The Studies On Microbial Degradation Metabolism Of Nicosulfuron In Water

Nicosulfuron is a member of the sulfonylurea herbicides,and been applied postemergence in maize.Nicosulfuron has broad and hight activity against annual gramineous,part of broadleaf and sedgesweed.Nicosulfuron has been widely used in China because of its low-dosage,good effect and safety to maize.Many pesticide corporations have started producing nicosulfuron.Nicosulfuron's transferability was strong, and it can contaminated groundwater.Especially,high concentration of nicosulfuron exists in industy wastewater manufactory of producing this kind of herbicide,therefore,studing on the degradation of nicosulfuron of water demonstrates the significance.In order to screen and get the microorganisms degrading nicosulfuron,the five strains of microorganisms with nicosulfuron being only source of carbon,nitrogen,and energy were got by enrichment culture.Two strains,which had the hightst degradation rate,were studied the degrading characteristics and pathway.The main results were summsrized as follows:1.In order to screen and get the microorganisms degrading nicosulfuron,the five strains of microorganisms with nicosulfuron being only source of carbon,nitrogen,and energy,which were numbered as YF1,YB1,YB2,YB3,and YB4,and YF1 was fungi, others were bacteria,were got by enrichment culture.All of the microorganisms were cultured in culture medium which containing different concentrations of nicosulfuron,then put in swing bed at 30℃and shook at 150 r·min^-1for 5 days,detected the concentration of nicosulfuron by using HPLC and calculated the degradation effficiency.It was shown that the degradation rates of the five strains of microorganisms were higher in low concentration than in high concentration for nicosulfuron,with YF1 having the highest degradation rate of 80.31%,secondly,YB1 and YB2 having the degradation rate of 78.18 %and 73.72%,respectively,however,YB3 and YB4 having lower degradation rate of 36.82%and 25.75%,respectively.It was also discovered that YF1 was Aspergillus niger, YB1 and YB2 were Bacillus sp.by primary identifying for the three strains of microorganisms with higher degradation rate.YB1 strain was Bacillus subtilis by futher identifying of 16S rDNA.2.In order to confirm the degrading characteristics and pathway of nicosulfuron-degrading YB1 strain,systematic screening has been used to figure out the favorable conditions and acting site of nicosulfuron degradation.The results showed that (1)the optimal culture medium was the basic mediumâ…¢,(2)among the nicosulfuron concentrations tested,the higher degradation rates of YB1 strain were found in treatments with 0.5 mg·L^-1～2 mg·L^-1,with the best concentration being 2 mg·L^-1which resulted in 82.1%degradation rate,and(3)the appropriate temperatures for nicosulfuron degradation ranged between 35℃and 40℃.Under such favorable conditions,the maximum degrading rate(86.2%)was obtained at an inoculating quantity of 1×10⁹ CFU·mL^-1.With mass nicosulfuron spectrometric analysis on the degradation products of YB1 strain,it was proved that the degradation site was sulfonylurea bridge.3.Systematic screening has been used to figure out the favorable degradation conditions of YF1.The results showed that(1)the optimal culture medium was the basic mediumâ…¢,(2)among the nicosulfuron concentrations tested,the best concentration was 2 mg·L^-1which resulted in 100%degradation rate,and(3)the appropriate temperatures for nicosulfuron degradation ranged between 35℃and 40℃.Under such favorable conditions,the maximum degrading rate(100%)was obtained at an inoculating quantity of 2.3×10⁷ CFU·mL^-1and cultivated in 5 days.4.A mixture of YB1 and YF1 strains caused the concentration of nicosulfuron lower than the limited detection(LOD)after 72 h culture with a 0.0038 rate constant of degradation and the degrading velocity was higher than either of the strains.