Sorption-Desorption Behavior Of Spirotetramat And Degradation Behavior Of Its Hydrogel Beads In Soil

Spirotetramat exhibits an excellent systemic translaminar efficacy for control of a broad spectrum of sucking insects.The environment behavior datum for spirotetramat is still insufficient since it entered China in 2011.So it is necessary to do a systematic study on he environment behavior of it in different climate regions in our country to minize the environment risk.In this paper,a method for determing spirotetramat in soils was developed,the environment behavior of spirotetramat in soils was investigated,four kinds of spirotetramat hydrogel beads were prepared and characterized by different methods.The degradation of spirotetramat hydrogel beads in soils were studied as well.The major findings are as follows:1.A cheap and easy method for determining spirotetramat in solis was developed.The regression equation of spirotetramat was Y=6545.27653C+63159.78986(R2=0.999),and the RSD was between 2.61%?7.95%?2.The leaching behavior of spirotetramat was investigated,the results showed that spirotetramat dosen't move in meadow black soil,and moves hardly in purplish soil,humid-thermo ferralitic and waterloggogenic paddy soil,and the leaching risk is very low.3.The adsorption-desorption behavior of spirotetramat on four soils was studied.The results showed that the equilibration time of spirotetramat in soils ascends and the adsorption rate descends with the initial concentrations of spirotetramat ascending.The adsorption capacity secquence of the four soils was as follows:meadow black soil>purplish soil>waterloggogenic paddy soil>humid-thermo ferralitic.Adsorption behavior of spirotetramat in soils conformed to Freundlich model.The constant k1 drawed from linear model were between 2.9557 to 13.6643,which meant the leaching risk was very low.The leaching risk secquence of spirotramat on soils was as follows:meadow black soil<purplish soil<waterloggogenic paddy soil<humid-thermo ferralitic.Desorption behavior of spirotetramat on soils could be described by Freundlich model,negative hysteresis effect was found because of the desorption rate higher than adsorption.4.The effect of different factors on adsorption-desorption behavior of spirotetramat on soils was investigated and analyzed,and the results showed that:(1)Adsorption capacity of soils descends with the ascending of the ionic strength.(2)The adsorption capacity of purplish soil and waterloggogenic paddy soil ascended and then descended with the ascending of pH,while that of meadow black soil changed slightly.(3)The adsorption capacity of waterloggogenic paddy soil ascended when the content of humic acid increased.The constant k1 drawed from linear model changed from 32.52012 to 188.07578,and the desorption rate declined.(4)The adsorption capacity of soils fell when surfactant triton-100 added.(5)Negative hysteresis effect appeared under the circumstance of the four factors.5.Four kinds of spirotetramat hydrogel beads were prepared by extrusion-exogenous gelation method,and were characterized by different methods.The results showed that the encapsulation efficiency and drug-loading upgraded when adding chitosan into CaCl2 or adding starch into sodium alginate.Spirotetramat releasing behavior of the hydrogel beads followed Fick diffuse mechanism and could be described in a nonlinear Logistic model.The spirotetramat hydrogel beads were sensitive to pH.6.The degradation behavior of spirotetramat hydrogel beads and spirotetramat standard in representative soils were investigated,the results showed that the degradation of spirotetramat in soil could be described by linearty kinetics.Type of soil and pesticide formulation had obvious effect on DT50,while application rate had little effect.DT50 of spirotetramat hydrogel beads was longer than spirotetramat standard in soils.DT50 of spirotetramat on purplish soil shortened with the ascend of the moisture of the soils,while it changed little on waterloggogenic paddy soil.