Ionic liquids (ILs) are a class of emerging industrial chemicals, which are expected to be increasingly used by chemical industries as replacements for volatile organic solvents. With increasing usage, there is a potential for ILs to be accidentally released and thus become contaminants in aquatic environments. The most common ILs are composed of organic cations containing quaternary ammonium groups and inorganic or organic anions. The quaternary ammonium cations have been shown to be highly soluble in water and only minimally removed via biological wastewater treatment. While current knowledge of the toxicity of ILs indicates that some quaternary ammonium cations may pose a threat to aquatic ecosystems, little is known about the fate of IL cations in the aquatic environment or in drinking water treatment systems. To investigate the fate of IL cations in surface waters, we studied the direct and indirect photochemical transformation of four common structures of IL cations: imidazolium, pyridinium, pyrrolidinium, and piperidinium. Only reaction with hydroxyl radicals contributed to the transformation of IL cations resulting in estimated half-lives in sunlit surface waters between a few days and several months. Given their persistence in natural aquatic systems, IL cations could potentially be present in source waters for drinking water production. Therefore, additional studies of the reactions of IL cations during disinfection treatments and advanced oxidation processes (AOPs) were performed. While reactions with disinfectants were either negligible or very slow, increased transformation rates were observed for quaternary ammonium cations with radical species produced in UV-based AOPs. Our results indicate that even at low environmental loadings, quaternary ammonium compounds used as IL cations are potential environmental contaminants due to their persistence towards transformation in natural aquatic systems. Furthermore, advanced chemical treatment would be required to eliminate IL cations during drinking water treatment.

Fate of imidazolium, pyridinium, pyrrolidinium, and piperidinium ionic liquid cations in natural and technical aquatic systems

254th National Meeting (2017)

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