Toxicity of “green solvents” - The impact of butyl methylimidazolium ionic liquids on daphnids

Abstract

Ionic liquids have been described as green solvents, however, their presence in the aquatic environment may indicate a threat for key species. Focusing on the freshwater ecosystem, five ionic liquids containing the 1‑butyl‑3-methylimidazolium (BMIM) cation were compared for their acute toxicity and chronic responses on daphnids. Biochemical markers of physiology including the activity of phosphatases, β-galactosidase, peptidase, lipase and glutathione-S-transferase were used to assess changes in physiology of daphnids. Feeding and reproduction were investigated as surrogate phenotypic measures. Feeding rate was decreased in all exposures, and severely impacted in BMIM hexafluorophosphate, chloride, and tetrafluoroborate, while reproduction was unaffected by all ionic liquids. A diverse set of responses were triggered from each BMIM ionic liquid in reference to enzyme activities providing insight for the toxicity impact of these emerging contaminants. Phosphatase activities were significantly decreased in all exposure scenarios to ionic liquids, but different patterns of biochemical responses were documented among acute and chronic exposures and different ionic liquids, indicating distinct mechanistic patterns. The aforementioned results highlight the toxic potential of ionic liquids which are characterised so far as green solvents.