| Imazethapyr herbicide, an inhibitor in synthesis of branched-chain amino acid with excellent efficiency for controlling gramineous and some broadleaf weeds in cropland of soybeans and other leguminous crops, is one kind of imidazolinone herbicides and was developed earliest, as well as is used most widely by now. Because of the low price and good performance in weed out, the consumption of imazethapyr herbicide has been increasing rapidly since available in domestic markets. But due to its long residual time in soil, usage of the imazethapyr herbicide in long term and large amount, usually affects the following crops by chemical damage. In this paper, imazethapyr herbicide residues in soil were determined by a method of Accelerated Solvent Extraction- High Performance Liquid Chromatography ( ASE-HPLC ) analysis. The adsorption behavior of imazapyr in soil and the effect of the physicochemical properties of soil on this behavior were studied. The degradation scheme of imazethapyr was also discussed preliminarily. The studies were helpful to understand the fate of the herbicide and forecast the potential trend of pollution in soil. The main results follow as:1. An analysis method of ASE-HPLC was established for determination of the imazethapyr herbicide residues in soil. The solvent, temperature and pressure for the ASE were optimized, the results were contrasted with the conventional method of shaking extraction. The optimized extraction conditions are: herbicide residues are extracted by using ASE with ratio5:1, V/V of methanol to glacial acetic acid at 50℃ and 9MPa for 10min, then the extracts are analyzed by PDA (Photo-diode array) detector of HPLC at following chromatographic conditions: column: ODS, flow phase: methanol+water+acetic acid (50:46:4, V/V), flow rate: 1ml/min, detection wavelength: 254nm, column temperature: 38℃, sample injection: 20μl. the results showed that the recovery of ASE was higher than that of shaking extraction. In the optimized conditions, the recoveries for noted samples at two concentrations of 1μg/g and 10μg/g based on dry soil were 90% and 86%, respectively, the relative standard deviations (RSDs)<4.5%, and the lowest detection limit was 0.006μg/g.2. The absorption behaviors of imazethapyr herbicide in soil and the effect of the physicochemical properties of soil on the adsorption were studied. Six different soil samples from Shandong province were selected, which included brunisolic soil, cinnamon soil, fluvo-aquic soils, sajong black soil, paddy soil, and saline-alkaline soil. By batch equilibrium method, the shaking time for approaching the sorption equilibrium was determined. Then the effect of the different soils on the adsorption behaviors of imazethapyr was discussed. The results showed that the adsorption capacities of the 6 kinds of soils was paddy soil > brunisolic soil > saline-alkaline soil > sajong black soil > fluvo-aquic soils > cinnamon soil. The adsorption characteristic of imazethapyr herbicide in soils had relation to the physicochemical properties of the soils. The adsorption isotherms fit the Freundlich model, and the adsorption equilibrium constant have negative correlation with the soil pHs and the cation exchange concentrations, and positive correlation with the contents of organic substances in soils3. The degradations of imazethapyr in different soils and circumstances were studied preliminarily by laboratory culture method for 4 representative soils in Shandong province, China: brunisolic soil, cinnamon soil, fluvo-aquic soils and saline-alkaline soil, the effect of soil microbial biomass and water content on the degradation rate was studied. Meanwhile, the degradation experiment of imazethapyr in outdoor soil for growing soybean plants was also carried out, the result showed that: the degradation rate of imazethapyr in soil can be described as C=C0e-kt, and the degradation rates changed with different soils; the fastest one with a half life of 30.2 days was degradation in saline-alkaline soil, the following in decrease order were fluvo-aquic soils and cinnamon soil, with half lives of 51.4 days and 59.2 days respectively, the degradation in brunisolic soil was the slowest with a half life of 81.4 days. In addition, the imazethapyr degradations in soils were influenced by microorganisms and water contents, the more microbial biomass and water content in the soil were, the faster degradation and shorter half lives occurred. The degradation rate of imazethapyr in outdoor soil with a half life of just 3.1 days was obviously faster then that in indoor soil.. |
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