Short alkyl-chained Imidazolium-based Ionic Liquids: Promising green solution or potential environmental threat?

Ionic Liquids (ILs) are currently applied in a wide variety of fields, with promising outcomes in microalgae high value biocompounds extraction. The occurrence of these compounds in natural water systems, with their characteristic stability and low biodegradability, becomes a threat worthy of attention. In the present study, Dunaliella tertiolecta, Isochrysis galbana and Rhinomonas reticulata were exposed to 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM] TfN) for 72, 168 and 264 h, at 20 and 25 °C. Obtained results suggest that the N-containing cationic ring in the selected IL could act as a nitrogen source, aiding protein synthesis and growth in the three studied microalgae. Moreover, this specific IL might become a potential eutrophication agent when discharged in aquatic ecosystems, already pressured by climate change conditions. Important lipid contents, mainly in I. galbana and associated with increased cellular energy allocation values, could be related to mitochondrial stress, which is known to be a lipid accumulation promoting factor. Hence, we hypothesise that, since [BMIM] TfN does not appear to impair growth or biocompound accumulation, it could be a candidate for microalgae biomass pretreatment in biodiesel production. However, its life cycle and disposal must be carefully considered.