Most recent investigations concerning the toxicological and ecotoxicological risk potentials of ionic liquids are predominantly focusing on the cation moieties. In this study we elucidate, whether the anion species commonly used in ionic liquids are exhibiting intrinsic cytotoxic effects and if these effects can be rationalised by thinking in terms of structure-activity relationships (T-SAR). As test system to measure the cell viability as toxicologically relevant endpoint the IPC-81 rat leukemia cell line and the WST-1 assay were employed. Our results show an anion effect in ionic liquids on cytotoxicity for 10 of 27 tested anions. For the remaining 17 anions from our test kit no significant effect was found. With respect to structure-activity relationships, lipophilicity and/or vulnerability to hydrolytic cleavage seem to be the key structural features leading to the observed anion cytotoxicity. We also conclude that the model of concentration addition may be useful to estimate the EC 50 values of ionic liquids that have not been tested or even synthesised yet. This can help to design not only task specific but also inherently safer ionic liquids.

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We investigated the primary biodegradation of different N-imidazoles, imidazolium, pyridinium and 4-(dimethylamino)pyridinium compounds substituted with various alkyl side chains and their analogues containing functional groups principally based on OECD guideline 301 D. For the experiments we used two different types of inocula, a freeze-dried mix of bacteria and activated sludge microorganisms from a wastewater treatment plant. The aim of this study was to improve the knowledge base for the structural design of ionic liquids with respect to an increased biodegradability combined with a reduced (eco)toxicological hazard potential. We found a significant primary biodegradation for (eco)toxicologically unfavourable compounds carrying long alkyl side chains (C6 and C8). In contrast for (eco)toxicologically more recommendable imidazolium ionic liquids with short alkyl ((C6) and short functionalised side chains, no biological degradation could be found. The introduction of different functional groups into the side chain moiety thus offering a higher chemical reactivity did not lead to the expected improvement of the biological degradation. After an incubation period of 24 days for the 1-methyl-3-octylimidazolium cation we identified different biological transformation products carrying hydroxyl, carbonyl and carboxyl groups. Furthermore, shortened side chain moieties were identified indicating the degradation of the octyl side chain via b-oxidation. Moreover, we propose an electrochemical wastewater treatment as part of an alternative disposal strategy for non-biodegradable ionic liquids. We show for the first time that the 1-butyl-3-methylimidazolium cation was completely destroyed within four hours using an electrolysis double-cell (volume = 1.2 L) equipped with electrodes made of iridium oxide (anode), stainless steel (cathode), and a boron-doped diamond-coated bipolar electrode. The products formed electrochemically were easily accessible to biological degradation.

This study provides data on the behaviour and toxicity of selected imidazolium based ionic liquids in the terrestrial environment with the aim to contribute to a prospective hazard assessment. Using the plant growth inhibition assay with wheat (Triticum aestivum) and cress (Lepidium sativum) we investigated the influence of two different clay minerals (kaolinite and smectite) in varying concentrations and clay mineral mixtures as well as the influence of organic matter in varying concentrations on the toxicity of three imidazolium based ionic liquids differing in the alkyl side chain length. The obtained results were compared to the German standard soil Lufa 2.2. Overall the influence of the 2:1 layer mineral smectite on toxicity was stronger than for the 1:1 layer mineral kaolinite resulting in lower toxicities when smectite was present. Comparable results were achieved in the tests with different clay mineral mixtures. The influence of the clay minerals was substance concentration dependent and the side chain effect could not consistently be confirmed for the different soil mixtures. The 1:1 clay mineral kaolinite caused in some cases an increase in toxicity. The obtained results for the influence of organic matter on the toxicity proved to be much more consistent than for the clay minerals: here an increase in organic matter concentration always resulted in a decrease of the toxicity. Differences in plant species sensitivity could be shown, but not in a consistent manner. A site specific hazard assessment of ionic liquids should therefore take into account organic matter content, quantity and especially quality of clay minerals.

Components of natural waters (salts, NOM) mitigate negative impacts of nanomaterials via surface passivation and stabilisation against dissolution.