Remarkable hormesis induced by 1-ethyl-3-methyl imidazolium tetrafluoroborate on Vibrio qinghaiensis sp.-Q67

Time-dependent hormesis transfer from five high-frequency personal care product components to mixtures

There is potential for personal care products (PCPs) components and mixtures to induce hormesis. How hormesis is related to time and transmitted from components to mixtures are not clear. In this paper, we conducted determination of components in 16 PCP products and then ran frequent itemset mining on the component data. Five high-frequency components (HFCs), betaine (BET), 1,3-butanediol (BUT), ethylenediaminetetraacetic acid disodium salt (EDTA), glycerol (GLO), and phenoxyethanol (POE), and 14 mixtures were identified. For each mixture system, one mixture ray with the actual mixture ratios in the products was selected. Time-dependent microplate toxicity analysis was used to test the luminescence inhibition toxicity of five HFCs and 14 mixture rays to Vibrio qinghaiensis sp.-Q67 at 12 concentration gradients and eight exposure times. It is showed that BET, EDTA, POE, and 13 mixture rays containing at least one J-type component showed time-dependent hormesis. Characteristic parameters used to describe hormesis revealed that the absolute value of the maximum stimulatory effect (|Emin|) generally increased with time. Notably, mixtures composed of POE and S-type components showed greater |Emin| than POE alone at the same time. Importantly, the maximum stimulatory effective concentration, NOEC/the zero effective concentration point, and EC50 remained relatively stable. Nine hormesis transmission phenomena were observed in different mixture rays. While all mixtures primarily exhibited additive action, varying degrees of synergism and antagonism were noted in binary mixtures, with no strong synergism or antagonism observed in ternary and quaternary mixtures. These findings offer valuable insights for the screening of HFCs and their mixtures, as well as the study of hormesis transmission in personal care products.

Beneficial or harmful: Time-dependent hormesis induced by typical disinfectants and their mixtures with toxicological interaction

Disinfectants and their mixtures can induce hormesis. However, how the mixture hormesis is related to those of components and the interactions in disinfectant mixtures remain unclear. In this paper, the luminescence inhibition toxicities of chlorinated sodium phosphate (CSP), dodecyl dimethyl benzyl ammonium bromide (DOB), dodecyl dimethyl benzyl ammonium chloride (DOC), ethanol (EtOH), glutaraldehyde (GLA), hydrogen peroxide (H2O2), isopropyl alcohol (IPA), n-propanol (NPA), and 20 mixture rays in four mixture systems (EtOH-H2O2, DOB-H2O2, DOC-EtOH, and EtOH-IPA-NPA) containing at least one component showing hormesis to Vibrio qinghaiensis sp.-Q67 (Q67) were determined at 0.25, 3, 6, 9, and 12 h. The synergism-antagonism heatmap based on independent action model (noted as SAHmapIA) was developed to systematically evaluate the interactions in various mixtures. It was shown that five disinfectants (CSP, EtOH, H2O2, NPA, and IPA) and 17 mixture rays exhibited time-dependent hormesis. The hormetic component was responsible for the hormesis of the mixture rays. Most mixture rays showed low- concentration/dose additive action and high-concentration/dose synergism at different time. This study further exemplified the interrelationship between the hormesis in the mixtures and their components and implied the need to pay attention to the time-dependent hormesis and interactions induced by the disinfectants.

Mechanism of time-dependent toxicity of quinolone antibiotics on luminescent bacteria Vibrio qinghaiensis sp.-Q67

Four quinolone antibiotics (ciprofloxacin (CIP), enrofloxacin (ENR), sparfloxacin (SPA), gatifloxacin (GAT)) and their binary mixtures at environmentally relevant concentrations exhibited time-dependent hormesis on Vibrio qinghaiensis sp.-Q67 (Q67). The study aims to investigate the time-dependent toxicity of low-dose pollutants and the occurrence of hormesis. These indicators, total protein (TP), reactive oxygen species (ROS), superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA) and luminescence-related chemicals flavin mononucleotide (FMN), nicotinamide adenine dinucleotide (NADH), were measured to explore the mechanism of hormesis. The results showed a trend of increases in all indicators after 12 h of exposure, reaching maximal effects at 60 h and then decreasing as time progressed. At 36 h, 60 h and 84 h, the results showed a gradual increase followed by a decreasing trend in TP, FMN and NADH as the concentration in the group increased, whereas ROS, CAT, SOD and MDA showed the opposite trend. Notably, the degree of changes was related to the magnitude of hormesis. At low concentrations, the content of ROS and MDA decreased, the activity of CAT and SOD was lower, but the content of TP, FMN, NADH gradually increased, positively correlated with the promotion of Q67. At high concentrations, ROS and MDA content in Q67 increased, triggering the antioxidant defense mechanism (CAT and SOD activity increased), but TP, FMN, NADH content decreased, negatively correlated with the inhibited Q67. Therefore, our findings demonstrated two common patterns in these seven biochemical indicators on Q67. These findings have important practical implications for the ecological risk assessment of antibiotics in aquatic environment.

Toxicity of ionic liquids in marine and freshwater microorganisms and invertebrates: state of the art

The variety of applications and expected growth in ionic liquid production are raising concerns about the release of these compounds into aquatic systems. Up to date, 103 studies have provided ecotoxicological data regarding the exposure effects of Ionic Liquids towards aquatic microorganisms and invertebrate species: 61 were devoted to freshwater species (n = 28), while marine species (n = 12) were mentioned in 42. The aim of this review, by gathering published studies on ionic liquids and model aquatic organisms, was to present the toxic effects described in distinct species and to understand which are the main factors influencing the toxicity of some ionic liquids. In accordance with the most recognized pattern, freshwater species were featured in a higher number of publications than marine ones. After literature analysis, algal species were the most represented organisms in aquatic toxicity assessments. Among tested compounds, the imidazolium cations in combination with long alkyl-chain anions, showed to be the most toxic one. In analytical terms, it is not straightforward to find the undissociated compound in a natural compartment, as ionic liquids are composed of ionic components, easily subjected to dissociation. Given the aforementioned, the present review paper points out the need of increasing the number of organisms being assessed in ionic liquids toxicity assays, in order to start defining monitoring procedures. Moreover, such would allow a better understanding of ionic liquids contamination status and, also, the opportunity to remark the effectiveness of new in silico methods for the ecotoxicity assessment of this kind of substances.

Transfer pattern of hormesis into personal care product mixtures from typical hormesis-inducing compounds

Some personal care products (PCPs) and their chemical components showed a hormetic effect in the freshwater photobacterium Vibrio qinghaiensis sp. -Q67 (Q67) after long-term exposure. However, how hormesis transfers between chemical components and PCP mixture, and which chemical component plays a major role remain unknown. To this end, according to the seven compounds detected in one skin lotion (SK5) and their concentration ratios, many mixture rays were constructed to simulate the SK5. Of these seven compounds, three presented monotonic concentration-response curves (CRC) to Q67 at 0.25 and 12 h (called a S-shaped compound). The other four compounds showed hormetic CRCs after 12 h and monotonic CRCs at 0.25 h (called a J-shaped compound). Based on their mixture ratios, we designed one ternary mixture ray of all S-shaped compounds, one quaternary mixture ray of all J-shaped compounds, and four quaternary mixture rays of one J-shaped and three S-shaped compounds. It was shown that SK5 could be approximately simulated by the mixture ray of the seven compounds detected in SK5 and only the mixture rays containing at least one hormesis-inducing compound produced hormesis to Q67 at 12 h. Based on the concentration ratios of various compounds and comparison of four hormetic characteristic parameters to those of various mixture rays, it was found that the compound betaine (BET) is a key compound affecting the hormesis of mixtures. Additionally, we studied the hormesis mechanism of BET on Q67 via quorum sensing (QS). This preliminarily indicated that the autoinducer-2 triggered the QS pathway. This study elucidated the transfer pattern of hormesis into mixtures, which would be an efficient method to identifying the potential components that affect hormesis transfer in mixtures. We expect that this study will provide new insights into hormesis and its mixtures.

Similarities and Differences in Quorum Sensing-Controlled Bioluminescence between Photobacterium phosphoreum T3 and Vibrio qinghaiensis sp.-Q67

Quorum sensing is a density-dependent mechanism using chemical signal molecules termed autoinducers to regulate diverse biological processes in bacteria, including bioluminescence. However, the correlation between growth and light emission of two typical luminescent bacteria, Photobacterium phosphoreum T3 and Vibrio qinghaiensis sp.-Q67, is still unclear. This study investigates the variations of bioluminescence and the light-emission-involved gene expression of the above two strains, respectively, showing that bioluminescence is population density-dependent. Furthermore, the effect of crude extracts (175, 350, 700 and 1750 mg/L) from the bacterial culture that contains the potential autoinducers on the bioluminescence is explored. At the exponential and the early stationary growth phase, T3 did not exhibit an obvious light intensity and cell density change after adding crude extracts at 175 and 350 mg/L, while the light intensity decreased at 700 and 1750 mg/L, showing a luminescence inhibition. For Q67, the light intensity increased dramatically with crude extract concentration. These results suggest that the bioluminescence process of both T3 and Q67 is controlled by quorum sensing. Furthermore, the different response modes of these two strains to autoinducers imply that the two strains could be applied to different compounds for toxicity assesses.

Prediction on the combined toxicities of stimulation-only and inhibition-only contaminants using improved inverse distance weighted interpolation

The evaluation of ecological risks of contaminant mixtures to organisms is very challenging due to the non-linear response of organisms to each component, especially under the co-existence of both stimulators and inhibitors. Whether the stimulatory effect can reduce or even offset the inhibitory effect would be critical to the risk assessment and the treatment measures of mixed pollutants. Here, the combined toxicity of sodium fluoride (NaF), a stimulator with stimulation rate >100%, and six compounds that cannot induce hormesis (four ionic liquids (ILs) and two pesticides) were studied. The time-dependent toxicity of each toxicant on Vibrio qinghaiensis sp.-Q67 was investigated at 0.25, 2, 4, 6, 8, 10 and 12 h. Results showed that four ILs and two pesticides failed to induce hormesis, while NaF induced hormesis from 2 to 6 h and induced stimulation only after 6 h and reached its maximum (650%) at 12 h. All mixture rays with NaF induced hormesis at different times. In the four NaF-IL mixture systems, the absolute value of maximum stimulation demonstrated an upwards and then a downwards trend with the increasing of mixture ratio of IL. In two NaF-pesticide systems, the maximum stimulation effect declined with the increasing of the mixture ratio of pesticide. The toxicities of the mixture were successfully predicted by the improved inverse distance weighted interpolation, which are not able to be predicted by the commonly used concentration addition or independent action models. This paper shed lights on evaluating the hormesis of mixtures and the ecological risk of fluoride.

A Universal Delayed Difference Model Fitting Dose-response Curves

PURPOSE

Dose-response curves, which fit a multitude of experimental data derived from toxicology, are widely used in physics, chemistry, biology, and other fields. Although there are many dose-response models for fitting dose-response curves, the application of these models is limited by many restrictions and lacks universality, so there is a need for a novel, universal dynamical model that can improve fits to various types of dose-response curves.

METHODS

We expand the hormetic Ricker model, taking the delay inherent in the dose-response into account, and develop a novel and dynamic delayed Ricker difference model (DRDM) to fit various types of dose-response curves. Furthermore, we compare the DRDM with other dose-response models to confirm that it can mimic different types of dose-response curves.

DATA ANALYSIS

By fitting various types of dose-response data sets derived from drug applications, disease treatment, pest control, and plant management, and comparing the imitative effect of the DRDM with other models, we find that the DRDM fits monotonic dose-response data well and, in most circumstances, the DRDM has a better imitative effect to non-monotonic dose-response data with hormesis than other models do.

RESULTS

The MSE of fits of the DRDM to S-shaped dose-response data (DS2-G) is not lower than those for four other models, but the MSE of fits to U-shaped (DS7) and inverted U-shaped dose-response data (DS10) were lower than for two other models. This means that the imitative effect of the DRDM is comparable to other models of monotonic dose-response data, but is a significant improvement compared to traditional models of non-monotonic dose-response data with hormesis.

CONCLUSION

We propose a novel dynamic model (DRDM) for fitting to various types of dose-response curves, which can reflect the dynamic trend of the population growth compared with traditional static dose-response models. By analyzing data, we have confirmed that the DRDM provides an ideal description of various dose-response observations and it can be used to fit a wide range of dose-response data sets, especially for hormetic data sets. Therefore, we conclude that the DRDM has a good universality for dose-response curve fitting.

Toxicological interaction of multi-component mixtures to Vibrio qinghaiensis sp.-Q67 induced by at least three components

It has been stated by researchers that the antibiotic polymyxin B sulfate (POL) is a key component inducing time-dependent antagonism in freshwater luminescent bacteria, Vibrio qinghaiensis sp.-Q67, exposed in the ternary mixture system of the ionic liquids, pesticide and antibiotics. However, the previous statement is limited to ternary and quaternary mixtures without considering situations such as the binary system. In order to prove the direct inducing of antagonism by POL in a more complete and systematic way, two categories of experiments (adding POL in non-antagonistic ternary system and decomposing antagonistic ternary system with POL into the binary system) have been conducted in this paper. The results showed that quaternary mixture systems (adding POL to non-antagonism ternary mixture, up verification) exhibit antagonistic action in a majority of rays, at some point in the experiment. However, by decomposing the antagonistic ternary mixtures with POL into binary mixtures (down verification), the combined toxicities of binary mixtures at all time points in the experiment are additive. Obviously, the POL has a significant contribution to antagonism only in the ternary and quaternary mixtures, but not in the binary mixtures. We can draw a new conclusion that the antagonism of the multi-component mixtures is induced by at least three components (including POL), with complex chemical interactions. Therefore, considering POL's influence of antagonism as an example, future environmental protection practitioners and academic researchers should construct more scenarios of mixtures when assessing the influences and reactions of certain chemicals causing pollutions.

Using Delaunay triangulation and Voronoi tessellation to predict the toxicities of binary mixtures containing hormetic compound

Concentration addition (CA) was proposed as a reasonable default approach for the ecological risk assessment of chemical mixtures. However, CA cannot predict the toxicity of mixture at some effect zones if not all components have definite effective concentrations at the given effect, such as some compounds induce hormesis. In this paper, we developed a new method for the toxicity prediction of various types of binary mixtures, an interpolation method based on the Delaunay triangulation (DT) and Voronoi tessellation (VT) as well as the training set of direct equipartition ray design (EquRay) mixtures, simply IDV_equ. At first, the EquRay was employed to design the basic concentration compositions of five binary mixture rays. The toxic effects of single components and mixture rays at different times and various concentrations were determined by the time-dependent microplate toxicity analysis. Secondly, the concentration-toxicity data of the pure components and various mixture rays were acted as a training set. The DT triangles and VT polygons were constructed by various vertices of concentrations in the training set. The toxicities of unknown mixtures were predicted by the linear interpolation and natural neighbor interpolation of vertices. The IDV_equ successfully predicted the toxicities of various types of binary mixtures.

Hormesis of some organic solvents on Vibrio qinghaiensis sp.-Q67 from first binding to the β subunit of luciferase

Hormesis is a biphasic concentration–response relationship. During the luminescence inhibition test ofVibrio qinghaiensissp.-Q67 (Q67), some organic solvents display the hormesis phenomenon.

Time- and anion-dependent stimulation on triphosphopyridine nucleotide followed by antioxidant responses in Vibrio fischeri after exposure to 1-ethyl-3-methylimidazolium salts

A toxicity database of over 157 ionic liquids (ILs) was established on Vibrio fischeri (VF). The database contained mainly monotonic concentration-response relationship, and its application in risk assessment was challenged by potential non-monotonic hormetic effects of ILs. In the present study, the hormetic effects of 1-ethyl-3-methylimidazolium salts ([emim]X, X = BF4, Cl and Br) were confirmed on VF, and biochemical explanations were explored in a time-dependent manner. On luminescence, [emim]BF4 showed inhibitory effects compared with the control, and the median effective concentration (EC50) increased from 3.15E-02 to 8.88E-02 mol/L from 0.25 to 24 h. Notably, [emim]BF4 also showed stimulatory effects at 18 h when the maximum stimulation (Emin) was 51.8% higher than the control, and at 24 h when the Emin increased to 120% higher than the control. Compared with [emim]BF4, [emim]Cl had higher EC50 values which increased over time, while it had less maximum stimulation which also increased over time. In results of [emim]Br, there were only inhibitory effects. At the biochemical level, the stimulatory effects of [emim]BF4 and [emim]Cl on triphosphopyridine nucleotide (NADPH) and nicotinamide adenine dinucleotide (NADH) were earlier than those on luminescence. Moreover, NAD(P)H showed stimulation in [emim]Br which did not have hormetic effects on luminescence. Meanwhile, the effects of [emim]X on flavin mononucleotide, adenosine-triphosphate, reactive oxygen species, superoxide dismutase, catalase, reduced glutathione and lipid peroxidases showed consistent time-dependent changes with those on luminescence. The results indicated different roles between NAD(P)H and other biochemical indices, e.g., the antioxidant responses, in the stimulation of [emim]X on luminescence.

Hormetic effect and mechanism of imidazolium-based ionic liquids on the nematode Caenorhabditis elegans

In the present study, we used Caenorhabditis elegans assay system to investigate in hormetic effects of imidazolium-based bromide Ionic Liquids (ILs) and explored the possible underlying mechanism. Firstly, C. elegans was treated with ILs with different alkyl chain lengths at different concentrations. We found that exposure to ILs at 0.01 mg/L extended the mean lifespan of C. elegans and the ILs with longer alkyl chain showed more obvious effects. To investigate the possible mechanism, the nematodes were exposed to the three ILs at 0.01 mg/L for 2, 5, 7, 9 and 11 days. The levels of reactive oxygen species (ROS) in C. elegans increased significantly when treated for 2 days and then declined gradually compared to those of respective controls as time went on. After exposure for 11 days, the ROS levels and liposuscin accumulation were significantly lower in the treated groups than those of control group. Meanwhile, the expression of aging-related genes sod-5 and daf-16 were both massively up-regulated for the three ILs examined. Our results show that low concentration of ILs exert hormetic effect on C. elegans. ROS generation and expression of aging-related genes may play important roles in the IL-induced hormetic effect on C. elegans.

Time-dependent effects of [apyr]BF(4) and key contributors to their mixture stimulation on Vibrio qinghaiensis sp.-Q67 at apical and biochemical levels

Earlier reports studied the time-dependent effects of imidazolium-based ionic liquids ([amim]X) in the aspect of biochemical explanation and that of key contributor in mixture effects. Presently, the effects of N-alkylpyridinium-based ILs ([apyr]BF4) were studied combining the above two aspects, i.e., the time-dependent effects of [bpyr]BF4, [hpyr]BF4 and [opyr]BF4 on luminescence and biochemical indicators in Vibrio qinghaiensis sp.-Q67, and those of the mixtures. In individual results, the inhibition on luminescence increased over concentrations and the side chain length, showing concentration- and side chain-dependence. Moreover, the inhibition of [apyr]BF4 decreased from 0.25 to 24h, showing a time-dependence. Notably, [hpyr]BF4 stimulated the luminescence at 24h. The biochemical effects, including inhibition and stimulation, were well correlated to those on luminescence. In mixture results, the inhibition on luminescence was lower than the predicted effects by concentration addition model which was based on individual results. Moreover, the mixture stimulation on luminescence was significantly higher than individual ones, and the mixture stimulation on biochemical indicators was even greater than that on luminescence. In mixture effects, [bpyr]BF4 was the positive contributor, and [hpyr]BF4 was the negative contributor. Similarities and differences between [amim]X and [apyr]BF4 indicated underlying mechanisms of the commonly observed hormetic effects of ionic liquids.

Blocking the entrance of AMP pocket results in hormetic stimulation of imidazolium-based ionic liquids to firefly luciferase

The hormesis characterized by low-concentration stimulation and high-concentration inhibition has gained significant interest over the past decades. Some organic solvents and ionic liquids (ILs) have hormetic concentration responses (HCR) to bioluminescence such as firefly luciferase and Vibrio qinghaiensis sp.-Q67. In this study, we determine the effects of 1-alkyl-3-methylimidazolium chlorine ILs ([Cnmim]Cl, n=2, 4, 6, 8, 10 and 12) to firefly luciferase in order to verify the mechanism of hormesis. The luminescence inhibition toxicity tests show that the stimulation effects of [C8mim]Cl and [C10mim]Cl are obvious, [C6mim]Cl and [C12mim]Cl are minor, and [C2mim]Cl and [C4mim]Cl are rare. The enzyme kinetics show that [C8mim]Cl and [C10mim]Cl are the competitive inhibitors with ATP while [C2mim]Cl and [C4mim]Cl are the noncompetitive ones. Molecular dynamics simulation results reveal that imidazolium rings of [C8mim] and [C10mim] locate at the entrance of luciferin pocket which is adjacent to AMP pocket, while alkyl-chains insert into the bottom of the luciferin pocket. Combining the results from inhibition test, kinetics assay and molecular simulation, we can deduce that occupying AMP pocket by imidazolium ring is responsible for hormetic stimulation.

Hormetic effect of ionic liquid 1-ethyl-3-methylimidazolium acetate on bacteria

The biological effect of ionic liquids (ILs) is one of the highly debated topics as they are being contemplated for various industrial applications. 1-ethyl-3-methylimidazolium acetate ([EMIM][Ac]) showed remarkable hormesis on anaerobic Clostridium sp. and aerobic Pseudomonas putida. Bacterial growth was stimulated at up to 2.5 g L(-1) and inhibited at >2.5 g L(-1) of [EMIM][Ac]. The growth of Clostridium sp. and P. putida were higher by 0.4 and 4-fold respectively, in the presence of 0.5 g L(-1) [EMIM][Ac]. Assessment of the effect of [EMIM][Ac] under different growth conditions showed that the hormesis of [EMIM][Ac] was mediated via regulation of medium pH. Hormetic effect of [EMIM][Ac] was evident only in medium with poor buffering capacity and in the presence of a fermentable substrate as the carbon source. The hormetic effect of [EMIM][Ac] on bacterial growth is most likely associated with the buffering capacity of acetate anion. These observations have implications in ILs toxicity studies and ecological risk assessment.

Benefits from hazards: mixture hormesis induced by [emim]Cl despite its individual inhibitions

The threshold model based on monotonic concentration-response curves (CRCs) is unsuitable to assess the risk of chemicals with non-monotonic CRCs. The non-monotonic CRCs of mixtures may relate to the characteristics of some individual component. To reveal the cause of the mixtures resulting in the non-monotonic CRCs, we used the microplate toxicity analysis to determine the toxicity effects of six 1-alkyl-3-methyl-imidazolium ([amim]X) salts and their mixtures on Vibrio qinghaiensis sp.-Q67 (Q67). It was shown that the CRCs of six [amim]X salts are monotonic S-shaped while those of the senary mixtures designed by the uniform design ray (UD-ray) are all non-monotonic. The mixtures were further split into two ternary mixtures, one containing 1-ethyl-3-methyl-imidazolium ([emim]X) salts (noted as UTE) and the other one containing 1-butyl-3-methyl-imidazolium ([bmim]X) salts (noted as UTB). It was found that the CRCs of UTE mixtures are all non-monotonically J-shaped, while only one (UTB-R3) among UTB mixtures has a little stimulating effect and the CRCs of the other three mixtures (UTB-R1, UTB-R2 and UTB-R4) are monotonic. The CRCs of the binary mixtures designed by the direct equipartition ray design (EquRay) procedure were further examined. The CRCs of the mixtures containing [emim]Cl are non-monotonic J-shaped while those of the mixtures without [emim]Cl are still monotonic. Thus, it can conclude that it is [emim]Cl that causes the non-monotonic CRCs in [amim]X mixtures, even though the CRC of individual [emim]Cl is monotonic.

Growth, bioluminescence and shoal behavior hormetic responses to inorganic and/or organic chemicals: a review

A biphasic dose response, termed hormesis, is characterized by beneficial effects of a chemical at a low dose and harmful effects at a high dose. This biphasic dose response phenomenon has the potential to strongly alter toxicology in a broad range. The present review focuses on the progress of research into hormetic responses in terms of growth (in plants, birds, algae and humans), bioluminescence, and shoal behavior as end points. The paper describes how both inorganic and organic chemicals at a low dose show stimulatory responses while at higher doses are inhibitory. The article highlights how factors such as symbiosis, density-dependent factors, time, and contrasting environmental factors (availability of nutrients, temperature, light, etc.) affect both the range and amplitude of hormetic responses. Furthermore, the possible underlying mechanisms are also discussed and we suggest that, for every end point, different hormetic mechanisms may exist. The occurrences of varying interacting receptor systems or receptor systems affecting the assessment of hormesis for each endpoint are discussed. The present review suggests that a hormetic model should be adopted for toxicological evaluations instead of the older threshold and linear non-threshold models.

Toxicity of ionic liquids: eco(cyto)activity as complicated, but unavoidable parameter for task-specific optimization

Rapid progress in the field of ionic liquids in recent decades led to the development of many outstanding energy-conversion processes, catalytic systems, synthetic procedures, and important practical applications. Task-specific optimization emerged as a sharpening stone for the fine-tuning of structure of ionic liquids, which resulted in unprecedented efficiency at the molecular level. Ionic-liquid systems showed promising opportunities in the development of green and sustainable technologies; however, the chemical nature of ionic liquids is not intrinsically green. Many ionic liquids were found to be toxic or even highly toxic towards cells and living organisms. In this Review, we show that biological activity and cytotoxicity of ionic liquids dramatically depend on the nature of a biological system. An ionic liquid may be not toxic for particular cells or organisms, but may demonstrate high toxicity towards another target present in the environment. Thus, a careful selection of biological activity data is a must for the correct assessment of chemical technologies involving ionic liquids. In addition to the direct biological activity (immediate response), several indirect effects and aftereffects are of primary importance. The following principal factors were revealed to modulate toxicity of ionic liquids: i) length of an alkyl chain in the cation; ii) degree of functionalization in the side chain of the cation; iii) anion nature; iv) cation nature; and v) mutual influence of anion and cation.

Bioassay based luminescent bacteria: interferences, improvements, and applications

Due to the merits of being time-saving, cost effective and simple operation, the luminescent bacteria toxicity assay (LBTA) has been widely used for environmental pollution monitoring. Based on numerous studies since 2007, this critical review aims to give an overview on the mechanisms, developments and applications of LBTA. Firstly, based on the introduction of the mechanisms of LBTA, this review shows the interferences from the characteristics of testing samples (such as inorganic nutrients, color, turbidity) and summarizes the improvements on pretreatment method, test methods and test systems in recent years. Regarding the factors that affect the toxicity prediction of single chemicals, the correlation between the toxicity index expressed as median effective concentration (EC50) and characters (such as Kow, the alkyl chain length, the anion and the cation) of known chemicals, especially the emerging ionic liquids (ILs), were given an in-depth discussion. The models for predicting the joint effect of mixtures to luminescent bacteria were also presented. For the factors that affect the toxicity of actual waters, the correlation of toxicity of actual samples to luminescent bacteria and their conventional indexes were discussed. Comparing the sensitivity of the LBTA with other bioassays could indicate the feasibility of the LBTA applied on specific samples. The summary on the application of LBTA to environmental samples has been made to find the future research direction.

Combined toxicity of pesticide mixtures on green algae and photobacteria

Different organisms have diverse responses to the same chemicals or mixtures. In this paper, we selected the green algae Chlorella pyrenoidosa (C. pyrenoidosa) and photobacteria Vibrio qinghaiensis sp.-Q67 (V. qinghaiensis) as target organisms and determined the toxicities of six pesticides, including three herbicides (simetryn, bromacil and hexazinone), two fungicides (dodine and metalaxyl) and one insecticide (propoxur), and their mixtures by using the microplate toxicity analysis. The toxicities of three herbicides to C. pyrenoidosa are much higher than those to V. qinghaiensis, and the toxicities of metalaxyl and propoxur to V. qinghaiensis are higher than those to C. pyrenoidosa, while the toxicity of dodine to C. pyrenoidosa is similar to those to V. qinghaiensis. Using the concentration addition as an additive reference model, the binary pesticide mixtures exhibited different toxicity interactions, i.e., displayed antagonism to C. pyrenoidosa but synergism to V. qinghaiensis. However, the toxicities of the multi-component mixtures of more than two components are additive and can be predicted by the concentration addition model.

The time-dependent hormetic effects of 1-alkyl-3-methylimidazolium chloride and their mixtures on Vibrio qinghaiensis sp. -Q67

The hormetic effects of ionic liquids (ILs) were paid more ecological attentions. However, the time-dependent hormetic effects of ILs and their mixtures remained to be studied. In this paper, the time-dependent toxicities of five single ILs, 1-ethyl-, 1-butyl-, 1-hexyl-, 1-octyl-, and 1-dodecyl-3-methylimidazolium chlorides (named as [C2mim]Cl, [C4mim]Cl, [C6mim]Cl, [C8mim]Cl, and [C12mim]Cl, respectively), and their five-component mixtures to Vibrio qinghaiensis sp.-Q67 were determined at five exposure time points. For single ILs, [C2mim]Cl displayed significant hormetic effects at 2, 4, 8, and 12h; and [C4mim]Cl exhibited significant hormetic effects at 4, 8 and 12h; while [C6mim]Cl, [C8mim]Cl and [C12mim]Cl have not significant hormetic effects. At the same time point, the longer the side chain is, the larger the inhibition at high concentration is, and the less the stimulation at low concentration is. Meanwhile, the maximum stimulation effects were found between 4 and 8h. All six IL mixtures designed by uniform design ray showed significant hormetic effects at 8 and 12h. By means of the variable selection and modeling method based on the prediction (VSMP), it was found that the higher the concentration of [C2mim]Cl is, the stronger the mixture hormetic effect is and the higher the concentration of [C12mim]Cl is, the weaker the hormetic effect is.

Time-dependent hormetic effects of 1-alkyl-3-methylimidazolium bromide on Vibrio qinghaiensis sp.-Q67: luminescence, redox reactants and antioxidases

The green credentials of ionic liquids (ILs) are being challenged due to the increasing evidence of their toxicity. The hormetic effects further raised their ecological concern. However, it remained poorly studied on the time-dependent changes of the hormetic effects and the mechanisms. In this study, we investigated the time-dependent hormetic effects of four 1-alkyl-3-methylimidazolium bromide ([amim]Br), including 1-ethyl ([emim]Br), -butyl ([bmim]Br), -hexyl ([hmim]Br) and -octyl ([omim]Br), on the luminescence of Vibrio qinghaiensis sp.-Q67. The results showed that [amim]Br with shorter side chains, [emim]Br and [bmim]Br, caused obvious hormetic time-dependent toxicities. The effective concentration (EC) values for the hormetic effects of [emim]Br and [bmim]Br increased with time. [amim]Br with longer side chains, [hmim]Br and [omim]Br, produced sigmoid concentration-dependent inhibitions on the luminescence, and the EC50 values almost unchanged. To illustrate the mechanism, we subsequently examined the responses of redox reactants and antioxidases. [emim]Br and [bmim]Br significantly induced FMN (flavin mononucleotide), NADH (reduced nicotinamide adenine dinucleotide), SOD (superoxide dismutase) and CAT (catalase), and the inductions increased with time, which is similar to the time-dependent changes of their hormetic effects on Q67. Meanwhile, [hmim]Br and [omim]Br did not cause significant effects on the redox reactants and antioxidases. In conclusion, the hormetic effects of [amim]Br on the luminescence, redox reactants and antioxidases showed the dependence on both exposure time and side chains. Our findings provided insights into the time-dependent biological process of the hormetic effects of [emim]Br and [bmim]Br on the photobacterium and its biochemical indicators.

Modeling non-monotonic dose-response relationships: model evaluation and hormetic quantities exploration

Non-monotonic (biphasic) dose-response relationships, known as hormetic relationships, have been observed across multiple experimental systems. Several models were proposed to describe non-monotonic relationships. However, few studies provided comprehensive description of hermetic quantities and their potential application. In this study, five biphasic models were used to fit five hormetic datasets from three different experimental systems of our lab. The bisection algorithm based on individual monotone functions was proposed to calculate arbitrary hormetic quantities instead of traditional methods (e.g., model reparameterization) which need complex mathematical manipulation. Results showed that all the five biphasic models could describe those datasets fairly well with coefficient of determination ( R(2) adj) greater than 0.95 and root mean square error (RMSE) smaller than 0.10. The best-fit model could be selected based on EC(R10), RMSE, and a supplemental criterion of Akaike information criterion (AIC). Hormetic quantities that trigger 10% stimulation at the left (EC(L10)) and right (EC(R10)) side of stimulatory peak were calculated and emphasized for their implication in hormesis exploration for the first time. Furthermore, the EC(L10), proposed as an alarm threshold for hormesis, was expected to be useful in risk assessment of environmental chemicals. This study lays a foundation in the quantitative description of the low dose hormetic effect and the investigation of hormesis in environmental risk assessment.

Significant contributions of ionic liquids containing tetrafluoroborate and trifluoromethanesulfonate to antagonisms and synergisms in multi-component mixtures

Recent toxicity studies on ionic liquids (ILs) are challenging their postulation as green solvents. Previous reports on mixtures containing ILs make it urgent to reveal the responsible components for the toxicity interactions. For that purpose, eight ILs, four consisting of 1-ethyl-3-methylimidazolium ([emim]) and the others of 1-butyl-3-methylimidazolium ([bmim]), were selected as mixture components. The concentrations of eight ILs in mixtures were set up by the uniform design. The inhibition toxicities of single ILs and mixtures to Vibrio qinghaiensis sp.-Q67 were determined by microplate toxicity analysis. Combined toxicity was evaluated by the difference between the effects observed and predicted by the concentration addition model. Using the variable selection and modeling method based on the prediction (VSMP), it was found that the antagonism/synergism induced by the mixtures of eight ILs was related to [emim]BF(4)/[emim]CF(3)SO(3). To further illustrate the toxicity interactions, eight ILs were split into two mixture groups, one containing four [emim]-based ILs and the other four [bmim]-based ILs. The [emim]-group exhibited synergism while [bmim]-group resulted in antagonism. It was interesting that both the synergism and antagonism well related to the concentration ratio of ILs with BF(4)(-). When ILs with BF(4)(-) were deleted from corresponding mixtures, the toxicity interactions (synergism/antagonism) disappeared.