Impacts of four ionic liquids exposure on a marine diatom Phaeodactylum tricornutum at physiological and biochemical levels.

With the increasing applications in various industrial areas, toxicity of ionic liquids (ILs) has gained much attention in recent years. In this work, 1-octyl-3-methylimidazolium nitrate ([C8 mim]NO3 ), 1-octyl-3-methylimidazolium chloride ([C8 mim]Cl), N-octyl-3-metylpyridinium chloride ([C8 mpy]Cl) and N-octyl-3-metylpyridinium bromide ([C8 mpy]Br) were used to investigate the impacts of different types of cations and anions on their toxicity to a marine diatom Phaeodactylum tricornutum. Results showed that the four ILs had poor degradability under the culture conditions used in this study, and significantly inhibited the growth of this diatom with 96-h EC50 values of 24.0, 33.6, 16.1 and 14.4mgL-1 for [C8 mim]NO3 , [C8 mim]Cl, [C8 mpy]Cl and [C8 mpy]Br, respectively. The data indicated that types of cations and anions would affect the toxicity of ILs to this diatom. Additionally, photosynthesis of this diatom was inhibited because significant decrease of chlorophyll a content and damage of PSII reaction centers were observed when it was exposed to the four ILs. Remarkable physiological and biochemical responses occurred in the cells of this diatom to alleviate the damaging effects of the four ILs. For example, content of soluble protein and activities of superoxide dismutase (SOD) and catalase (CAT) in the cells of this diatom increased significantly to form a protective mechanism against the toxicity of ILs, although they decreased in the cultures with high concentrations of ILs (≥20mgL-1 ). Thus, these results would not only provide strong evidences for evaluating the ecological risks and toxicity of ILs to marine ecosystem, but also help for understanding their toxic mechanisms to marine diatoms.