Study On Degradation Property Of Sulfonylurea Herbicides By White-rot Fungi

In recent years,the pollution caused by a large number of chemical pesticides is increasing,which is harmful to people's health and the growth of crops.Sulfonylurea herbicide is a super efficient herbicide,which is widely used to control broad-leaved weeds and gramineous weeds in cereal crops.This kind of herbicide has a long residual period in the soil,and can cause the damage of sensitive crops,which makes the agricultural production suffer economic loss.Microorganisms can significantly degrade herbicide residues,but also has the characteristics of safety,no secondary pollution,low cost of repair,so the use of microorganisms to degrade such herbicides has attracted people's attention.In this study,white rot fungus was used to degrade two herbicides.Through screening the dominant degradation strains,exploring the impact of environmental factors on degradation and optimizing degradation conditions,the basis for biodegradation of pesticides was provided.The main results are as follows:1.The degradation effects of three white rot fungi?Phlebia sp.-606,Funalia trogii-751,Irpex lacteus-W?on two herbicides were studied.The results showed that W strain was the dominant degradation strain of chlorimuron-ethyl,with a degradation rate of 56.1%;while the 606 strain was the dominant degradation strain of tribenuron-methyl,with a degradation rate of 90.3%.2.Single factor analysis and response surface optimization of chlorimuron-ethyl and tribenuron-methyl degradation by white rot fungi were carried out by three factors of herbicide initial concentration,pH and temperature.The results showed that when the initial concentration of chlorimuron-ethyl was 40 mg/L,the pH value of the solution was 5.7,and the temperature was 30.7?,the degradation rate of chlorimuron-ethyl was the highest on the 7th day,72.40%;when the initial concentration of tribenuron-methyl was 40 mg/L,the pH value of the solution was 6.0 and the temperature was 21.4?,the degradation rate of tribenuron methyl reached 99.10%on the 5th day.3.The half-life of white rot fungi in degradation of two herbicides was obtained through the digestion dynamic experiment.The half-life of chlorimuron-ethyl was 4.696days,and that of tribenuron-methyl was 1.077 days.Compared with the control group,the degradation time of the experimental group was significantly shorter,indicating that white rot fungus can enhance the degradation rate of herbicides.4.The metabolites of chlorimuron-ethyl and tribenuron-methyl were detected by liquid chromatography-mass spectrometry.The sulfonylurea bridge of chlorimuron-ethyl is broken and then cyclized to form 2-amino-4-chloro-6-methoxypyrimidine and 2-sulfamoyl benzoic acid.Through the cleavage of sulfonylurea bridge of tribenuron-methyl,2-methoxy-4-methylamino-6-methyl-1,3,5-triazine and methyl 2-aminosulfonylbenzoate are generated,and the functional group-SO₂-is removed by condensation reaction to obtain methyl 2-?1-?4-methoxy-6-methyl-1,3,5-triazin-2-yl?-3-methylureido?benzoate and then the functional group N-methylamine is removed to obtain methyl2-?N-?4-methoxy-6-methyl-1,3,5-triazin-2-yl?formamido?benzoate.5.In the soil medium,the degradation rate of chlorimuron-ethyl by white rot fungus is40%-65%,and that of tribenuron-methyl is more than 90%.The results showed that it was possible to use white rot fungi to repair contaminated soil,which provided a theoretical basis for the bioremediation of sulfonylurea herbicides.