Ionic liquids have often been touted as the ultimate green solvent, but just how green is green? Researchers in Germany have come up with a way of testing the ecotoxicology of different ionic liquids using an 'ecosystem in a box'.

Bernd Jastorff at the University of Bremen and colleagues have tested the toxicological effects of a variety of ionic liquids across the range of biological complexity - from enzymes to whole organisms, of both aquatic and terrestrial origin.  Previous studies on the toxicology of ionic liquids have been performed in vitro or just on single organisms, and some effects of structure on toxicity are well known, but this work represents the development of a general strategy for investigating the toxicity of ionic liquids.

The green credentials of ionic liquids will depend on a general strategy for investigating the toxicity of ionic liquids

'Suppliers of chemicals are increasingly being held responsible for the effect their products have on the environment,' said Marianne Matzke, a member of the research team. 'It's important that both the technical properties are optimised and the hazards minimised at the same time in the development of new ionic liquids. A strong collaborative effort between all the interested parties - chemists, biologists and ecologists - is needed to achieve this.'

Ken Seddon, an ionic liquids expert at Queen's University, Belfast, UK, said, 'it's important that sweeping generalisations are not made about the toxicity of ionic liquids.  There are literally millions of possible combinations of cations and anions, and this work represents a first and very important step in understanding the effects of structure on toxicity.  There are very few centres worldwide capable of achieving this and the collaboration between suppliers of ionic liquids like Merck and the academic community is key.'

The plan is to create a well defined structure activity relationship for the toxicity of ionic liquids.  'Our eventual goal would be to design a totally biodegradable, non-toxic ionic liquid with the properties desired by the chemists,' said Matzke.

Stephen Davey