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.

Comparative analysis on the photolysis kinetics of four neonicotinoid pesticides and their photo-induced toxicity to Vibrio Fischeri: Pathway and toxic mechanism

Neonicotinoids are widely used pesticides all over the world and pose severe water pollution. Although they can be degraded via absorbing sunlight, few attentions have been paid to the environmental risks of their photolysis products. In this paper, the photo-toxicity was investigated for four neonicotinoids (dinotefuran, nitenpyram, thiamethoxam and clothianidin) based on a series of experiments (i.e., photolysis kinetics, radical scavenging, bioluminescent inhibition test to Vibrio Fischeri and intermediate identification) and in-silico calculation of photolysis pathway. The results show that direct photolysis dominates the photolysis of the four neonicotinoids under simulated sunlight radiation. The bioluminescent inhibition kinetics shows that all four neonicotinoids have photo-induced toxicity to V. fischeri, but with different light-induced responses. Scavenging radicals (·OH and ¹O₂) will decrease the photo-induced toxicity of all the four neonicotinoids, indicating radicals play important roles to the photo-chemical reactions of intermediates. Dissolved organic matters exhibit slightly shading effect to the photolysis rates of four parent compounds. However, the ROSs generated by DOM can accelerate the photo-chemical reactions of intermediates, leading to different photo-induced toxicity in present of DOM. According to the detected intermediates and Gaussian calculations, there are different photolysis pathways and mechanisms for the four neonicotinoids. The calculation for photo-sensitization reactions with ³O₂ indicates that both energy transfer reactions and electron transfer reactions can be produced under simulated sunlight radiation, which further consolidate that reactive oxygen species are involved in the photolysis process. A theoretical model has been developed to explain the toxicity variations of four neonicotinoids in different aqueous conditions.

Combined lethal toxicities of pesticides with similar structures to Caenorhabditis elegans are not necessarily concentration additives

Studies have shown that the mixture toxicity of compounds with similar modes of action (MOAs) is usually predicted by the concentration addition (CA) model. However, due to the lack of toxicological information on compounds, more evidence is needed to determine whether the above conclusion is generally applicable. In general, the same type of compounds with similar chemical structures have similar MOAs, so whether the toxicities of the mixture of these compounds are additive needs to be further studied. In this paper, three types of pesticides with similar chemical structures (three organophosphoruses, two carbamates and two neonicotinoids) that may have similar MOAs were selected and five binary mixture systems were constructed. For each system, five mixture rays with different concentration ratios were designed by the direct equipartition ray design (EquRay) method. The mortality of Caenorhabditis elegans was regarded as the endpoint for the toxicity exposure to single pesticides and binary mixtures. The combined toxicities were evaluated simultaneously using the CA model, isobologram and combination index. The structural similarity of the same type of pesticides was quantitatively analyzed according to the MACCS molecular fingerprint and the slope of dose-response curve at pEC₅₀. The results show that the toxicities of neonicotinoid mixtures and carbamate mixtures are almost antagonistic. The entire mixture system of dichlorvos and dimethoate produced synergism, and four of the five mixture rays of dimethoate and methamidophos induced antagonism, while among the mixture rays of dichlorvos and methamidophos, different concentrations showed different interaction types. The results of structural similarity analysis show that the size of structural similarity showed a certain quantitative relationship with the toxicity interaction of mixtures, that is, the structural similarity of the same type of pesticides may show an additive action in a certain range.

Quantitative evaluation and the toxicity mechanism of synergism within three organophosphorus pesticide mixtures to Chlorella pyrenoidosa

Organophosphorus pesticide (OPP) pollutants in the environment pose toxicity risks to living organisms, and the possible toxicity mechanism needs to be further clarified. Therefore, the individual and combined toxicity of three OPPs namely acephate (ACE), trichlorfon (TRI) and glyphosate (GIY) towards a freshwater green alga Chlorella pyrenoidosa (C. pyrenoidosa) was investigated by the time-dependent microplate toxicity analysis method. Here, a ternary mixture system of the three OPPs including five rays with different concentration ratios was designed by the uniform design ray method. The standard additive reference model, concentration addition (CA), was used to analyse toxicity interaction within ternary mixtures and the toxicity interaction intensity was characterized using a deviation from CA model (dCA). Besides, the effects of the three OPPs and their mixtures on the chlorophyll (CHL) content, superoxide dismutase (SOD) activity and malondialdehyde (MDA) content of C. pyrenoidosa were also investigated to explore the possible mechanisms. The results show that toxicity of the three pesticides and their ternary mixture rays is time-dependent and the combined toxicity correlates well with the components, ACE and GLY. It is likely that there is a significant time-dependent synergism in ternary mixtures induced by ACE and GLY. The synergism intensity of the ternary mixtures is not more than 30% at the whole experimental concentration level. The CHL reduction rate and MDA content of C. pyrenoidosa increase, while the SOD activity of C. pyrenoidosa decreases with the lengthening of exposure time under the action of the three pesticides and their ternary mixtures. So, the possible mechanism of the three pesticides and their mixtures may be by affecting the photosynthesis, and then causing oxidative damage to C. pyrenoidosa cells. The results can provide reference for the combined toxicity assessment of OPPs to living organisms.

Significant effects of two pesticides on the bacteriostatic activity and antioxidant ability of green tea polyphenols

Green tea polyphenols (GTPs) are widely used in food preservation because of their strong bacteriostatic activity and antioxidant ability, and whether pesticides as common pollutants in food will affect the function of GTPs is worthy of attention.

Time-dependent synergism of five-component mixture systems of aminoglycoside antibiotics toVibrio qinghaiensissp.-Q67 induced by a key component

A large number of antibiotics are entering the aquatic environment accompanying human and animal excreta, which will threaten the survival of aquatic organisms and even human health. It has been found that binary mixtures of aminoglycoside (AG) exhibit additive action and can be evaluated well by a classical model, concentration addition (CA) in our past study. Therefore, to investigate the toxicity interaction within multi-component mixtures of AG antibiotics, five antibiotics, kanamycin sulfate (KAN), neomycin sulfate (NEO), tobramycin (TOB), streptomycin sulfate (STS), and gentamicin sulfate (GEN), were selected to construct five-component mixture systems by a uniform design ray method. The toxic effects (luminescence inhibition) of single antibiotic and five-antibiotic mixture systems towards a photobacterium Vibrio qinghaiensis sp.-Q67 (V. qinghaiensis) in different exposure time (0.25, 2, 4, 8, and 12 h) were determined by the time-dependent microplate toxicity analysis method. The concentration-effect data were fitted by a nonlinear least square method, toxicity interaction within mixture systems was analyzed by a CA model, and the interaction intensity was characterized by deviation from the CA model (dCA). Besides, the toxicity mechanism of five antibiotics and their five-component mixtures to V. qinghaiensis was analyzed by electron microscopy. The results show that toxicity of five antibiotics and their five-component mixture systems to V. qinghaiensis is time-dependent and has strong long-term toxicity. Different from binary AG antibiotic mixture systems, five-antibiotic mixture systems exhibit obviously time-dependent synergism. In addition, toxicity of the five-antibiotic mixtures can be 1.4 times higher than that of the mixtures without synergisms at the same concentration level. According to dCA, synergism intensity (dCA) curves of rays move slowly from the high concentration region to the medium or lower one and the maximum dCA values also increase, decrease, or first increase, then decrease with the lengthening of exposure time. The inhibition activity and synergism intensity of mixture rays have good correlation with the concentration ratios of STS, the key component for synergism. The cell morphology of V. qinghaiensis indicates the strong toxicity of five antibiotics and their mixture rays is not due to the destruction of cell structure, but the inhibition of the light-emitting activity of the photobacterium.

There was time-dependent synergism in the five-component mixture systems of five antibiotics, which induced by STS.

Predicting the hormesis and toxicological interaction of mixtures by an improved inverse distance weighted interpolation

The prediction of toxicological interactions and hormesis of chemical mixtures is important because organisms are mostly exposed to numerous contaminants and typically to low dose of these mixtures, and it is still a challenge. Although many models have been developed to predict the mixture toxicities such as concentration addition (CA) and independent action (IA), they cannot solve these challenges perfectly. This study has developed an improved inverse distance weighted (IDW) interpolation for prediction of the mixture toxicities. IDW uses the mixture and the single compound as scatter points in space, and the space can be constructed by the concentration axes of various components in the mixture system. Some known mixtures (or the single compound) closest to the unknown mixture are selected as interpolation nodes. To be more accurate in calculation, a new normalization method for concentration has been proposed through dividing the concentration of the mixture and the single compound by the respective EC₅₀ values. Sixteen binary mixture systems are selected for leave-one-out cross-validation and three binary mixture systems are selected for external validation. The results show that the accuracy of IDW is ≥95% for three types of mixtures including no hormetic component, one hormetic component (show no toxicological interaction), and two hormetic components. The IDW also show higher prediction accuracy than that of CA and IA. The IDW developed in this study can be used to predict the toxicity of various mixture systems, thus providing predictive information for chemical mixtures risk assessment.

Polyethylene glycol 400 significantly enhances the stimulation of 2-phenoxyethanol on Vibrio qinghaiensis sp.-Q67 bioluminescence

Previous studies demonstrated long-term stimulation of some commercial personal care products (PCPs) on freshwater luminescent bacteria Vibrio qinghaiensis sp.-Q67 (Q67). However, whether a certain component can affect mixture's hormetic effect is still unknown. In this paper, two of ingredients in PCPs, 2-phenoxyethanol (PhE) and polyethylene glycol 400 (PEG400), were selected as object compounds to explore the relationship between concentration-response (CR) of mixtures and that of a single component. It was found that PEG400 has monotonic CR (MCR) on Q67 both at the short-term (0.25 h) and long-term (12 h) exposures while PhE has MCR at 0.25 h and hormetic CR (HCR) at 12 h. Here, the concentration-response curves (CRCs) of PEG400 at 0.25 and 12 h are overlapped each other and the CRCs of PEG400 are on the right of PhE. If the pEC₅₀ is taken as a toxic index, the toxicities of PEG400 at two times are basically the same, and those of PhE are the same, too, but PhE is twice as toxic as PEG400. For the mixtures of PEG400 and PhE, all rays except R1 have MCRs at 0.25 h while all rays have HCRs at 12 h where the higher the mixture ratio of PhE is, the more negative the maximum stimulation effect is. More importantly, the E_min values of all rays are more negative (1.79-3.17-fold) than that of PhE worked alone, which implies that the introduction of PEG400 significantly enhances stimulative effect of PhE. At 0.25 h, all binary mixture rays but R1 produce a low-concentration additive action and high-concentration synergism. At 12 h, all rays display additive action, antagonism, additive action, and synergism in turn when the concentration changes from low to high. The overall findings suggested toxicological interactions should be considered in the risk assessment of PCPs and their potential impacts on ecological balances.

Using an interpolation-based method (IDVequ) to predict the combined toxicities of hormetic ionic liquids

In the field of computational toxicology, predicting toxicological interaction or hormesis effect of a mixture from individuals is still a challenge. The two most frequently used model concentration addition (CA) and independent action (IA) also cannot solve these challenges perfectly. In this paper, we used IDV_equ (an interpolation method based on the Delaunay triangulation and Voronoi tessellation as well as the training set of direct equipartition ray design (EquRay) mixtures) to predict the toxicities of binary mixtures composed of hormetic ionic liquids (ILs). One of the purposes is to verify the predictive ability of IDV_equ. The other one is to improve the risk assessment of ILs mixtures especial hormetic ILs, because the toxicity reports of ILs mixtures are rarely reported in particular the toxicity of the hormetic ILs mixtures. Hence, we determined time-dependent toxicities of four ILs and their binary mixtures (designed by EquRay) to Vibrio qinghaiensis sp.-Q67 at first. Then, mixture toxicities were predicted and compared using the IDV_equ and CA. The results show that, the accuracy of IDV_equ is higher than the accuracy of CA. And, more important, to some mixtures out of the CA application, IDV_equ also can predict the mixture effects accurately. It showed that IDV_equ can be applied to predict the toxicity of any binary mixture regardless of the type of concentration-response curve of the components. These toxicity data provided useful information for researching the prediction of hormesis or toxicological interaction of the mixture and toxicities of ILs mixtures.

Commercial personal care product mixtures exhibit hormetic concentration-responses to Vibrio qinghaiensis sp.-Q67

The biological effects related to personal care products (PCPs) are almost induced by some active ingredients in the PCPs rather than the PCP itself. In this study, 23 common and widely used toner, skin water, and make-up water (TSM) commodities were directly taken as mixture samples, and Vibrio qinghaiensis sp.-Q67 (Q67) was used as the test organism. The toxicities of the TSMs to Q67 were determined via microplate toxicity analysis at 0.25 h and 12 h. Each TSM commodity can be regarded as a complicated mixture (relative concentration is 1). It was shown that the concentration-response curves (CRCs) of 23 TSMs are monotonic sigmoid-shaped (S-shaped) at 0.25 h, the CRCs of six TSMs are also S-shaped but the other 17 TSMs are non-monotonic hormetic or J-shaped at 12 h. In addition, to effectively characterize the nature of the stimulation and inhibition phases, it is suggested that five parameters such as the EC_L (the median stimulation effective concentration (left)), E_min (the maximum stimulation effect), EC_min (the maximum stimulation effective concentration), ZEP (zero effect point where the effect is 0 and the concentration is ZEP), and EC₅₀ can depict the non-monotonic CRC. To the best of our knowledge, this is the first study about the hormetic CRCs of commercial PCP mixtures.

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.

Time-dependent and Pb-dependent antagonism and synergism towards Vibrio qinghaiensis sp.-Q67 within heavy metal mixtures

Toxicity interaction has aroused many researchers' interest in the combined toxicity of pollutants. Recently, some published studies have shown that the toxicity of some mixture pollutants is time dependent and well correlated with certain components in the mixture. Therefore, to investigate whether toxicity interaction is affected by the exposure time or certain components, synergism and antagonism within typical environmental contaminants of heavy metal mixtures were analyzed in different exposure times. Herein, three binary and one ternary mixture systems were designed by using three heavy metals: cadmium chloride, lead chloride (Pb) and manganese(ii) chloride tetrahydrate (Mn). For each mixture system, five mixture rays with different concentration ratios were arranged by direct equipartition ray design and uniform design ray methods. The toxicities of the three heavy metals and 20 mixture rays towards photobacteria Vibrio qinghaiensis sp.-Q67 (Q67) were determined by the established time-dependent microplate toxicity analysis (t-MTA) in different exposure durations of 0.25, 2, 4, 8 and 12 h. It was shown that the toxicities of three heavy metals (Cd, Pb and Mn) as well as their binary and ternary mixture rays to Q67 were also time dependent, but different metals or mixture rays showed different time characteristics. Surprisingly, some mixture rays exhibited antagonism or synergism with time dependency and the time characteristics varied in different mixture systems. Furthermore, the binary or ternary mixture systems with Pb displayed antagonism, while the Cd–Mn mixture system without Pb exhibited additive action or synergism, which indicated that Pb was probably the causative agent of antagonism produced by mixtures.

Toxicity interaction has gained much interest in the research of toxicity of mixture pollutants.

The time-dependent synergism of the six-component mixtures of substituted phenols, pesticides and ionic liquids to Caenorhabditis elegans

Traditional environmental risk assessment rarely focused on exposures to multi-component mixtures which may cause toxicological interactions and usually ignored that toxicity is a process in time, which may underestimate the environment risk of mixtures. In this paper, six chemicals belonging to three categories, two substituted phenols, two pesticides and two Ionic liquids, were picked to construct a six-component mixture system. To systematically examine the effects of various concentration compositions, the uniform design ray method was employed to design nine mixture rays with nine mixture ratios and for every mixture ray 12 concentration levels were specified by the fixed ratio ray design. The improved combination index was used to evaluate the combined toxicities of the mixtures to Caenorhabditis elegans (C. elegans) in the exposure times of 6, 12 and 24h. It was shown that the mixture rays display time-dependent synergism, i.e. the range of synergistic effect narrows and the strength of synergism runs down with exposure time, which illustrates that the mixture toxicity of some chemicals is not a sum of individual toxicities at some exposure times and it is necessary to consider the toxicological interaction in mixtures.

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.

Polymyxin B sulfate inducing time-dependent antagonism of the mixtures of pesticide, ionic liquids, and antibiotics to Vibrio qinghaiensis sp.-Q67

In the real environment, organisms are simultaneously exposed to different types of chemicals.

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.