| Microplastics exist in every corner of the environment,and their own characteristics and synergy with other pollutants make microplastic pollution more and more serious.This paper systematically studied the distribution characteristics of microplastics in the farmland-channel-river system in the Wangbeng section of the Huaihe River Basin.At the same time,the microscopic characterizations of four typical microplastics,including PE(polyethylene),PS(polystyrene)and PVC(polyvinyl chloride,imported from South Korea and Xinjiang Tianye)from two sources before and after aging were analyzed in the laboratory.The kinetics,isothermal adsorption and desorption experiments of a total of40 kinds of microplastics on non-point source pollutants ammonia nitrogen,nitrate nitrogen and phosphorus under different aging methods and aging time were carried out,and the effects of influencing factors(pH and soil)on adsorption were analyzed.The adsorption mechanism of microplastics was discussed.The following conclusions are drawn from the study:(1)In the Huaihe River Basin,microplastics were detected at all sampling points.The content of microplastics in water was significantly less than that in sediment and soil,and the abundance range was 22.2 – 108.8 ind/L.The abundance range of microplastics in soil was 2880 – 10260 ind/kg.In sediment,the abundance of microplastics in N3 was the largest,reaching 13580 ind/kg.The shapes of microplastics are divided into fibers,films and fragments,which are mainly fibrous,but no debris microplastics are detected in the sediment.The size of microplastics at each point is involved in the range of 20 –3000 μm.The larger the size is,the smaller the microplastic content is.In addition,eight kinds of microplastics were detected.Transparent microplastics accounted for 91% of the total microplastics.(2)UV irradiation,hydrogen peroxide oxidation treatment and high temperaturefreezing treatment can all effectively age the microplastics used in the experiment.After aging,the gloss of the microplastics decreases,the color changes,and the microplastics are pulverized.With the increase of aging time,the color change of microplastics will deepen.It can be seen from the SEM images that with the aging process,the surface of microplastics becomes more rougher,and the surface layer splits into smaller particles,showing flake or spherical protrusions.The aging degree deepened with the increase of aging time,and a large number of oxygen-containing functional groups were formed.(3)Adsorption behavior of phosphorus,ammonia nitrogen and nitrate nitrogen on microplastics can be well fitted by pseudo-second-order kinetic model and intraparticle diffusion model.The adsorption capacity of high temperature-freezing aging,hydrogen peroxide oxidation and ultraviolet aging three forms of aging microplastics are greater than the original microplastics,and with the increase of aging time,the adsorption capacity is also stronger,the increase of specific surface area and oxygen-containing surface groups is the main reason.The adsorption process was affected by factors such as the adsorption sites of microplastic surface activity and electrostatic force,and physical and chemical adsorption occurred simultaneously.(4)The adsorption isothermal data of phosphorus,ammonia nitrogen and nitrate nitrogen under a total of 40 kinds of microplastic adsorption under various aging treatments can be well fitted by the Linear and the Freundlich isothermal models.The adsorption intensity index n of Freundlich model is greater than 1 except for individual cases,which is preferential adsorption.Temkin model fitting correlation coefficient R2 above 0.6,the fitting effect is not as good as the first two.(5)The pH value had a certain effect on the adsorption of phosphorus,ammonia nitrogen and nitrate nitrogen by microplastics,and alkaline conditions were more conducive to the adsorption.Microplastic pollutants cannot be completely desorbed in pure water,and the desorption rate is small.The hydrophobicity of microplastic itself is not conducive to desorption.In the soil-microplastic system,the increase of microplastic content has no obvious effect on the promotion of soil adsorption of pollutants and does not change due to the content of microplastics or other factors.(6)In the study of microplastic adsorption of pollutants in Huaihe River water,the adsorption of total phosphorus by microplastic is less than ammonia nitrogen,nitrate nitrogen and total nitrogen.Under various aging modes,the adsorption capacity of microplastics was significantly enhanced with the increase in aging degree.These results clearly reveal the characteristics and mechanisms of the interaction between microplastics and non-point source pollutants,explain the environmental aging process of microplastics and the characteristics of its adsorption of pollutants,and provide a basis for understanding its environmental behavior.At the same time,they provide a theoretical basis for further research on microplastic.Figure [89] Table [60] Reference [123]... |
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