Proactive aquatic ecotoxicology: A hazard assessment of room-temperature ionic liquids

Humans have altered the environment such that pristine, non-impacted ecosystems arguably no longer exist. To prevent further environmental degradation, human actions need to be assessed proactively, and those which pose too great a risk to human or environmental health altered. The importance of proactive science is especially true with the development of new chemical technologies. “Green” chemicals are those that minimize waste, maximize efficiency, and/or reduce toxicity; an emerging group of such green chemicals are room-temperature ionic liquids (ILs), which are under development to replace traditional volatile organic solvents. ILs clearly improve upon volatile solvents in many industrial processes, however their potential for negative effects if released into aquatic environments remains largely unknown. My overall research objective was to evaluate the hazards posed by ILs to freshwater planktonic communities, and to explore how proactive evaluation of these hazards could generate environmentally safer chemicals. In laboratory experiments, I tested the effects of 1-butyl-, 1-hexyl-, and 1-octyl-3-methylimidazolium bromide on freshwater phytoplankton growth demonstrated that increasing alkyl-chain length on an IL increases its toxicity, and that the presence of replete nutrients can mitigate the toxic effects of ILs to phytoplankton, specifically Chlamydomonas reinhardtii. Further, the feeding rates of the zooplanktor Daphnia magna on the phytoplanktor C. reinhardtii were found to increase in the presence of two different ILs under relatively constant exposures, while a short, 24-h pulse exposure had minimal long-term effects on feeding. These results were combined with those of other studies to develop a mathematical model demonstrating the effects of both chemical (ILs) and biological (invasive species) stressors on a simple aquatic community. Interval analysis and Monte Carlo techniques were used to examine the effects of data variability on model projections, and showed that variation in C. reinhardtii growth rates had larger effects on model outcomes than that of D. magna feeding rates. Overall, my research has demonstrated the importance of environmental conditions, species interactions, and exposure types on IL impacts, and highlights the need to explicitly include ecology in the toxicological evaluations of chemicals. This research can help guide the development of ILs towards effective, efficient, and most importantly, greener alternatives.