Alteration between inhibition and stimulation in individual and mixture effects of [amim]Br and [apyr]Br on Aliivibrio fischeri: Time and side-chain dependence

Abstract

The exposure reality of chemicals is usually in mixtures, the effects of which are usually extrapolated from individual results. Yet, such extrapolation is challenged by the alteration between monotonic concentration-response curves (CRCs) and non-monotonic hormetic CRCs in individual and mixture effects. In the present study, we aimed to investigate the occurrence of such alterations using 1-alkylimidazolium bromide ([amim]Br) and 1-alkylpyridinium bromide ([apyr]Br) ionic liquids (ILs) as model chemicals. Effects of four [amim]Br, four [apyr]Br, and their quaternary mixtures designed by uniform design were measured on Aliivibrio fischeri in a time-dependent fashion. Results showed that the individual [amim]Br showed monotonic CRCs. Their inhibition increased over the length of the side-chain and decreased over the exposure time. The [amim]Br mixtures showed non-monotonic hormetic CRCs, where the stimulations increased over exposure time. The individual [apyr]Br had non-monotonic hormetic CRCs, and their stimulation increased over the length of the side-chain. Meanwhile, the [apyr]Br mixtures had monotonic CRCs without any stimulation. Notably, the positive contributors to the mixture effects were [emim]Br or [epyr]Br which had the shortest side-chain among the components. The findings can facilitate accurate prediction on the environmental effects of ILs with specific considerations on hormetic and mixture effects.