Study On Detection Methods、Occurrence Characteristics And Risk Assessment Of Microplastics In Liujiaxia Reservoir

Microplastics are micro-pollutants with light weight,small particle size,large specific surface area and stable chemical properties.They are easy to absorb other toxins and form compound pollutants that float in the water,destroy the body function of water organisms,and eventually pose a threat to human health.The microplastic pollution of inland freshwater has gradually attracted attention.After the reservoir is impounded,the water flow in the reservoir is limited,and the diffusion of pollutants is limited and greatly affected by human activities.Therefore,it is the main gathering place of microplastics in inland freshwater system.Taking Liujiaxia Reservoir as the research object,this paper established a typical and efficient standardized detection method of pretreatment and composition analysis for the water quality of the reservoir,analyzed the physical morphological characteristics,polymer chemical composition and spatial abundance distribution of microplastics in surface water of Liujiaxia Reservoir,and used the potential ecological risk index method to comprehensively evaluate the microplastics in Liujiaxia reservoir The ecological risk level provides data support for the control scheme and treatment method of reservoir microplastic pollution.The main work and conclusions of this paper include:(1)In view of the slow water flow rate and relatively static water body in Liujiaxia Reservoir,this paper adopted Manta trawl method to collect microplastics,successfully obtaining different types and abundance of microplastics in the water body of the reservoir.In view of the characteristics of clear water quality and high stability of the reservoir,this paper established the corresponding pretreatment methods and steps,and carried out the recovery experiment of the established pretreatment scheme with standard microplastic particles,to verify the feasibility and accuracy of this pretreatment scheme to recover microplastics from water samples.(2)Through the identification of actual environmental samples,this paper investigated the feasibility of Fourier infrared spectroscopy and microconfocal laser Raman spectroscopy for the detection and characterization of the chemical composition of microplastics in natural water bodies,and studied the experimental methods,analytical methods and applicable conditions of the two methods.The conclusions are as follows: For microplastics with particle size greater than 2 mm,Fourier infrared spectrometer can be used for composition analysis by thin film method,and the spectral map can be automatically matched with the chemical composition by Thermo Scientific OMNIC spectral analysis software,with matching degree ≥60% is preliminarily identified as this type of polymer,and then match the characteristic absorption peaks of this type of standard polymer one by one to analyze its functional group structure and determine its polymer type.For microplastics less than 2 mm,the single point scanning mode of microconfocal laser Raman spectrometer was used to analyze the chemical composition of each type of suspected microplastics with different apparent characteristics such as shape and color on the filter membrane.The spectrogram was also analyzed using the above method to determine the polymer type.(3)The results of the study on the occurrence characteristics of microplastics in Liujiaxia Reservoir showed that the abundance of microplastics in the surface water of Liujiaxia Reservoir was 0.52±0.21 items/m3 in 2021 and 0.58±0.17 items/m3 in 2022.A total of 11 kinds of microplastics were identified in Liujiaxia reservoir,and the main polymer types were polyethylene terephthalate(PET),polypropylene(PP),polyethylene(PE),polystyrene(PS)and polyvinyl chloride(PVC),of which PET and PP accounted for more than half.The color of microplastics is mainly transparent and blue,the shape is mainly debris and fiber,and the smaller the particle size,the more quantity.The abundance of microplastics in reservoir is unevenly distributed in space,but stable in time.Compared with other comparable studies nationwide,the level of microplastic pollution is at a moderate level.(4)The potential ecological risk assessment results of microplastics in Liujiaxia Reservoir are as follows: In 2021,the potential ecological risk index(PERI)of microplastics in surface water of Liujixia Reservoir ranges from 0.0004 to 0.1085,spanning three risk levels(no significant risk,low ecological risk and medium ecological risk),and its average PERI index is 0.0217,which is in low ecological risk.In 2022,the PERI index of surface water microplastics in Liujixia Reservoir ranged from 0.0001 to 0.0482,spanning two risk levels(no significant risk and low ecological risk),and its average PERI index was 0.0005,which was in no significant risk.