The Residue Degradation Of Clothianidin In Paddy Field And Its Photodegradation

Clothianidin is a kind of new and safe neonicotinoid insecticides having characteristics of low toxicity, long persistence and high efficacy. In the recent years, it has been increasingly applied to rice, fruit, tea, ornamental crops and other kinds of crops. We comprehensively researched the degree of the residues and degradation of the20%clothianidin suspending agent in rice and paddy soil. We aim to evaluate the adverse effects of clothianidin on environmental systems and investigate the pattern of clothianidin photodegradation in aqueous media. Our study supports that it is safe to use clothianidin in rice in the case without causing ecological impacts. The main conclusions of this study are:(1) Developed a liquid chromatography to detect clothianidin residues in rice environments. By using this liquid chromatography analysis, the minimum detectable amount of clothianidin was2×10-10g and the minimum detectable concentration in paddy soil, rice plants, rice and rice husk was O.Olmg/kg. When the concentration was within the range from0.01to1.00mg/kg, the average recovery rate of clothianidin in different rice samples was85.1%to104.1%and the standard deviation was1.1%to12.1%.(2) Conducted the experiments in three places:Changsha, Shijiazhuang and Guiyang. Clothianidin was digested in paddy water, soil and rice plants. Its half-life in paddy water:Hebei8.18d> Guizhou6.57d> Hunan4.0d; in the soil:Hebei11.99d> Guizhou9.92d> Hunan7.99d; in plants:Hebei15.51d> Guizhou11.68d> Hunan5.77. According to a first order chemical reaction kinetics equation, clothianidin is considered as a pesticide that is easily digested in rice.(3) In the growing stage of rice, we diluted20%of750-1125g/ha clothianidin by750L/ha water (the recommended dose of active ingredient clothianidin is150～225g/ha) and sprayed on the occurrence of rice pests. After more than14d pest control with clothianidin, the clothianidin residues in the harvested unpolished rice was in the range of LOD to0.082mg/kg, which not exceeded the MRL (O.lmg/kg). Therefore, we believe that20%of clothianidin suspending agent within prescribed dose is safe to be used in rice.(4) Observed the light degradation of clothianidin with a500W-high-pressure mercury lamp as a light source. Specifically the amount of dissolved oxygen by the light degradation of clothianidin was different in different aqueous media. We measured its half-life in pure water is46.2min.. The light degradation rates of clothianidin in different surface water:water> pure water> pond water> water. The photochemical degradation rate of Clothianidin in several different organic medium: acetone> methanol> acetonitrile> n-hexane.