Residual Behavior And Adsorption Of Kresoxim-methyl And Difenoconazole In Paddy Field

Kresoxim-methyl was the first listing of strobilurin fungicides. It had a unique mechanism of action,broad spectrum of activity,and environmentally friendly features,was widely used on vegetables,fruit and cereal crops.Difenoconazole was a triazole fungicides, mainly used on the controling of rice sheath blight, rice blast.In this thesis, the residue degradation and adsorption behavior of kresoxim-methyl and difenoconazole were probed in the paddy field.For the evaluation of the environmental impact of kresoxim-methyl and difenoconazole,these studies would provide a scientific basis, and also provide a theoretical guidance for its reasonable use. The main conclusions were summarized as follows:(1) The residue of kresoxim-methyl and difenoconazole in paddy soil and rice plant samples were extracted by mixed liquid of acetone-water (v:v=2:1) and acetone separently,in rice straw,rice hull and brown rice samples were extracted with ethanol,all those above extract and the paddy water samples were re-extracted with acetic ether.The separation was performed on HP-5capillary column under programmed temperature,detected by GC-ECD.The quantification was performed by external standard.The added recoveries of this method ranged from73.7%to118.0%.The minimum detectable amounts of kresoxim methyl and difenoconazole was1.0×10-11g and2.0×10-11g, respectively.(2) Under the natural conditions of Hunan Changsha,Zhejiang Hangzhou,Guizhou Guiyang, the degradation dynamics of kresoxim-methyl and difenoconazole in the paddy water, paddy soil and rice plant all could be discribed by the one-grade chemical reaction kinetics equation.The average degradation half-life of kresoxim-methyl in paddy water, soil and rice plants was6.95d,7.77d and5.70d,respectvely;while the average degradation of difenoconazole in paddy water, paddy soil and rice plants was7.35d,8.15d and5.86d.These results showed that kresoxim-methyl and difenoconazole both were the degradable fungicides.(3) The final residue test indicated that when the rice plant was sprayed2to3times with40%kresoxim-methyl and difenoconazole WP in the dosage of200mg/kg and300mg/kg, and the last application was done at21days before harvesting,the residue of kresoxim-methyl in paddy soil ranged from0.009mg/kg to0.025mg/kg,in rice straw from0.209mg/kg to0.925mg/kg,in rice hull from0.176mg/kg to0.606mg/kg,in brown rice was lower than0.05mg/kg.While the residue of difenoconazole in paddy soil was lower than0.009mg/kg,in rice straw from0.071mg/kg to0.281mg/kg,in rice hull from0.061mg/kg to0.183mg/kg,in brown rice was less than0.05mg/kg.According to these above results,we recommended to apply40%kresoxim-methyl and difenoconazole WP to the paddy field two times at a dose of200mg/kg;its safe interval was21days before harvesting.(4) The adsorption equilibrium time of kresoxim-methyl in five different soil tested was about12h to16h,its adsorption process was consistent well with the Linear isotherm equation or Freundlich isotherm equation.Its adsorption in the black soil from Heilongjiang was the strongest,while in the red soil from Changsha was the weakest.The main influencing factor among the soil physical and chemical properties of soil was pH value.The free energy of adsorption of kresoxim-methyl in five soil tested was between13.09kJ·mol-1and13.82kJ·mol-1,it indicated that the adsorption of kresoxim-methyl in the five soil tested was physical adsorption.(5) The addition of surfactant SDBS weakened the adsorption capacity of kresoxim-methyl on soil,while the addition of surfactant TWEEN80enhanced the adsorption capacity of kresoxim-methyl on soil. When the concentration of SDBS was in the vicinity of the critical micelle concentration(CMC),the adsorption of kresoxim-methyl in the red soil and the black soil all reached the lowest point. When the concentration of TWEEN80was15mg/L,the adsorption of kresoxim-methyl increased more than the other concentration such as8mg/L or30mg/L in the red soil;But the adsorption of kresoxim-methyl in black soil was a little change when its concentration of TWEEN80ranged from8mg/L to30mg/L.