Institute of Environmental Health, College of Environmental and Resource Sciences , Zhejiang University , Hangzhou , Zhejiang 310058 , People's Republic of China.
College of Science and Technology , Ningbo University , Ningbo , Zhejiang 315211 , People's Republic of China.
J Agric Food Chem. 2019 Feb 13;67(6):1631-1637. doi: 10.1021/acs.jafc.8b04813. Epub 2019 Feb 4.
The enantioselective effects of chiral herbicides on aquatic organisms have received increasing attention. As one kind of freshwater algae responsible for most algal blooms, Microcystis aeruginosa can produce hepatotoxic microcystin and cause serious health concerns for drinking water. Thus, the effects of chiral herbicides on M. aeruginosa are of vital significance but poorly understood, especially as the structures of chiral herbicides become more complex. In this study, the enantioselective effects of four metolachlor enantiomers based on carbon center and axis chirality on M. aeruginosa were investigated for the first time at an enantiomeric level. The results of the investigation into algal growth inhibition, chlorophyll a content, and cell integrity indicated that ( S)-metolachlor [( S)-Met] was significantly more toxic than any other isomer. The toxicity ranking of different enantiomers at the highest concentration (15 mg/L) against M. aeruginosa was ( S)-Met > (α R,1' S)-Met > (α S,1' S)-Met > (α S,1' R)-Met > (α R,1' R)-Met, with (α S,1' S)-Met and (α R,1' S)-Met displaying a synergistic effect. Additionally, the Fe distribution in M. aeruginosa presented distinct enantioselectivity, which may contribute to the enantioselective toxicity of metolachlor. Furthermore, metolachlor upregulated the expression of genes mcyD and mcyH in an enantioselective manner, indicating that this herbicide can potentially promote the synthesis and efflux of microcystin, thus aggravating agricultural water contamination to different extents. Overall, this study will help to understand the ecotoxicity of metolachlor at a deeper level and provide theoretical insights into the enantioselective behaviors of metolachlor.
手性除草剂对水生生物的对映体选择性效应受到越来越多的关注。铜绿微囊藻作为引发大多数水华的淡水藻类之一，能够产生肝毒性微囊藻毒素，对饮用水安全构成严重威胁。因此，手性除草剂对铜绿微囊藻的影响至关重要，但目前了解甚少，尤其是随着手性除草剂结构变得更加复杂。本研究首次在对映体水平上研究了基于碳中心和轴手性的四种甲草氯对映体对手性除草剂对铜绿微囊藻的对映体选择性效应。通过对藻类生长抑制、叶绿素 a 含量和细胞完整性的研究，结果表明(S)-甲草氯[(S)-Met]比其他任何异构体的毒性都大。在最高浓度（15mg/L）下，不同对映体对手性除草剂对铜绿微囊藻的毒性排序为(S)-Met＞(αR,1'S)-Met＞(αS,1'S)-Met＞(αS,1'R)-Met＞(αR,1'R)-Met，其中(αS,1'S)-Met 和 (αR,1'S)-Met 表现出协同作用。此外，铜绿微囊藻中 Fe 的分布表现出明显的对映体选择性，这可能是甲草氯对映体选择性毒性的原因之一。此外，甲草氯以对映体选择性的方式上调了 mcyD 和 mcyH 基因的表达，表明该除草剂可能会促进微囊藻毒素的合成和外排，从而在不同程度上加剧农业水污染。总体而言，本研究将有助于更深入地了解甲草氯的生态毒性，并为甲草氯的对映体选择性行为提供理论见解。
