Stephanie Steudte

Ionic liquids as lubricants or lubrication additives: An ecotoxicity and biodegradability assessment

This paper reports on the (eco)toxicity and biodegradability of ionic liquids considered for application as lubricants or lubrication additives. Ammonium- and pyrrolidinium-based cations combined with methylsulphate, methylsulphonate and/or (CF(3)SO(2))(2)N(-) anions were investigated in tests to determine their aquatic toxicity using water fleas Daphnia magna, green algae Selenastrum capricornutum and marine bacteria (Vibrio fischeri). Additional test systems with an isolated enzyme (acetylcholinesterase) and isolated leukaemia cells from rats (IPC-81) were used to assess the biological activity of the ionic liquids. These compounds generally exhibit low acute toxicity and biological activity. Their biodegradability was screened according to OECD test procedures 301 B and 301 F. For choline and methoxy-choline ionic liquids ready biodegradability was observed within 5 or 10 d, respectively. Some of the compounds selected have a considerable potential to contribute to the development of more sustainable products and processes.

The Biodegradation of Ionic Liquids : the View from a Chemical Structure Perspective

The idea of green or sustainable chemistry is to develop highly efficient technical processes and applications using chemicals with a reduced or zero hazard potential for man and the environment. This approach is perfectly applicable to ionic liquids (ILs). These substances have potential applications in different fields (economic interests), and so far millions of possible structures have been de- signed, thousands of which have actually been produced, providing a broad base for the structural design of ILs with optimal technologi- cal properties and at the same time posing a reduced hazard to humans and the environment. In parallel with the rapidly growing (eco) toxicological knowledge regarding ILs, the available data regarding their biodegradability are also increasing. The following sections in- troduce the reader to biodegradation test procedures and present an overview of existing aerobic and anaerobic biodegradation data con- cerning ILs. Besides pure biodegradation kinetics, this discussion covers data on biological degradation products (metabolites) and abi- otic degradation processes. Throughout this review special emphasis will be placed on structure-biodegradability relationships and the question whether the 10 th principle of Green Chemistry, namely, Design chemicals and products to degrade after use: design chemical products to break down to innocuous substances after use so that they do not accumulate in the environment, is or is not fulfilled for some IL structures. The discussion of this data should help to improve the future design of inherently safer ILs, thereby reducing the risks they may pose to humans and the environment.

Biodegradability of 27 pyrrolidinium, morpholinium, piperidinium, imidazolium and pyridinium ionic liquid cations under aerobic conditions

The chemical and thermal stability of ionic liquids (ILs) makes them interesting for a large variety of applications in nearly all areas of the chemical industry. However, this stability is often reflected in their recalcitrance towards biodegradation, which comes with the risk of persistence when they are released into the environment. In this study we carried out a systematic investigation of the biodegradability of pyrrolidinium, morpholinium, piperidinium, imidazolium and pyridinium-based IL cations substituted with different alkyl or functionalised side chains and using halide counterions. We examined their primary degradability by specific analysis and/or their ultimate biodegradability using biochemical oxygen demand tests according to OECD guideline 301F. Biological transformation products were investigated using mass spectrometry. A comparison of the biodegradation potential of these ILs shows that for all five head groups, representatives can be found that are readily or inherently biodegradable, thus permitting the structural design of ILs with a reduced environmental hazard.

Synthesis, toxicity, biodegradability and physicochemical properties of 4-benzyl-4-methylmorpholinium-based ionic liquids

A series of 4-benzyl-4-methylmorpholinium salts have been synthesized producing morpholinium ionic liquids with inorganic (chloride, nitrate, tetrafluoroborate, hydrogen sulphate) and organic (formate, acetate, methoxyacetate, 2-(2-methoxyethoxy)acetate, hexanoate, octanoate, dodecyl sulphate, 2-ethylbutyrate, lactate, crotonate, maleate, salicylate, saccharinate) anions. Their physicochemical properties, cytotoxicity to the promyelocytic leukaemia rat cell line IPC-81, oral toxicity and biodegradability were determined. The anion significantly determined the state of aggregation and cytotoxicity. The results enabled 4-benzyl-4-methylmorpholinium ionic liquids to be classified as being of moderate or low toxicity (EC50 between 0.15 and 14.13 mM). The acute toxicity for 4-benzyl-4-ethylmorpholinium acetate is between 300–2000 mg kg−1b.w. in female rats. The activity of these morpholinium salts against bacteria and fungi was very low. It was found that new 4-benzyl-4-methylmorpholinium-based ionic liquids with anions commonly used for dissolving cellulose, such as formate or acetate, can also be used as new biomass solvents.

Aquatic toxicity of four veterinary drugs commonly applied in fish farming and animal husbandry.

Doramectin (DOR), metronidazole (MET), florfenicol (FLO), and oxytetracycline (OXT) are among the most widely used veterinary drugs in animal husbandry or in aquaculture. Contamination of the environment by these pharmaceuticals has given cause for concern in recent years. Even though their toxicity has been thoroughly analyzed, knowledge of their ecotoxicity is still limited. We investigated their aquatic toxicity using tests with marine bacteria (Vibrio fischeri), green algae (Scenedesmus vacuolatus), duckweed (Lemna minor) and crustaceans (Daphnia magna). All the ecotoxicological tests were supported by chemical analyses to confirm the exposure concentrations of the pharmaceuticals used in the toxicity experiments, since deviations from the nominal concentration can result in underestimation of biological effects. It was found that OXT and FLO have a stronger adverse effect on duckweed (EC50=3.26 and 2.96mgL(-1) respectively) and green algae (EC50=40.4 and 18.0mgL(-1)) than on bacteria (EC50=108 and 29.4mgL(-1)) and crustaceans (EC50=114 and 337mgL(-1)), whereas MET did not exhibit any adverse effect in the tested concentration range. For DOR a very low EC50 of 6.37×10(-5)mgL(-1) towards D. magna was determined, which is five orders of magnitude lower than values known for the toxic reference compound K2Cr2O7. Our data show the strong influence of certain veterinary drugs on aquatic organisms and contribute to a sound assessment of the environmental hazards posed by commonly used pharmaceuticals.

Toxicity and biodegradability of dicationic ionic liquids

Ionic liquids (ILs) formed by multivalent cations are generally of higher thermal and electrochemical stability, which makes them attractive for use in high-temperature applications. Whereas the influence of structural elements on the physicochemical properties of dicationic ILs (DILs) is well established, such systematic investigations on their ecotoxicity and biodegradablility are still lacking. The present study investigates the influence of the dicationic structural elements on these characteristics and addresses the question whether already established structure–activity relationships of common ILs can be applied to DILs. Therefore, a set of 10 DILs with different linkage chain length, terminal alkyl side chain length, linkage chain polarity and head groups were synthesized and studied in several biodegradation and toxicity tests. The results showed that the acute toxicity was in many cases below the levels observed for monocationic ILs. However, none of the DILs could be degraded within the performed biodegradation experiments. Hence, DILs are a potential less toxic alternative to monocationic ILs, but further work on their design is necessary.

Ecotoxicity of artificial sweeteners and stevioside.

Produced, consumed and globally released into the environment in considerable quantities, artificial sweeteners have been identified as emerging pollutants. Studies of environmental concentrations have confirmed the widespread distribution of acesulfame (ACE), cyclamate (CYC), saccharin (SAC) and sucralose (SUC) in the water cycle at levels that are among the highest known for anthropogenic trace pollutants. Their ecotoxicity, however, has yet to be investigated at a larger scale. The present study aimed to fill this knowledge gap by systematically assessing the influence of ACE, CYC and SAC and complementing the data on SUC. Therefore we examined their toxicity towards an activated sewage sludge community (30min) and applying tests with green algae Scenedesmus vacuolatus (24h), water fleas Daphnia magna (48h) and duckweed Lemna minor (7d). We also examined the effects caused by the natural sweetener stevioside. The high No Observed Effect Concentrations (NOECs) yielded by this initial evaluation indicated a low hazard and risk potential towards these aquatic organisms. For a complete risk assessment, however, several kinds of data are still lacking. In this context, obligatory ecotoxicity testing and stricter environmental regulations regarding food additives appear to be necessary.

Hydrolysis study of fluoroorganic and cyano-based ionic liquid anions – consequences for operational safety and environmental stability

The hydrolytic stability of ionic liquid anions is a key property with regard to their technical applicability and environmental stability. From a technical point of view hydrolytic processes may lead to reduced durability, diminished technical performance and reduced operational safety in that corrosive and/or toxic hydrolysis products are formed. On the other hand, susceptibility to hydrolytic processes is advantageous where environmental stability and persistency are concerned, since hydrolysis is the most important abiotic degradation pathway in the environment. We investigated the hydrolytic stability of the most common ionic liquid anions, dicyanimide [N(CN)2]−, tricyanmethanide [C(CN)3]−, tetracyanidoboranate [B(CN)4]−, bis(trifluoromethylsulphonyl)imide [(CF3SO2)2N]−, trifluorotris(pentafluoroethyl)phosphate [(C2F5)3PF3]− and 1,1,2,2-tetrafluoroethanesulphonic acid [H(C2F4)SO3]−, as a function of pH (1, 7, 9 and 13) and temperature. The results show that there was no difference in hydrolytic stability as recorded for 1-ethyl-3-methylimidazolium (IM12) or for the alkali cations. All the anions were stable under neutral and slightly basic conditions (half-lives at 25 °C ⇒1 year). In strongly acidic and basic solutions, however, B(CN)4−, (CF3SO2)2N−, (C2F5)3PF3− and H(C2F4)SO3− were hydrolytically stable, whereas N(CN)2− and C(CN)3− were not. The kinetics of hydrolysis were recorded and Arrhenius plots were generated for the latter two anions. In addition, their hydrolysis pathways and the resulting products were identified via mass spectrometry. The cytotoxicity of hydrolysed IL solutions towards the mammalian cell line IPC-81 and the identified hydrolysis products (pure compounds) was investigated for a first estimate of their toxicological properties.

Biodegradability of fluoroorganic and cyano-based ionic liquid anions under aerobic and anaerobic conditions

The present study deals with the primary biodegradability of ionic liquids in order to obtain a greater insight into their fate under different environmental conditions. The focus was thereby on the biodegradation potential of ionic liquid anions when undergoing aerobic and anaerobic biological waste water treatment. Five technologically relevant fluoroorganic and cyano-based ionic liquid anions were investigated as alkaline salts (Li (CF3SO2)2N, K (C2F5)3PF3 and Na N(CN)2, K C(CN)3, K B(CN)4 respectively). Their biodegradability was determined in activated sludge over a period of around 60 days by specific analysis of the anion using ion chromatography. Additionally, the antimicrobial activity of the test compounds towards the activated sludge organisms was tested in inhibition studies. Because of the technologically desirable chemical, thermal and electrochemical stability of these anions, their biodegradability is questioned. The results seem to support the hypothesis: although the concentrations used did not inhibit the inoculum, none of these anions could be biodegraded under either aerobic or denitrifying conditions. The present paper provides information concerning the biodegradability of ionic liquids in waste water treatment plants and gives a first systematic view of the aerobic and anaerobic biodegradability of fluoroorganic and cyano-based ionic liquid anions and therefore supports further hazard assessment.

Ionic liquid long-term stability assessment and its contribution to toxicity and biodegradation study of untreated and altered ionic liquids

In contrast to well understood degradation mechanisms in conventional lubricants generally promoted by thermo-oxidative stress, the degradation of ionic liquids is widely unknown although they are considered as promising novel types of lubricants. Hence, the ionic liquid long-term stability has been evaluated by small scale artificial alteration experiments under thermo-oxidative conditions. The ionic liquid selection was based on non-functionalized and functionalized ammonium type cations with three different counter anions. The identification of ionic liquid degradation products accomplished by high end mass spectrometric methods, namely time-of-flight/reflectron time-of-flight mass spectrometry and linear quadrupole trap-orbitrap-mass spectrometry, revealed that ionic liquids which were composed of functionalized cation moieties were prone to degradation. Furthermore, the amounts of the most abundant degradation product formed under various artificial alteration conditions have been quantified by ultra high pressure liquid chromatography coupled to electrospray ionization linear quadrupole ion trap orbitrap mass spectrometry, suggesting that the ionic liquid degradation preferably takes place at higher temperatures after a longer period of time. The proposed degradation mechanism requires the presence of nucleophilic species such as methanesulphonate anion. The (eco)toxicological impact of the selected ionic liquids have been evaluated by comprehensive toxicity studies and biodegradation experiments. As the evaluation of selected ionic liquids revealed contrary assessments from stability and (eco)toxicological studies, the need for mutual and complementary consideration of the ionic liquids for a successful implementation of ionic liquid lubricants has been disclosed.