Aquatic Toxicology of Ionic Liquids (ILs)


The broad application of ionic liquids (ILs) as process chemicals, solvents, heat transfer and storage fluids, electrolytes, and additives is encouraging significant progress in the design of novel chemical and biotechnological processes and products [1]. Both academia and industry have been using ILs to boost established processes including laborious routes, replace nefarious chemicals, or minimize waste generation, as well as create innovative technologies and products [1–3]. What made ILs appealing was, in the first place, their recognized unique physical and chemical properties (e.g., non-flammability, nonvolatility, high thermal stability, solvation ability, and structural versatility) [4]. Together with their “designer solvent” status, ILs started to be defined as “green” and, more recently, “high performance” chemicals [5, 6]. Often, however, such headlines represent nothing but overgeneralizations that lead to critical misconceptions within IL field. Likely, the most controversial IL classification is that of “green solvent”. Even though ILs’ nonvolatility prevents the risk of atmospheric pollution – a plus over common volatile organic solvents – their water solubility makes them prone to enter and impact on aquatic ecosystems. ILs are not inherently green, since most of them possess equivalent or even higher toxicity than traditional organic solvents [7]. At the current stage, where ILs play an expanding role in industry [1, 2], they must be regarded as emerging contaminants [8], and the full disclosure of their aquatic toxicology is imperative. Efforts have been made along the years to clarify the toxic action of ILs over aquatic organisms. As reviewed [7, 9, 10], the set of published works follow at least one of three core strategies: (i) assessing structure-ecotoxicity relationships by changing the cation, anion, and respective alkyl chain lengths and functionalized groups; (ii) covering multitrophic bioassays, through distinct types of toxicity tests (e.g., acute toxicity and Microtox – undoubtedly the most studied – but also chronic, reproductive, and embryo toxicity); and (iii) attesting the environmental benignity of ILs designed for a specific application.


Francisca A. e Silva, João A. P. Coutinho, Sónia P. M. Ventura

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