The ecotoxicity of ionic liquids and traditional organic solvents on microalga Selenastrum capricornutum.

In this study, the effects of several ionic liquids and traditional organic solvents on the growth of the green microalga, Selenastrum capricornutum, were investigated. The toxicities were strongly related to the incubation time and chemical structures of the ionic liquids. The toxicities of tetrabutylphosphonium and tetrabutylammonium containing bromide anion were observed to decrease when the incubation time was raised from 48 to 96 h. Conversely, the toxicities of 1-butyl-3-methylimidazolium and 1-butyl-3-methylpyridinium containing bromide anion were found to increase with increasing incubation time. Of the ionic liquids tested, 1-butyl-1-methylpyrrolidinium bromide was found to be the least toxic, which is similar in toxicity level of dimethylformamide. In general, the toxicities of the ionic liquids were estimated to be two and four orders of magnitude greater than those of the organic solvents examined, although ionic liquids are being considered as green solvents.

Toxicity of imidazolium salt with anion bromide to a phytoplankton Selenastrum capricornutum: effect of alkyl-chain length.

Room-temperature ionic liquids are regarded as environmentally benign alternatives to volatile organic solvents. However, the product designs for this promising group of compounds should take account, not only the technological needs, but also the eco-toxicological hazards. Therefore, this study aimed to evaluate the toxicity of some important ionic liquids on the growth of the freshwater alga, Selenastrum capricornutum. The ionic liquids examined in this study included 1-propyl-3-methylimidazolium [PMIM], 1-butyl-3-methylimidazolium [BMIM], 1-hexyl-3-methylimidazolium [HMIM] and 1-octyl-3-methylimidazolium [OMIM] with a bromide anion. The susceptibility of alga to ionic liquids was strongly dependent on the alkyl-chain length. According to our results, a longer alkyl-chain resulted in stronger inhibition of algal growth. In general, the toxicity could be summarized as decreasing in the following order: [OMIM]>[HMIM]>[BMIM]>or=[PMIM]. Among the ionic liquids examined, [OMIM] [Br] was found to be most toxic to S. capricornutum, with EC(50) values ranging from 26.3 microM to 54.9 microM after an incubating time of 96 h. Although [BMIM] [Br] and [PMIM] [Br] was relatively less toxic than [OMIM] and [HMIM], their toxicity increased as increasing the incubation time from 48 h to 96 h. This fact indicates that these kinds of ionic liquids may become more toxic after being released and contacted to freshwater ecosystem.

Microalgal photosynthetic activity measurement system for rapid toxicity assessment.

A systematic biosensor is constructed for the estimation of toxic compounds based on photosynthetic activity measurement in Selenastrum capricornutum cells. The photosynthetic response was evaluated as a function of light intensity, cell concentration and initial dissolved oxygen. The inhibitory effect of some toxicants (1-butyl-3-methylimidazolium tetrafluoroborate, methanol) on dissolved oxygen production was also determined. In all cases, a toxic response was detected (i.e. a dose-related inhibition of photosynthetic activity was observed). For the present system, a time of only 2 h was needed to predict EC50 values as compared to 96 h for a conventional algal assay based on algal growth rate. Thus, the developed biosensor was proved to be useful as a rapid and simple test method in environmental toxicity assessment.