[Combined toxicity of cadmium and S-metolachlor to Scenedesmus obliquus].

The single and combined effects of Cd2+ and S-metolachlor on acute toxicity, total soluble protein content, superoxide dismutase (SOD) activity and cell membrane permeability of Scenedesmus obliquus (S. obliquus) were studied using the standard toxic testing methods. The results showed that the EC50 of Cd2+ and S-metolachlor decreased with time, and the acute toxicity of S-metolachlor was higher than that of Cd2+, EC(50-24h) of Cd2+ and S-metolachlor was 0.27 mg x L(-1) and 0.24 mg x L(-1), respectively, and EC(50.96h) was 0.16 mg x L(-1) and 0.13 mg x L(-1), respectively. The combined toxicity of Cd2+ and S-metolachlor showed a synergistic effects at low concentration, and antagonism effects at high concentration. After 96h-exposure, the total soluble protein content of S. obliquus decreased, the SOD activity first increased and then decreased, and the cell membrane permeability increased with the increasing concentration of both single and combined treatment.

[Influence of S-metolachlor and Cd2+ on photosynthesis of Scenedesmus obliquus].

The single and combined effects of Cd2+ and S-metolachlor on the chlorophyll content and chlorophyll fluorescence parameters of Scenedesmus obliquus were studied by using standard toxic testing method. Both Cd2+ and S-metolachlor had effects on the chlorophyll content and fluorescence parameters such as F0, FV/Fm, FV/F0, Y( II), qP, NPQ and rETR after 96 h-exposure, showing that Cd2+ and S-metolachlor damaged the PS II in algae, inhibited the primary reaction of photosynthesis, stopped the process of photosynthetic electron transport, and destroyed its ability of heat dissipation. The effects of Cd2 + on the chlorophyll content and fluorescence parameters were greater than those of S-metolachlor, and the effects increased with the increasing concentration. The average drop of Y( II ) was 62. 5% in the control group when the light intensity was 231 µmol (m2.s) -1 , and it was 68. 0% , 82. 5% and 100% respectively in Cd2+ -treated groups, and 66. 1% , 72. 1% and 79.6% respectively in S-metolachlor-treated group with the increasing concentration. The combined effects of Cd2+ and S-metolachlor on the chlorophyll fluorescence parameters were mainly due to the impacts of Cd2+.

[Influence of the coexistence of Zn2+ on the enantioselective toxicity of metolachlor to Scenedesmus obliquus].

To evaluate the enantioselective toxicity of chiral pesticide coexisting with heavy metal, the enantioselective toxicity of Rac-, S-metolachlor alone and coexisting with Zn2+ on Scenedesmus obliquus was studied by using standard toxic testing method. The results showed that the trend of the enantioselective toxicity of Rac- and S-metolachlor coexisting with Zn2+ was similar to that of Rac- and S-metolachlor alone. The growth inhibition rate of Scenedesmus obliquus was decreased by the coexistence of Zn2+ with high concentrations of metolachlor. The inhibition rates with 0.30 mg x L(-1) Rac- and S-metolachlor alone at 24 h were 49.61% and 59.73%, and in the coexistence of Zn2+ the values were 38.41% and 42.52%, respectively. The enantioselective toxicity of Rac- and S-metolachlor was expanded and the toxicity of S-metolachlor increased greater than that of Rac-metolachlor. The coexistence of Zn2+ showed partial increase in toxicity of metolachlor in low concentrations, while there was antagonistic effect in high content of metolachlor. The trend of Chlorophyll content of Scenedesmus obliquus at 96 h was in accordance with the growth inhibition.