Enantiomer-Specific Toxicity Of Hexabromocyclododecane To Maize

Hexabromocyclododecane(HBCD)is a typical chiral persistent organic pollutants(POPs).HBCD has characteristics of general POPs,and its unique enantiomers show different toxicity in organism.Therefore,it is necessary to study the selective toxicity effect of HBCD enantiomers.The results of this study would offer useful information for a more comprehensive assessment of the environmental risk of HBCD.The enantioselective toxicity effect of ?-hexabromocyclododecane(?-HBCD)on maize were investigated.Two enantiomers((+)?-HBCD and(-)?-HBCD)were prepared by high performance liquid chromatography.Young seedlings of maize were exposed to solutions of(+)?-HBCD,(-)?-HBCD and racemate HBCD((rac)?-HBCD)with different concentrations.Results indicated that the growth of maize seedlings were affected.The root biomass,shoot biomass,and root and shoot elongation of maize were inhibited significantly after exposure with the inhibition rates following the order(+)?-HBCD >(rac)?-HBCD >(-)?-HBCD.The antioxidant enzyme activities of superoxide dismutase(SOD)and peroxidase(POD)both in roots and shoots were significantly upregulated by exposure to lower concentrations of(+)?-HBCD.In contrast to(-)and(rac)?-HBCD,the activities of SOD and POD were all decreased by higher exposure concentrations of(+)?-HBCD.The intensities of histone H2 AX phosphorylation were increased at first with an increasing exposure concentration of both ?-HBCD enantiomers and racemate and then decreased.Moreover,the most significant induction was observed in the(+)?-HBCD treatment,indicating the enantio-specific DNA damage in maize.Different concentrations of HBCD enantiomers have significant influence on MDA content in the seedlings.Direct damage was observed in maize seedings after exposure to(+)?-HBCD and(rac)?-HBCD.MDA content increase with the increasing concentrations of(+)?-HBCD and(rac)?-HBCD.There are no significant difference with the normal seedings in the(-)?-HBCD treatment of lower concentrations.The higher exposure concentrations of(-)?-HBCD induced oxidative stress with the MDA content decreasing.The light microscopy and transmission electron microscopy(SEM)of plant samples were analyzed further.Results showed that the cell damage of roots was the most serious after exposure to(+)?-HBCD than(rac)?-HBCD.Roots status was not affected in the(-)?-HBCD treatment with normal cells structure and shape.All of these results demonstrated thesignificant enantioselectivity oxidative damage of ?-HBCD to maize with a higher toxicityof(+)?-HBCD than(rac)?-HBCD and(-)?-HBCD.