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

Toward revealing the role of the cation in the phytotoxicity of the betaine-based esterquats comprising dicamba herbicide

In this study, two homologous series of esterquats comprising alkyl (from ethyl to octadecyl) betainate cations and bromide as well as dicamba anions were successfully synthesized, starting from a renewable raw material - glycine betaine. Due to the favorable octanol-water partition coefficient and utilization of biodegradable cations of natural origin, synthesized esterquats can be considered promising alternatives to currently applied dicamba-based formulations. In addition, the obtained results allowed us to verify whether the organic cations in quaternary ammonium salts containing herbicidally active anions (such as dicamba) play the role of biologically inactive adjuvants that only enhance the efficiency of the active ingredient or if they simultaneously exhibit a significant degree of phytotoxicity. Analysis of the influence of alkyl betainate esterquats containing nonherbicidal (bromide) anions on seedlings of white mustard revealed that alkyl betainate cations promote the germination of white mustard seeds; however, the subsequent growth of the seedlings was significantly inhibited. Further studies performed on white mustard and cornflower plants in a stage of 4-6 leaves allowed us to conclude that in the case of sensitive plants, the high phytotoxicity can be attributed to the presence of the dicamba anion, whereas for more resistant plants the additional influence of the cation on the phytotoxic effect is visible. Esterquats comprising a dodecyl substituent or longer had high surface active properties. Nonetheless, their contact angle values were not correlated with phytotoxicity data, indicating an additional influence of the cation on this stage of plant development. Interestingly, subsequent dose-response experiments conducted for two selected dicamba-based products confirmed that the greatest phytotoxicity was expressed by compounds containing a decyl substituent.

Effects of pyridinium-based ionic liquids with different alkyl chain lengths on the growth of maize seedlings

The effects of four water-soluble pyridinium-based ionic liquids (ILs) differing in alkyl side chain length, namely, N-ethyl pyridinium bromide ([EPy]Br), N-butyl pyridinium bromide ([BPy]Br), N-hexyl pyridinium bromide ([HPy]Br), and N-octyl pyridinium bromide ([OPy]Br), on the growth of maize seedlings were investigated for the first time. The results revealed that the phytotoxicity of these ILs was significantly correlated with their concentration and alkyl side chain length. The 8-day 50% inhibition values indicated that the toxicity increased as the length of the alkyl chain increased: [EPy]Br < [BPy]Br < [HPy]Br < [OPy]Br. In addition, root growth was found to be more sensitive to ILs than stem growth. In response to exposure to ILs of increasing concentration, we observed different trends in the pigment contents and specific antioxidant enzyme activities in maize seedlings, whereas the contents of malondialdehyde were significantly increased. In addition, RNA sequencing analysis, performed to examine the gene expression profiles of maize leaves under [HPy]Br and [OPy]Br treatments, revealed that a larger number of genes were differentially expressed in response to [OPy]Br treatment. Furthermore, pathway enrichment analysis revealed that both [HPy]Br and [OPy]Br treatments, and particularly the latter, caused a down-regulation of genes involved in photosynthesis and carbohydrate and nitrogen metabolism. Our findings thus indicate that pyridinium-based IL toxicity might be associated with oxidative stress and changes in gene expression profiles.

Mineral composition and growth of tomato and cucumber affected by imidazolium-based ionic liquids

Imidazolium-based ionic liquids (ILs) have unique and tunable features with high potential in industrial use. However, the utilization of the ILs in industrial processes has recently arisen the question of their disposal and the effect on the environment. Therefore, in the present study, we investigated the effect of two commercial imidazolium-based ILs, 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) and 1-decyl-3-methylimidazolium chloride ([Dmim][Cl]) on the growth and chemical composition of widely grown vegetables - tomato and cucumber. Different concentrations (10, 100 or 1000 mg L^-1) of [Bmim][Cl] and [Dmim][Cl] were applied to the soil on which tomato was cultivated. After the harvest of tomato fruits, the same soil was used to grow and analyze the growth and chemical composition of cucumber. ILs significantly reduced shoot biomass and yield of tomato and significantly changed concentrations of N, K, Ca, Fe and Mn in the leaves, whereas concentrations of P, Cu and Zn were at the level of respected controls. The number of fruits of cucumber, grown on the soil previously treated with ILs, was significantly reduced along with yield, and mineral composition of leaves was significantly altered, with the exception to Cu. [Dmim][Cl] in general affected both tomato and cucumber more than [Bmim][Cl]. The application of IL with a longer alkyl substituent ([Dmim][Cl]) increased the temperature inside the tomato canopy and accelerated the senescence of plants.

Evaluating the hazardous impact of ionic liquids - Challenges and opportunities

Ionic liquids (ILs), being related to the design of new environmentally friendly solvents, are widely considered for applications within the "green chemistry" concept. Due to their unique properties and wide diversity, ILs allow tailoring new separation procedures and producing new materials for advanced applications. However, despite the promising technical performance, environmental concerns highlighted in recent studies focused on the toxicity and biodegradability of ILs and their metabolites have revealed that ILs safety labels are not as benign as previously claimed. This review refers to the fundamentals about the properties and applications of ILs also in the context of their potential environmental effect. Toxicological issues and harmful effects related to the use of ILs are discussed, including the evaluation of their biodegradability and ecological impact on diverse organisms and ecosystems, also with respect to bacteria, fungi, and cell cultures. In addition, this review covers the tools used to assess the toxicity of ILs, including the predictive computational models and the results of studies involving cell membrane models and molecular simulations. Summing up the knowledge available so far, there are still no reliable criteria for unequivocal attribution of toxicity and environmental impact credentials for ILs, which is a challenging research task.

Phytotoxicity and Effect of Ionic Liquids on Antioxidant Parameters in Spring Barley Seedlings: The Impact of Exposure Time

The influence of the ionic liquids (ILs) tetrabutylammonium bromide [TBA][Br], 1-butyl-3-methylimidazole bromide [BMIM][Br], and tetrabutylphosphonium bromide [TBP][Br] added at different concentrations to the soil were studied for the growth and development of spring barley seedlings. Samples were harvested at three different time points: day 7, 14, and 21 after addition of ILs. The results show that [TBP][Br] was the most toxic. The introduction of this IL at the dose of 100 mg kg−1 of soil DM decreased the growth of seedlings at all test dates. The addition of the studied ILs to the soil in higher doses resulted in an increase in peroxidase and catalase activity, which may indicate the occurrence of oxidative stress in plants. An increase in the content of plant dry matter weight, contents of H2O2 and proline and a decrease in the content of photosynthetic pigments in barley seedlings were also observed. The malondialdehyde content and superoxide dismutase activity fluctuated randomly during the experiment. As a result, it was found that the phytotoxicity of ILs and the magnitude of oxidative stress in seedlings depended more on the added doses of these compounds than on the measurement date.

The reaction of cucumber to the introduction of ionic liquids into the soil

This paper presents the influence of two bromides, tetrabutylammonium and tetrabutylphosphonium, on the growth and development of cucumber seedlings. The tests were performed at two dates, i.e. 10 and 20 days, after the introduction of increasing amounts of ionic liquids (ILs) into the soil. The applied ILs showed phytotoxicity dependent mainly on the concentration of the substance, which is proved by the inhibition of the length of aboveground parts and their roots and the yield of cucumber fresh mass, from which EC50 values were calculated. The phytotoxicity symptoms were the result of oxidative stress, one of the manifestations of which was a decrease in assimilative pigments, linearly correlated with an increase in bromide concentration in the medium. The stress is also proven by the large increase in hydrogen peroxide, malondialdehyde and free proline in cucumber leaves. The reaction of this plant to oxidative stress was an increase in the activity of antioxidative enzymes such as catalase and peroxidase. As a result of statistical analysis, it was proved that all changes of biomarkers of phytotoxicity of examined ILs and oxidative stress indicators in cucumber seedlings depended more on the applied concentration of these salts than on the date of the study.

The effect of polar head group of dodecyl surfactants on the growth of wheat and cucumber

The increasing application of various surfactants nowadays, may lead to the contamination of the natural environment and represent potential threat to terrestrial higher plants. In this article, the effect of 13 surfactants, with dodecyl alkyl chain and various aromatic (imidazolium, pyridinium, thiazolium) and aliphatic (guanidinium, ammonium, thiosemicarbazidium) polar heads, on germination, development and growth of wheat and cucumber was investigated. The study aimed to prove how changes in lipophilicity of surfactants and their various structural modifications (existence of the aliphatic or aromatic polar group, the introduction of oxygen and sulfur) influence toxicity towards investigated plants. The calculated lipophilic parameter (AlogP) is shown to be a useful parameter for predicting potential toxicity of the compound. The strategy of using surfactants with aliphatic polar heads instead of aromatic prove to be a promising strategy in reducing harmful effect, as well as the introduction of polar groups in the structure of cation. From all investigated compounds, surfactants with imidazolium polar head displayed the most harmful effect towards wheat and cucumber. The cucumber seeds were more sensitive to the addition of surfactants comparing to wheat. All obtained experimental results were additionally investigated using computational methods, simulating the transport of surfactants through a lipid bilayer. The influence of cation tendency to fit in lipid bilayer structure was correlated with toxicity. For the first time, it is concluded that cation ability to mimic the structure of bilayer have less harmful effect on plant development.

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.