Automated high-throughput Vibrio fischeri assay for (eco)toxicity screening: application to ionic liquids

An automated high-throughput Vibrio fischeri assay was developed and further applied to the evaluation of ionic liquids (ILs) (eco)toxicity. The assay was based on the reduction of bacterial bioluminescence in the presence of test compounds and the results were presented as EC(50). The assays were performed with eight commercially available ILs with distinct cationic head groups, alkyl side chains and anions. EC(50) values between 6.5 and 691.9 mmol L(-1) were obtained for the tested ILs, being hmim [Cl] the most toxic and bmim [Cl] the less toxic ones, confirming the influence of the different structural elements. Moreover, all the tested ILs exhibited a (eco)toxicity lower than Cu(II), used as a positive control during the optimization and analysis steps. The automated assay assured the precise control of the contact time between V. fischeri and test compound by means of a simple protocol that guaranteed adequate aspiration and handling of the solutions as well as the precise implementation of a computer controlled stop period. Furthermore, a significant reduction of the assay costs was achieved through automation mainly by a drastic reduction of the volume of bacterial suspension and test compound. The methodology was validated by comparison with a microplate assay; it was stated that the results, obtained after a 3min contact time, changed proportionally relatively to Cu(II) in both assays. This confirmed the applicability of the methodology as an (eco)toxicity screening assay, with reduction of time and increase of robustness and repeatability (n=10; rsd<1.1%). It is expected that due to its simplicity and reduced cost the developed assay can be integrated in the early stage of development of new compounds as a rapid screening test.