Biodegradation, toxicity and eco-toxicity of a class of oxygenated imidazolium-based ionic liquids

Aerobic degradation of ionic liquids by the action of microorganisms present in soil was monitored for the first time. The tests, followed over six months, were carried out on the alkylated ionic liquids (BMIM BF4 and N(CN)2) and on the mono-oxygenated analogues (MOEMIM BF4 and N(CN)2). Only the n-butyl derivatives were found to be degradable; in contrast, no significant production of CO2 was observed in the tests with the methoxyethyl derivatives. The eco-toxicological properties of all presented ionic liquids were evaluated in acute toxicity tests with the crustacean Daphnia magna (immobilization) and the bacterium Vibrio fischeri (inhibition of bioluminescence). The EC50 values indicate that the presence of one oxygen atom in the lateral chain of the cation mojety reduced the acute effect towards both D. magna and V. Fischeri (the EC50 value increases from 56 mM of BMIM BF4 to 865 mM of MOEMIM N(CN)2) . However, the addition of further ethoxyl units has a different effect in the two species: while the toxicity to V. fischeri markedly increases with the length of the oxygenated lateral chain (the EC50 value of the most toxic oxygenated ionic liquid, M(OE)4MIM N(CN)2 is 455 mM), differences in the toxicity to D. magna are rather marginal and do not show a clear trend. Moreover D. magna seems sensitive to the anion, the BF4 salts being slightly, but consistently, more toxic than the N(CN)2 salts.