| Pyrazoxystrobin,((E)-2-(2-((3-(4-chlorophenyl)-1-methyl-1H-pyrazole-5-yloxy) methyl)phenyl)-3-methoxyacrylate) is a novel strobilurin fungicide independently developed by ShenYang Research Institute of Chemical Industry in China. It has highly effective and broad-spectrum activity against Pseudoperonospora cubensis, Blumeria graminis, Erysiphe cichoracearum, Plasmopara viticola and Magnaporthe grisea. It obtained temporary registration in China in2009for cucumber downy mildew with a use rate of80to100g active ingredient per hectare. Radioisotope tracing is a quick and accurate traceable technique. Clarifying the environmental behavior and fate is important for its environmental safty evalutation. So far many studies have used isotope labeled pesticide to study the behavior and fate, as it enabled precise analysis and source tracing. As there was no isotope labeled pyrazoxystrobin could be bought from the market both home and abroad, its environmental behavior and fate information was rarely reported. Here we synthesized [pyrazol-14C] pyrazoxystrobin and used it as a tracer for the further study.Based on the industrial synthesis of pyrazoxystrobin and the feature of the labeled compond, we established a synthetic route starting from4-chlorobenzoic acid as carbon-14labeled carbon source via substitution, cyclization and condensation. After Preparative High Performance Liquid Chromatography (PHPLC), the total chemical and radiochemical yield were both43.93. Its chemical structure was identified through HPLC-Mass Spectrum (MS)(ESI), MS (EI) and’H-Nuclear Magnetic Resonance (1HNMR). The purity was determined by HPLC with more than98%in mass ratio. HPLC-Liquid Scintillation Counter (LSC) and Thin Layer Chromatography-Isotope Imaging Analysis (TLC-IIA) determination demonstrated that its chemical and radiochemical purity was more than98%with specific activity of (5.042±0.076) mCi/mmol.We studied the adsorption-desorption behavior of pyrazoxystrobin by using the synthesized [pyrazol-14C] pyrazoxystrobin as an isotope tracer. The adsorption fitted Freundlich equation well and the Gibbs free energy was lower than40KJ/mol suggesting the adsorption was physical adsorption, which might be caused by hydrogen, ion exchange or dipole bond formation. The adsorption was affected by soil properties. The absorbed pyraoxystrobin was difficult to be desorbed from soil with0.01M CaCl2solution.The soil TLC-ⅡA study showed pyraoxystrobin was difficult to migrate in the three-selected soil. The column leaching study of the loamy soil2found95.02%of the added pyraoxystrobin was remaining in the0～4cm layer soil after60d treatment. No radioactivity could be detected in the leachate, indicating that pyraoxystrobin was not easy to migrate to subsoil by rainfall.We studied the extractable residue (ER), bound residue (BR) and mineralization of pyraoxystrobin. During100d incubation the ER was increasing while BR and mineralization were decreasing. After100d, BR was12.4%(S1),9.9%(S2),1.7%(S3) and mineralization was5.4%(S1),2.83%(S2),1.69%(S3), respectively. BR was much less than70%so it could fit the European Union principle. Comparing the sterilized and nonsterilized soil2, we found that the sterilized one had a less ER but larger BR/mineralization, which showed that the soil microbe affected its residue in soils. The mineralization rate was less than5.4%of the initial radioactivity, suggesting that pyraoxystrobin was difficult to completely detoxify by mineralization.The dissipation half-life of pyraoxystrobin parent compound in four tested soils were43.8d、80.6d、169.0d and123.7d respectively. A total of four radioactive metabolites were indentified by high performance liquid chromatography together with liquid scintillation counter. Through mass spectrum analysis, the possible structure included2-(2-(((3-(4-chlorophenyl)-1-methyl-1H-pyrazol-5-yl)oxy)methyl) phenyl)acetaldehyde (M1, RT=10min), methyl3-hydroxy-2-(2-(((1-methyl-1H-pyrazol-5-yl)oxy)methyl)phenyl)propanoate (M2, RT=17min), methyl (Z)-2-(2-(((3-(4-chlorophenyl)-1-methyl-1H-pyrazol-5-yl)oxy)methyl)phenyl)-3-hydroxyacrylate (M3. RT=26min),3-(4-chlorophenyl)-5-methoxy-]-methyl-1H-pyrazole (M4, RT=37min). Demethoxyl. hydroxylation, reduction reaction and ether bond breakage contributed to pyraoxystrobin degradation in aerobic soil. |
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