Photodegradation And Hydrolysis Of Benfuracarb And Determination Of Endosulfan By ELISA

The regulation and kinetics of direct and indirect photodegradation and hydrolysis for benfuracarb, a kind of carbamate insecticide, in different buffers and soils was discussed. The effect of pH, temperature, moisture and the thickness of soil etc. on its degradation were also investigated. A rapid test method by Enzyme-linked immumosorbent assay (ELISA) for endosulfan in black tea, green tea and wheat was established, based on the results in different conditions. The main results from the study were:1. Rapid and sensitive quantitative and qualitative methods for benfuracarb and its main degradation products in water by gas chromatography-nitrogen phosphorous detector (GC-NPD) and gas chromatography-mass spectrometry (GC-MS) were established without cleanup. The recovery, limit of detection (LOD) and the coefficient of variation (CV) range of the method were 75%～110%, 0.01～0.02mg/kg and 5.70%～14.7%, respectively. The method met the requirements of the national standard of China for rapid test of pesticide residue.2. Benfuracarb mainly hydrolyzed in acidic and strong alkaline (pH 13.2) buffers. It was stable in neutral and weak alkaline (pH 6.7～pH 10.5) buffers. This study demonstrated that hydrolysis of the parent compound in buffers of pH 1.2～pH 3.3 was too quick to get the half life. The result proved that its hydrolytic rates in different buffers were pH 1.2～3.3＞pH 13.2＞pH 6.7＞pH 10.5. The degradation followed a first-order kinetics at pH 6.7～13.2, and was affected by temperature. The hydrolytic rate at 55℃was quicker than that at 25℃. The difference for the increase of every 10℃was 2.4～2.8 times at pH 6.7 and pH 10.5, respectively. The main hydro-products were carbofuran and carbofuran-7-phenol confirmed by GC-MS.3. This study showed two types of photodegradation of benfuracarb: direct and indirect. The direct photolysis process under UV irradiation occurred through a first-order kinetic reaction. The rate of photodegradation decreased with the increase of the initial concentration of benfuracarb, which had good liner relationship with the half lives of the kinetic curves. The study revealed that acetone, hydrogen peroxide (H₂O₂) and titanium dioxide (TiO₂) played the role of photosensitization, photocatalyzation and photooxidation, respectively, in indirect photodegradation of benfuracarb. The highest photosensitive rate by using acetone was 100% which increased as time changed. The half life and completely degradation time of benfuracarb in aqueous acetone was 57.3% and 33.3% shorter than the control. The use of TiO₂ and H₂O₂ could not only accelerate the decomposition of the parent compound, but also its photoproduct carbofuran. The photodegradation rates of benfuracarb in different conditions were H₂O₂ (0.5mmol/L)＞TiO₂(160mg/L)＞acetone (5mL/L)＞direct photodegradation.4. The photodegradation of benfiiracarb was affected by pH, which degraded very quickly with strong acidic buffers, quickly at acidic buffer, slowly in neutral or weak base conditions. The main photoproducts of benfiiracarb identified in this study were carbofuran, 3-hydroxy carbofuran, carbofuran-7-phenol, 3-hydroxy-carbofuran-7-phenol and 3-keto-carbofuran-7-phenol. A product, 2, 3-dihydro-2, 2-dimethyl-7-benzofuranyl isopropyl aminosulfenyl carbamate (m/z = 296), in buffer of pH 3.2 was found first time.5. The study on benfiiracarb in three kinds of regional soils in China: red soil, brown soil and black soil showed that the photodegradation of the parent and total residues increased under UV light. The formation and degradation of the product carbofuran was accelerated, as well. The rate of degradation of benfiiracarb in red soil was more rapid than in black and brown soils both with UV light and in darkness. Benfiiracarb in red soil was unstable and quickly degraded into carbofuran.6. Photodegradation of benfuracarb in both black and brown soils followed the first-order kinetics. The degradation rate enhanced as the increase of moisture content and the decrease of the thickness of the soils. The organic matter and clay might increase the rate. According to the study, pH was the key factor for the photodegradation of benfiiracarb. Carbofuran was the main photoproduct in the soils, which was stable in red soil in darkness with a half life of 11.42d. This indicated that application of benfuracarb in acidic soil could cause environmental pollution.7. The products of benfuracarb were different in different conditions. Most of them were formed via cleavage of the N-S bound and carbamate group, and oxidative or radical reaction of the C3 benzylic position, and finally were mineralized. A possible photolytic pathway and mechanism of the parent product is here proposed and discussed.8. Rapid and low cost ELISA methods for determination of endosulfan isomers and their metabolite endosulfan sulfate in black tea, green tea and wheat were investigated, based on the titration of Horseradish peroxidase (HRP) conjunction, effect of different solvents, matrix, and dilution and clean-up on the assay. For the unpurified method, the endosulfan in tea samples was directly tested after diluted the extract 500 times in phosphate buffer saline (PBS) without further cleanup. The LOD of the method was 2mg/kg. For the purified method, the tea samples were extracted by acetonitril and cleaned up by solid phase extract (SPE). Its LOD was 0.06 mg/kg which was similar with GC-MS.9. The ELISA method for wheat was established in which the sample was extracted by methanol and diluted 5 times in PBS/Tween-20 without further clean-up. The LOD of the method was 0.02mg/kg.