| As a great agricultural country, pesticides has been used extensively in China, therefore the environmental pollution resulted from pesticides usage was significant. It is well known that as many as25%of all pesticide active ingredients are chiral, and this ratio is increasing as compounds with more complex structures are introduced into use. Enantiomers of a chiral chemical generally undergo the same physical and chemical processes and reactions in the environment, however, the enantiomers may behave differently in biologically mediated environmental processes and their biological effects (e.g., toxicity, mutagenicity, carcinogenicity, endocrine-disrupting activity) are typically enantioselective. Some studies also found that environmental factors can affect the chiral preference of pesticides.With the wide applications of chiral ionic liquids (CILs), the development of knowledge for the prospective design of inherently.safe CILs has become more urgent. However, enantioselective differences in CILs toxicities are poorly understood. The main conclusions of this work are drawn.(1) Individual and combined presence of dichlorprop (DCPP) and Cu provoked a boom in ROS, which in turn stimulated the response of antioxidant defences, impaired subcellular structure and physiological function, finally resulted in the increase of cell grow inhibition rate. In absence of Cu, the ROS contents of the herbicidally active (R)-enantiomer was higher than that of (S)-enantiomer, suggesting an (R)-enantiomer preferential production of ROS. When treated with DCPP and Cu simultaneously,(R)-DCPP preferential production of ROS was observed. However, when DCPP was interacted with Cu for24h before adding into the algae solution, this interaction reversed the enantioselective production of ROS. It was interestedly found that the enantioselective generation of ROS was compatible with response of antioxidant defences and the inhibition rate in Scenedesmus obliquus. This finding implied that ROS play a primary role in chemical contaminant toxicity to Scenedesmus obliquus and the interaction between contaminants can tune the enantioselectivity of chiral herbicide dichlorprop and should be considered in future risk assessment.(2) The effects of herbicide imazethapyr (IM) on the Cu(II) ecotoxicity to the aquatic unicellular alga Scenedesmus obliquus were investigated. It was found that the toxicity of Cu can be mediated by IM. In order to explore the mechanisms involved, complex formation, its catalytic activity, Cu species and the distribution of Cu and Fe in the algal cell were characterized. These results showed that Cu(II) and IM formed an octahedral complex with the mole ratio of IM:Cu=2:1. Such complex did have the role of catalytic the disproportionation of hydrogen peroxide. By the analysis of Cu K-edge XAFS spectroscopy, it indicated that when treated with Cu, the Cu was bound to polygalacturonic acid (on cell wall) and once inside the cell, they may complex with GSH (in cell). As far as the cell was treated by IM and Cu simultaneously (IM-Cu), the IM-Cu interaction may be the main form. Once Cu combined with IM, it will be difficult to interact with cell wall. In addition, using scanning transmission soft X-ray microscopy, it was interestingly found that Cu can induce the change of the distribution of essential trace element Fe while IM-Cu not. This finding implied importance of interactions between heavy metals and organic contaminants, which can mediate toxicity of heavy metals and should be considered in future risk assessment.(3) The investigation into the toxicities of lactate chiral ionic liquids toward two green algae, Scenedesmus·obliqnus and Euglena gracilis. For S. obliquus, there is a distinct difference between the toxicities of L-(+)-EMIM L and D-(-)-EMIM L; the EC50value of L-(+)-EMIM L was more than5000μM, while EC50value of D-(-)-EMIM L was2255.21μM. Thus, D-(-)-EMIM L is more toxic to S. obliqnus than L-(+)-EMIM L. This trend was maintained with L-(+)-BMIM L and D-(-)-BMIM L but was not observed with increases in carbon chain lengths. This finding may be due to the changes of the toxicity weights of the cations and anions, as the toxicity weights of the cations increase with increasing carbon chain lengths. The results of ROS showed that the D-(-)-lactate ionic liquids may produce more ROS than the L-(+)-lactate ionic liquids, besides, the L-(+)-EMIM L and D-(+)-EMIM L with the same concentration showed different degree of aggregation per unit area. The D-(+)-EMIM L showed stronger aggregation and the particle size was relatively bigger, and this may be the reasons of the enantioselective toxicity. However, the phenomenon described above was not observed for E. gracilis. E. gracilis is different from S. obliquus in subcellular structure, lacking cell walls. Moreover, the nutrient means of the two algae are also varied. These results indicate that we should be able to scale the effects of CILs across organisms more accurately and improve our ability to predict their effects in natural environments. In the meantime, to minimize the potential for environmental harm, the enantioselective toxicities of CILs with short alkyl chains should be taken into consideration.(4) Dramatic differences between the toxicity of the enantiomers of DCPP to Arabidopsis thaliana were observed:the enantiomer of R-DCPP shows a higher level of toxicity. The assessment of plant growth was carried out by measuring the fresh weight of leaves and the length of root after exposure to the DCPP enantiomers and the results showed that fresh weight of control treatment was16.9mg, R-DCPP treatment was6.32, S-DCPP14.36and Rac-DCPP8.35mg. The root length of control treatment was49.53mm and for R-DCPP, S-DCPP, Rac-DCPP was4.87,34.2and7.7, respectively. The enantiomers of DCPP also stimulated the response of antioxidant defences and the activity of SOD of R-DCPP treatment was higher than the S-DCPP treatment while the activity of CAT, POD was lower than the S-DCPP treatment and the GSH content was also lower and all the treatments were lower than the control treatment. These results indicate that the antioxidant system was damaged and may not scavenge the excess ROS.(5) The toxicity of IM to Arabidopsis thaliana also showed enantioselective differences. The fresh weight of leaves of control treatment was17.21, and for R-IM, S-IM, Rac-IM was5.25,15.36,7.36mg, respectively. The length root was51.42,4.21,43.2and7.62mm, respectively. The distribution of trace elements in leaves and roots were also determined when treated with IM. The results of leaves showed that the trace elements in control leaf were evenly distributed and the S-IM treated showed the same trend, while the R-IM and Rac-IM treated leaf was aggregated distributed and the expression of gene related to trace elements did not show significant enantioselective differences. However, the distribution of trace elements in root did not show difference. |
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