Degradation And Metabolism Of Pesticide Abamectin In Environment

Pesticide Abamectin is being popularized to use all over the world today, but some important environmental behaviors of Abamectin such as microbial and photolytic degradation, degradation mechanism and adsorption characteristics in soil et al have not been reported until now. In order to comprehensively evaluate environmental security of Abamectin, the degradation and metabolism of pesticide Abamectin in environment were studied. The main conclusions obtained are listed as follows:Chapter one is review, in which research advance of Abamectin is briefly introduced and summarized.Chapter two is an analytical method about residue determination of Abamectin in soil and water by HPLC. The result shows that when HPLC adopts 254 nm as scan wavelength, and the mixture of acetonitrile and water according to appropriate proportion as flowing phase, the parameters such as accuracy, repetition and precision et al for the method are all good to satisfy the essential rules of pesticide residue determination.Chapter three is the degradation of Abamectin in soils. The results show: (1) The decomposition of Abamectin is fastest in Aquic Cambosols while slowest in Udic Cambosols in five kinds of different soils. (2) Organic matter content in soil is the most important factor which influences the degradation half-life of Abamectin in soil, and their relative coefficient (r) arrives at 0.9323, but pH value, total nitrogen, CEC and field maximum moisture capacity correlate little. (3) Soil organic matter, soil temperature and pesticide concentration can obviously affect Abamectin degradation in soil, in addition, the degradation half-life of Abamectin in sterilized soil is far more than that in non-sterilized soil, which maybe contributes to microorganism in soil.Chapter four is the microbial degradation of Abamectin. The results are found: (1) The dominant bacteria which can effectively degrade Abamectin was isolated fromexperimental soil , and it was identified by 16S rDNA as Stenotrophomonas maltrophilia. (2) After the inoculation of dominant bacteria into soil Abamectin degradation is further augmented, moreover, the trend behaves more distinct at low amount of dominant bacteria. (3) The dominant bacterium can degrade Abamectin up to about 500 mg/L, and the optimum temperature, pH value and concentration of Abamectin are 35癈, 7.0 and 100 mg/L, while Hg2+ can distinctly inhibit the strain biomass and biodegradation. (4) In addition, the optimal temperature, initial pH value and culture time for enzyme production are 35, 7.0, 96 h, respectively, but Hg2+ can notably restrain enzyme production. (5) The optimal pH value and temperature for enzymatic degradation are 7.5 and 37.5, moreover, the Michaelis-Mentn's constant, maximum reaction rate and maximum degradation rate of the crude enzyme extracted from the dominant bacterium for Abamectin are 6.78 nmol/mL, 3.26 nmol/min and 81.5 nmol/(min mg), respectively. (6) Four possible microbial metabolites of Abamectin are found by the analysis of TIC and MS chromatogram, and their retention time are 4.977 min, 6.653 min, 8.949-9.451 minand 13.188 min, and MW are 362, 450, 528 and 586, respectively.Chapter five is the hydrolysis of Abamectin. The experimental results indicate: (1) Abamectin is stable in neutral water and its hydrolysis easily takes place in alkaline (pH11.O) and acid (pH3.0) water. (2) The higher of hydrolysis rate is observed with the rise of temperature, and hydrolysis rate constant increases averagely about two times with the increase 10 of temperature, and the activation energy (Ea) for the hydrolysis of Abamectin is found to be 54.02 kJ/mol, and the relation formula between hydrolysis rate constant and temperature is lnK=-6.498 X 103 / T+ 17.192 (r=0.9954). (3) Abamectin degrades faster in non-sterilized water, and hydrolysis rate constant is 2.74 times than in sterilized water, which attributes to microorganism in water. (4) Furthermore, the half-life of Abamectin is a little longer in natural water, maybe due to soluble organic matter in natural...