Environmental behavior of the chiral acetamide pesticide metalaxyl:: Enantioselective degradation and chiral stability in soil
Environmental behavior of the chiral acetamide pesticide metalaxyl:: Enantioselective degradation and chiral stability in soil
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DOI：
10.1021/es010134s
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发表时间：
2002-01-15
影响因子：
11.4
通讯作者：
Balmer, ME
中科院分区：
文献类型：
--
作者：
Buser, HR;Müller, MD;Balmer, ME
外消旋甲axyl目前在许多国家被甲axyl- m所取代，甲axyl- m是一种对映体上富含生物活性r -对映体的杀菌剂，这种“手性转换”有望减少农药释放到环境中的量以及对非目标生物的潜在副作用。对这类手性化合物的环境行为的详细了解应该包括手性稳定性（对映体的相互转化）的信息。本研究采用对映选择性气相色谱-质谱联用技术（GC-MS），在实验室条件下研究了甲叶茅酯及其初级羧酸代谢物（MX-acid）在土壤中的降解/耗散。外消旋体和对映体R-和s -化合物分别在不同的实验中孵育。对甲axyl的降解具有对映选择性，对真菌有活性的r -对映体比无活性的s -对映体降解得快，导致外消旋化合物孵育时残基富集s -甲axyl。相对较高的对映体选择性表明降解/耗散主要是生物性的。结果表明，40-50%的甲axyl转化为mx -酸，剩余的甲axyl通过其他途径降解。mx -酸的降解也是对映选择性的。甲氨甲酯和mx -酸在土壤中均具有稳定的构型，没有R-对映体与s -对映体的相互转化，反之亦然。此外，甲axyl向mx -酸的转化过程中构型保持不变。降解遵循近似的一级动力学，但表现出明显的滞后阶段。
Racemic metalaxyl is currently being replaced in many countries by metalaxyl-M, the fungicide enantiomerically enriched with the biologically active R-enantiomer, This "chiral switch" is expected to reduce the amount of pesticide released into the environment as well as potential side-effects an nontarget organisms. Detailed knowledge of the environmental behavior of such chiral compounds should include information on the chiral stability (interconversion of enantiomers). In the present study, the degradation/dissipation of metalaxyl and its primary carboxylic acid metabolite (MX-acid) in soil was investigated under laboratory conditions using enantioselective gas chromatography-mass spectrometry (GC-MS). Racemic and the enantiopure R- and S-compounds were incubated in separate experiments. The degradation of metalaxyl was shown to be enantioselective with the fungicidally active R-enantiomer being faster degraded than the inactive S-enantiomer, resulting in residues enriched with S-metalaxyl when the racemic compound was incubated. The relatively high enantioselectivity suggests that degradation/dissipation was largely biological. The data indicated a conversion of 40-50% of metalaxyl to MX-acid, and the remaining metalaxyl being degraded via other pathways. The degradation of MX-acid was also enantioselective. Metalaxyl and MX-acid were both configurationally stable in soil, showing no interconversion of R- to S-enantiomers, and vice-versa. Furthermore, the conversion of metalaxyl to MX-acid proceeded with retention of configuration. Degradation followed approximate first-order kinetics but showed significant lag phases.