These criteria have to be considered as soon as possible in the ILs structure development. First studies concerning ILs toxicity were reported in the 1950s and since the 1990s many publications have dealt with this topic as ILs have become popular in green chemistry [110, 140, 141]. A good knowing of IL toxicity is necessary to develop an industrial application [110].

Pham et al. published a quite exhaustive report summarizing many of the results described in literature [110]. In 2010, another review treated of ILs ecotoxicity (in water and soils) and toxicity on humans [142]. It is crucial to consider that toxicity is dependent of the biological target’s nature. Indeed, an IL can be harmless towards a specific microorganism and very toxic towards another one.

Ecotoxological

Fig. 12.5 Biological targets used for ILs toxicity evaluation

To assess regarding ILs toxicity towards microorganisms, microbial activity in the presence or not of ILs can be compared. For instance, Zhang et al. [143] showed that the activity of Aureobasidium pullulans was not affected by the presence of [C4Mim][PF6], contrarily to some other solvents like hexane or dibutylphtalate. Matsumoto et al. [52] examined the toxicity of 1-R-3-methylimidazolium hexafluorophosphate ILs with R = butyl, hexyl or octyl, on a lactic acid bacteria, Lactobacillus delbruekii; they observed that lactic acid production decreases with the augmentation of the alkyl chain. However, the study realized on various lactic acid bacteria showed that the IL tolerance is related to the acid production (micro­bial activity in the presence of IL < microbial activity in the presence of water).

Figure 12.5 presents the biological targets used for ILs’ toxicity evaluation [110].