Study On The Occurrence Characteristics In Hetao Irrigated Area And The Adsorption Properties Of Glyphosate Onto Microplastics

Microplastics?particle size<5mm?is a new type of pollutant,which is widely existed in Marine and soil ecosystems.Due to its wide source and distribution,it is easy to absorb pollutants in the environment,and poses a great threat to the ecosystem.In 2016,microplastics pollution,global climate change,ozone depletion and other issues became major global environmental problems.The existing research mainly focused on the distribution and toxic effects of microplastics in the ocean.However,limited by the methods of separation and identification of microplastics in soil,the ecological effects of microplastics in soil ecosystem are poorly understood.Land is one of the main sources of microplastics in the ocean,and the spatial and temporal distribution and migration process of microplastics are closely related to the whole ecosystem.Therefore,it is very important to study the occurrence characteristics of microplastics in land soil and their driving mechanism of bead and gully.Hetao irrigated area is one of the three oversize irrigated areas in China.It is an important commodity grain and oil production base in China.However,due to the unsound agricultural film recovery mechanism and the use of a large number of agricultural products,there may be more microplastics accumulated in the soil.Therefore,in this article,through indoor test out the recognition of soil micro plastic minimal impact digestion method,and through the collection and hetao irrigation area different types of irrigation,drip irrigation and border irrigation and effect of fixed number of year?effect of 5,10 and20 a?of soil samples,from the perspective of qualitative and quantitative analysis of the micro plastic in the distribution of the study area.The interaction between microplastics and glyphosate and its potential mechanism were studied by means of indoor simulation.Results of these studies are as follows:The results showed that among the 7 different digestion methods,H₂O₂ digestion?30%,25??reduced the quality of microplastics by?2⁵?%,the fluorescence intensity on the surface of H₂O₂ digested microplastic decreased slightly,the surface morphology and element composition presented slight variations,but the characteristic peak of microplastic particles in FT-IR infrared spectra still existed,which had no significant influence for the recognition of microplastic.However,the other six digestion methods all reduced the quality of microplastics with varying degrees,and had caused damage to the surface of microplastic such as light scratch,deep crack and scaly lobes.The results showed that the average abundance of microplastics in soil under the different mulching years?5,10,20 a?in Hetao Irrigation District was 2 526.00,4 352.80,6070.00 pieces/kg.The maximum microplastic was 2133.50 pieces/kg in every layer of soil appeared at 0-10 cm soil layer by mulching 20 a,and the minimum microplastic was678.00 pieces/kg at 20-30 cm soil layer by mulching 5 a.The abundance of soil microplastics was affected by different plastic-mulching years and irrigation methods.The abundance of microplastic in drip irrigation farmland was slightly larger than the surface irrigation farmland,and it decreased with the increase of soil depth.The major categories of microplastics were fibers?23.34%?,fragments?26.31%?,films?38.57%?and grains?11.78%?,and the film class than in different soil layer is higher,;the colors of microplastics included black,transparent,green,red,blue,etc.,with the proportions 24.56%,23.83%,19.34%,16.52%and 15.75%respectively.In the 0-10 cm soil layer,the main color of microplastics was black and it accounted for 30.25%of the total microplastic;in the>10-20 and>20-30 cm soil layer,the main color of microplastics were transparent,accounted for 30.15%and 29.23%of the total microplastic.The particle size exhibited a downward trend with the increase of the mulching years,and the majority of particle size less than 1 mm.In addition,with the increase of mulching years,microplastics particle size in>0-10,>10-20,>20-30 cm soil layer was gradually decreased,and there was no significant relationship between size and irrigation method?P>0.05?.The surface features of microplastic samples were rough and irregular pores existed on it,and fiber,thin film and fragments microplastics had regular micropores,while the grain microplastic surface pores were irregular and concave.The porous properties of microplastics in soil made the characteristic of greater specific surface area carried by it.This characteristic could increase the adsorption of other pollutants and microorganisms from the soil;and there were stable iron oxides and rare earth elements on the surface.There are mainly polyethylene?PE?,polypropylene?PP?,polystyrene?PS?in the farmland soil of hetao irrigation area.According to the adsorption model analysis,the adsorption of glyphosate on microplastics conforms to the quasi-secondary kinetic model.Compared with polypropylene and polyethylene,polyvinyl chloride has the highest adsorption capacity to glyphosate.The adsorption isotherm can be described by the Freundlich model?R2>0.99?,and the adsorption amount increases with the increase of temperature,indicating that adsorption is a spontaneous process.