This Review aims to integrate the most recent and pertinent data available on the (bio)degradability and toxicity of ionic liquids for global and critical analysis and on the conscious use of these compounds on a large scale thereafter. The integrated data will enable focus on the recognition of toxicophores and on the way the community has been dealing with them, with the aim to obtain greener and safer ionic liquids. Also, an update of the most recent biotic and abiotic methods developed to overcome some of these challenging issues will be presented. The review structure aims to present a potential sequence of events that can occur upon discharging ionic liquids into the environment and the potential long-term consequences.

This work is based on the evaluation of the protein binding affinity, partition coefficients (with a biomimetic membrane) and surfactant properties of three pharmaceutically active ionic liquids based on the salicylate anion. Fluorescence spectroscopy was used for the evaluation of the binding of ionic liquids to human serum albumin and for the determination of critical micelle concentrations. Partition coefficients were determined using micelles of hexadecylphosphocholine and UV-Vis derivative spectroscopy. The results indicate that all the compounds bind strongly and spontaneously to human serum albumin and exhibit the ability to form micelles. The determined partition coefficients were up to 6 times higher than those of the starting materials, evidencing that the ionic liquid form has greater affinity for the lipid phase than the inorganic salt form of salicylate. Generally, the studied salicylate ionic liquids exhibit an interesting pharmaceutical profile presenting favorable properties regarding the incorporation of the compounds in antimicrobial pharmaceutical formulations. It was evidenced that the tested ionic liquids can exert direct effects on cell membranes as indicated by their surfactant properties and high ability to partition to hydrophobic environments.

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A new automated chemiluminescence method resorting to sequential injection analysis (SIA) was developed to rapidly determine biochemical oxygen demand (BOD). The assay is based on the redox reaction between quinone and Baker’s yeast in the presence of organic substances. The formed active oxygen species reacted with luminol, under the catalytic action of ferricyanide, and increased chemiluminescence signal. The automation of the assay ensured a precise control of the reaction conditions and enabled a reduction of more than 75-times in the reagents consumption and effluents production comparatively to BOD5. The sampling rate was widely improved with a flow rate of 8 cycles per hour. The method was applied to determine the BOD of ionic liquids (ILs) incorporating different chemical elements and deep eutectic solvents (DESs) combining choline chloride with varying hydrogen-bond donors. Differences in BOD and biodegradability were observed between tested compounds, with DESs showing, in general, higher BOD values and greater biodegradation than ILs. The results obtained in the developed bioassay demonstrated statistical correlation with the BOD5 method. Therefore, the developed methodology is a simple, economic and high-throughput alternative screening bioassay to the conventional method, with the potential to preliminarily assess the potential biodegradability of chemicals in the environment.

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