The Biodegradation of Ionic Liquids - the View from a Chemical Structure Perspective

The idea of green or sustainable chemistry is to develop highly efficient technical processes and applications using chemicals with a reduced or zero hazard potential for man and the environment. This approach is perfectly applicable to ionic liquids (ILs). These substances have potential applications in different fields (economic interests), and so far millions of possible structures have been designed, thousands of which have actually been produced, providing a broad base for the structural design of ILs with optimal technological properties and at the same time posing a reduced hazard to humans and the environment. In parallel with the rapidly growing (eco)toxicological knowledge regarding ILs, the available data regarding their biodegradability are also increasing. The following sections introduce the reader to biodegradation test procedures and present an overview of existing aerobic and anaerobic biodegradation data concerning ILs. Besides pure biodegradation kinetics, this discussion covers data on biological degradation products (metabolites) and abiotic degradation processes. Throughout this review special emphasis will be placed on structure-biodegradability relationships and the question whether the 10th principle of Green Chemistry, namely, Design chemicals and products to degrade after use: design chemical products to break down to innocuous substances after use so that they do not accumulate in the environment, is or is not fulfilled for some IL structures. The discussion of this data should help to improve the future design of inherently safer ILs, thereby reducing the risks they may pose to humans and the environment.