Abstract
Ionic liquids (ILs) are solvents with salt structures. Typically, they contain organic cations (ammonium, imidazolium, pyridinium, piperidinium or pyrrolidinium), and halogen, fluorinated or organic anions. While ILs are considered to be environmentally-friendly compounds, only a few reasons support this claim. This is because of high thermal stability, and negligible pressure at room temperature which makes them non-volatile, therefore preventing the release of ILs into the atmosphere. The expansion of the range of applications of ILs in many chemical industry fields has led to a growing threat of contamination of the aquatic and terrestrial environments by these compounds. As the possibility of the release of ILs into the environment s grow systematically, there is an increasing and urgent obligation to determine their toxic and antimicrobial influence on the environment. Many bioassays were carried out to evaluate the (eco)toxicity and biodegradability of ILs. Most of them have questioned their “green” features as ILs turned out to be toxic towards organisms from varied trophic levels. Therefore, there is a need for a new biodegradable, less toxic “greener” ILs. This review presents the potential risks to the environment linked to the application of ILs. These are the following: cytotoxicity evaluated by the use of human cells, toxicity manifesting in aqueous and terrestrial environments. The studies proving the relation between structures versus toxicity for ILs with special emphasis on directions suitable for designing safer ILs synthesized from renewable sources are also presented. The representants of a new generation of easily biodegradable ILs derivatives of amino acids, sugars, choline, and bicyclic monoterpene moiety are collected. Some benefits of using ILs in medicine, agriculture, and the bio-processing industry are also presented.
Highlights
Ionic liquids (ILs) have been known since 1914
IL at the conc. > 0.9 mM was toxic to wheat seedlings, germination was reduced to 38.0% in the presence of 4.4 mM [BMIM][BF4] compared with the control, The activities of amylase, POD increased in shoots and roots, but it decreased when the IL conc. exceeded
The toxicity tests of imidazole IL performed on this organism revealed the following issues: the growth decrement ranged between 8.5 and 42.5% depending on the concentration of the IL, 55% decrease in reproduction, inhibition of the activity of ATPase in the presence of the IL (1–5 mg/kg of the soil) [143]
Summary
Ionic liquids (ILs) have been known since 1914. They are a class of salts with low melting points that is achieved by the high bulkiness and asymmetry of the ions, thereby preventing the molecule packing from promoting crystallization [1]. Owing to their high hydrophobicity and relatively low viscosities, ammonium, phosphonium and a few dicationic imidazolium-based MILs have been used as extraction solvents for the preconcentration of nucleic acids and polyaromatic hydrocarbons from complex sample matrices [18,19] Another class of MILs is represented by water-soluble N-substituted imidazole ligands (with butyl-, benzyl-, or octyl-groups as substituents) coordinated to different metal centers (Ni2+, Mn2+, or Co2+) as cations. Much of the published data considers the evaluation of the physicochemical properties of ILs covering decomposition temperatures, ionic conductivities, viscosities, mutual solubilities with water, densities, melting point or surface tension Such a wide range of properties is closely related to the structure of ILs, i.e., the involvement of both the anion and cation. They can be applied for drug production and as components of delivery systems [3]
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