The Research On Dynamic Degradation And Final Residues Of Carbendazim In Watermelon And Rice By HPLC

Carbendazim is classified as a kind of benzimidazole fungicide. It is a colorless crystalline powder as pure grade and brown as product. It is insoluble in water, slightly soluble in chloroform, acetone and other common organic solvents. It is a kind of high efficient, broad-spectrum fungicide. The main results of the study can be summarized as follows:1、In this study, a high performance liquid chromatography method was initially developed for determining carbendazim residues in watermelon, rice, paddy, paddy water and soil. The carbendazim residue in samples was dissolved in the mixture of methanol and hydrochloric acid (O.lmol/L), adjusted to pH6.8-7.5with NaOH (2mol/L), extracted with methylene chloride. Then the extraction was diluted by diluted methanol (HPLC) and the residue of the object was determined by HPLC-UV. The results showed that the minimum detectable amount of carbendazim was1.0x10-10g. The minimum detectable concentrations in watermelon and soil were0.01mg/kg and0.02mg/kg, respectively. Those in rice, paddy water and paddy were0.04mg/kg,0.005mg/kg and O.Olmg/kg, respectively. The average recoveries in watermelon and rice were more than80.2%and the coefficients of variation were less than4.10%at the concentration levels of0.05mg/kg,0.5mg/kg and1.0mg/kg. It can be drawn that the method is characterized by high sensitivity, accuracy and excellent reproducibility, which can meet the measuring requirements of carbendazim.2、The research of the kinetics of the degradation of carbendazim in watermelon and soil in different ecological environment was carried out in Changsha and Guangzhou. In the research, the experimental watermelon and soil were sprayed by the product of carbendazim (20%carbendazim WP) once at higher dosage (1.5times more than the recommended) of8kg/hm2(the concentration of carbendazim at1.6kg/hm2), diluted with running water (750L/hm). As is shown from the research, the degradation of carbendazim in watermelon and soil features is rapid and follows pseudo-first-order kinetics. The half-lives of carbendazim in watermelon ranges from1.32d to2.72d and the half-life in soil ranges from1.87d to2.13d.3、The research of the kinetics of the degradation of carbendazim in rice plant, paddy and paddy water in different environment was carried out in Changsha, Hangzhou and Changchun. In the research, the experimental rice and paddy were sprayed by the product (22%carbendazim SC) once at higher dosage (1.5times more than the recommended) of 2.1kg/hm2(the concentration of carbendazim at0.462kg/hm2), diluted with running water (750L/hm). As is shown from the research, the degradation of carbendazim in rice, paddy and paddy water features is rapid and follows pseudo-first-order kinetics. The half-lives of carbendazim in rice plant ranges from2.07d to3.14d, it ranges from5.49d to7.31d in paddy water and ranges from2.44d to3.66d in paddy soil.4、The research on the residue of carbendazim in watermelon and soil in different environment was carried out in Changsha and Guangzhou. When the product(20%carbendazim WP) was applied thrice at most at recommended dosage of0.825g per individual plant (the concentration of carbendazim at0.165g per individual plant) and higher dosage of1.238g per individual plant, diluted with running water (250mL per individual plant), the final residues of carbendazim in the watermelon that harvested more than10days after the last application were below the maximum residue limit (MRL)0.5mg/kg of watermelon in China5、The research on the residue of carbendazim in rice and paddy soil in different environment was carried out in Changsha, Hangzhou and Changchun. When the product (22%carbendazim SC) was applied thrice at most at recommended dosage of1.05kg/hm2(the concentration of carbendazim at0.231kg/hm2) and higher dosage of1.575kg/hm2in rice field,diluted with running water (750L/hm2), the final residues of carbendazim in the rice that harvested more than14days after the last application were below the maximum residue limit (MRL)0.5mg/kg of cereal in China.6、According to the study, several suggestion will be presented as follows:In China, as to watermelon, the harvest are edible, which are applied with the20%carbendazim WP thrice (7days as intervals)at most at the dosage of8kg/hm2(the concentration of carbendazim at1.6kg/hm2), diluted with running water (250mL per individual plant), in the infancy of watermelon Fusarium wilt and reaped more than10days after the last application. As to rice, the harvest are edible, which are applied with the22%carbendazim SC thrice (7days as intervals)at most at the dosage of2.1kg/hm2(the concentration of carbendazim at0.462kg/hm2), diluted with running water (750L/hm2), in the infancy of rice Botrytis cinerea and reaped more than14days after the last application.