咪唑烟酸在土壤中的微生物降解及其代谢物分析

Degradation and Metabolism of Imazapyr by Microorganisms in Soils

通过分析咪唑烟酸在4种典型土壤中灭菌和非灭菌条件下的降解动力学差异,初步探讨了土壤中的微生物对其降解的贡献率。结果表明,咪唑烟酸在非灭菌条件下的半衰期为29～44d,在灭菌条件下的半衰期为81～134d,在非灭菌条件下的降解速率比灭菌条件下提高1 3～3 4倍。在小粉土中微生物降解的理论半衰期约为48d,为灭菌条件下的近3倍,充分说明了土壤中的微生物在咪唑烟酸的降解中起着非常重要的作用。运用LC-ESI-MS检测到4种微生物降解产物,它们的分子量分别为219,222,201和149,并由此推断了咪唑烟酸在土壤中降解转化的主要途径为:首先被微生物转化成更为稳定的氨盐产物,然后再进一步脱甲基、羧基和异丙基及咪唑啉酮环的开裂和重排等。

A comparison of the degradation kinetics of imazapyr was conducted in four typical soils under sterilized and non-sterilized conditions, and the rates of degradation by microorganisms preliminarily investigated. The results showed that the half-life values ranged from 29 to 44 days in non-sterilized soils and from 81 to 134 days in sterilized soils. The degradation rate constants in non-sterilized soils were found to substantially increase, (1.3)～(3.4) times higher than that in sterilized soils. The theoretical half-life of imazapyr by microbial degradation in powder soil was about 48 days, nearly 3 times of that under sterilized conditions. The preceding conclusions fully proved that the intrinsic microbes in soils play an important role in the degradation of imazapyr. Four metabolic products, which molecular weights were 219, 222, 201 and 149, respectively, were analyzed on the basis of the spectral data of LC-ESI-MS. The principal degradation pathway for imazapyr in soils was proposed as follows: the incorporation of imazapyr into NH^+_4, yielding a stable isopropylammonium salt; then further decarboxylation, demethylation, loss of isopropyl group, cleavage and rearrangement of imidazolinone ring and so on.