The Study On Residues Of Spinosad In Paddy And Soil

A analytical method of the residues of spinosad in paddy and soil was established using highperformance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), and thedissipation dynamic and residue of spinosad in paddy and soil were investigated.The method was based on QuEChERS methodology. The samples were extracted withacetonitrile, and purified with primary secondary amine (PSA) and graphitized carbon black(GCB), finally analyzed by high performance liquid chromatography tandem mass spectrometry(HPLC-MS/MS). The method showed good linearity, and the linear correlation coefficients (R2)of spinosyns A and D were above0.99. The limits of detection (LOD) for spinosyns A and D inpaddy water were0.001mg/L, in paddy soil, rice plants, rice, rice husk and rice straw were0.005mg/kg, respectively. The limits of quantification (LOQ) for spinosyns A and D in paddy waterwere0.005mg/L, and in other matrices of rice were0.06mg/kg、0.01mg/kg, respectively. Theaverage recoveries of spinosyn A and D in paddy soil, water and rice samples were72.9%~107.9%with the relative standard deviations (RSD)1.1%-13.5%.The rice field trials of spinosad were carried out in Beijing, Hubei and Zhejiang province in2010and2011. The decline study of spinosad residue in paddy soil, water and rice plantssuggested that the decline curves accorded with the first-order kinetics equation Ct=C0e-kt, and thehalf-lives of spinosad were5.06-8.88d、0.15-4.61d and0.37-4.79d, respectively. For ultimateresidue, the residues in brown rice7d after last application at low dosage65g/hm2and high dosage97.5g/hm2for3to4times were lower than0.3610mg/kg.The results showed that the established method was simple, specific and sensitive. Thedissipation of spinosad was quick in paddy soil,water and rice plants. The ultimate residue waslower than the MRL1.0mg/kg in brown rice. It was safe for spinosad to set a PHI as7d at therecommended dosage used in paddy.