The current interest on Ionic liquids (ILs) is motivated by their exceptional properties, such as negligible vapour pressure, high thermal stability high ionic conductivity and wide electrochemical window, being especially interesting as advanced materials for smart electrochemical devices as supercapacitors, dye-sensitized solar cells or lithium and aluminium batteries.

In spite of their applicability and the high probably of a spill and filtration into terrestrial and aquatic environment, studies about their toxicity on these environments are very unusual.

In this work, the ecotoxicity of a mixture of an ionic liquid, ethylammonium nitrate (EAN), and aluminium nitrate salt (Al(NO₃)₃) was studied. This mixture has singular interest as electrolyte in electrochemical applications. The ecotoxicity of pure EAN and aluminium nitrate were also investigated. Changes on microbial activity of two soils with different organic matter content (measured by microcalorimetry) and on the bioluminescence generated by the bacteria Aliivibrio fischeri (Beijerinck) Urbanczyk through Microtox® test, when exposed to solutions of different concentrations of these compounds, were analysed.

Heat released by soil microorganisms decreases with the dose for both soils and the three compounds, except for the lowest concentrations which present similar power-time curves than the corresponding control. There is a lag period in heat release, longer as the dose increases and when Al is present. Pure IL seems to be less toxic than mixtures and pure salt on both soils. Opposite response was observed for A. fischeri, for which the highest EC₅₀ values were obtained for pure salt and the lowest for pure EAN.