| Azoxystrobin is Strobilurin fungicide, developed by Syngenta Participations AG in 1996. Azoxystrobin has obvious control effect on almost all the fungal disease caused by ascomycetes, basidiomycetes, imperfect fungi and oomycetes fungus, and have good activity on powdery mildew, rust, septoria nodorum, sheath blight, net blotch, downy mildew, rice blast and so on. It can be used for the prevention and treatment of drug-resistant pathogens which resist 14-demethylation inhibitors, phenyl amides, dicarboximide and benzimidazole fungicide. Environmental behavior of pesticides is an important content of safety evaluation of pesticides; pesticides’residue dynamic research is the basis of guide the scientific using pesticide and defining maximum residue limit. In order to evaluate the residues in environmental media and rational use, the residues of azoxystrobin in paddy field and environment behavior (Including the photolysis, soil degradation, hydrolysis, soil adsorption and migration and leaching in the soil) were researched. The main results were as follows:1. An analytical method for azoxystrobin residues was set up in Water, soil, paddy straw, brown rice and rice husk samples. The results showed:The recoveries of azoxystrobin in different paddy samples ranged from 81.81 to 109.3% at 0.05-lmg/L, the relative standard deviations (RSD) ranged from 0.96% to 8.58%. The limit of detection (LOD) was 0.05 mg/L in different rice field samples. These results indicated that the method could be applied for residue determination of azosystrobin.2. The results of residues degradation dynamics of azosystrobin at three paddy fields of Nanjing Nanchang Nanning in two years showed that the degradation dynamics accord with the kinetic equation. The half-lives of azosystrobin was 0.42-15.72d in paddy water, 2.79-12.36d in soil,3.15-9.32d in straw.24% azoxystrobin ·hexaconazole suspension concentrate was sprayed for 2 times and 3 times, each time intervals for 7 days, with the dose of 72 g.ai/ha and 108 g.ai/ha in the incipient stage of rice sheath blight disease, the residues were detected after 14 days on the last use. The residues of azosystrobin in rice and soil were less than maximum residue limit (MRL) (0.05 mg/kg).3. Under the irradiation of Xenon lamp, the photochemical degradation of azoxystrobin was studied. The results showed that. The photolytic rate of azoxystrobin in different solvents was followed by acetonitrile>water>methanol>n-hexane>acetone, respectively. In 2-20mg/L concentration range, the photolytic rate became slower with the increasing concentration of azoxystrobin. Nitrate showed a promoting effect on the photodegradation of azoxystrobin. At the concentrations from 1 to 2 mg/L, nitrite could promote the photolysis rates, but it would inhibit the processes at the concentrations from 10 to 20mg/L. The presence of Fe+ and surfactant (SDS) showed photosensitizing effects on the photodegradation of azoxystrobin, however, humic acids and Fe2+ both quenched its photodegradation process.4. The result of hydrolysis test showed that azoxystrobin is belongs to medium hydrolysis of pesticide. In buffer solutions, the hydrolysis rates order was as follows: pH9>pH4>pH7. Temperature also had a effect on hydrolysis, which was increased with temperature increasing. Under the condition of pH4、7、9, the average of temperature coefficient (Q10) was 1.16、1.17、1.83, respectively. At the same time, the hydrolysis rates in the natural environment was faster than the indoor simulation experiment.5. The research of soil degradation showed:In aerobic conditions, the half-lives of azoxystrobin in red soil of Jiangxi, yellow-brown soil of Nanjing, and black soil of northeast were 33.16,44.15 and 45.30 d, respectively. In anaerobic conditions the half-lives were 43.05,63.59 and 77.88 d, respectively. In sterilized conditions the half-lives were 68.63,99.02 and 110.02 d, respectively. It indicated that soil microorganisms played a main role in soil degradation of azoxystrobin, especially the aerobic microorganisms.6. The adsorption and desorption of azoxystrobin was studied. The result showed that adsorption and desorption isotherms of azoxystrobin in three kinds of soils was in accord with Freundlich equation, the adsorption coefficient (Kf) were 0.6817.4.8818、5.9538, respectively. In yellow-brown soil of Nanjing and red soil of Jiangxi, azoxystrobin displayed hard-adsorption and more difficult to adsorption in black soil of northeast. The adsorption isotherms of chlorfenapyr were L-type. The average adsorption free energy (△G) was-13.39 kJ/mol. The adsorptions of azosystrobin were physical adsorption.7. Soil thin layer chromatography and Soil column leaching method were used to study the mobility of azoxystrobin. The results showed that azoxystribin in the tested three kinds of soils displayed non-mobile and non-leaching, which indicated that azoxystrobin has no pollution of groundwater under normal use. The mobility of azoxystrobin in three soils changed over the physical and chemical properties of soil. It showed the following sequence:red soil of Jiangxi> yellow-brown soil of Nanjing> black soil of northeast, which related to the content of soil organic. |
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