Comparative algal toxicity assessment of a novel hydrophobic ionic liquid used in metal extraction processes

Author(s): Andreas Gradwohl, Tobias Danzl, Victoria Brauneis, Markus Rumpel, Katharina Sansone, Wolfgang Kandioller, Michael Schagerl, Franz Jirsa
Abstract: The task-specific ionic liquid di-[trioctyl-(8-phenyloctyl)-phosphonium] pamoate, [TOPP]₂[PAM], was designed as a highly hydrophobic substance for “greener” metal extraction. During metal extraction, it exhibits considerably reduced leaching into the aqueous phase compared to similar phosphonium-based ionic liquids. In order to assess the ecotoxicological potential of this novel compound, we investigated its algal toxicity towards the three freshwater green algae species Acutodesmus obliquus , Chlorella vulgaris and Raphidocelis subcapitata . In addition, algal toxicity was compared to commercially available ionic liquids Aliquat® 336, Cyphos® IL 101 and the task-specific ionic liquid trihexyltetradecylphosphonium 3-hydroxy-2-naphthoate, [P₆₆₆₁₄][HNA], over a prolonged period (7 days). In order to reach sufficient IL concentrations in the testing media, [TOPP]₂[PAM] was leached either with or without support of ultrasonication. When leaching was supported by ultrasonication, the half-maximal inhibitory concentration (IC₅₀) for [TOPP]₂[PAM] ranged from 0.05 mg L⁻¹ for C. vulgaris , 0.23 mg L⁻¹ for A. obliquus to 0.45 mg L⁻¹ for R. subcapitata . This classifies the substance as a short-term (acute) aquatic hazard in the category ‘Acute 1’. Yet, during leaching without ultrasonication, these concentrations were reached only for C. vulgaris , yielding an IC₂₀ for A. obliquus and an IC₁₀ for R. subcapitata instead. This demonstrates a clear advantage over Aliquat® 336 and Cyphos® IL 101, where IC₅₀ values were easily reached. The results show a significantly reduced growth inhibition compared to commercial compounds when applying [TOPP]₂[PAM] according to suggested metal extraction procedures. Further comparisons to [P₆₆₆₁₄][HNA] demonstrated the advantage of using ILs with functional anions to reduce toxic effects on freshwater green algae. Evaluating the algal vitality with pulse-amplitude modulated fluorescence also demonstrated the lower impact of ILs with functional, hydrophobic anions.
Organisation(s): Department of Inorganic Chemistry, Mass Spectrometry Centre, Department of Botany and Biodiversity Research, Functional and Evolutionary Ecology
External organisation(s): University of Vienna
Journal: Environmental Chemistry and Ecotoxicology
Volume: 8
Pages: 577-589
No. of pages: 13
ISSN: 2590-1826
DOI: https://doi.org/10.1016/j.enceco.2025.12.008
Publication date: 2026
Peer reviewed: Yes
Austrian Fields of Science 2012: 104023 Environmental chemistry, 106027 Ecotoxicology, 209006 Industrial biotechnology
Keywords
ASJC Scopus subject areas: Environmental Chemistry, Ecology, Evolution, Behavior and Systematics, Ecology
Portal url: https://ucrisportal.univie.ac.at/en/publications/34f4b137-0668-409b-8bf9-81488972eff8