Migration Behaviors And Degradation Characteristics Of Mesotrione In Soils

Chemical and pesticide risk assessment of environmental pollution has become a hotspot of Environmental Sciences. Method for residual analysis of Mesotrione in plant sample and environmental samples were studied in this thesis. Using this residue determination method, the environmental behavior of Mesotrione was studied, such as soil adsorption, leaching, soil degradation and photodegration in lab. The all characteristics of Mesotrione in paddy and saline-alkali soils had been also studied and compared with the results obtained in lab. This study contributed to understanding the transference and transformation process of Mesotrione in environment and to evaluating its fate and potential hazards in environment systematically. Results of this study would provide a scientific basis for registration, safe and reasonable using, and eliminating of possible arising pollution of Mesotrione. The main conclusions were listed as follows:1) Mesotrioe in water samples was extracted by methylene chloride and determined by reversed-phase high-performance phy (RP-HPLC). After the pH value of the water samples was adjusted to4by phosphoric acid or sodium hydroxliquid chromatogra ide, and then extracted twice by methylene chloride under25℃for15min. The extract liquor was evaporated by rotary evaporator nearly dry and dissolved in acetonitrile in constant volume finally. HPLC was used to determine mesotrione with a XDB-C18column, UV detector at220nm, and acetonitrile-phosphoric acid aqueous solution (pH=4.0) as the mobile phase. Results showed that linear range of meotrione was0.5-100.0mg/L, and the correlation coefficient (r2) was0.9996, the standard deviation (SD) was0.46, the variation coefficient (CV) was0.472%, the average recovery rate was88.9%under the optimum condition.2) The adsorption of Mesotrione on two of soil (Yixing paddy soil, Yancheng saline-alkali soils) was investigated by the method of the classical oscillation balance. The results indicated that the adsorption of Mesotrione on all two types of soil followed Freundlich equation. The adsorption velocity was rapid. The adsorption balance could be reached in1h. The adsorption capability of these two soils was Yixing paddy soil> Yancheng saline-alkali soils. These indicated that the adsorption of Mesotrione in soil was mainly physical adsorption. It was a spontaneous adsorption process, and the higher temperature, the more the amount of adsorption. The experimental results showed that:adsorption kinetics of mesotrione met second-order rate equation. There is a significant correlation among the the adsorption and the organic and the soil pH.3) Leaching law and migration of the herbicide mesotrione were studied under flooded conditions using physical simulating artificial rainfall method. The soil leaching column was filled with paddy soil or saline soil with the diameter of10cm and the height of25cm. Results showed that after10hour’s continuous leaching, the column retain amount was increased with the deepness. The amount of mesotrione in15～21cm layers paddy soil was27.35mg/kg, which was less than39.07mg/kg in saline soil. About4%of added mesotrione was leached through the columns which indicated that mesotrione has high Leaching characteristics. For the weakly acidic structured mesotrione, the leaching properties would be affected by soil and leaching solution pH. Mesotrione dissociated from the molecular to anionic form with the increased soil and leaching solution pH. It was concluded that mesotrione was easy to leach into deep soil and bring some risks to groundwater, especially in soils with high pH values, such as saline soil.4) The simulate degradation and solar light photodegradation of mesotrione in three typical soils was investigated. The affecting factors on mesotrione degradation had been studied with sterilized soil as a contrast. The experiment results showed that the degradation rate in3kinds of typical soils in the following order:Yixing soil>Huainan soil>Yancheng soil. The half-life times of mesotrione degradation were12.16d,27.73d and34.68d in unsterilized Yixing paddy soil, Huainan paddy soil and Yancheng saline-alkali soil, and38.51d,86.64d,138.63d in sterilized soils, respectively. The half-life times under solar light were8.56d,18.73d and25.67d. All the degradation process with the match the first-order kinetic equation. The degradation rate of mesotrione in unsterilized soils was faster than that in sterilized soils, which indicated that microorganisms played an important role in the mesotrione degradation in soils. Moreover, solar light could accelerate the mesotrione degradation. The different physical and chemical properties of soils could affect the soil microbial activity and community structure, and then affect the degradation behavior of herbicides in soils ultimately. The research results would provide basic data and scientific basis for in-depth study of mesotrione environmental fate.