Degradation Of Pyribenzoxim In Soil, Rice Straw, Grain And It's Behavior Of Hydrolyosis And Photolysis In Aqueous Solution

Pyribenzoxim is a new broad-spectrum pyrimidine salicylic herbicide to control weed in rice fields.Related residual study about pyribenzoxim had not still been reported so far in China.To make clear its safety application in rice fields and the products,the residual analytical methods, dynamic of pyribenzoxim and its behavior of hydrolysis and photolysis in aqueous solution were studied in this paper.A high performance liquid chromatograph method were established to determine pyribenzoxim in paddy water,soil,rice straw and grain,meantimes,the clean up processes were discussed between coagulation purification method and SPE purification method.As contained fewer impurities,water samples was extracted by dichloromethane and concentrated,determined by HPLC with UV (ultraviolet)detector.The average recoveries of paddy water ranged from 86.0%～97.6%,the C.V was between 4%～9%.The method cleaned up by coagulation the samples were extracted by acetone,and cleaned up by coagulation and determined by HPLC with UV(ultraviolet)detector.The average recoveries of soil ranged from 85.1%～99.9%,the C.V was 3%～19%.The average recoveries of rice straw ranged from 88.9%～101.3%,the C.V was 3%～16%.The average recoveries of grain ranged from 86.1%～105.8%,the C.V was 1%～10%.The method cleaned up by SPE used SPE-C₁₈cleaned up the soil and grain samples The average recoveries of soil ranged from 86.4%～90.4%,the C.V was 1%～8%.The average recoveries of grain ranged from 86.4%～95.2%, the C.V was 2%～9%.Used ENVI-Carb cleaned up rice straw samples.The average recoveries of rice straw ranged from 86.5%～89.1%,the C.V was 4%～8%.The analysis of two methods is sensitive and accurately,the method of cleaned up by coagulation is faster and easier.Residual dynamics experiment of pyribenzoxim were conducted in Henan Zhengzhou and Yunnan Kunming during 2005～2006.The results showed that Half-life of 5%pyribenzoxim EC were 2.77～4.07 days in soil with 500 g·a.i/ha doseage and 1.76～3.22 days in rice straw with 30 g·a.i/ha doseage in Henan Zhengzhou.And Half-life of 5%pyribenzoxim EC in Yunnan Kunming were 3.37～3.90 days in soil with 500 g·a.i/ha doseage and 2.35～3.43 days in rice straw with 30 g·a.i/ha doseage.The intervals to harvest were 83d and 118d in Hennan and Yunnan provinces.When 5%EC of pyribenzoxim was applied to the rice at the recommended dosages of 30 g,a.i/ha and 60g,a.i/ha one time for the weed control,The final residues of pyribenzoxim in paddy soil,rice straw,and grains were all below the limit of quantification(soil＜0.005mg/kg,rice straw＜0.025mg/kg, grain＜0.01mg/kg).Hydrolysis kinetics of pyribenzoxim in paddy water were conducted in Henan Zhengzhou and Yunnan Kunming during 2005～2006.The results showed that under applied level of 500 g.ai/ha. Half-life of pyribenzoxim were 3.44～3.89 days in paddy water in Henan Zhengzhou and 3.41～3.63 days in Yunnan Kunming.Photolysis kinetics of pyribenzoxim in aqueous solution with different light-intensity and pH were studied in the laboratory.Results of the test showed that the stronger light-intensity was,the more pyribenzoxin degradated.The half-life of pyribenzoxim under light-intensity of 2440 lux,4240 lux,7110 lux and 8480 lux were 3.84h,1.04h,0.93h and 0.77hours.Otherwise,the half-life of pyribenzoxim under the light-intensity of 4240lux in pH4,pH6,pH7,pH8,pH10 were 1.07h,2.14h,2.98h,3.19h and 3.21hours respectively.And its photolysis rate order were pH6＞pH8＞pH7＞pH10＞pH4.