The Toxicity Of Metolachlor To Microcystis Aeruginosa Under Eutrophication Conditions

Eutrophication resulted from overusing nitrogen fertilizers is one of the most serious environmental problems of the farmland soil and surface water in China, thus the ecological toxicity effect of metolachlor may face the synergy influence of enantiomers and nitrogen, as well as some other nutrition. Microcystis aeruginosa, which is characterized by wide distribution, is responsible for most of the algal blooms. The study of the effects of metolachlor on the membrane integrity of microcystis aeruginosa cells will give some theoretical insights into the set of the concentration criteria for the water quality standard in future.(1) High performance liquid chromatographic separation of metolachlor. Metolachlor was optimally separated into four stereoisomers on AY-H chiral column, using Hexane/EtOH (96/4) as the mobile phase with the flow rate of 0.6 mL/min at 25 ℃. Complete baseline separation was achieved. This simple and efficient method lays the foundation for the subsequent research of metolachlor’s enantioseselective effect.(2) The influence of Rac-metolachlor and S-metolachlor to microcystis aeruginosa’s cell integrity and microcystis toxins’s synthesis under different nutrient conditions was studied. Compared to Rac-metolachlor, S-metolachlor has greater toxicity to microcystis aeruginosa. The higher the nitrogen concentration was, the greater toxicity of Rac-metolachlor and S-metolachlor to microcystis aeruginosa would be. When the concentration of nitrogen was fixed, with the increase of S-metolachlor’s exposure concentration, extra-MC-RR’s concentration tended to rise, but the intra-MC-RR’s concentration decreased. Although the total concentration of toxin was reduced, the proportion of extracellular toxins still had been enhanced. When the concentration of the Rac-metolachlor was increased, the microcystis aeruginosa’s ability to release the toxins was also improved. When the S-metolachlor’s exposure concentration was fixed, with the increase of nitrogen concentration, the total concentration of toxin increased. Compared with the control group, the ratio of extracellular toxins in all toxins kept on rising in the S-metolachlor treatment group. In the control group, with the increase of nitrogen concentration, the ratio of extracellular toxins in all toxins also increased. In addition, after adding S-metolachlor, the ratio of extra-MC-RR became increasingly larger. In the Rac-metolachlor treatment group, with the increase of nitrogen concentration, the increase of the ratio of extracellular toxins in all toxins is not obvious when compared to S-metolachlor treatment group. Both Rac-metolachlor and S-metolachlor could improve the microcystis aeruginosa’s ability to release the toxins, but nitrogen had different influence on the two process.(3) The toxicity of Metolachlor to Microcystis aeruginosa:aRS＞aSS＞aSR＞aRR. Using scanning transmission soft X-ray microscopy, it was found that Metolachlor can induce the change of the distribution of essential trace element Fe. The results showed that mcyD and mcyH showed significant difference between the control and all the treated groups. aSS greatly changed the expression of mcyD and mcyH, compared with aRR. aRS greatly changed the expression of mcyD and mcyH, compared with aSR. It showed that molachlor changed the expression of genes coding for microcysis toxins transporter.