Toxicity and biodegradability of ionic liquids: New perspectives towards whole-cell biotechnological applications

► The potential of four ILs was evaluated in terms of toxicity and biodegradability. ► Only [BMIM][PF6] and [BMIM][NTF2] were not toxic at a concentration of 5% (v/v). ► Long-term fluoride (F−) release showed concentration (≤2.98 mg L −1) below the toxic threshold. ► Short and long-term biodegradability tests showed no IL biodegradability. ► Therefore, both ILs can be considered as compatible with whole-cell biotechnological processes. The potential of four ILs for whole-cell biotechnological processes was evaluated in terms of toxicity and biodegradability. From the four ILs tested, only Aliquat completely inhibited the microbial glucose uptake at a concentration of 5%, while [PEGMIM][PF 6] was completely soluble in water. Therefore, these ILs were discarded for further studies. On the other hand, [BMIM][PF 6] and [BMIM][NTF 2] were not toxic at a concentration of 5% (v/v) (specific concentrations of 170 and 180 g IL g Biomass −1, respectively), while IL addition at 10% (v/v) slightly inhibited the metabolic activity relative to controls deprived of IL. Addition of both [BMIM][PF 6] and [BMIM][NTF 2] produced an acclimation time of approximately 24 h before the microorganisms were able to uptake the substrate. Further experiments on IL toxicity due to long-term fluoride (F −) release showed that despite the fact that F − was detected in the aqueous phase, its concentration was very low (≤2.98 mg L −1) and hence not toxic for the microorganisms. Finally, short- and long-term biodegradability tests showed that neither [BMIM][PF 6] nor [BMIM][NTF 2] was biodegradable. Therefore, [BMIM][PF 6] and [BMIM][NTF 2] can be considered as compatible with whole-cell biotechnological processes.