Degradation Dynamic And Residual Law Of Three Nitenpyram In The Paddy Environment Of Different Ecological Zones

In this study, the residual determination methods of nitenpyram in rice, paddy soil, paddy water, and husk were firstly established, and then used to investigate the degradation and residual of three formulations of nitenpyram in paddy environment from different eco-logical zones in China.The results can provide the residual determination methods of niten-pyram in rice and environmental samples, and provide the scientific basis for evaluating the environmental safety and residue toxicology of nitenpyram and developing the reasonable usage standard of nitenpyram on rice. Specific research conclusions are as follows:(1) The residual determination of nitenpyram in rice, paddy soil, paddy water, plant and husk were developed by high performance liquid chromatography (HPLC). The minimum detectable concentrations of above samples were:0.05 mg/kg,0.05 mg/kg,0.01 mg/L,0.05 mg/kg and 0.10 mg/kg, respectively. The adding recoveries of this method ranged from 82.36% to 97.10%, and the relative standard deviations were 1.41%～5.15%. The detection method of nitenpyram residues in this study can be applied in the residue toxicology, rice trade and quality control and environmental monitoring.(2) The degradation of nitenpyram accorded with the first-order kinetics equation in the simulated paddy soil and water. In the paddy soil and water, the average degradation half-lives of the original drug of nitenpyram were 16.2 h and 6.9 h, respectively, and 18.5 h and 8.4 h for wettable powder (WP), respectively. The results showed that nitenpyram has a short half-life of degradation in the simulated paddy environment, and the half-life of niten-pyram WP was longer than that of the original drug of nitenpyram.(3) The average degradation half-lives of three formulations of nitenpyram (50% solu-ble powder (SP),50% WP and 5% Ultra-low volume (ULV) liquid) in the rice plants from Hunan province were 2.5 d,1.9 d and 1.0 d, respectively. The average degradation rates of three formulations of nitenpyram generally followed the order of SP> WP> ULV, which is related to the nature and applied way of the pesticide.(4) The degradation of nitenpyram in the rice plants from different ecological zones (Hunan, Jilin and Guizhou, located in the hilly region of the middle and lower reaches of the Yangtze river, the Northeast Plain and Yunnan-guizhou plateau of China, respectively) ac- corded with the first-order kinetics equation, and the half-lives were 1.8±0.7 d、2.3±0.6d、 1.9±0.3 d, respectively. The results demonstrated that, the degradation of nitenpyram in the rice plants of different ecological areas were fast, but the degradation rates existed a little difference with the average half-lives in the range of 2 d.(5) Under the condition of field experiment, three different formulations nitenpyram were sprayed on rice plants according to the recommended dose and high dose which is 1.5 times as much as the recommended dose. The maximum spray times were three times (or four times) in each season with a 7-14 d interval. The residual amount of nitenpyram in rice which harvested in 7,14 and 21 d(or 14,21 and 28 d) after the last spray were not de-tected(<0.05 mg/kg), which is lower than the MRL value (0.5 mg/kg) of nitenpyram for rice in Japan.(6) Seen from all the experiment results, nitenpyram has a fast degradation in the rice plants, and the half-life less than 3.5 d. In three different ecological zones of China, three formulation nitenpyram were sprayed on rice according to the recommended dose and ap-plied way, The residual amount of nitenpyram in rice which harvested more than 14 d after the last spray were not detected(<0.05 mg/kg). Based on the above results, the technical standards of nitenpyram used on rice reasonably can be formulated.