Imidazolium based ionic liquids in soils: effects of the side chain length on wheat (Triticum aestivum) and cress (Lepidium sativum) as affected by different clays and organic matter

Abstract

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.