplastics through den,sity separation and microscopy,its shape,particle size and color are recorded.And micro Fourier transform infrared spectrometer(μ-FT-IR)was used to determine its polymer composition,the distribution and migration laws of Microplastics on the banks of the Daliao River are initially revealed.Then by discussing the type and polymer composition of large plastics(>2.5cm)on the beach,the potential sources of microplastics are discussed.The research results can provide data support for formulating relevant environmental protection laws and regulations and ecological risk assessment.The main findings are as follows:(1)In September,microplastics pollution was common in the sediments of the banks of the Daliao River.The abundance ranged from 106.7-406.7/kg(dry weight),and the average abundance was 241.2/kg(dry weight).The abundance of microplastics in the high tide line sediments of Binhe Road(BHL)and Huandao Road(HDL)in Liaobin District is the highest among them,which may be related to the population density and industrial activities in the area where the station is located.In terms of shape,fiber microplastics accounted for the highest proportion(62.81%),followed by fragments(22.96%).The average particle size of microplastics is 1.32 mm,and the particle size of most microplastics is less than 2 mm(82.66%).A total of 13 polymers were identified,with Polyethylene Terephthalate(PET)being the highest proportion(32.66%),followed by Polypropylene(PP)and Polyacrylonitrile(PAN)(22.86%and 16.33%,respectively).Microplastics are rich in color,and the number of colorless and white microplastics is mostly(20.85%and 19.85%respectively),and the others are colored microplastics.Compared with other studies at home and abroad,the pollution of microplastics in the sediments of the bank of the Daliao River in September was at a moderate level,and the sources of microplastics were abundant in terms of color and composition.(2)Pollution of microplastics is also common in the sediments of the Daliao River bank in November.The presence of microplastics was found in all samples,and the average abundance of microplastics in shore sediment was 196.9/kg,lower than in September.The particle size of microplastics is still mainly less than 2 mm(78.69%),but the average particle size is higher than September,which is 1.42mm.It is speculated that the changes in abundance and particle size may be related to the decrease in runoff after the Daliao River entered the dry season.Similar in shape to September,fiber microplastics accounted for the highest proportion,67.53%,followed by fragments 18.92%.A total of 12 polymers were identified,PET still dominates(28.09%),but PAN and Polyamide(PA)used in winter clothing have increased to a certain extent compared with September,which may be significantly higher than the temperature in the Northeast Lower related.Colorless and white microplastics accounted for 26.49%and 19.12%,respectively,and other colored plastics were evenly distributed.On the whole,the microplastics pollution in the sediments of the banks of the Daliao River in November is not much different from that in September.The microplastic pollution is still at a moderate level,but there has been some seasonal changes.(3)An evaluation of the large-scale plastic pollution in the five beaches revealed that the highest abundance of large-scale plastics appeared in the beaches at the relatively low population density of the Tianzhuang Terrace(TZT).Among the large plastics,Polyethylene(PE)accounts for the highest proportion(58.62%),while PE in microplastics only accounts for 6.44%.Among microplastics,PET,which accounts for a relatively high proportion,accounts for only 4.6%of large plastics.It is speculated that most of the microplastics in the banks of the Daliao River may come from direct discharge,rather than from the degradation of large plastics.(4)By comparing the microplastics in the high tide line and river sediments,the migration process of microplastics was discussed.The analysis found that the dynamic conditions of the water(wind field,tide)and its physical properties(density,size)have a certain effect on the drift process of microplastics,and the density and shape may affect the settlement process of microplastics.