Up to now the issues of mixture toxicity and combination effects were neglected within a prospective hazard assessment of ionic liquids (ILs). However when being released to the environment, mixtures of ILs or mixtures of ILs and other pollutants are likely to occur and therefore the impact of mixture toxicity should be taken into account. Thus this study investigates the effects of three differently composed mixtures containing ILs as well as ILs and the heavy metal cadmium on limnic green algae (Scenedesmus vacuolatus) and wheat (Triticum aestivum). For an evaluation of the results, two well established concepts of concentration addition (CA) and independent action (IA) were used. Both (CA and IA) underestimated the effects of the mixtures consisting exclusively of ILs leading to the assumption that interactions between the mixture components or between the mixture components and the environmental matrix occurred. The general applicability of CA and IA must be questioned. For the mixture of ILs and cadmium the deviations from the predictions were moderate (and less toxic than expected) so that CA can be recommended as a starting point for the analysis of combination effects of ILs and heavy metals. In general the presence of cadmium reduced the toxicity for both the aquatic as well as the terrestrial organisms. The green algae reacted approximately two orders of magnitude more sensitive to the mixture scenarios than wheat and proved to be a good reference test system for the evaluation of measured effects within a prospective hazard assessment of ionic liquids.