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This paper reports on a detailed study of the influence of salinity on the biological activity of 1-alkyl-3-methylimidazolium chlorides on two green algae Oocystis submarinaand Chlorella vulgaris, one diatom Cyclotella meneghinianaand one blue-green alga Geitlerinema amphibium. All these organisms inhabit the Baltic Sea, an environment naturally varying greatly in salinity. The toxicity effects of ILs towards cyanobacterial and algal organisms were tested in fresh water and in water of four different salinities—8, 16, 24 and 32 PSU—reflecting the whole range encountered in the Baltic Sea. Increasing the salinity was found to exert a significant influence on ionic liquid toxicity in all cases. The lower toxicity is probably due to the reduced permeability of ionic liquid cations through the algal cell walls. Higher chloride concentrations offer a good ion-pairing environment for imidazolium cations, which therefore compete with hydroxyl or silanol functional groups in cell-wall structures. The results of this work indicate that at higher salinities algal growth is inhibited to a significantly lesser extent. With the same IL concentration, the toxicity decreases by eight–ten times in the algae or about three times in the cyanobacterium in the 0–32 PSU salinity range. [ABSTRACT FROM AUTHOR]

Many studies done so far on the aquatic ecotoxicity of ionic liquids have dealt with phytoplankton organisms. Nonetheless, benthic organisms are just as important if we are to fully understand the prospective fate and effects of ionic liquids in the aquatic environment. An investigation was therefore undertaken into the toxicity of 1-alkyl-3-methylimidazolium ionic liquids towards the diatom Bacillaria paxilliferand the cyanobacterium Geitlerinema amphibium, species characteristic of the benthic environment. As in the first part of this study (A. Lataa, M. Ndzi and P. Stepnowski, Green Chem., 2009, 11, 580–588), five 1-alkyl-3-methylimidazolium chlorides (from ethyl to decyl) were chosen as the test kit compounds for examining the expected alkyl chain length effect, together with 1-butyl-3-methylimidazolium tetrafluoroborate, dicyanamide, trifluoromethanesulfonate and methyl sulfate and α-methyl[poly(oxy-1,2-ethanediyl)]sulfate for investigating the influence of anions on the toxicity of ionic liquids towards the algal species under investigation. A pronounced alkyl chain effect was found with both organisms. The results indicate that P. amphibiumis more sensitive than B. paxillifer.It was also found that the use of trifluoromethanesulfonate and dicyanamide as counteranions in the IL structure gave rise to the most pronounced toxic effects in comparison with the other anions tested. It is assumed that the greater toxicities of long alkyl chain ILs will most probably not pose a greater threat to benthic organisms, since these compounds will undergo rapid and very strong adsorption to sedimentary matter. Short-chain compounds, which are known to be reversibly bound to sediments, may still pose a significant risk to benthic ecosystems, however. [ABSTRACT FROM AUTHOR]

This paper reports on an investigation into the toxicity of 1-alkyl-3-methylimidazolium ionic liquids (ILs) towards two green algae (Chlorella vulgarisand Oocystis submarina) characteristic of freshwater and brackish environments, as well as two brackish and marine diatoms (Cyclotella meneghinianaand Skeletonema marinoi). The test kit of IL compounds consisted of five 1-alkyl-3-methylimidazolium chlorides (from -ethyl to -decyl) for evaluating the expected alkyl chain length effect, together with 1-butyl-3-methylimidazolium tetrafluoroborate, dicyanamide, trifluoromethanesulfonate, methyl sulfate an α-methyl[poly(oxy-1,2-ethanediyl)]sulfate for investigating the influence of the anion on IL toxicity towards various algal species. A pronounced alkyl chain effect was confirmed with all the organisms studied. EC50values were linearly very well correlated with the number of carbon atoms in the IL alkyl chains. The results indicate that diatoms are far more sensitive than green algae to ILs. Cell size also plays an important part in the intoxication process: a tenfold difference in cell size results in a 100% more sensitive reaction to ionic liquids in both the green algae and diatoms. No significant differences were observed between alkylimidazolium salts and an alkylpyridinium compound of similar lipophilicity. It was also found that the use of tetrafluoroborate and trifluoromethanesulfonate as counteranions in the IL structure gave rise to the most pronounced toxic effects in comparison with the other anions tested. In the case of tetrafluoroborate this is probably caused by the potential hydrolysis of this entity, which leads to the formation of fluoride and a further increase in toxicity. Whereas in the case of trifluoromethanesulfonate it is likely caused by relatively high lipophilicity of this anion, additionally known to be strongly associated with alkylimidazolium cations, that in turn may enhance cell wall penetration. [ABSTRACT FROM AUTHOR]