| It was very important for assessing the bio-environmental safety of pesticide to study its degradation law and residue level,this work could provide the principle to guide scientific use and establish logical use principle of pesticides.Photodegradation of pesticides was one of important degradation pathways occurring in natural environment which had a direct impact on exerting its efficiency or assessing its effects on environment. Qingkuling is one of prospective high-effect organosulfur fungicide with moderate toxicity, it was beneficial to preventing or curing rice's diseases. Therefore it was very significant to study the degradation behavior and residue level in paddy field and its photodegradation in aqueous solution.The degradation and residual behavior of qingkuling in paddy field were investigated in Changsha.On the basis of these, photodegradation kinetics of qingkuling were studied in aqueous solution of different water quality conditions under sunlight illumination or high-pressure mercury lamp illumination.The main results were summarized as following:(1)A series experiments such as choosing the extract,the elution liquid and the sorbent in preceding process of establishing clean-up method. Trichloromethane as the extract in water sample,methanol-water mixture(1:1,V/V) as the extract in rice samples,trichloromethane and methanol mixture(1:1,V/V) as the elution liquid,florisil as the sorbent were determined finally.The component ,proportion,flow velocity and pH value of mobile phase as well as column temperature and detection wavelength were optimized,and the HPLC detection conditions were determined and confirmed elementarily.According to pesticide residue and separation in actual samples,gradient elution method was selected.Gradient elution detection conditions of qingkuling in plant,stalk and hull were: methanol-water mixture (30: 70, V/V),holding 6minutes,then turned to methanol-water mixture (40: 60, V/V),holding 4 minutes,and at last concerted to methanol-water mixture (50: 50, V/V), holding 2 minutes.lt took 12 minutes in the whole running process,and the retention time of qingkuling were 10.8 minutes. The gradient elution detection conditions of qingkuling in paddy water,soil and brown rice were : methanol-water mixture (30: 70, V/V),holding 3 minutes,then turned to methanol-water mixture (70: 30, WV),holding 5 minutes,it took 12 minutes in the whole running process, and the retention time of qingkuling were 6.5 minutes. The results showed that the averaged recoveries from untreated control samples fortified with qingkuling at rates of 0.05-5.0 mg/kg ranged from 79.23% to 103.19%, and the coefficient of variation was from 1.51% to 9.33% with good separation which could accord with the request of pesticide residue determination. The lowest detectable quantity was 1.82X10~10g and the lowest detectable concentrations of various samples were0.001mg/L,0.005mg/kg,0.01mg/kg,0.03mg/kg,0.03mg/kg and 0.03 mg/kg in water, soil, brown rice, hull, stalk and plant respectively. The retention time of qingkuling in various samples could be shortened properly in gradient elution, which was beneficial to impurities' separation and exclusion.(2)In 2002 and 2003 the degradation of qingkuling in rice plant, soil, paddy water samples could be described by first-order kinetics equation Ct=Coe~kt in natural environment in Changsha. The half life of qingkuling was 0.9d-1.0d, 4.4d-4.5d and 2.3d-2.6d in paddy water, soil and plant respectively. The degradation velocity order were paddy water>plant>soil. Residue of qingkuling was LOD-0.0381mg/kg, LOD-1.2440mg/kg, LOD-0.7561mg/kg, LOD in brown rice,hull,stalk and soil respectively. Residue distribution of qingkuling in paddy field were hull>stalk>rice>soil after application 20% qingkuling WP according to the recommended dosage (2250g/ha)and the high dosage(4500g/ha). Residue and behavior of qingkuling in rice reflected that it was an obvious contacting residue regulation. The MRL of qingkuling in brown rice could be cited to be 0.2mg/kg temporarily in our country. Just in order to prevent rice from a few of diseases, it was indicated that three application times mostly during the growth period of rice and 20...
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