Research On The Biodegradation Mechanism And Degradation Products Of Herbicide Chlorimuron-Ethyl

Chlorimuron-ethyl, ethyl2-(4-chloro-6-methoxypyrimidin-2-ylcarbamoylsulfamoyl) benzoate, is a sulfonylurea herbicide discovered and developed by Du Pont campany of United States in1980s. Chlorimuron-ethyl, as a super-effective and broad-spectrum postemergence herbicide controlling soybean field weeds, had good effect on the control of annual grass weeds, some broadleaf weeds and some sedge weeds. But chlorimuron-ethyl degraded very slowly and remained for long time in soil, which could cause injury to succeeding sensitive crop. Microorganisms can significantly degrade herbicide residues without environmental problem and toxicity. Therefore, the use of microbial treatment has a very important theoretical significance and great potential to chlorimuron-ethyl residual pollution. A solid phase extraction-high performance liquid chromatography-mass spectrometry method and biochemical assay method were established for determination the degradation of chlorimuron-ethyl herbicide by fungi strains at different conditions in this paper. Main degradation products of chlorimuron-ethyl were studied with HPLC, and LC-MS respectively. The mechanism and pathway of degradation were studied under different conditions.The results showed that:1. Optimum conditions for degradation of chlorimuron-ethyl herbicide by Aspergillus niger were as follows:concentration of chlorimuron-ethyl in basal medium was10mg·L-1, temperature of reaction solution was30℃, inoculum of Aspergillus niger was5.0mL.2. Degradation rates of different fungi strains were very differently. The order was:Aspergillus niger>Aspergillus flavus>F8. The results showed that the highest degradation yield was produced by Aspergillus niger (96.49%), followed by Aspergillus flavus (88.95%), while F8was the lowest (82.37%).3. Degradation rates of mixed fungi strains were higher than single fungi strain. The order was: Aspergillus niger and Aspergillus flavus>Aspergillus niger and F8. Degradation yields of these mixed fungi strains were higher than98.2%.4. Using different fungi strains, the pH of reaction solution reduced in pace with degradation of chlorimuron-ethyl. The pH value of Aspergillus niger reaction solution reduced from the initial7.55to3.42and the pH value of Aspergillus niger and Aspergillus flavus reaction solution reduced enormously from the initial7.51to3.27.5. Degradation products of hydrolysis and biodegradeation were different. Product A、B、C、 D、G、J were contained commonly in hydrolysis and biodegradeation. In addition, product E、F and H were contained in degradation by Aspergillus niger; product F was contained in degradation by Aspergillus flavus; product F and H were contained in degradation by Aspergillus niger and A spergillus flavus.6. The degradation mechanism and pathway of hydrolysis and biodegradeation were different. Chlorimuron-ethyl was degraded by means of hydrolyzed the ester group on the benzene ring and destroyed the sulfonylurea bridge of chlorimuron-ethyl. Methoxylpyrimidine ring was unstable and there was oxidation reaction occured. Pyrimidine ring was stable and there was no de-methoxy reaction occured. The mechanism of biodegradeation was more complex than hydrolysis. Hydrolysis products were degraded by fungi strains and degradation product could be further degraded by hydrolysis, oxidation, alcoholysis and cyclization reactions. At last, chlorimuron-ethyl isomer also degraded by Aspergillus niger, mixed fungi strains of Aspergillus niger and Aspergillus flavus, which made degradation yield higher.