Fate Of Oxadiargyl In The Environment Of Paddy Field

Method for residual analysis of oxadiargyl in plant samples and environmental samples was studied in this thesis. Using this residue determination method, we studied environmental behavior of oxadiargyl, such as soil adsorption, soil degradation, hydrolysis, and photodegradation in lab. Degradation characteristics of oxadiargyl in paddy field had been also studied and compared with the results obtained in lab. This study contributed to understanding the transference and transformation process of oxadiargyl 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 oxadiargyl. The main conclusions obtained were listed as follows:A gas chromatography analytical method for determining residue of oxadiargyl had been developed. This method developed from QuEChERS. It was proved to economize on solvent, time and labor, and was proved to work well in determining residue of oxadiargyl in plant, water, and soil samples. A Agilent 6890 gas chromatogrphy spectrometry equipped with ECD was involved in this method. The recoveries of oxadiargyl in water, soil, rice straw and grain ranged from 82.9% to 112.0%, and the RSDs ranged from 0.2% to 6.2%. LOQs were 0.001,0.001,0.005, 0.005 mg/kg respectively, and LODs was 0.01 mg/kg. This method had been recommended in the study of oxadiargyl's photodegradation, hydrodegradation, dissipation and field study for its accuracy, precision and sensitivity.The Kd values of oxadiargyl in yellow/red loam from Tong'an, loam from Ha' erbin, purplish clayey soil from Wuxi were 103.35,97.45 and 76.52, respectively. Kd values revealed high absorption capability of oxadiargyl. Adsorption free energy(â–³G) of oxadiargyl in soils were all below 40 KJ/mol, showing that the adsorption largely resulted from the physical action. There had a good positive correlation between adsorption coefficient (Kd) of oxadiargyl in three different kinds of soils and the soil properties OC, while pH, CEC, and clay content had little effect on Kd.For the half-lifes of Oxadiargyl in yellow/red loam, loam and purplish clayey soil were 233.6d,182.4d and 277.3d, respectively. Oxadiargyl had low dissipation rate in yellow/red loam and purplish clayey soil, and had medium dissipation rate in loam. The degradation rate had a good negative correlation with the soil properties OC, while pH, CEC. Clay content had little effect on degradation rate.Oxadiargyl had a relatively high hydrodegradation rate in alkali buffer with half-life of 3.7d at pH=9.6, and had a very low hydrodegadaton rate in acid and neutral buffer with half-lifes of 147.5d at pH=5.0 and 192.5d at pH=7.1. The fragmentation pattern of photoproduct indicated ring-opening reaction occurred in the bone of macrocyclic lactones of heterocycle while oxadiargyl hydrolyzed in solutions, and the oxadiargyl matrix turned to be N-(2,4-Dichloro-5-prop-2-ynyloxy-phenyl)-N'-(2,2-dimethyl-propionyl)-hydrazinecarboxylic acid.The half-life of oxadiargyl photodegradation under UV light was 3.09min. It was much higher than that under Xenon lamp which with a half-life of 1.43h. Lower half-life under simulation of solar radiation(Xenon lamp) would be enhanced with the treatments of strengthening light intensity and increasing temperature. When came to solvents used in study, acetone would result in higher photodegradation rate, and lower rate gained with acetonitrile, and no rate change with methanol. Humic acid in solution would increase the photodegradation rate slightly. But in presence or increasing dosage of TiO2, photodegradation rate would be accelerated sharply. The fragmentation pattern of photoproduct indicated loss of chlorine was the dominant process when oxadiargyl photodegraded in buffer solutions. 5-tert-Butyl-3-(4-hydroxy-3-prop-2-ynyloxy-phenyl)-3H-[1,3,4]oxadiazol-2-one or 5-tert-Butyl-3-(3-prop-2-ynyloxy-phenyl)-3H-[1,3,4]oxadiazol-2-one or 5-tert-Butyl-3-(2-hydroxy-5-prop-2-ynyloxy-phenyl)-3H-[1,3,4]oxadiazol-2-one was the possible photoproduct.Dissipation rates of oxadiargyl in rice paddy field water and soil were much rapider than that in laboratory experiment. In addition to degradation by oxadiargyl itself, rainfall and oxadiargyl being absorbed by soil would be the important factors leading to the rapid disspation rate of oxadiargyl in paddy water. Washing out by rainfall and being absorbed by rice plant would be the main reasons for the rapidly dissipation of oxadiargyl in paddy soil.