Life-Cycle Perspectives on Aquatic Ecotoxicity of Common Ionic Liquids

This study compares the aquatic ecotoxicity impacts of production- and use-phase release of five common ionic liquids (ILs). Integrating toxicity data, physical properties, and fate and transport parameters with the USEtox model, we report, for the first time, the freshwater ecotoxicity characterization factors for [Bmim](+)[Br](-), [Bmim](+)[Cl], [Bmim](+)[BF4](-), [Bmim](+)[PF6](-), and [BPy](+)[Cl](-) as 624, 748, 823, 927, and 1768 CTUe/kg, respectively. IL Production life cycle inventories were modeled and utilized to estimate their production-side ecotoxicity impacts. Literature on environmental aspects of ILs propagates either their green characteristics (no air emissions and high recyclability) or their nongreen aspects due to toxicity concerns of their release to water. This study adds a third dimension by showing that the upstream ecotoxicity impacts of producing ILs could outweigh the potential ecotoxicity impacts of direct release during use. Furthermore, for the studied ILs, an average of 83% of ecotoxicity impacts associated with their production can be linked to chemicals and materials released during the upstream synthesis steps, while only 17% of ecotoxicity impacts relate to life-cycle energy consumption. The findings underscore the need to develop sustainable synthesis routes, tight control over chemical releases during production, and careful selection of precursor materials and production processes.