The Residue And Dissipation Of Azoxystrobin In Paddy Field And Its Adsorption Behavior

In order to evaluate comprehensively and accurately the ecological environment safety of azoxystrobin and its related preparations in paddy field, provide available scientific evidence and important data support for its scientific and rational application of azoxystrobin. This paper systematically studied the residue and dissipation after azoxystrobin25%SC applied in paddy field and its adsorption and the influence factors in five kinds of soils and six kinds of soil minerals. The main contents were as follows:(1) Gas chromatography analysis methods was developed for the detemination of azoxystrobin residual amount in paddy ecosystem. The residues of azoxystrobin in the paddy water was extracted with dichloromethane, paddy soil was extracted with acetone and liquid-liquid extraction with ethyl acetate, the brown rice was extracted with mixed liquid of ethyl acetate and acetone (V:V=1:1), rice straw with mixture of ethyl acetate and n-hexane (V:V=1:1) for extraction and chaff sample was extracted with ethyl acetate. The separation was performed on HP-5capillary column, detected by GC-NPD and analyzed quantitatively with external standard method. The average recoveries of the method ranged from82.62%to118.63%and the relative standard deviations ranged from1.16%to9.27%.The minimum detectable amounts of azoxystrobin was5.0x10-11g. Analytical methods comply with the technical requirements for the analysis and detection of pesticide residues.(2) A residue and dissipation experiment was conducted to reveal residual dynamics and final residue of azoxystrobin in paddy in Changsha, Hangzhou and Nanning of China. The dissipation dynamics of azoxystrobin in the paddy water, paddy soil and rice plant meet the requirements of the chemical reaction kinetic equation. Dissipation half-live in the paddy water was5.18d-6.83d, in the paddy soil was8.06d-9.33d and in the rice plant was5.60d～6.79d. These results show that azoxystrobin in paddy field are degradable pesticides.(3) According to the results of residual experiment in Changsha, Hangzhou and Nanning of China, recommended rational application of azoxystrobin25%SC in paddy field.when azoxystrobin25%SC was sprayed in rice for third to prevent and control rice sheath blight and other diseases, spraying intervals for seven days. According to the recommended dose of337.5a.i.g/hm2, the safe period of azoxystrobin in rice could be set as28d.(4) The adsorption equilibrium time of azoxystrobin in five tested soils was about12to16hours, adsorption of azoxystrobin in five tested soils were consistent well with the Freundlich and Linear isotherm equation and adsorption was physical adsorption. The main factor that affected adsorption of azoxystrobin was soil organic matter content. The adsorption of azoxystrobin was strongest in the black soil from Heilongjiang, the adsorption was weakest in the red soil from Changsha. The pH changes had significant effect on adsorption:With the increasing of pH, the adsorption amount first decreased, the adsorption reached a minimum when pH was five and then increased gradually.(5) The adsorption equilibrium time of azoxystrobin in six tested soil minerals was about10to12hours. Adsorption of azoxystrobin in six tested soil minerals followed well the Freundlich and Langmuir isotherm equation. Azoxystrobin in the montmorillonite had the strongest adsorption, while in the zeolite, the adsorption of azoxystrobin was the weakest. In the pH ranges, with the increasing of pH, six kinds of soil minerals on the adsorption of azoxystrobin first decreased, the adsorption reached a minimum when pH was five and then increased gradually.(6) Due to the development of northern soil is not mature enough than southern soil, content of montmorillonite in soil is higher, proportion of kaolin is smaller. The adsorption of azoxystrobin in montmorillonite was greater, in Kaolin was smaller, the experimental result that the adsorption of azoxystrobin between in five kinds of soils and six kinds of soil minerals was consistent.(7) The adsorption of azoxystrobin in five tested soil and six tested soil minerals reached a minimum when pH was five.This showed that pH was five in environmental media, the repulsive force was the strongest between azoxystrobin and the soil grain, so that amount of adsorption was the lowest, but its causes have to be further studied.