Study On The Toxicity Difference And Selective Bioaccumulation Of Vancomycin - Like Enantiomers To

Epoxiconazole, which was first produced by BASF in 1985, is a chiral triazole fungicide with efficient and low toxicity. This fungicide is used extensively in agriculture. However, it can enter into the fresh water cycle and cause water pollution after prolonged and repeated application.In this study, the growth inhibition of scenedesmus obliquus were assayed, and the EC50 values were calculated to compare the toxicities of(-)-,(+)-and rac-epoxiconazole. Additionally, the pigment and malondialdehyd2e(MDA) contents, the superoxide dismutase(SOD) and catalase(CAT) activities were determined. Changes in the ultrastructural morphologies of algae cells were also observed by transmission electron microscopy(TEM). Furthermore, we evaluated the enantioselectivity of epoxiconazole during its bioaccumulation and degradation in S. obliquus.The results showed that the 96h-EC50 values of rac-epoxiconazole,(-)-epoxiconazole and(+)-epoxiconazole were 5.850, 4.296 and 2.488 mg/L, respectively. For the treatment of low dosage(1 mg/L), the total chlorophyll content of algae cell treated with rac-form and(-)-form were respectively 14.2% and 1.3% higher than that in control group. As the dosage increased, the contents of chlorophyll and carotenoid in algae cells were reduced. Enantioselectivity was also observed from the determined malondialdehyde contents and antioxidant enzyme activities of algae cells after incubation with epoxiconazole racemate or single enantiomer. In addition, the algae cells treated by the enantiomers of epoxiconazole also showed morphological changes, including plasmolysis phenomena, the disappearance of chloroplasts and nuclei, and the accumulation of lipid droplets and starch granules. S. obliquus can accumulate epoxiconazole, as well as had positive effects on the dissipation of epoxiconazole in water. In bioaccumulation experiments, for the racemate treatment, the maximal accumulation of(-)- and(+)-form were reached in the third day with amounts of 28.4 and 21.6 mg/kg, then the reduction and enantioselectivity reversion were occurred. For the individual-enantiomer treatment, no enantiomerization or enantioselectivity occurred, and the accumulation mount of(-)- and(+)-epoxiconazole were1.53 and 1.75 times higher than those of algae exposed to the racemate, in an enrichment in(-)-epoxiconazole was observed during the first three days of algal cell exposure to the racemate; however,(+)-epoxiconazole became preferred after four days of exposure, showed a prefer enrichment of individual enantiomers of epoxiconazole than its racemate.