Study On The Residue Analysis And Digestion Of 50% Klebsi Dust WP On Tomato

Captan is organic sulfur fungicides, recently in China, it is mainly used for controlling tomato blight. However, the dynamic and final residue of captan is not yet studied systematically in tomato and crosponding soil.In current work, a gas chromatography(GC) method was developed to determine the residues of captan in tomato matrix. And scientific basises for the safely use and residue determination of captan in tomato matrix were carried out. The QuEChERS(Quick, Easy, Cheap, Effective, Rugged, Safe) method was used for sample pretreatment procedure, after extract with acetonitrile, Gas Chromatography was employed for detection after cleaning up by graphitized carbon black(GCB). The limit of detection was 1.00×10-9 g and the limit of quantification was 0.05 mg/kg. The spiked levels of captan were 0.05, 1, and 10 mg/kg in both tomato and soil. The recoveries were ranged 80.40 to 98.24 % with RSDs between 2.83 and 3.41 % in soil; ranged 90.40 to 100.9 % with RSDs between 2.44 and 3.72 % in tomato. The method was suitable for captan determination in tomato matrix.The field trials of 50 % captan(wettable powder, WP) were performed in Guizhou, Hunan and Tianjin province during the agricultural season in 2013 and 2014. The results indicated that there was no obvious differencees in the degradation of captan in tomato, in 2013, the half lives of captan were 5.77, 5.98 and 7.13 days, in Guiyang, Changsha, and Tianjin, respectively; and in 2014, the half lives in Guiyang, Changsha, and Tianjin were 4.31 days, 5.14, and 5.69 days, respectively. However, the degradation of captan is very fast in soil, the half life were about 1.02 days in 2013, 1.33 days in 2014. The results of final experiment showed that the residue of 50 % captan WP was 0.05-2.27 mg/kg(in tomato) and 0.05-0.92 mg/kg(in soil) at harvest time(the formulation was applied 3-4 times), which was much lower than these MRLs of China(5 mg/kg), European Union(3 mg/kg). Therefore, 50 %captan WP can be applied safely on tomato with the recommended dosage and time.Meanwhile, the factors of soil degradation were also invsitgated, the results showed that, microorganism in soil can accelerate the degradation of captan anddegradation of captan in acid soils is relatively slow.