Study On The Microbial Degradation Of Quizalofop-p-ethyl In Soil

A analytical method was established for determining residues of quizalofop-p-ethyl (ethyl(RS)-2-[4-(6-cororo-2-quinoxalinoxalinyloxy)phenoxy]propanoate)and its main metabolite, by the high performance liquid chromatography under the condition optimized. It was applicable to determine residues of the herbicide and the metabolite in soil, sesame plant and sesame seed, and satisfied to meet the requirement of fortified recovery.It seems that micro-organism in soil played a very important role to decompose the herbicide with the results of microbial degradation, which the half-lifves of quizalofop-p-ethyl with a level of 50 mg/kg in clay and red soil were 9.9 and 15.7 days comparing with that in the two types of soil sterilized, 29.8 and 37.5 days, respectively.It was observed that micro-organisms in soil treated with the herbicide at a range of 2-50 mg/kg grown greatly different from those in control. The results showed that Bacteria, such as Bacillus and Pseudomonas were grown most fast; and then Staphylococcus, Vibrio and Escherichia were increased obviously; but that Actinomyce and Fungi were seemed to be inhibited by quizalofop-p-ethyl.Three dominant strains of bacteria in clay soil were obtained by the screening experiments, which were Acinetobacter Icoaceticus-baumanni c0//ex(NYA2), Bacillus megaterium(NYB\) and Bacillus cereus(NYB4). The results of microbial degradation of the herbicide showed that NYB1 and NYB4 had special ability to degrade the chemical from those bacteria tested in cultured media added a series volumes(5-20% in total volume) of bacteria suspension while the concentration of the herbicide at 50 mg/L in the media. And the results showed that NYB1 and NYB4 also promote the degradation process of quizalofop-p-ethyl in clay soil(20g) after added 2 mL of the bacteria suspension(OD46o=0.40), respectively.The filed trial results indicated that quizalofop-p-ethyl was degraded quickly in sesame plant and soil, and its half-lifves were 1.35 and 1.18 day, respectively. But the main metabolite of quizalofop-p-ethyl was decomposed much more slowly both in sesame plant and soil. The total residue of quizalofop-p-ethyl and its metabolite in sesame seeds after harvested was less than 0.02 mg/kg(the recommended MRL of FAO is 0.02 mg/kg in peanut seed). It could be suggested that there be safety or no obvious toxicity to human health while sesame seed be consumed as a food for people if the herbicide be applied by the way of the filed trial.