The Mechanism Research Of Glyphosate Degradation By Chemical And Microbial Methods

Chemical and microbial methods were used to degrade glyphosate in this paper,the degradation conditions were optimized to study the degradation effects.The intermediate metabolites of glyphosate degradation were studied to analyse the possible metabolic pathways at the optimal degradation conditions,then the mechanism of two methods were studied.Response surface methodology(RSM)was utilized to optimize the glyphosate degradation condition by H2O2 as the chemical method.The optimal degradation condition was:pH at 10.70,H2O2 initial concentration at 2.20 mL/L,temperature at 44.20 ? and reaction time at 5 h,at this condition the glyphosate(150 mg/L)degradation rate was 80.20%.The statistical significance of RSM was good,R2 =0.9823,the relation of factors and response values was fitted well by the regression equation,the model could be used to determine the optimal glyphosate degradation condition by H2O2.The main intermediate metabolites of glyphosate degradation by H2O2 were:sarcosine,glycine,glycolic acid,phosphoric acid,formaldehyde,formic acid and AMPA.AMPA,which is the most difficult to degrade and is toxic among the main intermediate metabolites was studied,the AMPA concentration was a process of rise first then fall.The glyphosate degradation pathway by H2O2 was speculated from the experimental results and existing literature and document:(1)Glyphosate was first oxidized to sarcosine and phosphoric acid by breaking C-P bond,sarcosine was then oxidized to glycine,glycine was oxidized to formic acid.(2)Glyphosate was first oxidized to AMPA and glycolic acid by breaking C-N bond,AMPA was then oxidized to methylamine which was then oxidized to formaldehyde.Aspergillus oryzae A-F02 was used to degrade glyphosate as the biological method.As glyphosate degraded by microorganism was mainly by enzymatic reaction,the degradation effect is determined by the enzyme producing ability of microorganism.The culture condition was optimized by RSM and the optimal degradation condition was:additional glucose concentration at 0.5%,pH at 7.2,temperature at 31 ?,glyphosate concentration at 1000 mg/L,at this condition the glyphosate degradation rate was 19.18%.The statistical significance of RSM was good,R2= 0.998,the relation of factors and response values was fitted well by the regression equation,the model could be used to determine the optimal glyphosate degradation condition by Aspergillus oryzae A-F02.The main intermediate metabolites of glyphosate degradation by Aspergillus oryzae A-F02 were studied.Among the main intermediate metabolites existed AMPA and methylamine without sarcosine and glycine,the glyphosate metabolic pathway by Aspergillus oryzae A-F02 was speculated from the experimental results and existing literature and document:Glyphosate was first reacted to AMPA by breaking C-N bond,AMPA was then reacted to methylamine by breakig C-P bond,methylamine was reacted to formaldehyde at last.It was found that previous catalysis reaction steps were not limited by AMPA and methylamine in the glyphosate degradation process by Aspergillus oryzae A-F02,the decomposition velocity of AMPA and methylamine were much faster than glyphosate degradation step,so we speculate that glyphosate reacted to AMPA was the rate-limiting step among the metabolic pathway.Glyphosate oxidoreductase which catalyzed glyphosate to AMPA was the key enzyme,AMPA and methylamine reacted to methylamine and formaldehyde by C-P lyase and semicarbazide-sensitive amine oxidase was favoring,which do not limit the metabolic pathway.