Acute toxicity of ionic liquids for three freshwater organisms: Pseudokirchneriella subcapitata, Daphnia magna and Danio rerio
Introduction
The use of bioassays on standard test organisms represents a fundamental approach in the definition of ecological risk in the aquatic environment for promising chemicals as ionic liquids (ILs). The environmental hazard assessment of chemicals consists of the identification of the effects that a chemical may have on organisms in the environment and the determination of the concentration of the chemical below which adverse effects in the environmental sphere of concern (e.g., aquatic) are not expected to occur. This concentration is known as the predicted no-effect concentration (PNEC). Starting from the available data, the PNEC may be calculated by applying an appropriate assessment factor to the effect values [e.g., median lethal concentration (LC50) or median effective concentration (EC50) or no observed effect concentration (NOEC)] derived from tests on organisms, such as crustaceans, algae, and fish. Environmental hazard assessment has been regulated by constantly updated EU directives and regulations (Dir. 67/548, 88/379, and 76/769; Reg. 793/93), which take into account scientific and technical progress. In order to improve the protection of human health and the environment through better and earlier identification of the properties of chemical substances, EU proposed a new regulatory framework for the Registration, Evaluation, and Authorisation of Chemicals (REACH) on 29 October 2003 (COM(03) 644). After 3 years of negotiation, REACH Regulation was adopted by the Plenary of the European Parliament at the end of 2006. According to the REACH Regulation, the registration process requires (eco)toxicological data for all chemicals produced in or imported into the European Union above one metric tonne per year.
Really, REACH has the aim not only of improving the protection of human health and the environment, but also of maintaining the competitiveness and enhancing the innovative capability of the EU chemicals industry. Over the past 10 years or so, research of new chemicals able to substitute for many environmental unfriendly compounds has been a field of intense investigation in the area of green chemistry and engineering. In particular, ILs have received considerable attention as potential green solvents for a wide range of applications. This is mainly due to their superior properties compared with conventional organic solvents, such as nonvolatility, nonflammability, and high thermal stability. However, some important claims about ILs have been recently discredited. It has been shown that a large group of ILs are combustible (Smiglak et al., 2006) and that some commercially available ILs may be toxic for different aquatic organisms, from bacteria to fish (Bernot et al., 2005a, Bernot et al., 2005b; Couling et al., 2006; Latala et al., 2005; Pretti et al., 2006; Wells and Coombe, 2006). Furthermore, although it has been evidenced that selected families of commonly used aprotic ILs can be distilled at 200–300 °C and low pressure (Earle et al., 2006), this feature practically has no effect on the environmental impact of ILs on the air compartment. The possibility to diffuse ILs into the atmosphere is extremely low. On the other hand, the water solubility of many ILs may allow their entering into the aquatic compartment. This may have important consequences, in particular if their application in large-scale processes increases (e.g., accidental spills, effluent discarges).
Recently, even if with a relevant delay with respect to their application as solvents for synthesis, catalysis, and extraction, important data (both experimental and calculated) on the environmental effect of ILs have been published, showing the increasing interest in the subject. To assess the aquatic toxicity of ILs on eukaryotic organisms, tests have been carried out mainly on imidazolium-based ILs related to the crustacean Daphnia magna (Bernot et al., 2005a; Garcia et al., 2005; Couling et al., 2006; Wells and Coombe, 2006; Samorì et al., 2007), the marine microalga Oocystis submarina, the diatom Cyclotella meneghiniana (Latala et al., 2005), the freshwater algae Scenedesmus quadricauda (Kulacki and Lamberti, 2008), and Pseudokirchneriella subcapitata (formerly known as Selenastrum capricornutum) (Wells and Coombe, 2006; Cho et al., 2008). Some information on common ILs is available also on molluscs such as the freshwater snail Physa acuta (Bernot et al., 2005b) and on the marine bacteria Vibrio fischeri (Couling et al., 2006; Matzke et al., 2007; Stolte et al., 2007), whereas the acute toxicity of several ILs on fish has been assessed using the zebrafish (Danio rerio) (Pretti et al., 2006).
Although limited in number, these studies have shown that ILs have different degrees of toxicity to aquatic organisms ranging from bacteria to fish, and that toxicity is primarily determined by the cationic moiety. More in particular, it is strongly affected by the side-chain length (Bernot et al., 2005a). Recently, there has also been evidence that anions can contribute to toxicity, but in most cases anion effects are less dramatic compared with the side-chain effect (Stolte et al., 2007; Matzke et al., 2007).
In crustaceans and algae, the mechanism of toxicity induced by ILs is still unknown. However, it has been suggested that toxicity in D. magna could be related to enzymatic inhibition and membrane disruption (Bernot et al., 2005a), whereas in fish toxic effects towards the branchial epithelium, with a supposed alteration of membrane stability, have been demonstrated for two ammonium ILs, having structural features similar to common cationic surfactants (Pretti et al., 2006). An extensive review on sustainability of ILs reporting a complete overview on (eco)toxicological data of ILs has been recently published (Ranke et al., 2006).
One of the main features of ILs is the possibility to tune the physico-chemical properties of these salts via the selection of specific anions and cations, making it possible, at least in principle, to design the best IL for any specific application. In order to obtain information on the possibility of modifying the structures of ILs to improve chemical properties, and reduce (eco)toxicity, the acute toxic effects of 18 ILs were investigated on three organisms from three different trophic levels: primary producers (green algae), primary consumers (cladocerans), and predators (fish). The test kit compounds comprised several aromatic, heterocyclic and non-cyclic quaternary nitrogen-containing compounds (ammonium, imidazolium, pyridinium, pyrrolidium, and morpholinium), and two sulfonium salts. In the case of the imidazolium salts, toxic effects were investigated in relation to the presence of specific functional groups on the longer alkyl chain or the substitution of an alkyl group on nitrogen with a hydrogen atom (Brønsted acidic ILs).
Section snippets
Ionic liquids
AMMOENG 100 and AMMOENG 130 were purchased from Solvent Innovation (GMBH). 1-Butyl-3-methylimidazolium bis(triflimide) ([bmim][Tf2N]), butylpyridinium bis(triflimide) ([bpy][Tf2N]), and N,N-methylbutylpyrrolidinium bis(triflimide) ([bmpyr][Tf2N]) were prepared following reported procedures (Cammarata et al., 2001). 1-(2-Cloroethyl)imidazolium chloride ([HC2Clim]Cl), methylimidazolium chloride ([Hmim]Cl), 1,1′-(1,2-ethanediyl)bis-imidazolium chloride [(C2(Him)2]2Cl),
Results
The data for all tested ILs are summarized in Table 1, Table 2, Table 3. All the investigated ILs can be considered as practically harmless for D. rerio (EC50 >100 mg/L, limit test) and, therefore, according to OECD guidelines for these latter ILs, the full test was not performed. In contrast, toxicity picture of the investigated ILs to D. magna was more complex (Table 2). Most ILs (IL6–IL8, IL11–IL18) had an EC50 >100 mg/L (full test was not performed) and could be categorized as practically
Discussion
The intention of the present study was to provide further information about the (eco)toxicological impacts of structural variations in ILs (considering the positively charged head groups, the substitution with one or more different side chains, and the corresponding anionic species) using relatively simple, quick, and inexpensive bioassays. This information may be particularly useful in the case of ILs, considering that it is a goal of many researchers to tune the physico-chemical properties of
Conclusions
In conclusion, the results based on the data of the present work and of literature demonstrated that (i) ILs show a different degree of acute toxicity to aquatic organisms, and the cation plays an important role. Long-chain quaternary ammonium salts having structures more similar to those of surfactants are toxic to freshwater algae, crustaceans, and fish. Among those tested, ILs not having a surfactant-like structure were generally not toxic for D. rerio. However, many show a toxicity to D.
Acknowledgments
This study was supported by the grants from the University of Pisa and from the Italian Ministry of Higher Education and Research (MIUR).
References (24)
- et al.
Marine toxicity assessment of imidazolium ionic liquids: acute effects on the Baltic algae Oocystis submarina and Cyclotella meneghiniana
Aquat. Toxicol.
(2005) - et al.
Acute and chronic toxicity of imidazolium-based ionic liquids on Daphnia magna
Environ. Toxicol. Chem.
(2005) - et al.
Effects of ionic liquids on the survival, movement, and feeding behavior of the freshwater snail Physa acuta
Environ. Toxicol. Chem.
(2005) - et al.
Development of cation/anion interaction scales for ionic liquids through ESI–MS measurements
J. Phys. Chem. B
(2007) - et al.
Molecular states of water in room temperature ionic liquids
Phys. Chem. Chem. Phys.
(2001) - et al.
Influence of anions on the toxic effects of ionic liquids to a phytoplankton Selenastrum capricornutum
Green Chem.
(2008) - et al.
Assessing the factors responsible for ionic liquid toxicity to aquatic organisms via quantitative structure—property relationship modeling
Green Chem.
(2006) - et al.
The sensitivity of Ceriodaphnia dubia and Daphnia magna to seven chemicals utilizing the three-brood test
Arch. Environ. Contam. Toxicol.
(1991) - et al.
The distillation and volatility of ionic liquids
Nature
(2006) - et al.
Biodegradable ionic liquids. Part II. Effect of the anion and toxicology
Green Chem.
(2005)
The effect of ammonia, chlorine, and chloramines toxicity on the mortality of Daphnia magna Straus
Pol. Arch. Hydrobiol.
Toxicity of imidazolium ionic liquids to freshwater algae
Green Chem.
Cited by (267)
Ecotoxicity studies reveal that organic cations in dicamba-derived ionic liquids can pose a greater environmental risk than the herbicide itself
2024, Science of the Total EnvironmentA review on (eco)toxicity of ionic liquids and their interaction with phospholipid membranes
2024, Journal of Molecular LiquidsProbing ionic liquid toxicity through biophysical and computational methods
2024, Journal of Molecular LiquidsSynthesis of oxidized carboxymethyl cellulose-chitosan and its composite films with SiC and SiC@SiO<inf>2</inf> nanoparticles for methylene blue dye adsorption
2024, International Journal of Biological MacromoleculesToxicity of “green solvents” - The impact of butyl methylimidazolium ionic liquids on daphnids
2023, Journal of Ionic Liquids