Enantioselective degradation and ecotoxicity of the chiral herbicide diclofop in three freshwater alga cultures
Enantioselective degradation and ecotoxicity of the chiral herbicide diclofop in three freshwater alga cultures
复制标题
手性除草剂敌草灵在三种淡水藻类培养物中的对映选择性降解和生态毒性
DOI：
10.1021/jf0728855
复制
发表时间：
2008-03-26
影响因子：
6.1
通讯作者：
Sheng, Guangyao
中科院分区：
文献类型：
--
作者：
Cai, Xiyun;Liu, Weiping;Sheng, Guangyao
芳氧基苯氧基丙酸酯是一类手性除草剂。它们有一对对映异构体，只有R（+）形式具有药物活性。禾草灵，这些除草剂的模型化合物，作为酯形式的外消旋体，禾草灵-甲基，由对映异构体的1：1混合物组成，被商业化。研究了禾草灵和禾草灵的对映体选择性水生毒性和生物降解性。禾草灵和禾草灵的S（-）对映体对藻类的毒性与相应的R（+）形式相似或更高，这取决于具体的物种。虽然没有发生对映体转化的禾草灵和禾草灵，这些除草剂在藻类培养中观察到的对映体选择性降解的差异表明，它们的应用形式是一个重要因素，决定其对映体选择性的环境行为。藻类的细胞渗透性和热处理表明，禾草灵在藻类培养物中的对映选择性降解主要由藻类的促进吸收，而对映选择性毒性主要由被动吸收。这些结果表明，由于手性农药对映体的降解差异以及可能的作用位点差异，96 h EC 50等急性毒性试验不足以评估手性农药的生态风险。研究结果表明，手性除草剂的对映体选择性降解和毒性可能导致其生态毒理效应难以预测，因此应特别关注目前使用的外消旋农药，因为活性较低或无活性的对映体可能造成更高的生态风险。
Aryloxyphenoxypropanoates are a class of chiral herbicides. They have a pair of enantiomers, only the R(+) form of which is herbicidally active. Diclofop, the model compound of these herbicides, is commercialized as the racemate of the ester form, diclofop-methyl, consisting of a 1:1 mixture of the enantiomers. This study evaluated the enantioselectivity in aquatic toxicity and biodegradation of diclofop and diclofop-methyl. The herbicidally inactive S(-) enantiorners of both diclofop-methyl and diclofop were similar to or higher than the corresponding R(+) forms in toxicity to algae, depending on specific species. Although no enantiomeric conversion occurred for diclofop-methyl and diclofop, the difference in the enantioselective degradation of these herbicides observed in algae cultures suggested that their application forms were an important factor determining their enantioselective environmental behavior. The cell permeability and heat treatment of algae revealed that the enantioselective degradation of diclofop in algae cultures was governed primarily by the facilitated uptake by algae, whereas the enantioselective toxicity was primarily governed by the passive uptake. These results suggested that the acute toxicity test such as the 96 h EC50 was insufficient to assess the ecological risk of chiral pesticides because of the differential degradation as well as possibly differential action sites of enantiomers. From this study, it was concluded that the enantioselective degradation and toxicity of chiral herbicides may result in their ecotoxicological effects being difficult to predict and that specific attention should thus be paid to currently used racemic pesticides as less active or inactive enantiomers may pose higher ecological risks.