Acute toxicity of oxygenated and nonoxygenated imidazolium-based ionic liquids to Daphnia magna and Vibrio fischeri

Room-temperature ionic liquids (RTILs) recently have generated great interest as a result of their potential commercial applications. In particular, because of their negligible vapor pressure and low inflammability, they have been suggested as green alternatives to traditional organic solvents. The toxicity and potential environmental risk of this heterogeneous class of chemicals, however, are poorly understood. An alkyl-substituted RTIL, 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), is one of the most widely used cations of RTILs, and information regarding its toxicity is relatively extensive. On the other hand, oxygenated chain-substituted ionic liquids, 1-methoxyethyl-3-methylimidazolium salts (moemims), are a new class of RTILs that have been poorly studied. Here, we compared the acute toxicity of [bmim][BF4] and moemims to the crustacean Daphnia magna (end point, 48-h immobilization) and the bacterium Vibrio fischeri (end point, 15-min inhibition of bioluminescence). The concentrations of [bmim][BF4] resulting in 50% of the maximum adverse effect (EC50s) for D. magna and V. fischeri were 5.18 and 300 mg/L, respectively, and were consistent with previously published values. The EC50s of the two moemims for D. magna are very similar, ranging from 209 to 222 mg/L in different experimental trials, and are higher by two orders of magnitude than the EC50 of [bmim][BF4]. The EC50s of 1-methoxyethyl-3-methylimidazolium tetrafluoroborate ([moemim][BF4]) and 1-inethoxyethyl-3-methylimidazolium dicyanamide ([moemim] [deal]) for V.fischeri are 3,196 and 2,406 mg/L, respectively. Results indicate that introduction of an oxygenated side chain in the imidazolium cation can greatly reduce the toxicity of RTILs and that these RTILs are less toxic than commonly used chlorinated solvents, such as tricloromethane, but are more toxic than nonchlorinated solvent, such as methanol and acetone.