Studies On Residual Degradation Of Clothianidin In Paddy Field And Dietary Risk Assessment

Pesticides' residue dynamic research is the basis of guide the scientific using pesticide and defining maximum residue limit.Clothianidin is a new type of high efficient broad-spectrum insecticide with contact toxicity,stomach toxicity and systemic action.It was applied in rice,vegetables,fruit and other crops to control pest of Hemiptera,Coleoptera,Diptera and Lepidoptera,such as aphids,leaf-hoppers,thrips and plant-hoppers.It was with high efficiency,broad spectrum,less dosage,low toxicity and high efficacy.This paper established an analytical method with HPLC for determining the residual quantity of clothianidin in paddy water,soil,rice plant,rice and rice hull.After field experiments in three different paddy fields,the residues degradation dynamics and the final residues quantity of clothianidin in water,soil,rice plant,rice and rice hull were determined.The main results were as followings:1.The high performance liquid chromatographic method was established for determining the residual quantity of clothianidin in rice and its environment.Residues were extracted with a mixture of acetonitrile and water,followed by cleaning with a neutral alumina column and silica,then determined by HPLC with acetonitrile and water as the mobile phase and ultraviolet detection at 265 nm.The results showed that the linear range of clothianidin were from 0.01 to 10 mg/L and R2 was 0.9999.And the average recoveries were 73.17%to 92.03%,the coefficient of variation ranged from 0.07 to 6.32%.The minimum detectable concentration of the clothianidin in soil,rice plant,and rice were 0.1 mg/kg,0.2 mg/kg in rice hunk and 0.01 mg/kg in water.The result shows that it is easy to operation,saving the solvent,little pollute to the environment,It indicated that the developed method could be applied for residue determination.2.Study the residual degradation dynamic of 50%clothianidin WG in rice and its environment in three different paddy fields for two years.The results showed that the degradation procedures of clothianidin in paddy water,soil and plant are all according with the first-order kinetic equation.In Guangdong,Anhui,Hubei,the half-lives of degradation of water were 1.25-1.71 d,1.08-2.15 d,1.56-2.00 d.While in soil,its were 3.72-4.17d,2.06-4.70 d,3.77-4.37d.And in plant,it were 1.49-2.85 d,1.86-3.20d,1.70-2.00 d.But the rates of residual degradation were different.There were so many factors which can affect the pesticide degradation in the environment,among them,temperature,rainfall and the microorganisms in soil played an important role.3.According to the experiments of terminal residue of 50%clothianidin WG,after 14 days on the last use of clothianidin with the recommended amount in paddy field,the residual quantities in soil were 0.056?0.084 mg/kg,0.051?0.468 mg/kg in rice plant,0.128?1.278 mg/kg in rice hulls and 0.050?0.285 mg/kg in rice.After 21 days on the last use of clothianidin with the recommended amount in paddy field,the residual quantities were 0.273?0.591 mg/kg in rice hulls and 0.066?0.092 mg/kg in rice.The residual quantities in soil and rice plant,were both lower than the minimum detectable concentration.After 28 days on the last use of clothianidin with the recommended amount in paddy field,all were both lower than the minimum detectable concentration.Therefore,the maximum dosage of 50%clothianidin WG was 225 g.ai/ha each time,applying at most 3 times at intervals for 7days.The safety interval is 21 days.Dietary risk assessment results show that the risk probability of clothianidin is 3.94%.It shows that the risk of clothianidin is acceptable under the condition.