Residue Dynamics Of Nitenpyram In Cabbage And Its Photodegradation

Nitenpyram is the second generation of neonicotinoid insecticides. It is applid to prevention and control against various sucking mouthparts pests in crops and fruit trees. In order to evaluate its residual behavior in environmental media and its stability under storage systems, dissipation dynamics and the terminal residue of nitenpyram in cabbage and soil and photochemical degradation of nitenpyram in organic solvents had been studied in this paper. The main results are as follows:1. Residue analytical methods of nitenpyram in cabbage and soil were established. Cabbage and soil samples were extracted with acetone-water, separated by capillary column and determined by gas chromatography-electron capture detector (GC-ECD). It was demonstrated from the results:The limit of detection of nitenpyram was 2.O×10-11 g, and the method detection limit (MDL) of Nitenpyram in the samples of cabbage and soil were 0.01 mg/kg. The average recoveries and coeffieient of variations of the method were 90.04%-94.13%,4.93%-7.39% for cabbage samples, and 92.23%-96.27%,2.01%-4.92% for soil samples. These results showed that the method accords with demands of residue analysis of Pesticide.2. The dissipation dynamics and final residues of nitenpyram in cabbage and soil were determinated through the field trials in Hunan, Hebei and Jiangsu provinces. It showed that the half life of nitenpyram in Cabbage and in soil were 1.17-4.29d,4.38-19.97d respectively, when the cabbage was treated for there-four times, on the 7th day after the last application, the final residue of nitenpyram in cabbage was below 0.0245mg/kg, and lower than the MRL in Japan (0.03mg/kg). The results suggested that nitenpyram 20% WP be used in cabbage at most four times at a dose of 30-45a.i.g/hm2 with a safe interval of 7 days from harvest. Considering the MRL value of nitenpyram in cabbage in Japan, the MRL value of nitenpyram in our country was suggested that in cabbage was 0.03 mg/kg.3. The main results of photochemical degradation of nitenpyram were summarized as follow:Nitenpyram photolyzed quickly in organic solvents under the irradiation of ultraviolet light (UV), and its photolysis followed the first order kinetics. The photolysis rate in the increasing order was as follow:methanol>acetone>n-hexane>acetonitrile. The photolysis rate of nitenpyram was affected by its concentration in methanol. The higher is concentration, the lower photolysis rate constant and the longer half-life is.Half-life of Nitenpyram was 6.36 min,7.96 min and 11.53 min, respectively, when the concentration of Nitenpyram was 2.0ug/mL,5.0ug/mL and 20.0ug/mL.4. Three photolysis products were detected and identified by HPLC-MS, The three major degradation products was N-(6-chloro-3-pyridylmethyl)-N-ethylmine, (E)-N-(6-chloro-3-pyridylmethyl)-N-ethyl-N'-methylformimidamide, (E)-N-(6-chloro -3- pyridylm ethyl)-N-ethylaceti-midamide.