Liu Huijun, Ye Weihong, Zhan Xiuming, Liu Weiping
Institute of Environmental Science, Department of Environmental Science, Zhejiang University, P.O. Box 3041, Hangzhou, Zhejiang Province 310029, China.
Ecotoxicol Environ Saf. 2006 Mar;63(3):451-5. doi: 10.1016/j.ecoenv.2005.02.002.
Racemic product of metolachlor contains two R enantiomers and two S enantiomers. S-metolachlor is now widely used instead of rac-metolachlor because the former is more effective in herbicidal activity than the latter. The acute and chronic toxicities of rac- and S-metolachlor to Daphnia magna were determined and compared in this study. The acute 24-h LC50s for rac- and S-metolachlor to D. magna were 69.4 and 51.2 mgL(-1), respectively, indicating that the acute toxicity of S-metolachlor is slightly higher than that of rac-metolachlor. In chronic test, lowest-observed-effect concentration (LOEC), no-observed-effect concentration (NOEC), days to first brood, length, longevity, number of broods per female, number of young per female, and the intrinsic rate of natural increase (r) were determined. The results showed that the LOEC and NOEC of rac-metolachlor were 0.01 and 0.001 mgL(-1), while those of S-metolachlor were 0.5 and 0.1 mgL(-1), respectively. The first brood day of D. magna was not affected by rac- or S-metolachlor. Longevity and the number of broods per female were significantly (P<0.05) affected when rac-metolachlor concentration was higher than 1.0 mgL(-1) but were not significantly affected until S-metolachlor concentration was higher than 10 mgL(-1). The length was affected at the same concentration of rac- and S-metolachlor. Number of brood per female was significantly reduced when rac-metolachlor concentration was higher than 0.01 mgL(-1) but not significantly reduced until S-metolachlor concentration was higher than 0.5 mgL(-1). The r values were significantly reduced when the rac-metolachlor concentrations were above 0.01 mgL(-1) but not reduced only when S-metolachlor concentration was higher than 0.5 mgL(-1). The results of chronic toxicity indicated that rac-metolachlor was significantly (P<0.05) more toxic than S-metolachlor to D. magna.
异丙甲草胺的外消旋产物包含两种R对映体和两种S对映体。由于S-异丙甲草胺在除草活性方面比外消旋异丙甲草胺更有效，所以现在S-异丙甲草胺被广泛使用。本研究测定并比较了外消旋异丙甲草胺和S-异丙甲草胺对大型溞的急性和慢性毒性。外消旋异丙甲草胺和S-异丙甲草胺对大型溞的急性24小时半数致死浓度（LC50）分别为69.4和51.2 mgL(-1)，这表明S-异丙甲草胺的急性毒性略高于外消旋异丙甲草胺。在慢性试验中，测定了最低观察效应浓度（LOEC）、未观察效应浓度（NOEC）、首次产卵天数、体长、寿命、每只雌体的产卵数、每只雌体的幼体数以及自然增长内在率（r）。结果表明，外消旋异丙甲草胺的LOEC和NOEC分别为0.01和0.001 mgL(-1)，而S-异丙甲草胺的分别为0.5和0.1 mgL(-1)。大型溞的首次产卵天数不受外消旋异丙甲草胺或S-异丙甲草胺的影响。当外消旋异丙甲草胺浓度高于1.0 mgL(-1)时，大型溞的寿命和每只雌体的产卵数受到显著（P<0.05）影响，但直到S-异丙甲草胺浓度高于10 mgL(-1)时才受到显著影响。在相同浓度的外消旋异丙甲草胺和S-异丙甲草胺作用下，大型溞的体长受到影响。当外消旋异丙甲草胺浓度高于0.01 mgL(-1)时，每只雌体的产卵数显著减少，但直到S-异丙甲草胺浓度高于0.5 mgL(-1)时才显著减少。当外消旋异丙甲草胺浓度高于0.01 mgL(-1)时，r值显著降低，但只有当S-异丙甲草胺浓度高于0.5 mgL(-1)时r值才降低。慢性毒性结果表明，外消旋异丙甲草胺对大型溞的毒性显著（P<0.05）高于S-异丙甲草胺。
