| Hexaflumuron, one of the benzoylphenylurea insect growth regulators, was developed by Dow AgroSciences. It has been widely used in insect control Because of its high selectivity, non-target organism, and low toxicity, it is mainly used to control Helicoverpa armigera Hubner, Plutella Xylostella (L), Spodoptera exigua Hiibner and Mythimna separata. In order to evaluate the residues in environmental situations, the residues of hexaflumuron in cabbage field and the processes of hydrolysis, photodegradation, soil degradation, absorption and leaching were researched. The main results were listed:1. An analytical method for determing the hexaflumuron residues in cabbage and soil was established by gas chromatography (ECD) after extracted with acetonitrile. The method showed quite good linearity between the concentrations of hexaflumuron and the peak areas in the range of 0.05-10 mg/L with r=0.9998. The limits of detection (LOD) was 0.018 ng. Morever, the average recoveries were 85.41 to 93.44% in cabbage and 88.41 to 96.05%in soil, and the relative standard deviations (RSD) ranged from 2.17 to 7.52% in cabbage and 4.37 to 7.33% in soil, respectively. The limits of quantification (LOQ) was 0.02 mg/kg. At the same time, an analytical method for determing the hexaflumuron residues in water and soil was established by high performance liquid chromatography (HPLC) after extracted with acetonitrile. The HPLC method showed fairly good linearity between the concentrations of hexaflumuron and the peak areas in the range of 0.05-10 mg/L with r=0.9997. Its LOD was 0.01 mg/L.Furthermore, the average recoveries were 84.98 to 97.15%in water and 89.40 to 96.10% in soil, and RSD ranged from 3.52 to 6.12% in water and 4.57 to 7.35% in soil, respectively. The established method is simple, accurate, reproducible and practical, and could be applied for residue determination of hexaflumuron.2. The residue results of degradation dynamics of hexaflumuron in three cabbage fields in two years showed that the degradation dynamics could accord with the kinetic equation in all cases. The half-lives of hexaflumuron were 2.21 to 4.74 d in cabbage and 4.67 to 6.34 d in soil, respectively.2% microemulsion of emamectin benzoate and hexaflumuron was sprayed for 2 and 3 times, each intervals for 10 days, with the dose of 9 and 13.5 g.ai/h..Harvest intervals were 5 and 7 days and the residues of hexaflumuron in cabbage and soil were less than maximum residue limit (MRL) (0.02 mg/kg).3. It is aimed to present our investigation and analysis of the influences of the hydrolysis characteristic features of hexaflumuron in the laboratory conditions, as well as the the effects of different temperatures, pH values and concentrations of copper ion (Cu2+) and surfactant (sodium dodecyl sulfate, SDS) on the hydrolysis of hexaflumuron in liquid media. The results have shown that, the hydrolysis process of hexaflumuron tend to follow the first-order kinetics in all cases. In addition, the hydrolysis in alkaline solution conducted in the most prompt way, in comparison with those in the acid and neutral solutions. It was found the hydrolysis process can be accelerated with the rising temperature, with the temperature coefficient being 1.11. The activation entropy indicated a significantly negative correlation with the temperature, although activation energy has no obvious relationship with the temperature. Nevertheless, in buffer solution of pH=9 at 35 ℃, the hydrolysis of hexaflumuron was remarkably accelerated with the increase of Cu2+concentration in the range of 25-500 μg/L. Moreover, the sodium dodecyl sulfate could play an inhibitory role while the restraining degree can be enhanced with the increasing concentrations of SDS in the range of 100-900 mg/L.4. This work aimed to investigate the photodegradation kinetics and pathways of hexaflumuron in liquid media. Photodegradation occurred under simulated solar and UV irradiation according to first-order kinetics. The photodegradation rates follow the order of UV irradiation> solar irradiation; pH 5.0> pH 7.0> pH 9.0; and n-hexane> methanol> ultrapure water> acetone in terms of solvent. The photodegradation rate was higher in the presence of nitrate ions, nitrite ions, ferrous ions, humic acid, sodium dodecyl sulfate and hydrogen peroxide due to photosensitization, whereas ferric ions reduced the degradation rate. Moreover, this work also identified the photodegradation products by GC-MS. It was possible to identify three photodegradation products in methanol for the first time. Cleavage of the urea linkage was proposed as a reasonable photodegradation pathway.5. The results of soil degradation process showed that, in aerobic conditions, the half-lives of hexaflumuron in the loess, or the yellow-brown soil in Nanjing, the red soil in Jiangxi and the black soil in China Northeast were 14.23,16.08 and 11.63 d, respectively. In anaerobic conditions the half-lives were 11.93,13.38 and 10.19 d, respectively. Under sterilized conditions, the degradation half-lives were 43.05,49.87 and 40.53 d, respectively. It indicated that hexaflumuron has been degraded mainly by the biodegradation in the soils and the activities of anaerobe are likley to have positive influences on the soil degradation process of hexaflumuron.6. The adsorption and desorption of hexaflumuron was also studied. The results indicated the adsorption-desorption isotherms all can quitely fit the Freundlich model in three different soils with the adsorption constants of 15.62,3.48,9.62, respectively, which showed good correlations with organic matter (OM) and cation exchange capacity (CEC) with the correlation coefficient being 0.9986 and 0.9577. The extent of hexaflumuron adsorbed by soils matched the following sequence:black soil of Northeast> yellow-brown soil of Nanjing> red soil of Jiangxi. Adsorption isotherm of hexaflumuron in clay and loam were both L shape and in sand was the S shape. The free energy of sorption ranged from-15.22 to-16.27 kJ/mol, which was less than 40 kJ mol-1, suggesting that the adsorption type of hexaflumuron belonged to the physical adsorption.7. The leaching abitity of hexaflumuron in different soils were studied by soil thin layer chromatography(TLC) and soil column leaching. The results showed that hexaflumuron showed comparatively low mobility and leaching degree in three tested soils, which indicated that hexaflumuron has little potential risk for groundwater contamination under normal use. The mobility of hexaflumuron in three soils was as follows:red soil of Jiangxi> yellow-brown soil of Nanjing> black soil of Northeast China. |
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