Residues determination and dissipation dynamics of dinotefuran and its metabolites in rice ecosystem

To evaluate the residue and dissipation behavior of dinotefuran in rice ecosystem, the residual trial of dinotefuran in rice were carried out in Hainan, Hunan and Heilongjiang. A new method for the residue determination of dinotefuran (DNF) and its metabolites 1-methyl-3-(tetrahydro-3-furylmethyl)urea (UF) and 1-methyl-3-(tetrahydro-3-furylmethyl)guanidine (DN) in soil, paddy water, rice plant, brown rice, and rice husk was developed using ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The samples were extracted by acetonitrile or water containing 1% acetic acid, purified by QuEChERS method, gradiently eluted in aqueous solution containing methnol and water, and quantified by external standard method. Results showed that there was a good linear correlation between the concentrations of the three analytes and their peak areas with R² higher than 0.999. The limits of detection (LOD) of DNF, UF and DN were 1, 0.4, and 4 pg, respectively. The limits of quantification (LOQ) of dinotefuran and its metabolites in rice plant, soil, paddy water, brown rice and rice husk were 0.1 mg/kg, 0.02 mg/kg, 0.01 mg/L, 0.02 mg/kg, and 0.1 mg/kg, respectively. The average recoveries of the three analytes varied from 71% to 102% with the relative standard deviation (RSD) ranged from 1.2% to 8.3%. However, the RSD in rice husk was from 4.4% to 20%. For the dissipation half-lives, DNF in rice plant was 0.41-2.7 d, DNF in soil was 1.6-4.2 d, DNF in paddy water was 0.90-2.2 d; DN in rice plant was 2.9-13 d, DN in soil was 64-65 d, DN in paddy water was 4.2 d; and UF in rice plant was 0.43-3.1 d. The 20% suspension concentrate of dinotefuran was evenly sprayed at 120-180 g a.i./hm² for 2 to 3 times in the heading stage of rice with a 21-day interval between sprays. The highest residue of dinotefuran in brown rice sampled at day 14 and 21 after the last pesticide application was 0.11 mg/kg, which is below the maximum residue limit 1 mg/kg of brown rice set by China.