| Nitenpyram, which was exploited by Takeda, Japan in1989, belongs to a new class of insecticides known as neonictinoids. The entrance of nitenpyram to environment such as atmosphere, soils, ponds, rivers, lakes is inevitable because of application of nitenpyram, which may cause the environmental pollution and ecology impact. Acording to ’Experimental guideline for environmental safety evaluation of chemical pesticides’, the methods of determination of nitenpyram residues in water and soil were performed and the main environmental behaviors of nitenpyram in soils such absorption, mobility, and degradation, the hydrolysis and photodegradation were systematic studied.An analytical method for determining nitenpyram residues in water and soil was described. For nitenpyram in water, were analyzed by HPLC-DAD directly. The coefficients of determination (R2) of this method were found to be0.9998, and their calibration curves are linear in the range of0.1-20mg·L-1with a limit of determination being0.05mg·L-1. The recovery data was range from98.10%～102.93%for water, with the RSD being1.26%～3.48%. Residues in soil were extracted with dichloromethane, analyzed by GC-ECD. The coefficients of determination (R2) of this method were found to be0.9998, and their calibration curves are linear in the range of0.2-10mg·L-1with a limit of determination being0.02mg·kg-1.The recovery data was range from84.25%～93.25%for soil, with the RSD being3.32%～4.47%. The method satisfied the requirements of pesticide residue analysis.The kinetics of hydrolysis of nitenpyram was studied in different pH buffer and temperature under the laboratory condition and in natural water under simulating field environment. The hydrolysis rate of nitenpyram fits first-order kinetic equation. The hydrolytic rate of nitenpyram was slow in the acidic and neuter solution, but fast in basic solution. The half life was458.9d,415d and20.3d in the solutions of pH5,7and9at25℃, respectively. The hydrolytic rate of nitenpyram increased with the increasing temperature, the average temperature coefficient of hydrolysis for nitenpyram was2.34. The activation entropy showed a significantly negative correlation with the temperature, but no obvious correlations between the activation energy or activation enthalpy to temperature were observed. Under simulating field environment, light intensity and microorganisms may had significant effect on the degradation of nitenpyram in water. The main hydrolytic product, N-(6-chloro-3-pyridylmethyl)-N-ethyl-nitro-methyl-acetamide and N-methyl-(6-chloro-3-pyridyl)-ethyl amine were initially identified by HPLC-MS, and the hydrolysis mechanism of nitenpyram were analyzed.The photolysis trend of nitenpyram in different kinds of solvents under high pressure mercury lamp, xenon lamp and sunlight illuminating was investigated. The affecting factors were studied under different conditions including light sources, organic solvents, the initial concentrations and pH. The photolysis of nitenpyram fits first-order kinetic equation. The photolytic rate of nitenpyram in water under different light sources was significant different to each other. The half life under high pressure mercury lamp, sun light and xenon lamp was42.3s,6.9min, and55min, respectively. The photolytic rate of nitenpyram in methanol was faster than that in acetone. The photolytic rate was influenced by initial concentration of nitenpyram. The photolytic rate showed negative correclation with the initial concentration of nitenpyram and was slightly affected by the pH value.Half lives of nitenpyram in Nanjing yellow-brown soil, Jiangxi red soil and Northeast China black soil were29.4d,38.9d and6.9d, respectively, while in those three sterilized soils, the half lives were40.5d,49.9d and11.4d, respectively. It indicated that soil microorganisms had effect on the degradation of nitenpyram in soil. The main influence factors of degradation rate were organic matter content. Under simulating field environment, degradation of nitenpyram in soil followed the first order reaction well, Because degradation often accompanied by hydrolysis, photolysis and volatilize, affected by light intensity, difference in temperature and some other factors, its half-life was far lower than under light condition.The adsorption of nitenpyram in three kinds of soils were studied with batch equilibrium technique. Adsorption isotherms of nitenpyram on the soils could be described well by Freundlich equation, correlation coefficent R2>0.98. Adsorption isotherm of nitenpyram in the three kinds of soils exhibited L-type isotherm. The adsorption constant (Kd) of nitenpyram in Nanjing yellow-brown soil, Jiangxi red soil and Northeast China black soil was0.37,0.44and2.59respectively, which suggested that nitenpyram was difficult to adsorb by those three soils. The adsorption ability of soils to nitenpyram was ranked as follow:Northeast China black soil>Jiangxi red soil>Nanjing yellow-brown soil, which suggested that the soil adsorption capacities of nitenpyram were positively related with the contents of soil organic matter. The amounts of the adsorption free energy (△G) of nitenpyram on the three soils were all less than40kJ·mol-1, which indicated that the nitenpyram adsorption was dominated by physical adsorption, its adsorption mechanism could be the actions of H-band, dipolar bond, van der waals force and hydrophobic bond, while the chemical bond adsorption action was not existed. Adsorption is reversible.The mobility of nitenpyram in three kinds of soils were studied with soil thin layer chromatography. Rf (relative flow) of nitenpyram in Nanjing yellow-brown soil, Jiangxi red soil and Northeast China black soil were0.72,0.7,0.38, respectively. The mobility of methomyl in three soils above mentioned belonged to mobile pesticide, mobile pesticide and middling mobile pesticide, respectively. Mobility of nitenpyram in soil was in order of Nanjing yellow-brown soil> Jiangxi red soil> Northeast China black soil. |
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