Studies On Residues Degradation Dynamics Of20%Buprofezin WP In Citrus

Buprofezin, an insect growth regulator, belongs to the family of thiadiazine. The insecticide could inhibit the chitin synthesis, interfere the metabolism of the insects. In addition, it also had remarkable effects on many pests, such as plant hopper, leafhopper and whitefly.20%buprofezin wettable powder (WP) was mainly used for the prevention of unaspis yanonensis, which was produced by Zhejiang Hangzhou Dadi Pesticide Co.Ltd.In this study, a determination method for buprofezin residue in citrus and soil was developed. The sample was extracted by methanol. After being centrifuged and oscillated, the supernatant fluid was analysed by GC. The minimum detectable quantity and the limit of detection were0.15ng and0.0075mg/kg, respectively. The working range was between0.2mg/L to10mg/L. The recoveries for citrus pericarp, citrus pulp, whole citrus and soil were from78.0%to98.8%,75.4%to91.6%,77.2%to93.8%and79.5%to99.6%, respectively. The releative standard dievation (RSD) for the four samples were from1.85%to2.82%,2.64%to3.85%,3.01%to4.18%and1.07%to4.41%, respectively. The results showed that the method was suitable for buprofezin residue determination in citrus and soil. And the results of repeatability, reproducibility, precision and accuracy could meet the demand of pesticide residue assay issued by the Chinese government. Based on the developing method, the degradation dynamics and residue trials of buprofezin in citrus orchard were carried out in August2008. And the trial site was located in Jinan district of Fuzhou city.The degradation dynamics trial showed that the20%quantity of original accumulation of buprofezin WP in citrus pericarp, citrus pulp, whole citrus and soil were1.2801mg·kg-1,0.1525mg·kg-1,1.0930mg·kg-1and1.0860mg·kg-1, respectively. The half-life of buprofezin in citrus pericarp citrus pulp, whole fruit and soil were6.23d,1.96d,6.06d and3.65d.On the other hand, the residue trial showed that there were none of buprofezin residue could be detected in citrus pericarp, citrus pulp and whole citrus when the time passed by21d. Moreover, the quantity of buprofezin residue in soil was between LOD to0.0681mg-kg-1. All of the residue in citrus and soil were lower than the maximum residue limit (MRL) set by the government. Author proposed that the safety interval should be21d for buprofezin in citrus when the20%buprofezin WP was applied for citrus. The maximum dosage should17.5g/mu and26.25g/mu, and the spray time should not be more than2times.