Discovering less toxic ionic liquids by using the Microtox® toxicity test

• New toxicity data of 16 ionic liquids determined by using the Microtox assay.
• ILs based on pirrolidinum and hydroxyalkylimidazolium cations showed low toxicity.
• Decrease in toxicity by using IL containing non-aromatic cations.
• Imidazolium-based ILs´ toxicity decrease by inclusion of OH group in the side chain.

New Microtox® toxicity data of 16 ionic liquids of different cationic and anionic composition were determined. The ionic liquids 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate, [BMPyr+][TFO-], 1-butyl-1-methylpyrrolidinium chloride, [BMPyr+][Cl−], hydroxypropylmethylimidazolium fluoroacetate, [HOPMIM+][FCH2COO−], and hydroxypropylmethylimidazolium glycolate [HOPMIM+][glycolate−] were found to be less toxic than conventional organic solvent such as chloroform or toluene, accoding the Microtox® toxicity assays. The toxicity of pyrrolidinium cation was lower than the imidazolium and pyridinium ones. It was found that the inclusion of an hydroxyl group in the alkyl chain length of the cation also reduce the toxicity of the ionic liquid. To sum up, the Microtox® toxicity assays can be used as screening tool to easily determined the toxicity of a wide range of ionic liquids and the toxicity data obtained could allow the obtention of structure–toxicity relationships to design less toxic ionic liquids.