Assessing chemical toxicity of ionic liquids on Vibrio fischeri: Correlation with structure and composition

• Measurement of the toxicity on Vibrio fischeri of twenty-nine ionic liquids by Microtox®.
• Vibrio fischeri toxicity of fourteen ionic liquids had not been measured before.
• Comparison between experimental results and estimated values by a QSAR method.
• Examination of the main effects on the Vibrio fischeri toxicity of the ionic liquids.
• Empirical correlation between Vibrio fischeri toxicity and Kow of the ionic liquids.

One of the most important properties of ionic liquids is their non-volatility, making them potentially “green” alternatives to volatile organic compounds. However, they are widely soluble in water, meaning that they can be released into aquatic ecosystems and so contribute to water pollution. Nevertheless, although the toxicity of ILs has been widely assessed in the literature, the information is still scarce due to the great number of ionic liquids that have been synthesized. The present work reports the toxicity of twenty-nine imidazolium-, pyridinium- and ammonium-based ionic liquids towards the bioluminescent photobacterium Vibrio fischeri. When the effect of the type of anion, the length of the alkyl chain of the cation, the cation core and the presence of a functionalized side chain in the cation on ionic liquid toxicity were analyzed, the main influence was seen to be exercised by the alkyl chain length. A Quantitative Structure-Activity Relationships-based method was used to compare the experimental results with previously estimated values and very good agreement was obtained. A relationship between the toxicity, expressed as Log EC50, and the 1-octanol-water partition coefficient was established.