| As a new kind of environmental pollutants,microplastics with a particle size of less than 5 mm have received widespread attention in recent years.Microplastics are strong hydrophobicity,small size and large specific surface area.The surface of microplastics is very easy to adsorb heavy metals,organic matter and pathogenic microorganisms in the environment.Microplastics are used as the carrier of toxic chemicals and harmful microorganisms,which can cause direct or potential harm to animals,plants,ecosystems and even humans.Therefore,quantitative analysis and ecological risk assessment are the hot spot of the current microplastics pollution research.However,there is still a lack of research on separation and analysis methods and ecological risk assessment of microplastics in the environment.In this study,the rapid synergistic cloud point extraction(RS-CPE)combined with micro-Fourier-transform infrared spectroscopy(μ-FTIR)was established for preconcentration and determination of microplastics and the proposed method was applied to the investigation of microplastics pollution and ecological risk assessment in the Guangzhou section of the Pearl River in conjunction with risk assessment models,and satisfactory results were obtained.The following are the main research contents and results of this article:The first chapter summarized the pollution status and hazards of microplastics,as well as the development of microplastics analysis,detection and pretreatment methods.At the same time,it also introduced the research progress of microplastics risk assessment in the environment.Finally,the research background and content of the subject were discussed.In the second chapter,a method combining RS-CPE with μ-FTIR for the determination of microplastics in environmental samples has been established.The four most common microplastics including polystyrene(PS),polyethylene(PE),polypropylene(PP)and polyamide(PA)were selected as the objects.Triton X-114 was chosen as the extractant.N-butanol was employed as a synergistic inducer,which can not only reduce the cloud point temperature of the system with the inorganic salt,but also reduce the viscosity of the system to facilitate subsequent detection.In the experiment,the factors that affect the efficiency of the experiment,such as the type and amount of surfactant,inorganic salts and synergistic inducers,and instrument detection conditions,were discussed in detail.Under optimal conditions,the recoveries of PS,PE,PP and PA reached 80.3%-96.7%,and the relative standard deviations of the target(RSD)were less than 7.6%,the method was successfully applied to the analysis and detection of microplastics in environmental samples.This method also has the characteristics of less reagent dosage,environmentally friendly and non-destructive testing,and provides a new means for microplastics pretreatment and analysis and detection.In the third chapter,the Guangzhou section of the Pearl River which is one of the key research areas for microplastic pollution was selected as the research area.A sampling survey was conducted in the Guangzhou section of the Pearl River,and the established RS-CPE-μ-FTIR was used to analyze and detect the surface water samples collected in the study area.According to results,the average abundance of microplastics in the Guangzhou reach of the Pearl River was 1.74 n/L.The microplastics with a particle size less than 0.5 mm accounted for the largest proportion,accounting for 36.16%.The smaller the particle sizes of the microplastics,the greater the quantity.PE and PP were the most common types of microplastics;the content of white microplastics was the largest;granular microplastics were the most common,followed by films and spherical microplastics.In order to further understand the pollution and the ecological risks of microplastics in the Guangzhou section of the Pearl River,this paper adopted two water ecological risk assessment models:(1)Pollution load Index;(2)Risk quotient,and combined with surface water data to evaluate the ecological risks of microplastic pollution in the Guangzhou section of the Pearl River.The results of the two methods showed that the degree of microplastic pollution in the Guangzhou section of the Pearl River was at a moderate level,and the ecological risks of all sampling points were low.In the fourth chapter,in addition to water,soil is also the main environmental medium,and the microplastic pollution in the soil can reflect the long-term trend of microplastic pollution.This chapter carried out sampling surveys on the sediments of the Guangzhou section of the Pearl River.At the same time,the new method established in Chapter two was used as a pre-processing and analysis method to investigate the pollution of microplastics in the surface sediments of the Guangzhou section of the Pearl River.The results showed that microplastics are widely distributed in the surface sediments of the study area,and the average abundance of microplastics at sampling points is 556.7 n/kg.The particle size,shape and color of microplastics are different.The content of microplastics with a particle size of 0.5 mm or less was the most;particles were the most dominant form in sediment microplastic samples;white and colored microplastics have the highest proportion,respectively.The main components of the microplastic samples were PE and PP,and the total content of the two was over 50%.Compared with the sediment microplastic pollution in other regions,the microplastic amount of the surface sediments of the Guangzhou section of the Pearl River was at a moderate level.In order to assess the severity of microplastics pollution and the ecological risks caused by microplastics pollution to the Guangzhou reach of the Pearl River,this study combines two assessment models for evaluating the ecological risks of soil sediments:(1)Geo-accumulation index;(2)Ecological risk index were used to show the ecological risk of microplastics in the Guangzhou section of the Pearl River.The results showed that the ecological risk was generally at a low level,and the ecological risk of some sampling points was high.According to the survey data and ecological risk assessment data of surface water and sediment microplastic pollution,statistical methods and interpolation of the GIS system were used to comprehensively analyze the overall situation of microplastic pollution in the Guangzhou section of the Pearl River.The analysis results showed that there was no significant difference in the microplastic content of surface water and sediments between the urban reach and the suburbs of the Pearl River;and there was no direct correlation between the microplastic content of surface water and sediments.The inverse distance weight interpolation method in the GIS system was used to analyze the overall pollution of surface water and sediments.The results showed that the microplastic pollution in residential areas,industrial areas,and tourist areas was more serious,and there was an urgent need to strengthen microplastic pollution monitoring in these areas.In the fifth chapter,the main research results of the thesis were summarized,and the future research of microplastics analysis and risk assessment were prospected. |
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