Acute Toxicity, Oxidative Stress And Genotoxicity Induced By Four Imidazolium-based Ionic Liquids In Zebrafish (Danio Rerio)

Ionic liquids(ILs) are a new class of chemicals and are completely composed of anions and cations that are liquid at about room temperature. Due to the special physical and chemical properties of ILs, such as negligible vapor pressure, low melting points, good solubility as well as easy recycle and utilization, ILs are considered “green” solvents, and widely used in many areas, such as analytical chemistry, biocatalysis, biosensor, organic synthesis, electrochemistry and material process. As for their superior solubility in water, this is the most possible medium through which ILs will be industrial drained or accidental spilled into the aquatic environment. However, the dispersion of ILs in the aquatic environment is likely to cause damage to aquatic organisms. Therefore, it is necessary to study the potential toxicity of ILs on aquatic organisms to explore the safety of ILs in the environment. Zebrafish is a kind of model organism internationally recognized in developmental biology. They has been widely applied in application, life science and waier quality analysis, because of their small size, low cost breeding, strong vitality. Among various types of ionic liquids,imidazolium salts are one of the most pervasively used and investigated groups, but little information is available regarding the acute and subchronic toxicity towards aquatic organisms. In the present study, the acute and subchronic toxicity of four different structural imidazolium ILs in zebrafish were studied, which were 1-Butyl-3-methylimidazolium chloride([Bmim]Cl), 1-Butyl-3-methylimidazolium tetrafluoroborate([Bmim]BF4),1-octyl-3-methylimidazolium chloride([Omim]Cl) and 1-octyl-3-methylimidazolium tetrafluoroborate([Omim]BF4). Firstly, the acute toxicities of ILs in zebrafish were determinand, and the 96 h LC50 values were 632.8、604.6、152.3、144.0 mg/L. Then, according to the 96 h LC50 values, the concentration of subchronic toxicity experiment were from 0 to the values of 1/4 LC50. Finally, the effects of ILs on the ROS levels, antioxidant enzymes activities(superoxide dismutase, SOD and catalase, CAT), a detoxifying enzyme(glutathione S-transferase, GST), the malondialdehyde(MDA) content, and the degree of DNA damage inzebrafish were determined. The objective of the present study was to provide a scientific basis and support for further work evaluating the harmful of ILs in aquatic ecosystem.As shown in the present results, a marked induction or inhibition was found among these experimental indicators after exposure to different tested concentrations of ILs:1. The 96 h LC50 values induced by [Bmim]Cl, [Bmim]BF4, [Omim]Cl and [Omim]BF4were 623.9、604.6、152.3、144.0 mg/L, respectively. And they was low-toxic to zebrafish.Therefore, the 96 h acute toxicity of four ILs in zebrafish: [Omim]BF4 > [Omim]Cl>[Bmim]BF4 > [Bmim]Cl.2. Low concentration of ILs([Bmim]Cl and [Bmim]BF4 concentration of 20 mg/L;[Omim]Cl and [Omim]BF4 concentration of 5 mg/L) had no significant toxicity in zebrafish,but the high concentration of ILs([Bmim]Cl and [Bmim]BF4 concentration of 80-160 mg/L;[Omim]Cl and [Omim]BF4 concentration of 20-40 mg/L) could induce the oxidative stress in zebrafish. In low level groups, the ROS level, SOD, CAT and GST activities had no significant changes compared with the controls. However, In high level groups, the ROS level increased with increasing concentrations and exposure time, SOD activity increased at first and then decreased, CAT activity decreased and GST activity increased significantly.3. After exposure to high concentrations of ILs, the MDA content was significantly increased, which indicated that high concentrations of ILs could induce lipid peroxidation in zebrafish. Additionally, the degree of DNA damage significantly increased with increasing ILs concentrations and exposure time.4. In conclusion, the present study investigated and compared the toxicity of four different structural imidazolium ILs in zebrafish. The structure of ILs is important to evaluate the toxicity of ionic liquids, and cations play the key role on the toxicity of ILs, while anions have little impact. The order was presented as follows: [Omim]+ > [Bmim]+, BF4- > Cl-. The present results provide a scientific basis and support for further work evaluating the ecotoxicity of ILs and selecting environment-friendly ILs in future industrial application.