Residuesanddissipationdynamicsofpentoxazoneinricepaddy

An analysis method using ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was established for the determination of pentoxazone residues in the husked rice, rice hulls, rice plant, soil and paddy water. The residue and dissipation dynamics of pentoxazone in the rice paddy were investigated by field experiments. The calibration curve with good linearity was obtained in the concentration range of 0.01 to 1 mg/L. The average recoveries of pentoxazone in husked rice, rice hulls, rice plant, soil and paddy water were 75%-95% with relative standard deviations (RSDs) of 1.5%-9.5% at the spiked levels of 0.02, 0.05 and 0.5 mg/kg. The limit of detection (LOD) was 0.01 ng using this analytical method. The limits of quantitation (LOQ) of pentoxazone in those samples were all 0.02 mg/kg. The results of field experiments showed that the dissipation dynamics were fitted to the first-order kinetics equation, and the half-lives of pentoxazone in the rice plant and soil were 4.2-9.0 d and 7.0-11.6 d, respectively. When 90 g/L pentoxazone SC was sprayed once with the dose of 375 g a.i./hm² or 562.5 g a.i./hm², the final residues of pentoxazone in the husked rice were lower than 0.02 mg/kg at the harvest date. This study can be used as an important supportive data for the maximum residue limits (MRL) standard development of pentoxazone in the husked rice.