| Microplastics are generally defined as plastic fragments with a size of less than 5 mm.As a growing class of emerging pollutants in the environment,microplastics have small size,large quantity and wide distribution,and will release toxic additives.Microplastics can also be used as a carrier of pollutants,which are easy to be ingested by organisms and accumulate in the food chain and may pose a serious threat to the ecosystem and human health.Nowadays,most of the available literature concentrates mainly on the microplastics pollution in the marine environment,but few reports on the spatial and temporal distribution as well as the potential ecotoxicological effects of microplastics in the land environment,especially the farmland soil.It is of great significance to study the separation of soil microplastics and their adsorption characteristics of pollutants.In this study,a typical farmland soil in Qixian,Kaifeng City,Henan Province was taken as the research area.Through the optimization of different flotation solution,sample organic matter digestion solution,digestion temperature,digestion time and other conditions,the microplastic separation method applied to the actual samples was finally determined and optimized;Taking a farmland soil in Qixian County,Kaifeng City,Henan Province as an example,the collected farmland soil samples were separated,identified and analyzed and the spatial distribution characteristics of microplastics in the farmland soil were studied;In this study,organochlorine pesticide and heavy metal were selected as adsorption objects by indoor simulation method.The adsorption of polyethylene(PE)was analyzed,and the influence of concentration,solution/soil ratio,particle size and microplastic concentration,further defined the microplastic on the adsorption characteristics of typical pollutants in soil environment;Finally,a typical farmland soil with more plastic film was selected as the research area.A certain amount of waste mulch samples were collected and the pollutant content on its surface was measured by the method of artificial selection.At the same time,compared with the pollutant content in the soil,the adsorption characteristics of the microplastics in the actual farmland soil samples were preliminarily explored.The main contents and conclusions of the article are as follows:(1)Study on isolation method of microplastics in farmland soil environment.Through the optimization of different flotation solution,sample organic matter digestion solution,digestion temperature,digestion time and other conditions,the spill-centrifugal method for the separation of microplastics was determined.Through the simulated recovery experimen combined with the field soil sample separation in Zhongmu,Zhengzhou City,it is found that this method not only has a high recovery rate for micron and submicron grade microplastics in the soil,but also has a simple operation method,short time,and can be applied to the extraction of a large number of soil samples.(2)A study on microplastics distribution characteristics in typical farmland soil of qixian,kaifeng city.The spatial distribution characteristics of microplastics in farmland soil were obtained by using the optimized separation method to separate,identify and analyze the collected farmland soil samples.The study: 1)According to the abundance classification,the concentration of microplastics in the soil of this farmland ranges from 352-47794 n/kg,and the average content was about 9543 n/kg.The content of soil microplastics shows a patch distribution pattern in space,and the abundance of microplastics were high on both sides of the road and near the watering well,and there was a certain spatial heterogeneity.It shows that human factors have an important influence on the spatial distribution of microplastics;2)According to the shape classification,the representative shapes such as fibers,film,fragment and granule were mainly observed,and film types were dominant,accounting for 64.09 % of the total,fiber,fragment and granule account for 33.82 %,0.87 % and 1.22 % of the total,respectively;3)According to the size classification,the content of microplastics in farmland soil was significantly different.The proportion of 0-0.1 mm,0.1-0.2 mm,0.2-0.4 mm,0.4-1 mm,1-2 mm and 2-5 mm microplastics in the total amount is 1.56 %,37.96 %,21.81 %,25.64 %,10.98 % and 2.05 %,respectively.The microplastics particle size is negatively related to its content,that is,with the decrease of particle size,the cumulative amount of microplastics in the soil increases.In the observation range,the particle size of microplastics between 0.1-0.2 mm were dominant,accounting for 37.96 % of total.The proportion of microplastics <2 mm were more than 90 % of the total,which indicates that the microplastics in farmland soil is mainly small particle size;4)According to the color classification,the colors of microplastics are mainly transparent,blue,yellow,white,red,black,purple and brown,accounting for 56.75 %,16.35 %,6.96 %,5.95 %,5.45 %,3.63 %,1.79 % and 1.56 % of the total amount of microplastics,and the remaining 1.56 % are green and pink,which may be related to the colors of agricultural plastic products chosen by local farmers.(3)Study on adsorption characteristics between organochlorine pesticides and polyethylene microplastics.In this research,two organochlorine pesticides(HCHs and DDTs)were selected as adsorption objects.The adsorption of polyethylene(PE)on pollutants was analyzed by laboratory simulation experiment,and the effects of concentration,solution/soil ratio,particle size and microplastic concentration on the adsorption were studied.The results showed that the adsorption equilibrium time of HCHs and DDTs for PE microplastics was 12 h,and the quasi-second kinetic model could describe the adsorption kinetic data well.The adsorption of HCHs and DDTs by PE microplastics is affected by concentration,solution/soil ratio,particle size and microplastics concentration.Under unsaturated condition,the higher the concentration and the smaller the particle size,the lower the concentration of microplastics,and the more HCHs and DDTs adsorbed.With the increase of soil water ratio,the adsorption capacity of HCHs and DDTs increased first and then decreased.(4)Study on adsorption characteristics between heavy metals and polyethylene microplastics.In this research,six heavy metals(Cu,Cd,Pb,Zn,Ni,Cr)were selected as adsorption objects.The adsorption of polyethylene(PE)was analyzed by laboratory simulation experiment.The effects of solution/soil ratio,particle size,microplastics concentration and coexisting ions on the adsorption were studied.The results showed that the sorption kinetics of Pb,Zn,Cu,Cr,Cd,and Ni onto polyethylene was successfully described by the pseudo-second-order model.In addition,we demonstrated that the adsorption capacity of PE microplastics to six heavy metals is related to the solution/soil ratio,particle size and microplastics concentration.Under unsaturated condition,the larger the solution/soil ratio,the smaller the particle size,the lower the concentration of microplastics,and the more heavy metals adsorbed.At the same time,in Pb,Zn,Cu,Cr,Cd,and Ni coexisting solution systems,microplastics of PE selectively adsorbed six heavy metals.(5)A preliminary study on the adsorption law of microplastics to pollutants in farmland Soil.In this study,a typical farmland soil with more mulch was selected as the research area.A certain amount of waste mulch samples were collected and the pollutant content on its surface was measured by the method of artificial selection.At the same time,compared with the pollutant content in the soil,the adsorption characteristics of the micro plastics in the actual farmland soil samples were preliminarily explored.The results showed that OCPs and heavy metals were detected in the soil of the study area and on the surface of the waste plastic film.When heavy metals and OCPs coexist,the adsorption capacity of microplastics to OCPs is significantly higher than that of heavy metals.The contents of OCPs and heavy metals adsorbed on the surface of waste plastic film with a small particle size of 1-5 mm were higher than those adsorbed on the surface of waste plastic film with a particle size of more than 5 mm. |
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