Ionic liquids (ILs) are fast emerging as the solvents of choice in the chemical industry. Their relative non-volatility, non-flammability, wide liquid range and high conductivity make them serious candidates as green solvent alternatives to volatile organic solvents. In order to assess the relative safety of ILs, representative organisms were tested against ILs differing only in purity (as determined by color) and/or alkyl chain length. ILs were prepared identically with the exception of the reaction temperature. Our initial studies show that the purity of the IL does not contribute to its toxicity. As expected from previous reports in the literature, the size of the alkyl side chain contributes significantly to IL toxicity. These studies also demonstrate that although the presence of a cell wall has no effect on the degree of toxicity, the presence and type of bacterial glycocalyx determines the level of IL resistance. Results of the above studies were compared to a seed germination assay to determine which screen is most useful for identifying toxic ILs. Results indicate the seed germination assay is several-fold more sensitive to the ILs than the toxicity assay using microorganisms; seeds failed to germinate at IL concentrations that did not inhibit growth of bacteria, algae and fungi. These results raise concerns regarding the potential risk to microbial and plant ecosystems if ILs are released into the environment through effluent discharges or accidental spills. This work was supported in part at BNL by the U.S. DOE Office of Basic Energy Sciences under contract # DE-AC02-98CH10886.