Study On Residue Analysis Of Bispyribac-sodium By HPLC And Its Degradation In Aqueous Solution And Paddy Soils

Bispyribac-sodium is an ultra-high effect, low-toxicity, and wide-spectrum herbicide. Previous studies focused mainly on herbicidal efficacy and mechanism of bispyribac-sodium, little information was available about its behavior and ecological effect in paddy field. In order to extend its use and provide some fundamental data for assessing the bio-environment safety and scientific application of bispyribac-sodium, the degradation behavior and the influencing factors of bispyribac-sodium in different kinds of paddy soils, and photolytic degradation kinetics in Aqueous solutions were studied in this thesis. The main results were summarized as following:The residual determination of herbicide 20% Bispyribac-sodium WP in water and soils were investigated. The results showed: (1) A new analytical method for determining residues of bispyribac-sodium in water and soil by HPLC was developed. The soil samples were extracted with 4% NaHCO3 water solution, followed the extract was partitioned with petroleum ether and dichloromethane. The aqueous phase(containing the final residue) was acidified with 1mol/L hydrochloric acid and re-extracted with ethyl acetate. The quantification of the herbicide bispyribac-sodium residue was established by HPLC with a C₁8 column, a mixture of methanol plus water (75/25, V/V) containing 0.04% H3PO4 as mobile phase, with detection of UV wavelength at 250nm. The results showed that the average recoveries of the method ranged 82.42%⁹5.54%, at the fortified levels of 0.01-1.0mg/kg for the samples, and coefficient of variation was in range of 4.60%⁸.66%. The minimum detectable limits in water and soil were 0.002mg/L and 0.01mg/kg, respectively. The parameters such as accuracy, sensitivity, precision for the method were good to satisfy the essential rules of pesticide residue determination. (2) At the application rate of 67.5g(a.i.)/hm2, the half-life of Bispyribac-sodium in water and soil was 1.77d and 2.33d, respectively, suggesting that bispyribac-sodium belong to a low residue and degradable herbicide.The degradation of bispyribac-sodium in soils and its influence factors were investigated in the laboratory. The obtained results were listed as follow. (1) Degradation of bispyribac-sodium in soils was influenced by such the factors as water-hold capacity, physical-chemical properties of soils, microorganisms and temperature. Residue and degradation rate of bispyribac-sodium varied in the soilssuch as Reddish clayed soil, Newly allavial sandy soil and Purple clayed soil, and their half-life was 12.14d. 16.53d and 23.02d, respectively, suggesting that bispyribac-sodium should be very degradable pesticide.(2) Through sterilization, bispyribac-sodium was degraded more slowly than the non-sterilized ones, and the degradation rate coefficient was 0.0136, 0.0104 and 0.0076 with its half-life of 50.95d> 66.63d and 91.18d, respectively, indicating that microorganism would accelerate the degradation of bispyribac-sodium in soils. (3) Degradation rate of bispyribac-sodium increased with the increasing water-hold capacity of soils, and reached the high level 78.2% when water-hold capacity increased to 110%. Higher temperature could also enhance degradation rate of bispyribac-sodium and achieved the high level when temperature increased to 35°C. Degradation of bispyribac-sodium in soils speeded up with the increasing concentrations of bispyribac-sodium, and then fell beyond the tolerant concentration.The photolysis kinetics and mechanisms of bispyribac-sodium in aqueous solution were studied. The experimental results revealed that: (1) The light source had obvious effect on the photolytic degradation rate of bispyribac-sodium, their half-life under high-pressure mercury lamp and sunlight was 22.95h and 101.91min, respectively, under 300W high-pressure mercury lamp, bispyribac-sodium in pure water degraded 13.51 times faster than under sunlight illumination. (2)Different vessels had obvious effect on the photolytic degradation rate, its half-life in quartz tube and in glass tube was 22.95h, 113.61h, respectively under sunlight illumination. (3) In pure water, the photolysis rate of different concentration of bispyribac-sodium was in the order of 2.0mg/L > 5.0mg/L > lO.Omg/L under 300W high-pressure mercury lamp, Which means with the increase of initial concentration of bispyribac-sodium, the photolytic decomposition rate of bispyribac-sodium decreases in water. (4) Under the 300W high pressure mercury lamp, photolysis of bispyribac-sodium in phosphate buffer was conducted in buffer solution of different pH value showed that the photolysis rate were quicker in pH5 than that in other buffers and are in the order of pH5>pH7>pH9, indicating the photolytic degradation of bispyribac-sodium in acidity solution, maybe result in poor stability. (5) The experiments on influence of fertilizers on photolysis of bispyribac-sodium under the 300W high-pressure mercury lamp showed that KH2PO4 had photosensitizing effects on bispyribac-sodium, and they make photolysis half-life of bispyribac-sodium decreased. Otherwise, NH4HCO3 and urea both showed photo-quenching effects on...