Residue Dissipation Of Mesotrione And MCPA-Na In Rice Ecosystem

Mesotrione and MCPA-Na belong to triketones and phenoxy acetic acid herbicides,respectvely, and can be used to control annual broadleaf and sedge weeds in the paddy field. In this paper, dissipation and final amount of mesotrione and MCPA-Na residue from 9%pyrazosulfuron-ethyl·mesotrione·MCPA-Na WP were investigated in rice field ecosystem in order to provide reference data for establishiment of reasonable application guideline of the herbicide and environmental safety assessment. The main results are as following:1. A rapid multi-residue analytical method for the simultaneous determination of mesotrione and MCPA-Na was developed using dispersive solid phase extraction and high performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS). The analytes was extracted by ethyl acetate and cleaned up by PSA and C18, and then separated on a reversed phase C18 column using an gradient elution program of 0.1% aqueous formic acid and 0.1% methanol formic acid. Quantitative analysis was performed with electrospray ionization in positive/negative mode(ESI+) /(ESI-) under multiple reaction monotoring(MRM) mode.Results showed that there existed a linear relationship between the herbicide concentrtion and peak area within the concentration range of 0.001 ~ 2 mg/kg(mesotrione) and 0.005 ~ 5 mg/kg(MCPA),and their correlation coefficient was greater than 0.9997. add horizontal range, etc blank samples; average recoveries of mesotrione and MCPA in the samples such as field water,soil, plants, husks and brown rice spiked with 0.01 ~ 2 mg/kg(mesotrione) or 0.05 ~ 10 mg/kg(MCPA) were 75% ~ 102.5% and 89.9%~ 112.5%,respectively; The relative standard deviation(RSD) were 0.1% ~ 8.2% and 0.5% ~ 7.4%. The LOD of the method for mesotrione and MCPA was 0.005 ng and 0.025 ng,respectively, and LOQ was 0.01 mg/kg and 0.05 mg/kg,indicating that the method can meet the detection requirements of mesotrione and MCPA residues in rice ecosystem samples with its high efficiency, good sensitivity and accuracy,.2. The dissipation dynamics of mesotrione and MCPA in rice plant, soil, and water were studied. The results showed that when applied with a dosage of 318.6 g a.i./hm2,the dissipation of mesotrione and MCPA in plant and water. could be described by the first-order kinetic equation, and the half lives of mesotrione and MCPA were 1.04 d~3.53 d and 0.79 d~2.76 d in rice plant, and 1.10 d~11.40 d and 2.19 d~6.43 d in paddy water,respectively,and not detected in soils, indicating that tmesotrione and MCPA belong to low residue and easy degradableherbicide.3. Final residue of mesotrione and MCPA-Na in rice and soil were investigated when applied at the recommended dose and 1.5 times the recommended dosage. The results showed that final residue amount of mesotrione and MCPA in the samples such as the plants, soil and brown rice was not detected,suggesting that 59% pyrazosulfuron-ethyl?mesotrione?MCPA-Na WP was very safe when it was used to control the annual broadleaf and sedge weeds in the paddy field with the application dose of 177.0 ~ 212.4 g a.i/hm2 at 2 ~ 4 leaf stage of weeds after rice transplanting.