Research On Enantioselective Toxicity Of Metconazole To Microcystis Flos-Aquae And Its Compound Pollution With Antibiotics

In the actual environment,different enantiomers of the same pesticide may have different or even opposite toxic effects on organisms.Therefore,it is very important to investigate the ecological effects of chiral pesticides on the environment.In this paper,the enantiomers of metconazole(MEZ)racemes were separated by high-performance liquid chromatography;and then the enantioselective effects of MEZ on photosynthesis,proteins,cell ultrastructure and microcystin in Microcystis flos-aquae were investigated.At last,the combined toxic effects of MEZ and common antibiotics were studied.Here are the conclucions:(1)The resolution conditions of MEZ were as follows: chiral column of Chiralcel OD-H,column temperature 25 °C,mobile phase n-hexane/ethanol=97:3,flow rate 0.8m L/min,detection wavelength 220 nm,injection volume 20 μL.The order of the peaks is cis-1R,5S-MEZ,cis-1S,5R-MEZ,trans-1S,5S-MEZ,trans-1R,5R-MEZ.(2)The changes of the photosynthetic activity and protein contents for 8 days showed that 0.01～0.1 mg/L MEZ could decrease the contents of chlorophyll a in different degree;cis-MEZs(>0.03 mg/L)increased the carotenoid contents at first and decreased it on day 8;0.01～0.1 mg/L trans-MEZs also decreased the carotenoid contents;cis-MEZs(>0.03 mg/L)decreased Fv/Fm,however,there was no significant difference in Fv/Fm between trans-MEZs groups and control group(P>0.05);cis-MEZs(>0.03 mg/L)decreased the the rapid light response curve(RLCs).The RLCs of transMEZs groups were not significantly different from that of control group(P>0.05)or higher than that of control group(P<0.05);cis-MEZs(>0.03 mg/L)first increased the light utilization efficiency(α),but decreased on the day 8;The α of trans-MEZs groups increased at 0.001～0.01 mg/L,but there was no significant difference between0.03～0.1 mg/L groups and control group(P>0.05);0.01～0.1 mg/L cis-MEZs and 0.1mg/L trans-MEZs could inhibit the protein contents(PC,APC,PE and proteins)of M.flos-aquae.In general,the toxicities of MEZ were cis-1S,5R-MEZ > cis-1R,5S-MEZ >trans-1S,5S-MEZ and trans-1R,5R-MEZ.(3)The changes of cell structure of M.flos-aquae after 4 days show that cis-MEZs could cause cells deformation,plasmolysis.cis-MEZs could decrease thylakoid numbers and arranged thylakoid vertically.While trans-MEZs kept the original shape of algae cells,the number of thylakoids decreased slightly,the organelles were clear and the cells did not undergo lysis.(4)The effects of 0.03 mg/L MEZ enantiomers on microcystin-LR(MC-LR)was studied.On day 4,the intracellular MC-LR contents of cis-MEZs were higher than that of trans-MEZs groups.While the intracellular MC-LR contents of cis-MEZs were lower than that of trans-MEZs groups(P<0.05)or had no significant difference with trans-MEZs groups(P>0.05)on day 8.However,the extracellular MC-LR contents of cis-MEZs groups were always higher than that of trans-MEZs groups.The total MCLR contents of cis-MEZs groups were higher than that of trans-MEZs groups(5)Combined toxicity of MEZ and four antibiotics.The combined toxicity of MEZ,tetracycline,oxytetracycline,enrofloxacin and ciprofloxacin was evaluated by target methods.The evaluation results were all antagonistic,but they had limitations.Therefore,the toxicity effects of five-component mixtures on the whole effect ranges were predicted by the model method.The IA model had better prediction results than the CA model.Finally,the predicted toxicity effect was as follows: the low concentrations were synergistic,the medium concentrations were additive and the high concentrations were antagonistic.