The ability of two widely used imidazolium-based ionic liquids (ILs) to affect the physiological behavior of the green alga Dunaliella tertiolecta treated in culture media with different salinities (30 and 35‰) was investigated. Algae species were exposed to 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF 4 ]), 1-octyl-3-methylimidazolium tetrafluoroborate ([omim][BF 4 ]), and their binary mixture [bmim][BF 4 ]-[omim][BF 4 ] (ratio 1:1) for 96 h, in f/2 medium with different salinities (30 and 35‰). Every 24 h, the growth rate (μ) and the percent inhibition (% I) as well as the concentrations of carotenoids (in terms of carotene content) and chlorophyll a (Chl a) were determined. According to the results, the culture media salinity plays a key role in IL-mediated inhibitory effects on algae. In both salinities, ILs can act against algal growth rate rather than Chl a synthesis, merely due to the existence of a cross-linking with carotenoids, whose enhancement prior or in parallel with Chl a synthesis could play an important role against their growth restriction.

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