Growth Performance and Antioxidative Response of Chlorella pyrenoidesa , Dunaliella salina , and Anabaena cylindrica to Four Kinds of Ionic Liquids

Ionic liquids are widely used for lipid and pigment extractions from microalgae. It is possible that ionic liquids are discharged into environments. The evaluation of growth performance and antioxidative response of ionic liquids to microalgae is helpful to explore the stress regulation mechanism and investigate possible environmental risk. Ionic liquids induce production of reactive oxygen species (ROS) to microalgae. These oxidative stresses are possible from cations, anions, and salinity. In this study, the growth inhibitions of [BMIM]Br, [BMIM]Cl, [EMIM]Cl, and [EMIM]EtOSO3 to Anabaena cylindrica, Chlorella pyrenoidesa, and Dunaliella salina were evaluated. It was interesting that Br− and two kinds of cations, [BMIM] and [EMIM], had significant effects on growth inhibitions of these microalgae. IC50 values of these ionic liquids for A. cylindrica, C. pyrenoidesa, and D. salina were also estimated based on the results of growth inhibitions. It was proved that [EMIM]Cl is relatively harmless to C. pyrenoidesa and D. salina, and [EMIM]EtOSO3 is relatively or practically harmless to C. pyrenoidesa. [BMIM]Br and [BMIM]Cl are practically harmless to A. cylindrica and C. pyrenoidesa, and relatively harmless to D. salina. More than 0.8 g/L [EMIM]EtOSO3 led to bleaching of both A. cylindrica and D. salina at 48 h which was shown that the anion, EtOSO3−, had higher inhibition to A. cylindrica and D. salina than Cl−. In addition, high concentration of ionic liquids led to reductions of chlorophyll content in these three kinds of microalgae, increase of ROS levels and malondialdehyde contents for most of the cases. High concentration of ionic liquids also increased the activities of superoxide dismutase in three kinds of microalgae. There were positive correlations between ROS levels or MDA content, and inhibitions ratios of these ionic liquids to microalgae except [EMIM]Cl to A. cylindrica. These antioxidant enzymes were beneficial for reducing the ROS induced by ionic liquids.