Enantioselective Effect Of Chiral Contaminants Cysteine And Imazethapyr On Transformation And Ecotoxicology Of Ag In Water

Cysteine(Cys) is a sulfur-containing non-essential amino acid commonly found in the food, pharmaceutical, and personal care industries. The oxidizable thiol group also has a high affinity for heavy metals. Imazethapyr is a general use pesticide. Imazethapyr(IM) is an imidazole compound and widely used for several years. It existed in environment at a high concentration, long-term residual effects and high toxicity. Silver has a higher antibacterial activity, the highest electrical conductivity of any element and the highest thermal conductivity of any metal. Silver has widely used in the manufacture and living. Therefore, when different types of silver and Cys or IM coexist in the environment, it is important to research the enantioselective effect of Cys and IM on speciation transformation and ecotoxicology of Ag. The main concludions of this work are drawn.(1) L, D-Cys have impact on the chemical speciation of Ag+.Ag+complexes with L-or D-isomers of cysteine (Ag+-Cys) could be in situ photoreduced to form AgNPs without the assistant of any other reducing agents or protecting ligands. Surface of AgNPs were modified with cysteine. By cysteine surface modification, AgNPs has a chiral structure. In H2O, tap water, algae culture, daphnia magna medium, and arabidopsis thaliana medium, Ag+-Cys can form the AgNPs. This indicates that AgNPs could be synthesized in natural water. Moreover, L, D-Cys could affect generation of AgNPs, and L-Cys form more AgNPs than D-Cys. L-AgNPs agglomerated significantly in the algae culture and daphnia magna medium. When evaluating the behavior of AgNPs in the environment, the type and configuration of the organic matter should take into consideration.(2) Toxicity effect of chiral AgNPs solution on arabidopsis thaliana and algae. The groeth inhibition results showed that (L)-and (D)-AgNPs have enantioselective toxicity effect on Arabidopsis thaliana and Scenedesmus obliquus. L-AgNPs were more toxicity than D-AgNPs and Ag+alone, and D-AgNPs have no obvious inhibitory effect on the growth of Arabidopsis thaliana. Moreover,(L)-and (D)-AgNPs could affect the distribution of trace elements in Arabidopsis thaliana leaf, especially K and Ca elements. When Arabidopsis thaliana exposed to L-AgNPs, K and Ca elements distribute in the blade tip region. When Arabidopsis thaliana exposed to D-AgNPs, K and Ca elements Distribute in the petiole. It show that Two elements undergoes enantioselective distribution. Furthermore,(L)-and (D)-AgNPs could inhibit the growth of green algae and The destruction of their subcellular structures subcellular structures. When evaluating the toxic effect of Ag+, speciation transformation of Ag and enantiomers differences should be take into consideration.(3) The enantioselective effect of IM on speciation transformation and ecotoxicology of AgNPs. Combined toxicity of IM and AgNPs has an enantioselective effect on the inhibition of Arabidopsis thaliana growth. The chlorophyll content decreased with concentration of AgNPs increases. S-IM and AgNPs treatment was not quite different from the control. Compared with the treatment with the combinations of S-IM and AgNPs, the toxicity was significantly increased with Rac, R-IM and AgNPs treatments. After detected the generation of H2O2in Arabidopsis thaliana root and leaf, the combinations of Rac, R-IM and AgNPs produced more H2O2than that in the control and the combinations of S-IM and AgNPs. High concentrations of H2O2in plant could induced significant increases in activities of antioxidant enzyme. After exposed to the combinations of Rac, R,S-IM and AgNPs, the activities of CAT, POD, SOD and the concentration of MDA in leaf were significantly increasing. However, due to the root directly contact with contaminants, the structure of root cap cells was disrupted. It may destroy the enzyme synthesis system and decrease the enzyme activity. After treated with the combinations of Rac, R, S-IM and AgNPs, the free amino acid concentrations in root and leaf were significantly increased with the combination of Rac, R-IM and AgNPs treatments. And aspartic acid, threonine, and tyrosine were specific for Rac, R-IM treatments. IM could change the Zeta potential of AgNPs. In Arabidopsis thaliana medium Ag+release from AgNPs was detected. And Ag was detected in Arabidopsis root and leaf. This result demonstrated that AgNPs were uptaked by plant and transport from the root to other plant parts. Ag+release from AgNPs may effects the toxicity of the combinations of Rac, R, S-IM and AgNPs. The growth inhibition of Arabidopsis thaliana treated by the combinations of Rac, R, S-IM and Ag+is shown that Ag+was not toxic at a concentration rang of0.01-2μM and the combinations of Rac, R, S-IM and Ag+had enantioselective effects on ecotoxicology. It proved that Ag+contributes the toxicity of AgNPs. When evaluating the toxicity of the combinations of AgNPs and organic matter in the environment, Ag+release and the interaction between contaminants should be considered in future risk assessment.