Ionic liquids in soils: effects of different anion species of imidazolium based ionic liquids on wheat (Triticum aestivum) as affected by different clay minerals and clay concentrations

Bioconcentration of imidazolium ionic liquids: In vivo evaluation in marine mussels Mytilus trossulus

Although imidazolium ionic liquids (ILs) are beginning to be used more widely in many industrial fields e.g., as reaction media, electrolytes, stationary phases in gas chromatography), there is still little information about their potential environmental fate. Among the uncertainties regarding the risks associated with these compounds, bioconcentration is one of the key issues, about which many doubts have been raised in recent years. While in vitro data suggest that permanently charged compounds can also bioconcentrate, conclusive evidence in the form of studies on organisms, at least for selected compounds, is needed. Therefore, the main objective of this work was to determine whether imidazolium cations of ILs, namely 1-methyl-3-octylimidazolium ([IM18]⁺) and 1-methyl-3-dodecylimidazolium ([IM1-12]⁺), can bioconcentrate in marine invertebrates tissues. During 21-day experiments, Mytilus trossulus mussels were exposed to these cations individually, at a concentration of 10 μg/L. In our study, it has been demonstrated for the first time during in vivo study, that long-chain imidazolium ionic liquids can bioconcentrate. The determined BCF value for [IM1-12]⁺ of 21,901 ± 3400 L/kg makes this compound to be considered highly bioaccumulative according to commonly accepted criteria. However, the obtained BCF for [IM18]⁺ (with the value below 100) suggests that this cation has little potential for bioconcentration. On the other hand, no salinity or anion influence on the bioconcentration of the tested cations was observed. Our tests also confirm that imidazolium ILs exhibit acute toxicity only at relatively high concentration levels, as LC₅₀ reached 0.68 mg/L for [IM1-12][Br], and 11.66 mg/L for [IM18][C(CN)₃]. This further confirms that the risks associated with the potential presence of these compounds in the environment should be attributed to their high persistence and potential bioconcentration, rather than acute toxicity.

Emerging impacts of ionic liquids on eco-environmental safety and human health

Owing to their unique physicochemical properties, ionic liquids (ILs) have been rapidly applied in diverse areas, such as organic synthesis, electrochemistry, analytical chemistry, functional materials, pharmaceutics, and biomedicine. The increase in the production and application of ILs has resulted in their release into aquatic and terrestrial environments. Because of their low vapor pressure, ILs cause very little pollution in the atmosphere compared to organic solvents. However, ILs are highly persistent in aquatic and terrestrial environments due to their stability, and therefore, potentially threaten the safety of eco-environments and human health. Specifically, the environmental translocation and retention of ILs, or their accumulation in organisms, are all related to their physiochemical properties, such as hydrophobicity. Based on results of ecotoxicity, cytotoxicity, and toxicity in mammalian models, the mechanisms involved in IL-induced toxicity include damage of cell membranes and induction of oxidative stress. Recently, artificial intelligence and machine learning techniques have been used in mining and modeling toxicity data to make meaningful predictions. Major future challenges are also discussed. This review will accelerate our understanding of the safety issues of ILs and serve as a guideline for the design of the next generation of ILs.

Effect of diclofenac and naproxen and their mixture on spring barley seedlings and Heterocypris incongruens

Nonsteroidal anti-inflammatory drugs (NSAIDs) are a popular group of drugs used worldwide. These drugs are also available over the counter, which implies that their consumption is not strictly regulated. They are released through wastewater and feces and can have adverse effects on the environment. The present study aimed to evaluate the effect of two NSAIDs, diclofenac (DCF) and naproxen (NAP), and their mixture (DCF + NAP) on spring barley seedlings and ostracods Heterocypris incongruens. The tested drugs had a negative impact on bivalve ostracods and the studied plants. DCF was the most toxic toward ostracods, while spring barley seedlings were affected the most by NAP. The application of the tested compounds and their mixture resulted in a decrease in fresh weight yield and the content of photosynthetic pigments. In addition, an increase in H₂O₂ and proline content and changes in the activity of antioxidant enzymes (POD, APX, CAT, and SOD) were observed.

Review of the toxic effects of ionic liquids

Interest in ionic liquids (ILs), called green or designer solvents, has been increasing because of their excellent properties such as thermal stability and low vapor pressure; thus, they can replace harmful organic chemicals and help several industrial fields e.g., energy-storage materials production and biomaterial pretreatment. However, the claim that ILs are green solvents should be carefully considered from an environmental perspective. ILs, given their minimal vapor pressure, may not directly cause atmospheric pollution. However, they have the potential to cause adverse effects if leaked into the environment, for instance if they are spilled due to human mistakes or technical errors. To estimate the risks of ILs, numerous ILs have had their toxicity assessed toward several micro- and macro-organisms over the past few decades. Since the toxic effects of ILs depend on the method of estimating toxicity, it is necessary to briefly summarize and comprehensively discuss the biological effects of ILs according to their structure and toxicity testing levels. This can help simplify our understanding of the toxicity of ILs. Therefore, in this review, we discuss the key findings of toxicological information of ILs, collect some toxicity data of ILs to different species, and explain the influence of IL structure on their toxic properties. In the discussion, we estimated two different sensitivity values of toxicity testing levels depending on the experiment condition, which are theoretical magnitudes of the inherent sensitivity of toxicity testing levels in various conditions and their changes in biological response according to the change in IL structure. Finally, some perspectives, future research directions, and limitations to toxicological research of ILs, presented so far, are discussed.

Mechanisms of action of ionic liquids on living cells: the state of the art

Ionic liquids (ILs) are a relatively new class of organic electrolytes composed of an organic cation and either an organic or inorganic anion, whose melting temperature falls around room-temperature. In the last 20 years, the toxicity of ILs towards cells and micro-organisms has been heavily investigated with the main aim to assess the risks associated with their potential use in (industrial) applications, and to develop strategies to design greener ILs. Toxicity, however, is synonym with affinity, and this has stimulated, in turn, a series of biophysical and chemical-physical investigations as well as few biochemical studies focused on the mechanisms of action (MoAs) of ILs, key step in the development of applications in bio-nanomedicine and bio-nanotechnology. This review has the intent to present an overview of the state of the art of the MoAs of ILs, which have been the focus of a limited number of studies but still sufficient enough to provide a first glimpse on the subject. The overall picture that emerges is quite intriguing and shows that ILs interact with cells in a variety of different mechanisms, including alteration of lipid distribution and cell membrane viscoelasticity, disruption of cell and nuclear membranes, mitochondrial permeabilization and dysfunction, generation of reactive oxygen species, chloroplast damage (in plants), alteration of transmembrane and cytoplasmatic proteins/enzyme functions, alteration of signaling pathways, and DNA fragmentation. Together with our earlier review work on the biophysics and chemical-physics of IL-cell membrane interactions (Biophys. Rev. 9:309, 2017), we hope that the present review, focused instead on the biochemical aspects, will stimulate a series of new investigations and discoveries in the still new and interdisciplinary field of "ILs, biomolecules, and cells."

Ionic Liquids Toxicity-Benefits and Threats

Ionic liquids (ILs) are solvents with salt structures. Typically, they contain organic cations (ammonium, imidazolium, pyridinium, piperidinium or pyrrolidinium), and halogen, fluorinated or organic anions. While ILs are considered to be environmentally-friendly compounds, only a few reasons support this claim. This is because of high thermal stability, and negligible pressure at room temperature which makes them non-volatile, therefore preventing the release of ILs into the atmosphere. The expansion of the range of applications of ILs in many chemical industry fields has led to a growing threat of contamination of the aquatic and terrestrial environments by these compounds. As the possibility of the release of ILs into the environment s grow systematically, there is an increasing and urgent obligation to determine their toxic and antimicrobial influence on the environment. Many bioassays were carried out to evaluate the (eco)toxicity and biodegradability of ILs. Most of them have questioned their "green" features as ILs turned out to be toxic towards organisms from varied trophic levels. Therefore, there is a need for a new biodegradable, less toxic "greener" ILs. This review presents the potential risks to the environment linked to the application of ILs. These are the following: cytotoxicity evaluated by the use of human cells, toxicity manifesting in aqueous and terrestrial environments. The studies proving the relation between structures versus toxicity for ILs with special emphasis on directions suitable for designing safer ILs synthesized from renewable sources are also presented. The representants of a new generation of easily biodegradable ILs derivatives of amino acids, sugars, choline, and bicyclic monoterpene moiety are collected. Some benefits of using ILs in medicine, agriculture, and the bio-processing industry are also presented.

Toxic effect of three imidazole ionic liquids on two terrestrial plants

To determine the toxic effect of three imidazole ionic liquids (IILs) in terrestrial monocotyledonous and dicotyledonous plants, three IILs (1-butyl-3-methylimidazole tetrafluoroborate, 1-butyl-3-methylimidazole hexafluorophosphate, and butyl-3-methylimidazolium bi-[(trifluoromethyl)sulfonyl]imide) were investigated using rice and capsicum as target toxicity models. In hydroponic experiments, increasing the concentration of the IILs led to a decrease in the seed germination rate, a decrease in the reduced stem and root lengths, and an increase in the inhibition rate of the stem and root lengths; in addition, as the concentration increased, the reducing sugar content of rice and capsicum seedling leaves and roots first increased and then decreased, while permeability of the cell membranes of the stems and roots of the two plants also gradually increased. In terms of the effects on these indices in rice, the ranking of these three IIL anions was [TF2N]- > [PF6]- > [BF4]-; in terms of the effects on capsicum, the sequence was [BF4]- > [TF2N]- > [PF6]-. These findings provide a theoretical reference for the next step in the synthesis and the use of green ionic liquids.

Phytotoxicity of ionic liquids

Ionic liquids (ILs) have been one of the most interesting chemical entities over the last two decades and have been investigated by numerous scientists all over the world. However, during IL research, it has been shown that these compounds present toxicity to both terrestrial and aquatic plants, among others. The phytotoxicity of ILs depends on the type of cation, the length of the alkyl chain in the substituent or enantioselectivity, on the concentration used, and, it appears that the type of anion may also have an impact on toxicity. The toxic effects of ILs on plants also depend on the conditions under which such tests are conducted. The results may help facilitate the development of protective environmental measures against IL-induced negative effects, but they may also be used in various landscape-related areas, such as herbology, to design new substances with weed killing properties.

Biochemical Responses of Wheat Seedlings on the Introduction of Selected Chiral Ionic Liquids to the Soils

In this study, new chiral ionic liquids (CILs) were obtained from the natural-origin material (1 R,2 S,5 R)-(-)-menthol. The physicochemical characteristics of the studied imidazolium salts were investigated. The obtained 3-ethyl-1-[(1 R,2 S,5 R)-(-)-menthoxy-methyl]imidazolium salts are nonvolatile, nonflammable, and stable in air, in contact with water, and in commonly used organic solvents. The influences of the obtained chiral salts on physiological and biochemical parameters were determined for wheat ( Triticum aestivum L.) seedlings. Both salts led to changes in plant metabolism, which resulted in decreased assimilation pigments, decreased fresh weight, and increased dry weight and proline in wheat seedlings. Moreover, the growth of the above-ground parts and roots was inhibited. Additionally, there was a drop in the potential and germination capacity of wheat seeds after using the highest concentrations of the ionic liquids. The salts caused oxidative stress in wheat seedlings, which was demonstrated by increased malondialdehyde content. In response, the plants engaged their defensive system against free oxygen radicals, which resulted in increased catalase and peroxidase activity and decreased H₂O₂ levels in the plants. There were no changes in the activity of superoxide dismutase. All of the changes observed in the levels of determined biomarkers of oxidative stress in the plants were linearly correlated with the increase in the concentrations of the chiral ionic liquids in the soil. The salt with hexafluorphosphate anion exhibited slightly higher toxicity toward wheat seedlings than the other salt. The CILs led to premature aging of plants, which was demonstrated by the increase in peroxidase activity and a decrease of chlorophyll in the seedlings. The experiment also showed good correlation between the increase in peroxidase activity and the decrease in chlorophyll level, which proves that the decrease in chlorophyll content resulted from not only the increase in CILs concentration in the soil but also the increased POD activity, which leads to the damage of chlorophyll particles.

Growth inhibition and oxidative stress caused by four ionic liquids in Scenedesmus obliquus: Role of cations and anions

Ionic liquids (ILs) are widely used in various industrial applications. However, they are considered potential toxins in aquatic environments because of their physical stability and solubility. The growth inhibition and oxidative stress induced by four ionic liquids with different cations and anions on the green algae Scenedesmus obliquus was investigated in this study. The order of growth inhibition was 1‑hexyl‑3‑methylimidazolium nitrate ([HMIM]NO₃) > 1‑hexyl‑3‑methylimidazolium chloride ([HMIM]Cl) > N‑hexyl‑3‑metylpyridinium bromide ([HMPy]Br) > N‑hexyl‑3‑metylpyridinium chloride ([HMPy]Cl). Imidazolium IL had a higher growth inhibition effect than pyridinium IL, nitrate IL and bromide IL had a higher effect than chloride IL. Reactive oxygen species (ROS) level in S. obliquus increased with increasing IL concentrations. Green fluorescence in [HMIM]Cl treated algae showed increased brightness compared to the [HMPy]Cl treatment, and [HMIM]NO₃ treatment produced increased brightness compared to the [HMPy]Br treatment, suggesting that higher ROS levels were induced by [HMIM]Cl and [HMIM]NO₃. Soluble protein, catalase (CAT), and superoxide dismutase (SOD) activities were stimulated at lower concentrations but were inhibited at higher concentrations. Regression analysis suggested that ROS level is the main index responsible for oxidative stress induced by the four ILs. The ILs induced oxidative damage on S. obliquus, and ROS in high concentration treatments could not be effectively removed by the antioxidant system, leading to oxidative damage and ultimately resulting in growth inhibition and cell death.

Plant growth promoting N-alkyltropinium bromides enhance seed germination, biomass accumulation and photosynthesis parameters of maize (Zea mays)

N-Alkyltropinium bromides were synthesized and characterized as novel plant-growth promoting agents.

Anion functionalized ionic liquid from artificial sugar: a sustainable pathway for diverse bis-enol derivatives

An artificial sugar saccharine based anion-functionalized ionic liquid [Bmim]Sac was synthesized and used for new and straightforward strategies for the construction of a diverse range of bis-enols.

Evaluation of the impact of different alkyl length and type of substituent in imidazolium ionic liquids on cucumber germination, growth and oxidative stress

In this work, the effect on cucumber growth of seven different imidazolium-based ionic liquids, namely 1-(2-oxybutyl)-3-methylimidazolium chloride, [C₂OC₂mIm][Cl]; 1-(2-oxypropyl)-3-methylimidazolium chloride, [C₁OC₂mIm][Cl]; 1-(3-hydroxypropyl)-3-ethylimidazolium chloride, [OHC₃eIm][Cl]; 1-(3-hydroxypropyl)-3-methylimidazolium chloride, [OHC₃mIm][Cl]; 1-(2-hydroxyethyl)-3-methylimidazolium chloride, [OHC₂mIm][Cl], 1-butyl-3-methylimidazolium chloride, [bmim][Cl] and imidazolium chloride, [Im][Cl], were examined. The influence of polarity of the alkyl side chain of the imidazolium cation on the reduction of the ionic liquid's toxicity is investigated. For all investigated seedlings, significant reduction of biomass was noted, with the incoherent influence of the ionic liquid (IL) concentration. The total inhibition of germination was shown at the highest used concentration for some of the used ionic liquids. Although investigated ILs affected root and shoot growth of cucumber, the effect on stress marker (MDA) as well as biosynthesis of chlorophyll and carotenoids was negligible. The data collected in this research suggest that tuning of the lipophilicity of imidazolium cations by the introduction of polar groups in the side alkyl chain does not have pronounced effect on cucumber, as it was shown for other plant species.

Effects of imidazolium-based ionic liquids with different anions on wheat seedlings

The effects of five imidazolium ionic liquids with different anions were studied in hydroponically grown wheat seedlings at concentrations of 50, 100, 150, 200, 250, and 300 mg L^-1. The results showed that shoots and roots grew shorter and dry weight decreased with increasing concentrations of ionic liquids. Moreover, the antioxidant enzyme activities decreased and malondialdehyde (MDA) content was greater in the leaves of wheat seedlings subjected to ionic liquid (IL) treatments. The order of influence of ionic liquids on these indexes was [C₄mim][TfO]> [C₄mim][Cl]> [C₄mim][BF₄]> [C₄mim][Lact]> [C₄mim][Ala]. A transmission electron microscope (TEM) was used to observe leaf and root cellular structures, such as chloroplast, nucleus, mitochondria, and rough endoplasmic reticulum, in wheat exposed to ionic liquids at a concentration of 150 mg L^-1. The results showed that the cellular structures of wheat were affected, and the degree of the effect of five ILs was consistent with the general trend of the measured indexes in this study. Ionic liquids influence the growth of plants by impeding growth, disrupting metabolic physiology and changing cellular structures. The degree of toxicity of imidazolium-based ionic liquids with different anions varies.

The effect of imidazolium based ionic liquids on wheat and barley germination and growth: Influence of length and oxygen functionalization of alkyl side chain

In this work five different imidazolium based ionic liquids, namely: 1-(2-oxybutyl)-3-methylimidazolium chloride, [C₂OC₂mIm][Cl]; 1-(2-oxypropyl)-3-methylimidazolium chloride, [C₁OC₂mIm][Cl]; 1-(3-hydroxypropyl)-3-ethylimidazolium chloride, [OHC₃eIm][Cl]; 1-(3-hydroxypropyl)-3-methylimidazolium chloride, [OHC₃mIm][Cl]; 1-(2-hydroxyethyl)-3-methylimidazolium chloride, [OHC₂mIm][Cl], together with commercial 1-butyl-3-methylimidazolium chloride, [bmim][Cl] and synthesized protic imidazolium chloride, [Im][Cl], were prepared and their toxicity examined towards wheat and barley germination and growth. Introduction of the polar groups (in the form of hydroxyde and/or ether group) in the alkyl side chain of the imidazolium cation and their influence on the reduction of the ionic liquid's toxicity is demonstrated. The results indicate that toxicity of oxygen functionalized ILs is significantly lower against wheat comparing to non-functionalized analogues. In the case of barley, influence on germination follow the same trend as in the case of wheat, but for seedlings growth different trend is observed with more pronounced toxicity of ether functionalized ILs. From these results it was also shown that alkylation in the position N-3 atom of the imidazole significantly reduces toxicity of cation.

Comparison of the effect of ionic liquids containing hexafluorophosphate and trifluoroacetate anions on the inhibition of growth and oxidative stress in spring barley and common radish

Ionic liquids are a group of chemical compounds with chemical properties that are of great interest to various fields of science and industry. However, commercial use of these substances raises concern because they may threaten the natural ecosystems. The present study used 2 types of (-)-menthol-containing imidazolium chiral ionic liquids: 1-[(1R,2S,5R)-(-)-menthoxymethyl]-3-methylimidazolium hexafluorophosphate [Im-Men][PF₆ ] and 1-[(1R,2S,5R)-(-)-menthoxymethyl]-3-methylimidazolium trifluoroacetate [Im-Men][CF₃ CO₂ ]. The effects of these compounds on growth and development of spring barley (Hordeum vulgare) and common radish (Raphanus sativus L. subvar. radicula Pers.) were investigated. The present study demonstrated that chiral ionic liquids produced a relatively high phytotoxicity, by shortening the plants' lengths and roots, thus causing a decline in the experimental plants' fresh weights. The investigated ionic liquids also led to a reduction in photosynthetic pigment levels, changes in hydrogen peroxide and malondialdehyde content, and changes in the activities of superoxide dismutase, catalase, and peroxidase in both plants. Changes in these enzymes were used to indicate oxidative stress levels in spring barley and common radish. It was demonstrated that imidazolium ionic liquid-induced phytotoxicity depended largely on the type of anion. The liquid [Im-Men][PF₆ ] exhibited higher toxicity toward spring barley and common radish seedlings. Common radish was more resistant to chiral ionic liquids. Environ Toxicol Chem 2017;36:2167-2177. © 2017 SETAC.

Role of cation structure in the phytotoxicity of ionic liquids: growth inhibition and oxidative stress in spring barley and common radish

The present study determines the influence of three ionic liquids (ILs) containing cations with diversified structure on the growth and development of spring barley seedlings and common radish leaves. Increasing amounts of 1-butyl-1-methylpyrrolidinium hexafluorophosphate [Pyrrol][PF₆], 1-butyl-1-methylpiperidinium hexafluorophosphate [Piper][PF₆], and 1-butyl-4-methylpyridinium hexafluorophosphate [Pyrid][PF₆] were added to the soil on which both plants were cultivated. The results of this studies showed that the applied ILs were highly toxic for plants, demonstrated by the inhibition of length of plant shoots and roots, decrease of fresh mass, and increase of dry weight content. Common radish turned out to be the plant with higher resistance to the used ILs. The differences in the cation structure did not influence phytotoxity of ILs for spring barley. Furthermore, all ILs led to a decrease of photosynthetic pigments, which was directly followed by decreased primary production in plants. Oxidative stress in plants occurred due to the presence of ILs in the soil, which was demonstrated by the increase of malondialdehyde (MDA) content, changes in the H₂O₂ level, and antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). The changes in the chlorophyll contents and the increase of POD activity turned out to be the most significant oxidative stress biomarkers in spring barley and common radish. Both spring barley and radish exposed to ILs accumulated a large amount of fluoride ion.

Reaction of Spring Barley and Common Radish on the Introduction of Ionic Liquids Containing Asymmetric Cations to the Soil

The harmful effect of ionic liquids (ILs) on the environment is one of the important elements of scientific research conducted around the world. This study presents the effect of ionic liquids, containing the asymmetric cations benzyltrimethylammonium chloride [BenzTMA][Cl] and benzyltriethylammonium chloride [BenzTEA][Cl], on physiological and biochemical changes in common radish plants and spring barley seedlings. The examined ILs demonstrated low toxicity to higher plants. The compound that exhibited higher phytotoxicity to these plant species was [BenzTMA][Cl], whereas the plant that was more resistant to such ILs was common radish. Both the ionic liquids, particularly at higher concentrations, led to changes in the metabolism of plants, which resulted in a decrease of chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids content. The observed changes were positively correlated with increasing concentrations of the examined ILs in the soil. In the case of spring barley, a decrease in the fresh weight and an increase in the dry weight of the seedlings were also observed. The evidence of oxidative stress occurrence in spring barley was observed due to the accumulation of malondialdehyde and free proline, as well as due to an increase in the activity of catalase and peroxidase. The changes in these biomarkers indicating oxidative stress occurrence in common radish plants were much lower. An increase in the content of chloride ions was observed in both the plants.

Growth inhibition and efficiency of the antioxidant system in spring barley and common radish grown on soil polluted ionic liquids with iodide anions

Ionic liquids (ILs) constitute a huge group of substances that are increasingly common in the commercial use. This situation may lead to the contamination of the soil environment which being the basic of plants vegetation. This paper presents the effect of four ILs with I^- anion on the growth and development of spring barley (Hordeum vulgare) and common radish (Raphanus sativus L. subvar. radicula Pers) and changes in metabolism of the plants. Seedlings of spring barley and common radish cultivated on soil with increasing ILs concentration exhibited typical phytotoxicity symptoms. A considerable reduction of shoot and root lengths, decrease of fresh weight (FW) and increase of dry weight (DW) occurred in both test plants. Ionic liquids concentration increase in soil was correlated with the decrease of concentrations of all photosynthetic pigments in the plants. The observed increase of malondialdehyde (MDA) concentration and changes in the H₂O₂ level indicated presence of oxidative stress in spring barley and common radish, which usually led to the increase of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activity. The most reliable biomarker of oxidative stress was chlorophyll level and changes in POD activity.

The effect of the number of alkyl substituents on imidazolium ionic liquids phytotoxicity and oxidative stress in spring barley and common radish seedlings

Increasing amounts of two ILs: 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF₆] and 1-butyl-2,3-dimethylimidazolium hexafluorophosphate [BMMIM][PF₆], were introduced to soil in which spring barley (Hordeum vulgare) and common radish (Raphanus sativus L. subvar. radicula Pers.) seedlings were cultivated, in order to evaluate the phytotoxicity of ionic liquids with imidazolium cation with two or three alkyl substituents attached. The results of the study i.e. the inhibition of the length of plants and their roots, as well as the yield of fresh weight of plants, clearly showed that differences in the number of substituents did not affect the toxicity of these ILs. Although, radish was more resistant to the applied ionic liquids than barley. Ionic liquids led to a decrease in the content of all assimilation pigments and induced oxidative stress in the plants, as showed by an increase in malondialdehyde (MDA) content, and changes in the level of H₂O₂ and antioxidant enzymes: superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD). The best biomarkers of oxidative stress in both plants were the changes in chlorophyll content and the increase in POD activity. Both spring barley and radish exposed to [BMIM][PF₆] and [BMMIM][PF₆] accumulated a large amount of fluoride ions, which further increased the toxicity of these compounds for both plants.

Automated cytochrome c oxidase bioassay developed for ionic liquids' toxicity assessment

A fully automated cytochrome c oxidase assay resorting to sequential injection analysis (SIA) was developed for the first time and implemented to evaluate potential toxic compounds. The bioassay was validated by evaluation of 15 ionic liquids (ILs) with distinct cationic head groups, alkyl side chains and anions. The assay was based on cytochrome c oxidase activity reduction in presence of tested compounds and quantification of inhibitor concentration required to cause 50% of enzyme activity inhibition (EC50). The obtained results demonstrated that enzyme activity was considerably inhibited by BF4 anion and ILs incorporating non-aromatic pyrrolidinium and tetrabutylphosphonium cation cores. Emim [Ac] and chol [Ac], on contrary, presented the higher EC50 values among the ILs tested. The developed automated SIA methodology is a simple and robust high-throughput screening bioassay and exhibited good repeatability in all the tested conditions (rsd<3.7%, n=10). Therefore, it is expected that due to its simplicity and low cost, the developed approach can be used as alternative to traditional screening assays for evaluation of ILs toxicity and identification of possible toxicophore structures. Additionally, the results presented in this study provide further information about ILs toxicity.

Evaluation of the effect of tetraethylammonium bromide and chloride on the growth and development of terrestrial plants

Quaternary ammonium salts (QAS), which also include ionic liquids, constitute a vast group of chemical compounds that are increasingly common in the commercial use. This situation may lead to the contamination of the natural environment and may constitute a potential threat to all its elements, including terrestrial higher plants. This paper presents the effect of tetraethylammonium chloride [TEA][Cl] and tetraethylammonium bromide [TEA][Br] on the growth and development of spring barley and common radish. The applied QAS were characterized with phytotoxicity dependent on the concentration of compound and characteristics of the study plants. Spring barley turned out to be highly susceptible plant to the analyzed compounds, which was confirmed by % inhibition of length of plants, root length and fresh weight of plants and by calculated values for EC50, NOEC as well as LOEC. On the contrary, a common radish revealed the resistance to QAS used in the study; although, phytotoxic symptoms were still observed when high concentrations of dry weight of soil were applied (1000, 3000 and 5000 mg/kg). The applied QAS caused oxidative stress symptoms, mainly in spring barley seedlings, which were manifested by decreased assimilation of pigments content, increased hydrogen peroxide (H2O2) and malondialdehyde (MDA) content in plant cells and with a changed activity of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD).

Quaternary ammonium salts with tetrafluoroborate anion: Phytotoxicity and oxidative stress in terrestrial plants

This paper discusses the impact of four quaternary ammonium salts (QAS) such as tetraethylammonium tetrafluoroborate [TEA][BF4], tetrabutylammonium tetrafluoroborate [TBA][BF4], tetrahexylammonium tetrafluoroborate [THA][BF4], and tetraoctylammonium tetrafluoroborate [TOA][BF4] on the growth and development of spring barley and common radish. Analogous tests were performed with the inorganic salt ammonium tetrafluoroborate [A][BF4] for comparison purposes. Results indicated that the phytotoxicity of the QAS applied is dependent on the concentration of the substance and their number of carbon atoms. The most toxic compound was [TBA][BF4], causing the greatest drop in fresh weight of both study plants, similar to the phytotoxic effects of [A][BF4]. All the tested compounds caused oxidative stress in spring barley and common radish seedlings due to a drop in the chlorophyll content. Stress was also observed in plants, which was indicated by the increased level of ROS (reactive oxygen species) such as H2O2 and lipid peroxidation of MDA (malondialdehyde). Due to the stress, both plants displayed changes in the activity of antioxidative enzymes such as superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD). Based on the results of the study, it was concluded that changes in chlorophyll levels and peroxidase activity are the best biomarkers to determine oxidative stress in plants.

Effects of the ionic liquid 1-hexyl-3-methylimidazolium bromide on root gravitropism in Arabidopsis seedlings

The toxic effects of ionic liquids (ILs) have attracted increasing attention in recent years. However, the knowledge about the toxic effects of ILs on tropism in organisms remains quite limited. In this study, the effects of 1-hexyl-3-methylimidazolium bromide [C6mim]Br on root gravitropism were evaluated using Arabidopsis seedlings. Our results showed that the root growth and gravity response were significantly inhibited with increasing IL concentration. [C6mim]Br treatment affected the amount and distribution pattern of amyloplasts in root cap compared with controls. The auxin distribution marked with DR5rev::VENUS was altered in IL-treated seedlings. The signal intensity and gene expression of auxin efflux carriers PIN2 and PIN3 were obviously decreased by IL stress. Moreover, as consequences in response to gravity stimulus, the asymmetric DR5 signals in control root apex were impaired by IL treatment. The predominant PIN2 signals along the lower flank of root and PIN3 polarization in columella cells were also significantly reduced in seedlings exposed to IL. Our results suggest that the ionic liquid [C6mim]Br affects the amount and distribution of amyloplasts and disturbs the deployment of PIN2 and PIN3, thus impairing auxin flows in response to gravity stimulus and causing deficient root gravitropism in Arabidopsis seedlings.

Structural effects of ionic liquids on microalgal growth inhibition and microbial degradation

In the present study, we investigated structural effects of various ionic liquids (ILs) on microalgal growth inhibition and microbial biodegradability. For this, we tested pyridinium- and pyrrolidinium-based ILs with various alkyl chain lengths and bromide anion, and compared the toxicological effects with log EC50 values of imidazolium-based IL with the same alkyl chains and anion from literature. Comparing determined EC50 values of cationic moieties with the same alkyl chain length, pyridinium-based ILs were found to be slightly more toxic towards the freshwater green alga, Pseudokirchneriella subcapitata, than a series of pyrrolidinium and imidazolium except to 1-octyl-3-methylimidazolium bromide. Concerning the biodegradation study of 12 ILs using the activated sludge microorganisms, the results showed that the pyridinium derivatives except to 1-propyl-3-methylpyridinium cation were degraded. Whereas in case of imidazolium- and pyrrolidinium-based compounds, only n-hexyl and n-octyl substituted cations were fully degraded but no significant biodegradation was observed for the short chains (three and four alkyl chains).

Phytotoxicity of imidazolium-based ILs with different anions in soil on Vicia faba seedlings and the influence of anions on toxicity

To evaluate the toxic effects of ionic liquids (ILs) in soil on plants at the molecular and cellular levels and to assess the influence of anions on IL toxicity, the toxic effects of 1-decyl-3-methylimidazolium chloride ([Demim]Cl), 1-decyl-3-methylimidazolium bromide ([Demim]Br) and 1-decyl-3-methylimidazolium nitrate ([Demim]NO3) in soil on Vicia faba (V. faba) seedlings were studied for the first time. Our results show that these ILs had little impact on the growth of V. faba seedlings at 1, 5 and 25 mg kg(-1); however, the shoot length, root length, dry weight and pigment contents of the seedlings were significantly affected at 50 mg kg(-1). Furthermore, the EC50 values for effects of [Demim]Cl, [Demim]Br and [Demim]NO3 on the shoot length, root length and dry weight induced were consistent, indicating that the anion may have little influence on IL toxicity. ROS levels were also significantly enhanced at 50 mg kg(-1), resulting in cellular lipid peroxidation, DNA damage and oxidative damage.

Biochemical toxicity and DNA damage of imidazolium-based ionic liquid with different anions in soil on Vicia faba seedlings

In the present study, the toxic effects of 1-octyl-3-methylimidazolium chloride ([Omim]Cl), 1-octyl-3-methylimidazolium bromide ([Omim]Br) and 1-octyl-3-methylimidazolium tetrafluoroborate ([Omim]BF₄) in soil on Vicia faba (V. faba) seedlings at 0, 100, 200, 400, 600 and 800 mg kg⁻¹ were assessed for the first time at the cellular and molecular level. Moreover, the toxicity of these three ionic liquids (ILs) was evaluated, and the influence of anions on the toxicity of the ILs was assessed. The results showed that even at 100 mg kg⁻¹, the growth of V. faba seedlings was inhibited after exposure to the three ILs, and the inhibitory effect was enhanced with increasing concentrations of the three ILs. The level of reactive oxygen species (ROS) was increased after exposure to the three ILs, which resulted in lipid peroxidation, DNA damage and oxidative damage in the cells of the V. faba seedlings. In addition, the anion structure could influence the toxicity of ILs, and toxicity of the three tested ILs decreased in the following order: [Omim]BF₄ > [Omim]Br > [Omim]Cl. Moreover, oxidative damage is the primary mechanism by which ILs exert toxic effects on crops, and ILs could reduce the agricultural productivity.

Environmental Application, Fate, Effects, and Concerns of Ionic Liquids: A Review

Ionic liquids (ILs) comprise mostly of organic salts with negligible vapor pressure and low flammability that are proposed as replacements for volatile solvents. ILs have been promoted as "green" solvents and widely investigated for their various applications. Although the utility of these chemicals is unquestionable, their toxic effects have attracted great attention. In order to manage their potential hazards and design environmentally benign ILs, understanding their environmental behavior, fate and effects is important. In this review, environmentally relevant issues of ILs, including their environmental application, environmental behavior and toxicity are addressed. In addition, also presented are the influence of ILs on the environmental fate and toxicity of other coexisting contaminants, important routes for designing nontoxic ILs and the techniques that might be adopted for the removal of ILs.

The phytotoxicity of ionic liquids from natural pool of (-)-menthol with tetrafluoroborate anion

Over the last several decades, ionic liquids have become a promising alternative to conventional organic solvents. Initially, ionic liquids were described as "environmentally friendly" substances. However, the results of numerous studies proved that the effects of these compounds on individual ecosystems might be adverse. The presented paper discusses the effect of ionic salts containing natural chiral substituent: (1R,2S,5R)-(-)-menthol in cation and a tetrafluoroborate anion of a general formula of [Cn-Im-Men][BF4] of implementation into the soil on the growth of spring barley and common radish in their early development stages. The obtained results showed that the greatest phytotoxicity was exhibited by ionic liquids containing substituents with the smallest possible number of carbon atoms. The further increase in the length of the chain did not increase the toxicity of these salts for terrestrial plants. Moreover, a compound with a substituent having a chain length of 11 carbon atoms was found to be non-toxic to common radish. The experiment under discussion showed also the effect of these tetrafluoroborates, used in the form of spray, on the development of common sorrel, gallant soldier and white goosefoot. The tests carried out also showed that the most toxic were the compounds with 1 and 3 carbon atoms. The phytotoxicity of tetrafluoroborates was positively correlated with the concentration of these compounds in the soil and was dependent on the genetic features of the genres and varieties of plants used in the experiment.

Effects of alkyl-imidazolium ionic liquid [Omim]Cl on the functional diversity of soil microbial communities

As low-temperature molten salts, ionic liquids (ILs) were considered to be "green" solvents and have begun to see large-scale applications in the chemical reactions, in separation processes, in electrochemistry studies, etc. In recent years, the toxicity of ILs has started to draw attention. To evaluate the effects of the ionic liquid [Omim]Cl on indigenous microbial community in soil, Biolog-ECO plate method were used with the addition of four different concentrations of [Omim]Cl after four different incubation periods (7, 14, 21, 28 days). The present results showed that the average well color development (AWCD) was strongly activated when the soil was contaminated with [Omim]Cl in the early stages of the incubation. However, the activation effect disappeared with extended incubation time. Therefore, the toxic effects of the alkyl-imidazolium ionic liquid ([Omim]Cl) on the functional diversity of soil microbial communities may be reversible. In addition, the kinetic characteristics of microorganisms that used different categories of carbon sources indicated that phenolic compounds were the main C source in the sample soil.

Discovering less toxic ionic liquids by using the Microtox® toxicity test

New Microtox® toxicity data of 16 ionic liquids of different cationic and anionic composition were determined. The ionic liquids 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate, [BMPyr(+)][TFO(-)], 1-butyl-1-methylpyrrolidinium chloride, [BMPyr(+)][Cl(-)], hydroxypropylmethylimidazolium fluoroacetate, [HOPMIM(+)][FCH2COO(-)], and hydroxypropylmethylimidazolium glycolate [HOPMIM(+)][glycolate(-)] were found to be less toxic than conventional organic solvent such as chloroform or toluene, accoding the Microtox® toxicity assays. The toxicity of pyrrolidinium cation was lower than the imidazolium and pyridinium ones. It was found that the inclusion of an hydroxyl group in the alkyl chain length of the cation also reduce the toxicity of the ionic liquid. To sum up, the Microtox® toxicity assays can be used as screening tool to easily determined the toxicity of a wide range of ionic liquids and the toxicity data obtained could allow the obtention of structure-toxicity relationships to design less toxic ionic liquids.

The genotoxic and cytotoxic effects of 1-butyl-3-methylimidazolium chloride in soil on Vicia faba seedlings

Although considered as "green" solvents, the toxic effects of ionic liquids (ILs) on organisms have been widely investigated in recent years. However, studies on the toxic effects of ILs on plants all focus on toxicity in nutrient solution. In the present paper, the toxic effects of 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) on Vicia faba seedlings in soil at 0, 500, 1500, and 2500 mg kg(-1) on day 10 were studied. The present results showed that the growth of V. faba seedlings may be seriously inhibited when the IL concentrations were higher than 500 mg kg(-1). The EC50 values for shoot length, root length, and dry weight were 3886, 2483, and 3359 mg kg(-1), respectively. In addition, [C4mim]Cl caused lipid peroxidation and DNA damage at 500 mg kg(-1) and oxidative stress at 1500 mg kg(-1), which indicated that [C4mim]Cl may have genotoxicity and cytotoxicity on V. faba seedlings. Moreover, oxidative damage may be the main toxic mechanism of ILs.

Biodegradation of ionic liquids – a critical review

The importance of biodegradation data as part of the design of safer chemicals is presented using ionic liquids (ILs) as a model study.

A comparative study of the terrestrial ecotoxicity of selected protic and aprotic ionic liquids

Ionic liquids (ILs) are a fairly new and very promising group of compounds with a vast variety of possible structures and uses. They are considered to be potentially "green", but their impact on the environment tends to be neglected or not studied enough, especially when it comes to terrestrial ecotoxicity, where there are very few studies performed to date. This work presents a comparative study of the terrestrial ecotoxicity of selected representatives of two ILs groups: a new family of protic ILs (derived from aliphatic amines and organic acids) and some frequently used aprotic ILs (substituted imidazolium and piridinium chlorides). Toxicity of the ILs towards three terrestrial plant species (Allium cepa, Lolium perenne and Raphanus sativus) and soil microorganisms involved in carbon and nitrogen transformation was analyzed. Protic ILs have shown no toxic effect in most of the tests performed. The EC50 values for aprotic ILs are various orders of magnitude lower than the ones for protic ILs in all of the tests. The most toxic ILs are the most complex ones in both of the analyzed groups. Protic ILs seem to have a potential for biodegradation in soil, while aprotic ILs exhibit inhibitory effects towards the carbon transforming microbiota. These findings indicate that protic ILs can be considered as less toxic and safer for the terrestrial environment than the aprotic ILs.

The role of the anion in the toxicity of imidazolium ionic liquids

From the environmental protection point of view, the growing interest of ionic liquids in various industrial branches has raised concerns for the toxicity assessment of these compounds. The paper discusses the effect of salts containing the shared 1-ethyl-3-methylimidazolium [EMIM] cation as coupled with five different anions: bromide [Br], nitrate [NO3], p-toluenesulfonate (tosylate) [Ts], dimethylphosphate [dMP] and methanesulfonate [MS] on the growth and development of higher land plants - spring barley and common radish. The experiment was done according to the ISO Standard 11269-2:1995 and the OECD/OCDE Guide 208/2006. As the indications of phytotoxicity, the percentage of sprouts and the level of dry and fresh plant mass were used; in addition, the visual assessment of any signs of damage to the examined plant species, such as growth inhibition and chlorotic changes, was also made. Results of our study has proved the negative impact of ILs on the tested plants and the toxic effect of imidazolium salts was dependent primarily on the applied ionic liquids concentration. The common radish revealed the higher tolerance to the imidazolium as compared to spring barley. The anion type of ionic liquid was crucial for the toxicity against common radish.

Imidiazolium based ionic liquids: effects of different anions and alkyl chains lengths on the barley seedlings

We studied the effects of five imidiazolium based ionic liquids with different anions and length of alkyl chains linked to imidazolium ring on the early development of barley (Hordeum vulgare). The inhibitory effect depends on the ionic liquids concentration and chemical structure, whereby the most toxic one was [C10mim][Br], followed by [C7mim][Br], [C4mim][Br], [C4mim][CH3CO2] and [C4mim][BF4]. Both anion and cation structures affected the toxicity of ionic liquid indicating that selection of more biocompatible anions such as [CH3CO2] does not necessarily indicate lower toxicity. Alternation in the extent of oxidative stress and antioxidant enzymes activities were found in barley plants due to ionic liquid treatments. When seedlings were exposed to higher concentrations of ionic liquids, antioxidant system could not effectively remove reactive oxidative species, leading to lipid peroxidation and damage of the photosynthetic system. However, overall data indicated that the performance of barley seedling was improved when all measured enzymes involved in scavenging of reactive oxygen species (ROS) were increased with special emphasis on GPX activities. Since there are no studies about ionic liquid (IL) toxicity in plants, that simultaneously evaluates the antioxidative enzyme system in response to different ILs, this work is valuable for gaining knowledge about the protection mechanism of plants from oxidative stress caused by IL exposure.

Intrinsically green iron oxide nanoparticles? From synthesis via (eco-)toxicology to scenario modelling

Iron oxide nanoparticles (IONP) are currently being studied as green magnet resonance imaging (MRI) contrast agents. They are also used in huge quantities for environmental remediation and water treatment purposes, although very little is known on the consequences of such applications for organisms and ecosystems. In order to address these questions, we synthesised polyvinylpyrrolidone-coated IONP, characterised the particle dispersion in various media and investigated the consequences of an IONP exposure using an array of biochemical and biological assays. Several theoretical approaches complemented the measurements. In aqueous dispersion IONP had an average hydrodynamic diameter of 25 nm and were stable over six days in most test media, which could also be predicted by stability modelling. The particles were tested in concentrations of up to 100 mg Fe per L. The activity of the enzymes glutathione reductase and acetylcholine esterase was not affected, nor were proliferation, morphology or vitality of mammalian OLN-93 cells although exposure of the cells to 100 mg Fe per L increased the cellular iron content substantially. Only at this concentration, acute toxicity tests with the freshwater flea Daphnia magna revealed slightly, yet insignificantly increased mortality. Two fundamentally different bacterial assays, anaerobic activated sludge bacteria inhibition and a modified sediment contact test with Arthrobacter globiformis, both rendered results contrary to the other assays: at the lowest test concentration (1 mg Fe per L), IONP caused a pronounced inhibition whereas higher concentrations were not effective or even stimulating. Preliminary and prospective risk assessment was exemplified by comparing the application of IONP with gadolinium-based nanoparticles as MRI contrast agents. Predicted environmental concentrations were modelled in two different scenarios, showing that IONP could reduce the environmental exposure of toxic Gd-based particles by more than 50%. Application of the Swiss "Precautionary Matrix for Synthetic Nanomaterials" rendered a low precautionary need for using our IONP as MRI agents and a higher one when using them for remediation or water treatment. Since IONP and (considerably more reactive) zerovalent iron nanoparticles are being used in huge quantities for environmental remediation purposes, it has to be ascertained that these particles pose no risk to either human health or to the environment.

Terrestrial ecotoxicity of short aliphatic protic ionic liquids

A study of the ecotoxicity of different short aliphatic protic ionic liquids (PILs) on terrestrial organisms was conducted. Tests performed within the present study include those assessing the effects of PILs on soil microbial functions (carbon and nitrogen mineralization) and terrestrial plants. The results show that the nominal lowest-observed-adverse-effect concentration (LOAEC) values were 5,000 mg/kg (dry soil) for the plant test in two species (Lolium perenne, Allium cepa), 1,000 mg/kg (dry soil) for the plant test in one species (Raphanus sativus), and 10,000 mg/kg (dry soil) for carbon and nitrogen microbial transformation tests (all concentrations are nominal). Most of the median effective concentration values (EC50) were above 1,000 mg/kg (dry soil). Based on the obtained results, these compounds can be described as nontoxic for soil microbiota and the analyzed plants, and potentially biodegradable in soils, as can be deduced from the respirometric experiment. The toxicity rises with the increase of complexity of the PILs molecule (branch and length of aliphatic chain) among the three PILs analyzed.

Ionic liquids: a pathway to environmental acceptability

Ionic liquids were initially proposed as replacements for conventional organic solvents; however, their chemistry has developed remarkably and offers unexpected opportunities in numerous fields, ranging from electrochemistry to biology. As a consequence of ionic liquids advancing towards potential and actual applications, a comprehensive determination of their environmental, health and safety impact is now required. This critical review aims to present an overview of the current understanding of the toxicity and environmental impact of the principal ionic liquid groups, and highlights some emerging concerns. Each cation type is considered separately, examining the significance of the biological data, and identifying the most critical questions, some yet unresolved. The need for more, and more detailed, studies is highlighted (176 references).

Impact of ionic liquids in environment and humans: An overview

Ionic liquids enclose a large number of molecular structures consisting of a cation and an anion. Their physical state and their chemical properties can be tuned by different combination of the ions and a large number of ionic liquids have already been reported. Toxicity of ionic liquids is a subject of great importance concerning their likely use as greener solvents and new materials for a broad number of potential applications. This review provides relevant toxicological data published so far about this topic and includes a large range of ionic liquids based on different cations (imidazolium, pyridinium, pyrrolidinium, quaternary ammonium, quaternary phosphonium and guanidinium) and anions (halogens-Br, Cl, bis (trifluoromethyl)sulfonylamide, tetrafluoroborate, hexafluorophosphate, dicyanamide, acesulfame and saccharin, amongst others). In general, toxicity of ionic liquids depends on both ions and the effect of the cation alkyl chain length is very pronounced although the type of anion also exerts impact on the overall toxicity.

Accelerating the discovery of biocompatible ionic liquids

High throughput screening is the first stage of determining the ecotoxicity of ionic liquids. The available methods are reviewed, and a critical analysis of the problems and pitfalls is presented.

Environmental fate and toxicity of ionic liquids: a review

Ionic liquids (ILs) are organic salts with low melting point that are being considered as green replacements for industrial volatile organic compounds. The reputation of these solvents as "environmental friendly" chemicals is based primarily on their negligible vapor pressure. Nonetheless, the solubility of ILs in water and a number of literature documenting toxicity of ILs to aquatic organisms highlight a real cause for concern. The knowledge of ILs behavior in the terrestrial environment, which includes microbial degradation, sorption and desorption, is equally important since both soil and aquatic milieu are possible recipients of IL contamination. This article reviews the achievements and current status of environmental risk assessment of ILs, and hopefully provides insights into this research frontier.