Studies On Residual Degradation Of Paichongding In Paddy Field And Environment

Pesticides’ residue dynamic research is the basis of guide the scientific using pesticide and defining maximum residue limit. Paichongding is new type of high efficient broad-spectrum insecticide with contact toxicity, stomach toxicity and systemic action. It was used to control pest of Homoptera, especially planthopper and will be widely applied to fruits, wheat, beans, vegetables, rice and corn.This paper established an analytical method with HPLC for determining the residual quantity of paichongding in paddy water, soil, strew, rice and rice husk. After field experiments in four different paddy fields, the residues degradation dynamics and the final residues quantity of paichongding in water, soil, strew, rice and rice husk were determined. The main results were as followings:1. The high performance liquid chromatographic method was established for determining the residual quantity of paichongding in rice and its environment. Residues were extracted with a mixture of acetonitrile and water, followed by cleansing with a aluminum oxide neutral, then determined by HPLC with a linear gradient elution program of acetonitrile and water as the mobile phase and ultraviolet detection at 354nm. The results showed that the linear range of paichongding were from 0.5 to 10ppm and R2 was 0.9998. And the average recoveries were 70.81% to 102.18%, the coefficient of variation ranged from 1.02 to 9.89%. The minimum detectable concentration of the paichongding in water, soil, strew, and rice were all 0.1 mg/kg, and 0.2 mg/kg in rice husk.The result shows that it is easy to operation, saving the solvent, little pollute to the environment, and fit for the practical work.2. Study the residual degradation dynamic of 10% paichongding SC in rice and its environment in four different paddy fields in one year. The results showed that the degradation procedures of paichongding in paddy water, soil and plant are all according with the first-order kinetic equation. In Jiangsu, Jilin, Jiangxi,Shandong, the half-lives of degradation of water were 0.76d,0.85d,1.32d,1.12d; while in soil, its were 0.95d,0.89d,0.84d,0.75d and 1.02d,1.22d,1.22d,1.09d in strew. But the rates of residual degradation were different. There were so many factors which can affect the pesticide degradation in the environment, among them, the microorganisms in soil played an important role.3. According to the experiments of terminal residue of 10% paichongding SC, after 14 days on the last use of paichongding with the recommended amount in paddy field, the residual quantities in soil, rice plant, rice hulls and rice were both lower than the minimum detectable concentration. Therefore,10% paichongding SC can control the planthopper. The maximum dosage was 52.5 g.ai/ha each time, applying at most 3 times, each time intervals for 7days. The safety interval is 14 days. it will be safe to rice and environment as recommended.