Metabolomic analysis of Scenedesmus obliquus reveals new insights into the phytotoxicity of imidazolium nitrate ionic liquids.

Due to the persistence of ionic liquids (ILs) in aquatic environments, it is necessary to reveal their ecological risk to aquatic organisms. Herein, the biotoxicity of two alkyl-methylimidazolium nitrate ILs ([C10mim]NO3 and [C12mim]NO3) against Scenedesmus obliquus were studied. Results showed that the growth inhibition of S. obliquus increased with increasing concentrations of ILs, maximum values of 94.61% at 4 mg/L of [C10mim]NO3 and 97.34% at 0.8 mg/L of [C12min]NO3 were observed. The fluorescence parameters of photosystem II, such as light quantum yield and electron transfer rate, showed a negative relationship with the exposure dose. [C12mim]NO3 had a more significant effect than [C10mim]NO3. Moreover, the redox homeostasis of algae was disrupted; the accumulation of reactive oxygen species, leading to obvious inhibition of superoxide dismutase and catalase activities was observed. A metabolomic analysis indicated that the contents of most metabolites were reduced significantly, and fructose and galactose decreased significantly by 42.3% and 88.6%, respectively, in the [C10mim]NO3 treatment compared to those in the control. The inhibition of amino acid biosynthesis and glyoxylate and dicarboxylate metabolism explained the more serious biotoxicity of [C12mim]NO3 than that of [C10mim]NO3. This study facilitates a better understanding of the environmental safety and ecological risks of ILs.