Abstract：The toxicity of ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) to Scenedesmus obliqnus was studied in different concentration by using the standard toxicity test. Five different test endpoints were determined such as the growth inhibition rate (IC50), the content of chlorophyll a (Chla), chlorophyll b (Chlb), the superoxide dismutase activity (SOD) and the catalase activity (CAT), the permeability of algae cell, and the ultrastructural morphology of cell. The results indicated that the inhibition rate of algae growth increased and the content of Chla and Chlb in algae cell decreased with the [BMIM] Cl concentration. The 48h IC50, 72h IC50 and 96h IC50 were 103.77、76.44 and 68.49mg/L, respectively. The results also indicated that the activities of CAT and SOD decreased due to the oxidative stress and the permeability of algal cell decreased due to the cell membrane being destroyed with the increase of [BMIM] Cl concentration. Also, the ultrastructure of algal cell was affected by 80mg/L [BMIM] Cl, resulting in plasmolysis, chloroplast lamellae fractured and the number of crest in mitochondria reduced.
