The Residues And Adsorption Of Tebuconazole And Dimethachlon In Paddy Field

In order to study the residue, degradation and ecological environment effects, determine ecological environment safety and guide scientific, reasonable application of tebuconazole and dimethachlon in paddy field. This paper established analysis and detection methods of tebuconazole and dimethachlon simultaneously in paddy field by added recovery test, and systematically studied the residue, degradation of tebuconazole and dimethachlon after tebuconazole and dimethachlon70%WDG be applied in the paddy field. Then put forward the reasonable and scientific recommendations on using this drug in paddy field. Besides, the adsorption behavior of tebuconazole or dimethachlon and its influence fators in montmorillonite and kaoline were probed. Moreover, we studied the adsorption of tebuconazole or dimethachlon in montmorillonite and kaoline after modification with cationic surfactants. And primarily discussed the adsoiption mechanism of tebuconazole or dimethachlon in montmorillonite and kaoline before and after modification with fourier transform infrared spectroscopy. The main contents and results were as follows:(1) Gas chromatography analysis methods was established to detect simultaneously the residue of tebuconazole and dimethachlon in paddy water, soil, rice plants, rice straw, rice hull and brown rice samples. The residue of tebuconazole and dimethachlon in the paddy water was extracted with dichloromethane, paddy soil and rice plants was extracted with mixed liquid of methanol and water(V:V=7:3), and the extract was re-extracted with dichloromethane, rice straw, rice hull and brown rice was extracted with dichloromethane, the samples without paddy water were cleaned up by florisil column, then were detected by GC-ECD, and analyzed quantitatively with external standard method. The recoveries of tebuconazole and dimethachlon in brown rice was83.22%～103.81%and86.77%-98.28%, and their relative standard deviations was1.92%～5.35%and0.69%～2.67%respectively. The minimum detectable amounts of tebuconazole and dimethachlon was4.0×10-11ng and1.0×10-12g respectively. This analytical methods could comply with the technical requirements for the analysis and detection of pesticide residue.(2) In2011and2012year, a field experiment was conducted to reveal the residual dynamics and final residue of tebuconazole and dimethachlon after tebuconazole and dimethachlon70%WDG applied in paddy field in Changsha, Shijiazhuang and Nanning of China. The result of degradation dynamic test showed that the degradation dynamics of tebuconazole in paddy water, soil and plants could meet the requirements of the first-order chemical reaction kinetic equation, and dimethachlon in rice plants could meet it, too. The half-life of tebuconazole in paddy water, soil and rice plants were4.79d～5.75d,6.24d～6.75d and5.63d～6.33d respectively, while the half-life of dimethachlon in rice plants was4.42d～5.84d. These results showed that tebuconazole and dimethachlon are degradable fungicides in paddy field. With the final residue test that the rice plant was sprayed2to3times with tebuconazole and dimethachlon70%WDG in the dosage of210g a.i./ha and315g a.i./ha. each spraying intervals for ten days, the result showed that when the last application was done at14days, the maximum residual value of tebuconazole in brown rice was0.365mg/kg, and less than the tentative MRL values(1.0mg/kg) of tebuconazole in rice (brown rice), while the residue of dimethachlon in brown rice was less than the tentative MRL values(0.01mg/kg) in rice (brown rice). By these results, we recommended that the rational use of tebuconazole and dimethachlon70%WDG in paddy field was that tebuconazole and dimethachlon70%WDG was sprayed in rice with a dose of300g/ha (the content of effective component:210g a.i./ha) for2times at most, the safe period of tebuconazole and dimethachlon in rice could be set as14d.(3) Through adsorption equilibrium experiment, isothermal adsorption experiment and adsorption effect factors experiment, the results showed that the adsorption equilibrium time of tebuconazole or dimethachlon in montmorillonite and kaoline was about18to24hours, adsorption of tebuconazole or dimethachlon in two tested clay minerals followed well the Freundlich isotherm equation, when tebuconazole or dimethachlon existed alone in aqueous solution, the adsorption capacity of kaoline was lower than montmorillonite" s. When tebuconazole and dimethachlon co-existed in aqueous solution, the adsorption capacity of tebuconazole in montmorillonite and kaoline increased. When the aqueous solution pH value increased, the adsorption amount of tebuconazole increased firstly, and decreased latter. Dimethachlon decomposed in the alkaline environment, and the adsorption capacity was obviously low in the acidic condition. The adsorption capacity of tebuconazole or dimethachlon reached a maximum value when the pH value was seven. The influence of aqueous solution temperature on the adsorption was unconspicuous. (4) The cationic surfactant HDTMA, HDTMA/TMA (n/n.1/1) or TMA was applied to modify montmorillonite and kaolinite respectively, then the adsorption of tebuconazole or dimethachlon was probed in modified montmorillonite and kaoline. The result showed that when montmorillonite and kaoline was modified with different surfactants, their adsorption ability to tebuconazole or dimethachlon was enhanced, and HDTMA had a significant impact on adsorption of montmorillonite and kaoline, while TMA had very small impact on that of the two clay minerals. When tebuconazole and dimethachlon co-existed in the aqueous solution, the adsorption quantity of tebuconazole in modified montmorillonite and kaoline was increased, while that of dimethachlon reduced. Tebuconazole or dimethachlon in modified montmorillonite and kaoline were conducive to adsorbe.(5) Through Fourier transform infrared spectroscopy, it showed that the surfactant could’t change the basic skeleton structure of montmorillonite and kaoline. its crystal structure has not changed. The surfactant not only combined with montmorillonite on its surface, but maybe through cation exchange function reached into the inter layer of montmorillonite, while couldn’t reached into the inter layer of kaolin, only combined with it on its surface. The hydrophobic groups of montmorillonite and kaolin could increase after it was modified with different cationic surfactants, so the adsorption ability to tebuconazole or dimethachlon could increase significantly.