Studies On Residue Analytical Methods And Dissipation Of MCPA In Rice Ecosystem

The MCPA belongs to the phenoxy acid herbicides which widely used in our country. The residue analysis methods of MCPA in rice were developed in this paper and The dissipation dynamics of MCPA in rice ecosystem after the application of 12% MCPA soluble powder were studied. The safety evaluation of MCPA residues in rice was investigated. The results will provide a basis to guide the rational use of 12% MCPA soluble powder, and ensure the quality and safety of rice. The main results were summarized as following:1. Residue analytical methods of MCPA in Rice samplesRice,rice chaff,rice plants and rice soil first with 0.04mol·L-1 sodium hydroxide aqueous solution, mechanical oscillation extraction, adjusted pH below 3 with phosphoric acid, and then extracted with ethylacetate,constant volume with 2.5mL of Methanol/pure water(v:v=1:1),by HPLC-MS/MS determination. Three concentrations of 0.02mg.kg-1, 0.05 mg·kg-1,0.50mg.kg-1 were added in rice, when the MCPA recoveries of between 94%-111%,Coefficient of variation between 3.63%-8.75%; Three concentrations of 0.02 mg·kg-1,0.10 mg·kg-1,1.00 mg.kg-1 were added in rice chaff, when the MCPA recoveries of between 94%-102%,Coefficient of variation between 3.48%-6.77%; Three concentrations of 0.02 mg·kg-1,0.10 mg·kg-1,1.00 mg·kg-1 were added in rice plants, when the MCPA recoveries of between 88%-119%,Coefficient of variation between 3.54%-8.03%; Three concentrations of 0.01 mg·kg-1,0.10 mg·kg-1,1.00 mg·kg-1 were added in rice soil, when the MCPA recoveries of between 85%-96%,Coefficient of variation between 3.29%-8.86%;The final minimum detectable was 0.02 mg·kg-1 in both rice, rice chaff and rice plants. However the difference was appearing in rice soil, which was 0.01 mg·kg-1.The recoveries of Residue analytical method in rice were 85%-119%.and the coefficients of variation were less than 20%. The minimum detectable concentration of MCPA in rice was lower than maximum residue limits(The MRL of MCPA in rice was 0.05 mg·kg-1). the methods were meet the requirements of pesticide residue analysis.2. Residual dynamic of MCPA in riceThe field experiment design of MCPA in rice was carrying out in Anhui,Hubei,and Henan during 2012～2013. the dosage of 12% MCPA soluble powder is 165 g·ai ha-1.The initial residues of MCPA in rice plants were 0.19mg·kg-1～3.43mg·kg-1 eccept Hubei in 2013,The digestion rate of MCPA was above 50% after 14d, the degradation procedure of MCPA correspond to the mathematic pattern.In 2012, the half-life of 12% MCPA soluble powder in rice plants of ANHUI, HUNAN and HUBEI were 5.87d,2.70d and 7.62d respectively. In 2013, the half-life of 12% MCPA soluble powder in rice plants of ANHUI and HENAN were 4.28d and 14.43d respectively. In 2013, at HUBEI, the MCPA’s residue in rice plant was found that was lower than the minimum detectable concentration after 7d (0.02mg·kg-1)The initial residues of MCPA in rice water were 0.03 mg·kg-1 ～5.91 mg·kg-1 and the digestion rate of MCPA was above 50% after 7d. At ANHUI in 2012 and HENAN in 2013, the degradation procedure of MCPA was found correspond to the mathematic pattern, and the half-life were 3.96d and 1.36d respectively.The residue of rice water after 3d of Henan and Hubei in 2012 was lower than The minimum detectable concentration (0.01mg·kg-1). In 2012, at ANHUI and HUBEI, the residue was found reached the top in Id after the application, which were 0.03mg·kg-1 and 0.09mg·kg-1 respectively. In 2013, at Anhui, the digestion rate of MCPA in water was found reached 40% in 3d.And after 7d, the residue was lower than the minimum detectable concentration (0.01 mg·kg-1).The residue of rice water after 7d of Hubei in 2013 was lower than The minimum detectable concentration (0.01mg·kg-1)3. Safety evaluation of MCPA residues in riceThe results of the residue experiments for two years at two points in Anhui,Henan and Hubei indicated that, all the sample was not detected with under the dosage of 110 g·ai ha-1 or the dosage of 165 g·ai ha-1 used. According to the MRL of MCPA in rice is 0.05 mg·kg-1,so, the recommended dose of 12% MCPA soluble powder is safety if you at the rice harvest.