Growth inhibition and effect on photosystem by three imidazolium chloride ionic liquids in rice seedlings

Intergenerational toxic effects of parental exposure to [Cn mim]NO3 (n = 2,4,6) on nervous and skeletal development in zebrafish offspring

Ionic liquids (ILs) are thought to have negative effects on human health. Researchers have explored the effects of ILs on zebrafish development during the early stages, but the intergenerational toxicity of ILs on zebrafish development has rarely been reported. Herein, parental zebrafish were exposed to different concentrations (0, 12.5, 25, and 50 mg/L) of [Cn mim]NO3 (n = 2, 4, 6) for 1 week. Subsequently, the F1 offspring were cultured in clean water for 96 h. [Cn mim]NO3 (n = 2, 4, 6) exposure inhibited spermatogenesis and oogenesis in F0 adults, even causing obvious lacunae in the testis and atretic follicle oocytes in ovary. After parental exposure to [Cn mim]NO3 (n = 2, 4, 6), the body length and locomotor behavior were measured in F1 larvae at 96 hours post-fertilization (hpf). The results showed that the higher the concentration of [Cn mim]NO3 (n = 2, 4, 6), the shorter the body length and swimming distance, and the longer the immobility time. Besides, a longer alkyl chain length of [Cn mim]NO3 had a more negative effect on body length and locomotor behavior. RNA-seq analysis revealed several downregulated differentially expressed genes (DEGs)-grin1b, prss1, gria3a, and gria4a-enriched in neurodevelopment-related pathways, particularly the pathway for neuroactive ligand-receptor interaction. Moreover, several upregulated DEGs, namely col1a1a, col1a1b, and acta2, were mainly associated with skeletal development. Expression of DEGs was tested by RT-qPCR, and the outcomes were consistent with those obtained from RNA-Seq. We provide evidence showing the effects of parental exposure to ILs on the regulation of nervous and skeletal development in F1 offspring, demonstrating intergenerational effects.

Ionic Liquids as Environmental Pollutants-Analysis of the Effect of Tetrabutylammonium Chloride on the Growth and Development of Wheat and Cucumber

Ionic liquids are a huge group of chemical compounds that have found, or may, in the future, find, applications in various industries. These compounds are characterized by excellent physical, chemical, and biological properties, but a big problem is their environmental impact. One of the representatives of this group of compounds is tetrabutylammonium chloride ([TBA][Cl]). In this present study, the effects of [TBA][Cl] were evaluated on two popular plant species-a monocotyledonous plant-wheat (Triticum aestivum L.) and a dicotyledonous plant-cucumber (Cucumis sativus L.). The results showed that the compound caused a pronounced inhibition of plant growth and roots, as well as plant fresh weight yield. An increase in plant dry weight was observed at the same time. Despite the decrease in the content of photosynthetic pigments, no major changes were observed in chlorophyll fluorescence. All observed changes were strongly related to the applied concentration of the compound.

Effects of [Cnpy]Br (n=3,5) on the growth and physiology of rape seedlings

1-Alkylpyridinium bromide [C_npy]Br is a common intermediate in chemical synthesis. With the discharge of industrial wastewater, it enters the environment and is toxic to plants. In this study, the impacts of two pyridine-based ionic liquids (ILs), [C₃py]Br and [C₅py]Br, on the growth and physiology of rape seedlings were investigated at concentrations of 10, 50, 100, 200, 300, and 400 mg/L. Within the concentration range (10-400 mg/L) of [C₃py]Br and [C₅py]Br treatment, the root length, plant height, activities of antioxidant enzymes (SOD, POD, and CAT), and the contents of Chla and Chlb showed an increase at low concentrations and a decrease at high concentrations. [C₃py]Br and [C₅py]Br increased MDA content in rape seedlings leaves in a concentration-dependent manner. It was also found that [C₅py]Br was more toxic to rape seedlings than [C₃py]Br. The toxicity of pyridine ILs such as [C₃py]Br and [C₅py]Br to plants should be highly concerned.

Salinity fluctuation influences the toxicity of 1-octyl-3-methylimidazolium chloride ([C8mim]Cl) to a marine diatom Phaeodactylum tricornutum

In this work, a marine diatom (Phaeodactylum tricornutum) was exposed to 1-octyl-3-methylimidazolium chloride ([C₈mim]Cl) for 96 h at three different salinities (25, 35, and 45 ‰) for investigating their interactive effects. Results showed that values of EC₁₀ and EC₅₀ at 96 h of exposure were 0.29, 1.06, 2.01 μg L^-1 and 7.21, 7.71, 7.25 mg L^-1 when the salinities were 25, 35, and 45 ‰, respectively, meaning that salinity fluctuation affected the toxicity of [C₈mim]Cl to this diatom. Changes in chlorophyll a contents and chlorophyll fluorescence parameters suggested that [C₈mim]Cl and salinity fluctuation had a significant interactive effect on the algal photosynthesis. In addition, soluble protein content and activities of antioxidant enzymes in algal cells changed significantly. Increased malondialdehyde contents indicated that the combined stresses could induce excessive production of reactive oxygen species leading to oxidative damage to the algal cells.

Comparison of the toxic effects of non-task-specific and task-specific ionic liquids on zebrafish

Ionic liquids (ILs) are composed of only anions and cations and are liquid solvents at room temperature. Different functional groups were introduced into the ILs, conferring them with specific functions or purposes and thus forming special ILs, namely task-specific ILs (TSILs). Imidazolium-based ILs are the most widely used ILs in industrial production. To date, there have been some studies on the toxic effects of ILs on different organisms. However, the effect of functionalized groups on the toxicity of ILs is still unclear. In the present study, zebrafish were used as model organisms to study the toxic effects of 1-ethyl-3-methylimidazolium nitrate ([C₂mim]NO₃) and 1-hydroxyethyl-3-methylimidazolium nitrate ([HOC₂mim]NO₃). The results showed that both promoted an increase in reactive oxygen species (ROS) contents, leading to lipid peroxidation and DNA damage. Furthermore, integrated biological response analysis showed that [HOC₂mim]NO₃ was less toxic to zebrafish than [C₂mim]NO₃, which indicated that adding functional groups decreased the toxicity of ILs to organisms. The influence of chemical structure on IL toxicity was also reported. These results could provide a scientific basis for better synthesis and utilization of ILs in the future.

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.

Biosafety-inspired structural optimization of triazolium ionic liquids based on structure-toxicity relationships

Ionic liquids (ILs), owing to their low vapor pressure and excellent solvating ability, are being increasingly applied in various industries to replace highly toxic organic solvents. They mainly pollute aquatic environment and soils, directly endangering eco-environment and human health. Therefore, it is critical to understand and optimize structural motifs of ILs with reduced toxicity. Considering human oral exposure is the major route, our investigations employed a human cell panel (modeling oral exposures) including human stomach (GES-1), intestinal (FHC), liver (HepG2) and kidney (HEK293) cells using a series of experimental and computational approaches to explore the cytotoxicity and molecular mechanism of ILs. We discovered that the cytotoxicity of triazolium and imidazolium ILs was human cell line-dependent with cytotoxicity in an order of FHC > GES-1 > HepG2 > HEK293. For this reason, a toxicity assay using a single cell line was highly inappropriate. Compared to anions (Br^-, OTs^-, OTMBS^-) we tested, the cation of ILs played a major role in causing cytotoxicity. Ionic liquids with cations having longer hydrophobic sidechains (IL09 vs. IL01) readily insert into cell membranes with enhanced membrane and lipidomic perturbations, induce cytotoxicity by triggering cell cycle arrest and apoptosis. Reducing sidechain length and incorporating three nitrogen atoms (triazolium) instead of two (imidazolium) in the cation core alleviated cytotoxicity by reducing cell membrane perturbations and cell function interference. These findings provide important guiding principles for the design of the next-generation of "green" and safe ILs.

Phytoextraction, accumulation, and toxicological effects of 1-tetradecyl-3-methylimidazolium ionic liquid in ryegrass (Lolium perenne L.)

Ionic liquids are widely used in many fields due to their extremely tunable nature and exceptional properties. The extensive application of ionic liquids raises great concerns regarding their bioaccumulation potential and adverse effects on organisms. Green plants have a great potential for uptake of persistent xenobiotics from aquatic and terrestrial environment. However, the assimilation and bioaccumulation of 1-tetradecyl-3-methylimidazolium bromide ([C₁₄mim]Br) have not been studied in plants yet. In order to explore the phytoaccumulation of [C₁₄mim]⁺, ryegrass were exposed to [C₁₄mim]Br with hydroponic experiment. The effects of [C₁₄mim]Br dosages on growth index, chlorophyll content, malondialdehyde (MDA) content, and antioxidant enzyme activity of ryegrass were investigated. The toxic effects of [C₁₄mim]Br on ryegrass growth increased with increasing initial concentration. The high initial concentration treatment resulted in rapid changes in physiological characteristics in ryegrass tissue. [C₁₄mim]⁺ ions were mainly accumulated in root tissue and partly translocated to the above ground part of ryegrass. [C₁₄mim]⁺ was observed in the highest concentration (314.35 μg/g in root and 101.42 μg/g in aboveground parts of ryegrass) with 10 mg/L of [C₁₄mim]Br. Our results demonstrated that ryegrass can uptake and accumulate [C₁₄mim]⁺ and is therefore a suitable species for phytoremediation of trace amount of [C₁₄mim]⁺ and possibly other ionic liquids.

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.

The toxicological mechanism of two typical imidazole ionic liquids in textile industry on Isatis tinctoria

Ionic liquids (ILs¹) which are called "green solvents", are used widely in the textile industry as adjuvants due to their many advantages. However, their persistent residues may cause ecotoxicity. The aim of the study is to explore the toxicity of different anions on imidazole ILs and their toxicological mechanism. For the experiments 1-butyl-3-methylimidazole tetrafloroborate ([C₄mim]BF₄) and 1- butyl -3-methylimidazolium chloride ([C₄mim]Cl) were selected to study their toxic effects on Isatis tinctoria. ILs may affect the germination rate. Fresh weight, dry weight and Hill reaction activity decreased continuously with increasing of IL concentrations, showing an effect-dose relationship. Transmission electron microscopy (TEM) revealed that cell walls were fuzzy, starch granules had accumulated and the chloroplast structure was damaged. These changes will affected the function and electron transport efficiency of photosystemⅡ. Superoxide anion accumulation stimulated the activity of antioxidant enzymes (SOD, POD, CAT) and caused lipid peroxidation as well as an increased malondialdehyde content. ILs also reduced indirubin and total flavonoids contents, which reduced the pharmacological efficacy of Isatis tinctoria. This is demonstrated by three-dimensional fluorescence chromatogram. [C₄mim]Cl was more toxic than [C₄mim]BF₄. ILs caused toxic effects to Isatis tinctoria. The ecological toxicity of ILs should be considered when using them as additives in the textile industry.

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.

Ionic Liquids-A Review of Their Toxicity to Living Organisms

Ionic liquids (ILs) were initially hailed as a green alternative to traditional solvents because of their almost non-existent vapor pressure as ecological replacement of most common volatile solvents in industrial processes for their damaging effects on the environment. It is common knowledge that they are not as green as desired, and more thought must be put into the biological consequences of their industrial use. Still, compared to the amount of research studying their physicochemical properties and potential applications in different areas, there is a scarcity of scientific papers regarding how these substances interact with different organisms. The intent of this review was to compile the information published in this area since 2015 to allow the reader to better understand how, for example, bacteria, plants, fish, etc., react to the presence of this family of liquids. In general, lipophilicity is one of the main drivers of toxicity and thus the type of cation. The anion tends to play a minor (but not negligible) role, but more research is needed since, owing to the very nature of ILs, except for the most common ones (imidazolium and ammonium-based), many of them are subject to only one or two articles.

Enantioselective effects of the fungicide metconazole on photosynthetic activity in Microcystis flos-aquae

Enantiomers of chiral fungicides usually display different toxic effects on nontarget organisms in the surrounding environment, although there are rare reports on the enantioselective toxicity of metconazole (MEZ) to aquatic organisms, such as Microcystis flos-aquae (M. flos-aquae). To explore the enantioselective toxicity of MEZ in algae, the impact of various concentrations (0.001, 0.003, 0.01, 0.03 and 0.1 mg/L) of MEZ on M. flos-aquae over 8 days was investigated. Significant differences were observed between the four enantiomers in chlorophyll a (Chl a) contents, carotenoids, photochemical efficiency (F_v/F_m), rapid light-response curves (RLCs), utilization efficiency of light energy (α) and protein contents during treatment time. MEZ can enantioselectively stimulate the chlorophyll fluorescence parameters (RLCs, F_v/F_m and α) and carotenoid and Chl a contents of M. flos-aquae, especially at low concentrations (0.001 or 0.003 mg/L). At high concentrations of 0.03 or 0.1 mg/L, the chlorophyll fluorescence parameters (RLCs, F_v/F_m and α), protein and Chl a contents of M. flos-aquae exposed to cis-enantiomers were lower than those of M. flos-aquae exposed to trans-enantiomers. These observations indicated that the enantiomers of MEZ pose different toxicities to M. flos-aquae, with the cis-enantiomers more toxic than the trans-enantiomers. These results are beneficial for understanding the enantioselective effects of MEZ enantiomers on nontarget organisms and helpful for evaluating their eco-environment risk.

Effects of ionic liquid [N4444] AOT on rice seedling growth cytomembrane damage and rhizobacteria resistance

Ionic liquids (ILs) are solvents composed of ions, containing a large asymmetric cation with an anion. With increasing and widespread applications, the toxic effects of ILs have been considerable in recent years. This study explained the effects of the new functional ionic liquids [N₄₄₄₄] bis(2-ethylhexyl) sulfonyl succinate (AOT) on rice seedling and the growth of rhizobacteria. The rice seeds pretreated by [N₄₄₄₄] AOT revealed that it exhibited a significant negative impact on rice seedlings. The inhibition of rice growth increased with increasing concentration. When the concentration of [N₄₄₄₄] AOT increased to 0.25 and 0.5 mL L^-1, the germination potential decreased by 40.0% and 86.3%, respectively, compared with the control. The germination potential and germination rate of rice were reduced, and the stress effect of ionic liquid on the root parts was higher than the aerial parts. The biomass of rice seedlings was decreased by 34.8 to 91.2%. Iodinic propane staining showed that by increasing concentration, the root cell cytomembrane damage level was increased and also changed the cell shapes, especially under 0.25 mg L^-1 concentration stress. However, rhizobacteria of rice showed strong [N₄₄₄₄] AOT-resistant characteristics when the concentration was reached to 120 mg L^-1. The ILs even more promoted the growth of Enterobacter sp. NP1142 and Pantoea sp. BR23. It was indicated that IL [N₄₄₄₄] AOT can be degraded easily by rhizobacteria to eliminate the eco-risk of ILs.

Mitigating the toxic effects of CdSe quantum dots towards freshwater alga Scenedesmus obliquus: Role of eco-corona

The extensive use of semiconducting nanoparticles such as quantum dots in biomedical and industrial products can lead to their inadvertent release into the freshwater system. Natural exudates in the aquatic system comprising extracellular polymeric substance (EPS) and protein-rich metabolites can eventually adsorb onto the quantum dots (QDs) surface and form an eco-corona. The alterations in the physio-chemical and toxicological behavior of CdSe/ZnS QDs under the influence of eco-corona in the freshwater system have not been explored yet. In the present study, lake water medium conditioned with exudate secreted by Scenedesmus obliquus was utilized as an eco-corona forming matrix. The time-based evolution of the eco-corona on the differently charged CdSe/ZnS QDs was analyzed using transmission electron microscopy and dynamic light scattering. Aging of amine-QDs in algal exudate for 72 h showed enhanced aggregation (Mean Hydrodynamic Diameter- 1969 nm) as compared to carboxyl-QDs (1543 nm). Further, eco-coronation tends to impart an overall negative charge to the QDs. The fluorescence intensity of amine-QDs was quenched by 84% due to the accumulation of higher eco-corona. An integrative effect of surface charge and accumulated eco-corona layer influenced the Cd²⁺ ion leaching from the QDs. An enhancement in the algal cell viability treated with carboxyl - CdSe/ZnS (90%) and amine- CdSe/ZnS QDs (94%) aged for 72 h suggested that eco-corona can effectively mitigate the inherent toxicity of the QDs. The oxidative stress markers in the algal cells (LPO, SOD, and CAT) were in correlation with the cytotoxicity results. The algal photosynthetic efficiency depended on the deposition of eco-coronated QDs on the cell surface. Cellular uptake results indicated low Cd²⁺ concentration of nearly 13.9 and 11.5% for carboxyl- and amine- CdSe/ZnS QDs respectively. This suggests that eco-coronation directly influences the bioavailability of engineered nanoparticles.

Alkyl chain length affecting uptake of imidazolium based ionic liquids by ryegrass (Lolium perenne L.)

Imidazolium based ionic liquids (ILs) have been extensively used in the various industrial fields, however, the dependence of their structure on toxicity and bioavailability by plants is not clear. Thus, in this study, uptake of imidazolium based ILs with different alkyl chain lengths (e.g., [C₂mim]⁺ and [C₈mim]⁺) by ryegrass and their toxicity to plant growth were investigated. Results show that the two ILs could be removed by ryegrass with high efficiencies, and a higher uptake efficiency and accumulation was observed for [C₂mim]⁺ with shorter chain length compared with that for [C₈mim]⁺. A higher growth inhibition of ryegrass by [C₈mim]⁺ was observed compared with that by [C₂mim]⁺, indicating the long alkyl chain length of ILs had a negative effect on the plant growth. ILs taken up by ryegrass was retained in the roots and their translocation from roots to shoots was restricted. The IL concentration in roots was 0.68 mg/g-fresh weight for [C₂mim]⁺ and 0.08 mg/g- fresh weight for [C₈mim]⁺ when the ryegrass was exposed to 10 mg/L ILs. This study proved that plant assimilation of ILs depended on their alky chain lengths, which would be useful for understanding the fate of ILs with various structures in phytoremediation for ILs-contaminated water.

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.

Using a freshwater green alga Chlorella pyrenoidosa to evaluate the biotoxicity of ionic liquids with different cations and anions

With the extensive use of ionic liquids (ILs) in various industrial fields, their potential toxicity to aquatic ecosystem has attracted considerable attention. In this work, biotoxicity of ILs with different cations and anions was evaluated by using a freshwater green alga Chlorella pyrenoidosa. Results showed that 1-butyl-3-methylimidazolium chloride ([C₄mim]Cl), 1-octyl-3-methylimidazolium chloride ([C₈mim]Cl), 1-octyl-3-methylimidazolium nitrate ([C₈mim]NO₃), 1-octyl-3-methylimidazolium tetrafluoroborate ([C₈mim]BF₄), and 1-dodecyl-3-methylimidazolium chloride ([C₁₂mim]Cl) had a significant inhibition on the algal growth with EC₅₀ values of 23.48, 4.72, 3.80, 4.44, and 0.10 mg L^-1 at the 72 h of exposure, respectively. These data suggested that the toxicity of ILs increased with the increase of side alkyl chain length, while anions had little influences on their toxicity to this alga. Moreover, changes in chlorophyll a content and chlorophyll fluorescence parameters (F_v/F_m and Φ_PSII) indicated that the five ILs could damage the photosynthetic system of this alga resulting in the decrease of photosynthetic efficiency. The increased soluble protein content and antioxidase activity could be considered as an active response mechanism of this alga against the exposure of ILs. Content of malondialdehyde (MDA) in this alga increased significantly when it was exposed to ILs, suggesting that reactive oxygen species (ROS) were accumulated in the algal cells, which would cause injury of the algal biofilm and chloroplast. Therefore, results obtained in this work would help to explain the possible underlying toxic mechanisms of ILs to C. pyrenoidosa, and provide a significant theoretical support for assessing the toxicity of ILs to aquatic organisms.

Enantioselective effects of imazethapyr residues on Arabidopsis thaliana metabolic profile and phyllosphere microbial communities

Imazethapyr (IM) is a widely used acetolactate synthase-inhibiting chiral herbicide. It has long-term residuals that may be absorbed by the human body through the edible parts of plants, such as vegetable leaves or fruits. Here, we selected a model plant, Arabidopsis thaliana, to determine the effects of R-IM and S-IM on its leaf structure, photosynthetic efficiency, and metabolites, as well as the structures of microorganisms in the phyllosphere, after 7 days of exposure. Our results indicated enantiomeric differences in plant growth between R-IM and S-IM; 133 µg/kg R-IM showed heavier inhibition of photosynthetic efficiency and greater changes to subcellular structure than S-IM. R-IM and S-IM also had different effects on metabolism and leaf microorganisms. S-IM mainly increased lipid compounds and decreased amino acids, while R-IM increased sugar accumulation. The relative abundance of Moraxellaceae human pathogenic bacteria was increased by R-IM treatment, indicating that R-IM treatment may increase leaf surface pathogenic bacteria. Our research provides a new perspective for evaluating the harmfulness of pesticide residues in soil, phyllosphere microbiome changes via the regulation of plant metabolism, and induced pathogenic bacterial accumulation risks.

Oxidative stress response and proteomic analysis reveal the mechanisms of toxicity of imidazolium-based ionic liquids against Arabidopsis thaliana

Ionic liquids (ILs) are extensively used in various fields, posing a potential threat in the ecosystem because of their high stability, excellent solubility, and biological toxicity. In this study, the toxicity mechanism of three ILs, 1-octyl-3-methylimidazolium chloride ([C₈MIM]Cl), 1-decyl-3-methylimidazolium chloride ([C₁₀MIM]Cl), and 1-dodecyl-3-methylimidazolium chloride ([C₁₂MIM]Cl) on Arabidopsis thaliana were revealed. Reactive oxygen species (ROS) level increased with higher concentration and longer carbon chain length of ILs, which led to the increase of malondialdehyde (MDA) content and antioxidase activity, including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) and peroxidase (POD) activities. SOD, CAT, and GPX activities decreased in high ILs concentration due to the excessive ROS. Differentially expressed protein was analyzed based on Gene ontology (GO) and KEGG pathways analysis. 70, 45, 84 up-regulated proteins, and 72, 104, 79 down-regulated proteins were identified in [C₈MIM]Cl, [C₁₀MIM]Cl, and [C₁₂MIM]Cl treatment, respectively (fold change ≥ 1.5 with ≥95% confidence). Cellular aldehyde metabolic process, mitochondrial and mitochondrial respiratory chains, glutathione transferase and oxidoreductase activity were enriched as up-regulated proteins as the defense mechanism of A. thaliana to resist external stresses. Chloroplast, photosynthetic membrane and thylakoid, structural constituent of ribosome, and transmembrane transport were enriched as the down-regulated protein. Compared with the control, 8 and 14 KEGG pathways were identified forup-regulated and down-regulated proteins, respectively, in three IL treatments. Metabolic pathways, carbon metabolism, biosynthesis of amino acids, porphyrin and chlorophyll metabolism were significantly down-regulated. The GO terms annotation demonstrated the oxidative stress response and effects on photosynthesis of A. thaliana in ILs treatment from biological process, cellular component, and molecular function categories.

Exogenous phosphite application alleviates the adverse effects of heat stress and improves thermotolerance of potato (Solanum tuberosum L.) seedlings

Phosphite (Phi), an analog of phosphate (Pi) anion, is emerging as a potential biostimulator, fungicide and insecticide. Here, we reported that Phi also significantly enhanced thermotolerance in potatoes under heat stress. Potato plants with and without Phi pretreatment were exposed to heat stress and their heat tolerance was examined by assessing the morphological characteristics, photosynthetic pigment content, photosystem II (PS II) efficiency, levels of oxidative stress, and level of DNA damage. In addition, RNA-sequencing (RNA-Seq) was adopted to investigate the roles of Phi signals and the underlying heat resistance mechanism. RNA-Seq revealed that Phi orchestrated plant immune responses against heat stress by reprograming global gene expressions. Results from physiological data combined with RNA-Seq suggested that the supply of Phi not only was essential for the better plant performance, but also improved thermotolerance of the plants by alleviating oxidative stress and DNA damage, and improved biosynthesis of osmolytes and defense metabolites when exposed to unfavorable thermal conditions. This is the first study to explore the role of Phi in thermotolerance in plants, and the work can be applied to other crops under the challenging environment.

Toxicity Evaluation of Three Imidazolium-based ionic liquids ([C6mim]R) on Vicia faba Seedlings Using an integrated biomarker response (IBR) index

Ionic liquids (ILs) are regarded as green solvents and are frequently used in the chemical industry. However, ILs may impact plant growth if they are present in the soil environment. To compare toxicity of ILs with different anions in soil, three imidazolium-based ionic liquids (1-hexyl-3-methylimidazolium bromide, 1-hexyl-3-methylimidazolium nitrate, 1-hexyl-3-methylimidazolium tetrafluoroborate) were used to assess impact on Vicia faba. Following 10 d of exposure to these three ILs from 0 to 2500 mg kg^-1, shoot length, root length and dry weight of Vicia faba were determined. Pot trials revealed that ILs inhibited Vicia faba growth and according to EC₅₀ values, [C₆mim]BF₄ was the most toxic one. In addition, physiological indicators of Vicia faba were determined following 10 d of exposure at selected IL concentrations (0, 1, 10, 100 and 500 mg kg^-1). ILs led to the generation of reactive oxygen species and then caused oxidative damage, including lipid peroxidation, protein damage and DNA damage, which triggered an increase in antioxidant content and enzyme activity. The experimental results indicated that oxidative stress may be the primary underlying toxic mechanism for Vicia faba. Furthermore, based on the data of physiological experiment, integrated biomarker response (IBR) was calculated to compare the toxicity of the three ILs and toxic order was: [C₆mim]NO₃＜[C₆mim]Br＜[C₆mim]BF_4.

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.

Alteration between inhibition and stimulation in individual and mixture effects of [amim]Br and [apyr]Br on Aliivibrio fischeri: Time and side-chain dependence

The exposure reality of chemicals is usually in mixtures, the effects of which are usually extrapolated from individual results. Yet, such extrapolation is challenged by the alteration between monotonic concentration-response curves (CRCs) and non-monotonic hormetic CRCs in individual and mixture effects. In the present study, we aimed to investigate the occurrence of such alterations using 1-alkylimidazolium bromide ([amim]Br) and 1-alkylpyridinium bromide ([apyr]Br) ionic liquids (ILs) as model chemicals. Effects of four [amim]Br, four [apyr]Br, and their quaternary mixtures designed by uniform design were measured on Aliivibrio fischeri in a time-dependent fashion. Results showed that the individual [amim]Br showed monotonic CRCs. Their inhibition increased over the length of the side-chain and decreased over the exposure time. The [amim]Br mixtures showed non-monotonic hormetic CRCs, where the stimulations increased over exposure time. The individual [apyr]Br had non-monotonic hormetic CRCs, and their stimulation increased over the length of the side-chain. Meanwhile, the [apyr]Br mixtures had monotonic CRCs without any stimulation. Notably, the positive contributors to the mixture effects were [emim]Br or [epyr]Br which had the shortest side-chain among the components. The findings can facilitate accurate prediction on the environmental effects of ILs with specific considerations on hormetic and mixture effects.

Phytotoxicity and oxidative stress of perfluorooctanesulfonate to two riparian plants: Acorus calamus and Phragmites communis

Despite previous efforts and the rapid progress on elucidating the impact of perfluorooctanesulfonate (PFOS) on the environment, its effects on riparian plants, a key component of aquatic ecosystems, are still poorly understood. A 48-day hydroponic experiment was carried out on two typical riparian species (Acorus calamus and Phragmites communis) to examine the toxic effects of PFOS on these plants. The results showed that, at high concentration (more than 10 mg L^-1), PFOS could prevent chlorophyll accumulation (reduced by 13.7-22.2% at 10 mg L^-1 PFOS and 22.4-30.0% at 50 mg L^-1 PFOS for 48 days) and soluble protein synthesis (reduced by 2.3-9.0% at 10 mg L^-1 PFOS and 10.6-26.8% at 50 mg L^-1 PFOS for 48 days). Contrastingly, less than 1 mg L^-1 of PFOS could induce chlorophyll accumulation (increased by 18.6% in A. calamus roots, 11.3% in A. calamus leaves, and 13.6% in P. communis roots at 1 mg L^-1 PFOS for 3 days) and soluble protein synthesis (increased by 6.1% in A. calamus roots, 18.4% in A. calamus leaves, 9.7% in P. communis roots, 23.4% in P. communis stems, and 24.0% in P. communis leaves, at 1 mg L^-1 PFOS for 6 days). In addition, PFOS led to oxidative stress, as revealed by the elevated concentrations of malonaldehyde and hydrogen peroxide, and reduced the activities of antioxidant enzymes such as superoxide dismutase (reduced by 10.3% in P. communis stems at 50 mg L^-1 PFOS for 48 days), catalase (reduced by 20.6-50.3% in test species at 50 mg L^-1 PFOS for 48 days), and peroxidase (reduced by 24.9-37.7% in test species at 50 mg L^-1 PFOS for 48 days). The biomarkers of both plants changed rapidly in the first half of the experiment (0-24 days) and stabilized in the second half of the experiment (24-48 days). The risk and related factors of PFOS on riparian plants were evaluated by using these biomarkers. Experiments showed that P. communis was more resistant to low concentration (<10 mg L^-1) of PFOS than A. calamus.

Phytotoxicity and oxidative effects of typical quaternary ammonium compounds on wheat (Triticum aestivum L.) seedlings

The large-scale use of quaternary ammonium compounds (QACs) in medicines or disinfectants can lead to their release into the environment, posing a potential risk to organisms. This study examined the effects of three typical QACs, dodecyltrimethylammonium chloride (DTAC), dodecyldimethylbenzylammonium chloride (DBAC), and didodecyldimethylammonium chloride (DDAC), on hydroponically cultured wheat seedlings. After 14 days of exposure, both hormesis and phytotoxicity were observed in the wheat seedlings. The shoot and root fresh weight gradually increased as QAC concentrations rose from 0.05 to 0.8 mg L^-1. However, higher QAC concentrations severely inhibited plant growth by decreasing shoot and root fresh weight, total root length, and photosynthetic pigment content. Moreover, the increase in malondialdehyde and O₂^.- contents, as well as root membrane permeability, reflected an oxidative burst and membrane lipid peroxidation caused by QACs. However, the effects of QACs on the levels of these oxidative stress markers were compound-specific, and the changes in superoxide dismutase, peroxidases, and catalase activity were partly related to reactive oxygen species levels. Considering the order of median effective concentration values (EC₅₀) and the levels of oxidative stress induced by the three tested QACs, their phytotoxicities in wheat seedlings increased in the following order: DDAC < DTAC < DBAC, which mainly depended on their characteristics and applied concentrations. These results, which illustrated the complexity of QAC toxicity to plants, could potentially be used to assess the risk posed by these compounds in the environment.

Effect of differently methyl-substituted ionic liquids on Scenedesmus obliquus growth, photosynthesis, respiration, and ultrastructure

Concerns have been raised regarding the ecotoxicity of ionic liquids (ILs) owing to their wide usage in numerous fields. Three imidazolium chloride ILs with different numbers of methyl substituents, 1-decyl-imidazolium chloride ([C₁₀IM]Cl), 1-decyl-3-methylimidazolium chloride ([C₁₀MIM]Cl), and 1-decyl-2,3-dimethylimidazolium chloride ([C₁₀DMIM]Cl), were examined to assess their effects on growth, photosynthesis pigments content, chlorophyll fluorescence, photosynthetic and respiration rate, and cellular ultrastructure of Scenedesmus obliquus. The results showed that algal growth was significantly inhibited by ILs treatments. The observed IC_50,48h doses were 0.10 mg/L [C₁₀IM]Cl, 0.01 mg/L [C₁₀MIM]Cl, and 0.02 mg/L [C₁₀DMIM]Cl. The chlorophyll a, chlorophyll b, and total chlorophyll content declined, and the chlorophyll fluorescence parameters, minimal fluorescence yield (F₀), maximal fluorescence yield (F_m), maximum quantum yield of PSII photochemistry (F_v/F_m), effective quantum yield of PSII [Y(II)], non-photochemical quenching (NPQ) and non-photosynthetic losses yield [Y(NO)] were notably affected by ILs in a dose-dependent manner. ILs affected the primary photosynthetic reaction, impaired heat dissipation capability, and diminished photosynthetic efficiency, indicating negative effects on photosystem II. The photosynthetic and respiration rates of algal cells were also reduced due to the ILs treatments. The adverse effects of ILs on plasmolysis and chloroplast deformation were examined using ultrastructural analyses; chloroplast swelling and lamellar structure almost disappeared after the [C₁₀MIM]Cl treatment, and an increased number of starch grains and vacuoles was observed after all ILs treatments. The results indicated that one-methyl-substituted ILs were more toxic than non-methyl-substituted ILs, which were also more toxic than di-methyl-substituted ILs. The toxicity of the examined ILs showed the following order: [C₁₀IM]Cl < [C₁₀DMIM]Cl ≤ [C₁₀MIM]Cl.

Oxidative stress and genotoxic effects in earthworms induced by five imidazolium bromide ionic liquids with different alkyl chains

In this study, the acute and subchronic toxicity of 1-alkyl-3-methyl imidazole bromide ionic liquids (ILs) [C_nmim]Br (n = 2, 4, 6, 10, 12) was evaluated utilizing earthworms (Eisenia fetida) as a basis for their impact on terrestrial ecosystems. The filter paper tests and artificial soil tests were conducted as acute toxicity tests to investigate the LC₅₀ of ILs, while in subchronic toxicity tests, earthworms were exposed to ILs in artificial soil (5, 10, 20 and 40 mg kg^-1) for 28 d. Reactive oxygen species (ROS), antioxidant enzymes, detoxifying enzymes and oxidative damage were measured to determine subchronic effects of ILs on E. fetida. The results showed that when the earthworms were exposed to these five ILs in acute toxicity experiments, [C₂mim]Br had the lowest toxicity, as the alkyl length increased, the toxicity increased up to [C₁₀mim]Br: a "cut-off effect" (decreased toxicity) was observed at [C₁₂mim]Br. The results highlight the varying toxicity of ILs with different alkyl chains to E. fetida and provide valuable data for detailing the impact of ILs on ecological receptors.

Impacts of four ionic liquids exposure on a marine diatom Phaeodactylum tricornutum at physiological and biochemical levels

With the increasing applications in various industrial areas, toxicity of ionic liquids (ILs) has gained much attention in recent years. In this work, 1-octyl-3-methylimidazolium nitrate ([C₈mim]NO₃), 1-octyl-3-methylimidazolium chloride ([C₈mim]Cl), N-octyl-3-metylpyridinium chloride ([C₈mpy]Cl) and N-octyl-3-metylpyridinium bromide ([C₈mpy]Br) were used to investigate the impacts of different types of cations and anions on their toxicity to a marine diatom Phaeodactylum tricornutum. Results showed that the four ILs had poor degradability under the culture conditions used in this study, and significantly inhibited the growth of this diatom with 96-h EC₅₀ values of 24.0, 33.6, 16.1 and 14.4mgL^-1 for [C₈mim]NO₃, [C₈mim]Cl, [C₈mpy]Cl and [C₈mpy]Br, respectively. The data indicated that types of cations and anions would affect the toxicity of ILs to this diatom. Additionally, photosynthesis of this diatom was inhibited because significant decrease of chlorophyll a content and damage of PSII reaction centers were observed when it was exposed to the four ILs. Remarkable physiological and biochemical responses occurred in the cells of this diatom to alleviate the damaging effects of the four ILs. For example, content of soluble protein and activities of superoxide dismutase (SOD) and catalase (CAT) in the cells of this diatom increased significantly to form a protective mechanism against the toxicity of ILs, although they decreased in the cultures with high concentrations of ILs (≥20mgL^-1). Thus, these results would not only provide strong evidences for evaluating the ecological risks and toxicity of ILs to marine ecosystem, but also help for understanding their toxic mechanisms to marine diatoms.

Increased ZnO nanoparticle toxicity to wheat upon co-exposure to phenanthrene

Polycyclic aromatic hydrocarbons and zinc oxide nanoparticles are ubiquitous pollutants in the environment. However, little information is available about their toxicity interaction in food crops. In this study, seed germination and hydroponic experiments were conducted to assess the impact of ZnO (NPs and bulk at 250, 500 and 1000 mg L^-1) individual and combined with phenanthrene (1 mg L^-1) on wheat growth for 15 days. Under ZnO (NPs and bulk) alone and combined with phenanthrene exposure, dose-dependent toxicity in some indexes (germination rate, biomass, shoot height, root length) was observed. Both ZnO NPs and bulk inhibited plant growth at high concentrations, but no significant difference was observed between them (P > 0.05). The chlorophyll concentration of wheat leaves decreased by 0.43-0.60 fold when the levels of ZnO NPs and bulk treated were elevated. There was a negative correlation between ZnO (NPs and bulk) and total chlorophyll. Hill reaction activity also exhibited the same tendency. Through transmission electron microscopy, ZnO NPs were found in wheat seedling root apoplast and symplasm at 1000 mg L^-1 with or without phenanthrene. High doses (500 and 1000 mg L^-1) of ZnO (NPs and bulk) caused more DNA damage to wheat seedling root cells, and ZnO NPs induced stronger genotoxicity than bulk ones to wheat root cells. Superoxide dismutase (SOD) and catalase (CAT) activities of wheat seedling roots decreased at 1000 mg L^-1 ZnO (NPs and bulk), especially in the co-exposure treatments. Hence, ZnO (NPs and bulk) combined with phenanthrene cause more damage to wheat seedling roots, and even destroy the antioxidant system. Our findings are helpful for not only assessing the individual and combined toxicity between phenanthrene and ZnO (NPs and bulk), but also for understanding the different response of plants to individual and combined pollution.

Assessment of the toxicity and biodegradation of amino acid-based ionic liquids

Amino acid-based ionic liquids (AAILs) are generally thought of as green solvents and widely used in many regions without systematic assessment of their effect on the environment or human health. In this work, a series of AAILs with different cations and amino acid anions were prepared and characterized, after which their microbial toxicity, phytotoxicity, and biodegradability were evaluated. The results showed that not all AAILs had low toxicity against microorganisms and that some AAILs were highly toxic towards the targeted microorganisms. The phytotoxic effect of the AAILs on rice (Oryza sativa L.) further demonstrated that AAILs should not be presumed to be non-toxic to plants. Moreover, the biodegradability tests showed that majority of AAILs were not satisfactorily biodegradable. In summary, not all AAILs are non-toxic or biodegradable, and their effect on the environment and human health must be assessed before their mass preparation and application.

Acute toxicity of the fungicide azoxystrobin on the diatom Phaeodactylum tricornutum

Azoxystrobin (AZ) is an effective broad-spectrum fungicide. Due to its extensive application, AZ is detectable in aquatic ecosystems and thus influences aquatic organisms. In this study, the acute toxicity (96 h) of AZ at concentrations of 1.0 mg/L and 5.0 mg/L on the diatom Phaeodactylum tricornutum were examined. At the tested concentrations, AZ significantly inhibited P. tricornutum growth and destroyed its cellular structure. Furthermore, the mechanisms of AZ-induced toxicity on P. tricornutum changed as the exposure time extended. Forty-eight hours after exposure, AZ inhibited P. tricornutum growth primarily via inducing oxidative stress, which increased the activity of two main antioxidant enzymes, superoxide dismutase and peroxidase, and inhibited energy metabolism. However, after 96 h of treatment, the decline in the photosynthetic capacity of P. tricornutum demonstrated that the photosystem was the main AZ target. The pigment content and expression levels of genes related to photosynthetic electron transfer reactions were also significantly decreased. The present study describes AZ toxicity in P. tricornutum and is very valuable for assessing the environmental risk of AZ.

Ammonium 2,2'-thiodiacetates - Selective and environmentally safe herbicides

2,2'-Thiodiacetic acid derivatives have a wide application potential, mainly in coordination chemistry. This research indicates that quaternary ammonium 2,2'-thiodiacetate salts may also be potent herbicidal agents used in agriculture. To provide a rationale for this statement, the toxic effect by a alkyl and aryl quaternary ammonium salts (QASs) on plant growth was investigated. The phytotoxicity of these compounds was tested against cultivated monocotyledonous (spring barley) and dicotyledonous (common radish) plants, whereas herbicidal activity was investigated in relation to popular weeds species (white goosefoot, sorrel and gallant-soldier). The results showed that aliphatic QASs possessed a low phytotoxicity to food crops and that some of them (in particular triethylammonium salt) had potent and selective herbicidal properties against common weeds, such as sorrel and gallant-soldier. However, the investigated compounds appeared to be ineffective herbicides against white goosefoot.

Effects of 1-butyl-3-methylimidazolium chloride on the photosynthetic system and metabolism of maize (Zea mays L.) seedlings

Ionic liquids (ILs) are widely used in various chemical processes. However, a growing number of studies have found that ILs are potentially toxic to different types of living organisms, including crops. The present study analysed the effects of 1-butyl-3-methylimidazolium chloride ([C₄mim]Cl) on the photosynthetic system and metabolism of maize seedlings. Results showed that [C₄mim]Cl could significantly reduce maize leaf chlorophyll level and cause extensive leaf bleaching. The activity of photosystem II (PSII) was significantly inhibited when seedlings exposed to higher concentration of [C₄mim]Cl. The maximum quantum yield of PSII and the potential efficiency of PSII were reduced by 63% and 88% under 800 mg/L [C₄mim]Cl treatment in comparison with the control treatment. The RNA sequencing analysis performed to examine gene expression profiles of maize leaves under [C₄mim]Cl treatment revealed 639 differentially expressed genes (DEGs), 115 of which were categorized into different metabolic pathways. Among these DEGs, the seven genes involved in the photosynthetic Calvin cycle were down-regulated by [C₄mim]Cl exposure. For carbohydrates and amino acids metabolism, the genes for starch synthesis were down-regulated, while the genes for amino acids and protein degradation were up-regulated. The changes observed in these major metabolic pathways might be an important reason for [C₄mim]Cl toxicity.

Effect of imidazolium-based ionic liquids with varying carbon chain lengths on Arabidopsis thaliana: Response of growth and photosynthetic fluorescence parameters

As green and novel solvents, ionic liquids (ILs) are popular in many industries, which may threaten ecosystems. The effects of three imidazolium-based ILs with different alkyl chain lengths, including 1-octyl-3-methylimidazolium chloride ([C₈mim]Cl), 1-decyl-3-methylimidazolium chloride ([C₁₀mim]Cl), and 1-dodecyl-3-methylimidazolium chloride ([C₁₂mim]Cl) on growth and photosystem of Arabidopsis thaliana were investigated. Root length, fresh weight, cell membrane permeability, and chlorophyll content of whole plant were significantly affected by ILs. Vein clearing, leaf chlorosis, and browning on the A. thaliana leaf abaxial surface occurred, with a dose-response relationship. The effect of ILs on whole plant increased with alkyl chain lengths. Chlorophyll fluorescence parameters of photosynthetic system II (PSII) were all affected in [C₈mim]Cl and [C₁₀mim]Cl treatments, electron-transfer was blocked, and photochemical energy conversion was damaged. There were no significant changes in chlorophyll fluorescence of newly-growing leaves in [C₁₂mim]Cl treatment, but has severe effect on aged leaves. The number and size of starch granules and osmiophilic globules increased, plasmolysis and the chloroplast swelling occurred in [C₈mim]Cl, [C₁₀mim]Cl treatments and on aged leaves in [C₁₂mim]Cl treatment, but no significant damages occurred on newly-growing leaves of [C₁₂mim]Cl treatment, perhaps due to plant self-protection of plant. The results indicating the appropriate use of ILs is needed.

Inoculation with Bacillus subtilis and Azospirillum brasilense Produces Abscisic Acid That Reduces Irt1-Mediated Cadmium Uptake of Roots

Cadmium (Cd) contamination of agricultural soils represents a serious risk to crop safety. A new strategy using abscisic acid (ABA)-generating bacteria, Bacillus subtilis or Azospirillum brasilense, was developed to reduce the Cd accumulation in plants grown in Cd-contaminated soil. Inoculation with either bacterium resulted in a pronounced increase in the ABA level in wild-type Arabidopsis Col-0 plants, accompanied by a decrease in Cd levels in plant tissues, which mitigated the Cd toxicity. As a consequence, the growth of plants exposed to Cd was improved. Nevertheless, B. subtilis and A. brasilense inoculation had little effect on Cd levels and toxicity in the ABA-insensitive mutant snrk 2.2/2.3, indicating that the action of ABA is required for these bacteria to reduce Cd accumulation in plants. Furthermore, inoculation with either B. subtilis or A. brasilense downregulated the expression of IRT1 (iron-regulated transporter 1) in the roots of wild-type plants and had little effect on Cd levels in the IRT1-knockout mutants irt1-1 and irt1-2. In summary, we conclude that B. subtilis and A. brasilense can reduce Cd levels in plants via an IRT1-dependent ABA-mediated mechanism.

The toxicity of ionic liquid 1-decylpyridinium bromide to the algae Scenedesmus obliquus: Growth inhibition, phototoxicity, and oxidative stress

Although ionic liquids (ILs) are unlikely to act as air contaminants, their high solubility and slow degradation make them a potential threat to the aquatic environment. The IL 1-decylpyridinium bromide ([DPy]Br) is a common type of pyridine IL, which has varied applications such as in extraction, separation, and catalytic synthesis. Herein, the toxicity of [DPy]Br to S. obliquus is determined. Growth was inhibited by high-concentration [DPy]Br, whereas it had a hormetic effect at low concentrations. The IC_50-96h was approximately 0.06mg/L. The cell membrane permeability of S. obliquus increased with [DPy]Br concentration, indicating that [DPy]Br can cause damage to the algae cell structure. Chlorophyll content decreased at high [DPy]Br concentration; chlorophyll fluorescence parameters, such as the maximum effective quantum yield of PSII (F_v/F_m), potential activity of PSII (F_v/F₀), yield of the photochemical quantum [Y(II)], and the non-photochemical quenching coefficient (NPQ) were affected, suggesting that [DPy]Br can damage PSII. The ROS fluorescent images revealed that the morphology of cells changed gradually from fusiform to round. High ROS levels were observed with high concentrations of [DPy]Br, indicating that [DPy]Br induced oxidative stress on S. obliquus. The SOD and CAT activities increased when the concentration was lower than IC₅₀, whereas they decreased when the concentration was higher than IC₅₀. The relative ROS content was significantly correlated with growth inhibition rate, cell membrane permeability, chlorophyll content, and SOD and CAT activities. The increase of ROS content in algal cells is an important toxicological mechanism of [DPy]Br to S. obliquus.

Effect of ionic liquids with different cations and anions on photosystem and cell structure of Scenedesmus obliquus

The rapid increase in the production and practical application of ionic liquids (ILs) could pose potential threats to aquatic systems. In this study, we investigated the effects of four ILs with different cations and anions, including 1-hexyl-3-methylimidazolium nitrate ([HMIM]NO₃), 1-hexyl-3-methylimidazolium chloride ([HMIM]Cl), N-hexyl-3-metylpyridinium chloride ([HMPy]Cl), and N-hexyl-3-metylpyridinium bromide ([HMPy]Br), on photosystem and cellular structure of Scenedesmus obliquus. The results indicated that ILs are phytotoxic to S. obliquus. The contents of chlorophyll a, chlorophyll b and total chlorophyll decreased with increasing ILs concentrations. The chlorophyll fluorescence parameters of photosynthetic system II (PSII), including minimal fluorescence yield (F₀), potential efficiency of PSII (F_v/F_o), maximum quantum efficiency of PSII photochemistry (F_v/F_m), yield of photochemical quantum [Y(II)], and non-photochemical quenching coefficient without measuring F₀' (NPQ), were all affected. This indicates that ILs could damage PSII, inhibit the primary reaction of photosynthesis, interdict the process of electron-transfer and lead to loss of heat-dissipating ability. ILs also increased cell membrane permeability of S. obliquus, influenced the cellular ultrastructure, changed the morphology of algae cells and destroyed the cell wall, cell membrane and organelles. The results indicated that imidazolium ILs had greater effect than pyridinium ILs, NO₃^--IL and Br^--IL had greater effect than Cl^--IL. To minimize threats to the environment, the structure of ILs should be taken into consideration.

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.

Ammonium haloacetates - An alternative to glyphosate?

This study shows the design, synthesis and evaluation of eco(phyto)toxic and herbicidal activities of quaternary ammonium salts (QASs), derived from haloacetic acids, in context of the search for safer alternatives to the commonly used herbicide, N-(phosphonomethyl)glycine (glyphosate). The structure of the investigated QASs refers to the heteroatom sequence in the anion of glyphosate in which the (P-C)-N nitrogen atom was replaced by one or more halogens (F, Cl). The ecotoxicity of the synthesized QASs was tested against luminescent marine bacteria Vibrio fischeri (Microtox® test) and the crustaceans Heterocypris incongruens (Ostracodtoxkit F™). The phytotoxic effect of QASs was also studied with respect to spring barley (Hordeum vulgare) and common radish (Raphanus sativus L. radicula Pers.), whereas herbicidal activity was investigated in relation to popular weeds species gallant soldier (Galinsoga parviflora Cav.) and common sorrel (Rumex acetosa L.). The results showed that toxicity of the synthesized QASs depends on a number of halo-substituents, especially for bioluminescent bacteria Vibrio fischeri for which EC50 values were those varying the most. Phytotoxicity tests proved that the investigated QASs had a similar high, toxic effect both on monocotyledonous and dicotyledonous plants with exception of DIPA - DCA. Moreover, their herbicidal activity against common sorrel was comparable to glyphosate.

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.

Growth and physiological responses of a marine diatom (Phaeodactylum tricornutum) against two imidazolium-based ionic liquids ([C4mim]BF4 and [C8mim]BF4)

Ionic liquids (ILs) have been considered as "green" substitutes for traditional organic solvents in many existing biological and chemical areas. However, they have high solubility and poor biodegradability in water, suggesting that they could become persistent chemical pollutants in aquatic environment. The ability of two widely used imidazolium-based ILs to affect the growth and physiological characteristics of a marine diatom (Phaeodactylum tricornutum) was investigated in this study. The diatom was exposed to different concentrations of 1-butyl-3-methylimidazolium tetrafluoroborate ([C₄mim]BF₄) and 1-octyl-3-methylimidazolium tetrafluoroborate ([C₈mim]BF₄) for 96h within a batch-culture system. Results showed that [C₄mim]BF₄ and [C₈mim]BF₄ were very stable in seawater during 96h of exposure, and the compounds significantly inhibited the growth of P. tricornutum with 24, 48, 72 and 96h EC₅₀ values of 30.81, 28.53, 39.92, 45.88mgL^-1 and 30.17, 23.36, 28.62, 31.37mgL^-1, respectively. In addition, the photosynthetic activity and chlorophyll a synthesis of P. tricornutum were inhibited by [C₄mim]BF₄ and [C₈mim]BF₄, indicating that the structural integrity of chloroplasts of the diatom may be disrupted or damaged by the two ILs. Compared with that of the controls, reactive oxygen species (ROS) level was increased by 0.65, 1.17, 1.85, 3.13, 2.94 times and 0.55, 1.77, 2.42, 3.45, 3.47 times in 5, 10, 20, 40 and 60mgL^-1 [C₄mim]BF₄ and [C₈mim]BF₄ treatments, respectively. The excessive ROS may cause lipid peroxidation, shortage of metabolic energy and decline of photosynthetic efficiency, which may be the main reason for toxicity of the two ILs to marine diatoms. To withstand the damaging effects of excessive ROS, remarkable physiological and biochemical responses occurred in treatments with the two ILs to protect the cells of P. tricornutum. Parameters such as soluble protein content, soluble sugar content, and superoxide dismutase (SOD) and peroxidase (POD) activities of the diatom increased significantly with increasing concentrations of the two ILs at 96h of exposure relative to the controls. These findings not only provide strong background for evaluating the ecological risks and toxicity of ILs in marine environment, but also help to unravel the toxic mechanism of the two ILs to marine diatoms.

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.