Joint Toxic Action Research Articles

Evaluation of joint toxic action for antibiotics based on bacterial quorum sensing

Evaluation of joint toxic action for antibiotics based on bacterial quorum sensing

Spontaneous interactions between typical antibiotics and soil enzyme: Insights from multi-spectroscopic approaches, XPS technology, molecular modeling, and joint toxic actions

A large amount of antibiotics enters the soil environment and accumulates therein as individuals and mixtures, threatening the soil safety. However, there is little information regarding the influence of single and mixed antibiotics on key soil proteins at molecular level. In this study, setting sulfadiazine (SD) and tetracycline hydrochloride (TC) as the representative antibiotics, the interactions between these agents and α-amylase (an important hydrolase in soil carbon cycle) were investigated through multi-spectroscopic approaches, X-ray photoelectron spectrometry, and molecular modeling. It was found that both SD and TC spontaneously bound to α-amylase with 1:1 stoichiometry mainly via forming stable chemical bonds. The interactions altered the polarity of aromatic amino acids, protein backbone, secondary structure, hydrophobicity and activity of α-amylase. The SD-TC mixtures were designed based on the direct equipartition ray to comprehensively characterize the possible concentration distribution, and interactive effects indicated that the mixtures antagonistically impacted α-amylase. These findings reveal the binding characteristics between α-amylase and typical antibiotics, which probably influence the ecological functions of α-amylase in soil. This study clarifies the potential harm of antibiotics on soil functional enzyme, which is significant for the environmental risk assessment of antibiotics and their mixtures.

Histopathological investigation of some facial cosmetic products mixture exposed to fingerlings of mud catfish <i>(Clarias gariepinus</i>)

Cosmetics are one of the major pollutants in the aquatic ecosystem due to the quantum of production to meet the astronomical demand of users that eventually becomes harmful to organisms. Changes in physic-chemical parameters such as potential of hydrogen (pH), Electrical conductivity (EC), Temperature (T oC) Dissolved oxygen (DO) were investigated at the beginning and after 96 hours of cosmetic exposure. This study also investigated the effects of four facial cosmetic products (Powder, foundation, concealer, and primer) histopathologically in fingerlings of Clarias gariepinus (gills) exposed to binary, trinary, and quaternary mixtures in o laboratory bioassays for 48 hours and 96 hours. The results of pH, T C, EC and DO ranged from 6.21 - 6.64, o 25.40 - 26.70 oC, 0.04 - 0.14 mS/cm, and 10.00 -12.00 mg/l respectively. The joint action toxicity evaluation of the binary, trinary, and quaternary mixtures of the cosmetics prepared based on an equitoxic ratio against the test organism was in concordance with the model of synergism. Results showed the prevalence of severe lamellar necrosis in the gills of C. gariepinus which was observed across all combinations except in the combinations of Powder + Primer as well as Powder + Foundation + Concealer + Primer. Moderate lamellar necrosis and hypertrophied epithelium were observed in fish exposed to a mixture of Powder + Foundation + Concealer. The results obtained in this study suggested that the presence of facial cosmetics in the aquatic ecosystem could be dangerous to fish and subsequently human health via biomagnification. Therefore, there is an urgent need for environmental regulators to enforce safety standards for the emission of these selected cosmetics wastes into the waterways to prevent damage to aquatic organisms and public health issues.

Acute toxicity of binary mixtures for quorum sensing inhibitors and sulfonamides against Aliivibrio fischeri: QSAR investigations and joint toxic actions

Quorum sensing inhibitors (QSIs), as a kind of ideal antibiotic substitutes, have been recommended to be used in combination with traditional antibiotics in medical and aquaculture fields. Due to the co-existence of QSIs and antibiotics in environmental media, it is necessary to evaluate their joint risk. However, there is little information about the acute toxicity of mixtures for QSIs and antibiotics. In this study, 10 QSIs and 3 sulfonamides (SAs, as the representatives for traditional antibiotics) were selected as the test chemicals, and their acute toxic effects were determined using the bioluminescence of Aliivibrio fischeri (A. fischeri) as the endpoint. The results indicated that SAs and QSIs all induced S-shaped dose-responses in A. fischeri bioluminescence. Furthermore, SAs possessed greater acute toxicity than QSIs, and luciferase (Luc) might be the target protein of test chemicals. Based on the median effective concentration (EC50) for each test chemical, QSI-SA mixtures were designed according to equitoxic (EC50(QSI):EC50(SA) = 1:1) and non-equitoxic ratios (EC50(QSI):EC50(SA) = 1:10, 1:5, 1:0.2, and 1:0.1). It could be observed that with the increase of QSI proportion, the acute toxicity of QSI-SA mixtures enhanced while the corresponding TU values decreased. Furthermore, QSIs contributed more to the acute toxicity of test binary mixtures. The joint toxic actions of QSIs and SAs were synergism for 23 mixtures, antagonism for 12 mixtures, and addition for 1 mixture. Quantitative structure–activity relationship (QSAR) models for the acute toxicity QSIs, SAs, and their binary mixtures were then constructed based on the lowest CDOCKER interaction energy (Ebind-Luc) between Luc and each chemical and the component proportion in the mixture. These models exhibited good robustness and predictive ability in evaluating the toxicity data and joint toxic actions of QSIs and SAs. This study provides reference data and applicable QSAR models for the environmental risk assessment of QSIs, and gives a new perspective for exploring the joint effects of QSI-antibiotic mixtures.

Biochemical alterations in cotton leafworm, Spodoptera littoralis (Boisd.) related to emamectin benzoate and fipronil compared to their joint action

Cotton leafworm, Spodoptera littoralis (Boisduval), is one of the major destructive pests of ornamental, industrial, and vegetable crops. The efficacy of technical emamectin benzoate (EMB) and fipronil (FPR) was assessed against the 4th larval instar using leaf-dip bioassay method. EMB was more efficient than FPR based on 96 h LC50 values of 0.004 and 0.023 μg/ml, respectively. Joint toxic action of the dual exposure in sequence with time interval 24 h and in mix were evaluated at LC10:LC10, LC25:LC25 and LC50:LC50 after 96 h posttreatment, as well. Their impacts on detoxification enzymes, esterases (ESTs); alkaline phosphatase (ALP); and glutathione S-transferase (GST) as well as acetylcholine esterase (AChE) were also determined. The sequential exposure of EMB after FPR (S1) produced antagonism, potentiation, and potentiation effects, respectively while sequential exposure of FPR after EMB (S2) interacted as addition, potentiation, and potentiation respectively. The rest of binary mixtures (Mix) revealed antagonistic effect regardless of concentration. Orthogonal contrast analysis showed that the highest elevations of AChE, α-EST, β- EST and ALP enzymes were obtained from Mix at LC50:LC50 (181.6%, 288.4, 229.2 and 460.9%, respectively), LC25:LC25 (131.5%, 252.8, 205.60 and 252.0, respectively) and LC10:LC10 (106.6%, 215.6%, 201.8% and 170.0%, respectively). Differently, the greatest elevation of GST activity (157.7%) resulted from S1 at LC50:LC50, while it was significantly lower at LC25:LC25 and LC10:LC10 as well as Mix and S2 at all concentrations than corresponding concentrations of FPR. These findings shed some light on the role of GST in FPR toxicity and clarified the risk of these dual exposures in elevating detoxification enzymes dangerously compared to their individual insecticides. These dual exposures should be carefully handled. Although rotational exposure at low concentrations may enhance performance and mitigate resistance risk, rotational exposure at high concentrations and Mix may indirectly contribute to the evolution of cross-resistance to other insecticides.

Time-dependent hormetic effects of polypeptide antibiotics and two antibacterial agents contribute to time-dependent cross-phenomena of their binary mixtures

Polypeptide antibiotics (PPAs), silver nanoparticles (plural) (AgNP) and quorum sensing inhibitors (QSIs) are considered to be the ideal antibiotic substitutes. Due to the great potential for the combined use of these antibacterial agents, it is necessary to evaluate their joint effects. In this study, the joint toxic actions for the binary mixtures of PPA + PPA, PPA + AgNP, and PPA + QSI were judged via the independent action (IA) model based on the individual and combined toxicity of test agents to the bioluminescence of Aliivibrio fischeri during 24 h. It was observed that the single agents (PPAs, AgNP, and QSI) and the binary mixtures (PPA + PPA, PPA + AgNP, and PPA + QSI) all triggered the time-dependent hormetic effects on the bioluminescence, where the maximum stimulatory rate, the median effective concentration, and the occurrence of hormesis varied with the increase of time. While bacitracin triggered the maximum stimulatory rate (266.98 % at 8 h) among the single agents, the mixture of capreomycin sulfate and 2-Pyrrolidinone induced the maximum stimulatory rate (262.21 % at 4 h) among the binary mixtures. The cross-phenomenon that the dose-response curve of mixture crossed the corresponding IA curve was observed in all treatments, which also varied with time, exhibiting that the joint toxic actions and corresponding intensities possessed dose- and time-dependent features. Furthermore, three kinds of binary mixtures resulted in three different variation tendencies for the time-dependent cross-phenomena. Mechanistic speculation indicated that test agents possessed the stimulatory modes of action (MOAs) at low-dose and inhibitory MOAs at high-dose to induce the hormetic effects, and the interplays between these MOAs varied with time to trigger the time-dependent cross-phenomenon. This study provides the reference data for the joint effects of PPAs and typical antibacterial agents, which will benefit the application of hormesis in the exploration of time-dependent cross-phenomenon and promote the future development of environmental risk assessment of pollutant mixtures.

Factors affecting the toxicity and oxidative stress of layered double hydroxide-based nanomaterials in freshwater algae

Layered double hydroxide (LDH) nanomaterials are utilized extensively in numerous fields because of their distinctive structural properties. It is critical to understand the environmental behavior and toxicological effects of LDHs to address potential concerns caused by their release into the environment. In this work, the toxicological effects of two typical LDHs (Mg-Al-LDH and Zn-Al-LDH) on freshwater green algae (Scenedesmus obliquus) and the main affecting factors were examined. The Zn-Al-LDH exhibited a stronger growth inhibition toxicity than the Mg-Al-LDH in terms of median effect concentration. This toxicity difference was connected to the stability of particle dispersion in water and the metallic composition of LDHs. The contribution of the dissolved metal ions to the overall toxicity of the LDHs was lower than that of their particulate forms. Moreover, the joint toxic action of different dissolved metal ions in each LDH belonged to additive effects. The Mg-Al-LDH induced a stronger oxidative stress effect in algal cells than the Zn-Al-LDH, and mitochondrion was the main site of LDH-induced production of reactive oxygen species. Scanning electron microscope observation indicated that both LDHs caused severe damage to the algal cell surface. At environmentally relevant concentrations, the LDHs exhibited joint toxic actions with two co-occurring contaminants (oxytetracycline and nano-titanium dioxide) on S. obliquus in an additive manner mainly. These findings emphasize the impacts of the intrinsic nature of LDHs, the aqueous stability of LDHs, and other environmental contaminants on their ecotoxicological effects.

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) adsorbed on microplastics in drinking water: Implications for female exposure, reproductive health risk and its mitigation strategies through in silico methods

In this paper, molecular dynamics (MD) simulations were used to analyze the effects of different additive combinations in microplastics (MPs) on the female reproductive toxicity of perfluoroalkyl and polyfluoroalkyl substances (PFAS). It was found that 59.38% of plastic additive combinations had synergistic toxicity effects. And the plastic additive combination scheme with 31.10% decrease of joint toxic action was selected. By simulating the PFAS adsorption by MPs in drinking water through MD, it was found that hydrophobic PFAS was more easily adsorbed by MPs, and the van der Waals interaction energy may have an influential role in MPs adsorbing PFAS. The degree of interference with PFAS adsorption by MPs is greater when the MP is supplemented with a more hydrophobic additive. During AC adsorbing PFAS and MPs, it was found that some of the PFAS was adsorbed by MPs, and improving the adsorption of MPs by AC could also improve the removal rate of PFAS from drinking water. The effect of hydrophobic natural organic matter (NOM) on AC adsorbing PFAS and MPs was more significant, and the higher the molecular weight, the greater the effect on the adsorption performance of the AC. Within a certain range, ACs show an increasing tendency to adsorb PFAS and MPs with decreasing pore size and increasing amine functionalization. Machine learning method was used to get the influence rule of molecular parameters on improving PFAS function and reducing female reproductive toxicity. This study aims to mitigate the toxic hazards to female reproductive from current exposure to PFAS through drinking water, and to provide theoretical guidance for designing PFAS alternatives with low female reproductive toxicity.

Joint Toxic Action and Metabolic Mechanisms of Graphene Nanomaterial Mixtures in <i>Microcystis Aeruginosa</i>

Joint Toxic Action and Metabolic Mechanisms of Graphene Nanomaterial Mixtures in <i>Microcystis Aeruginosa</i>

Joint Action Toxicity of Arsenic (As) and Lead (Pb) Mixtures in Developing Zebrafish.

Arsenic (As) and lead (Pb) are environmental pollutants found in common sites and linked to similar adverse health effects. Multiple studies have investigated the toxicity of each metal individually or in complex mixtures. Studies defining the joint interaction of a binary exposure to As and Pb, especially during the earliest stages of development, are limited and lack confirmation of the predicted mixture interaction. We hypothesized that a mixture of As (iAsIII) and Pb will have a concentration addition (CA) interaction informed by common pathways of toxicity of the two metals. To test this hypothesis, developing zebrafish (1-120 h post fertilization; hpf) were first exposed to a wide range of concentrations of As or Pb separately to determine 120 hpf lethal concentrations. These data were then used in the CA and independent action (IA) models to predict the type of mixture interaction from a co-exposure to As and Pb. Three titration mixture experiments were completed to test prediction of observed As and Pb mixture interaction by keeping the Pb concentration constant and varying As concentrations in each experiment. The prediction accuracy of the two models was then calculated using the prediction deviation ratio (PDR) and Chi-square test and regression modeling applied to determine type of interaction. Individual metal exposures determined As and Pb concentrations at which 25% (39.0 ppm Pb, 40.2 ppm As), 50% (73.8 ppm Pb, 55.4 ppm As), 75% (99.9 ppm Pb, 66.6 ppm As), and 100% (121.7 ppm Pb, 77.3 ppm As) lethality was observed at 120 hpf. These data were used to graph the predicted mixture interaction using the CA and IA models. The titration experiments provided experimental observational data to assess the prediction. PDR values showed the CA model approached 1, whereas all PDR values for the IA model had large deviations from predicted data. In addition, the Chi-square test showed most observed results were significantly different from the predictions, except in the first experiment (Pb LC25 held constant) with the CA model. Regression modeling for the IA model showed primarily a synergistic response among all exposure scenarios, whereas the CA model indicated additive response at lower exposure concentrations and synergism at higher exposure concentrations. The CA model was a better predictor of the Pb and As binary mixture interaction compared to the IA model and was able to delineate types of mixture interactions among different binary exposure scenarios.

Toxicity, joint action effect, and enzymatic assays of abamectin, chlorfenapyr, and pyridaben against the two-spotted spider mite Tetranychus urticae

BackgroundIn the present study, the comparative toxicity of three different acaricides (abamectin, chlorfenapyr, and pyridaben) in technical and formulated forms was assessed on the eggs and adult females of a susceptible strain of Tetranychus urticae. Joint toxic effects of the tested acaricides were also performed against eggs and adults. In addition, the in vitro assay of the tested acaricides was evaluated against some target enzymes isolated from the adult females.ResultsThe LC50 values against eggs by leaf-disk-dip technique were estimated to be 294.27, 1032.93, and 9550.54 mg/L for abamectin, chlorfenapyr, and pyridaben, respectively. However, the LC50 values were 783.06, 666.55, and 731.36 mg/L for the formulations Agromectin, Challenger, and Sanmite, respectively. Abamectin was found to be the greatest lethal to the adults (LC50 = 5.39 mg/L) followed by chlorfenapyr (LC50 = 106.51 mg/L) after 24 h of the treatment by slide-dip technique. Pyridaben was least toxic (LC50 = 690.23 mg/L). Agromectin (LC50 = 0.94 mg/L) followed by Challenger (LC50 = 73.65 mg/L) while the Sanmite was the lowest toxic one (LC50 = 1160.60 mg/L) against the adults. The results of joint toxic action proved that all combinations between the technical or formulated acaricides exhibited potentiation effect and the toxicity was increased significantly against eggs and adults of T. urticae compared to the individual pesticide. The activity of acetylcholinesterase (AChE), adenosine triphosphatase (ATPase), acid and alkaline phosphatases (ACP and ALP), carboxylesterase (CaE), gamma-aminobutyric acid transaminase (GABA-T), and glutathione-S-transferase (GST) isolated from adults treated with 0.025, 0.05, 0.1, 0.5, 1, and 5 mg/L were significantly inhibited compared to the control.ConclusionThis study provides the theoretical basis for a rational application of abamectin, chlorfenapyr, and pyridaben mixtures in T. urticae control.

Hormetic dose-response of halogenated organic pollutants on Microcystis aeruginosa: Joint toxic action and mechanism

Quinolones (QNs), dechloranes (DECs), and chlorinated paraffins (CPs) are three kinds of new halogenated organic pollutants (HOPs), which originate from the use of flame retardants, lubricants and pesticides. Since QNs, DECs, and CPs are frequently detected in waters and sediments, it is necessary to investigate the toxic effects of these HOPs with dwelling phytoplankton, especially for cyanobacteria, to explore their potential hormetic effects and contributions to algal blooms. In the present study, we investigate single and joint toxicity of QNs, DECs and CPs on Microcystis aeruginosa (M. aeruginosa), a cyanobacterium that is frequently implicated with algal blooms. The results indicate single QNs and DECs induce marked hormetic effects on the proliferation of M. aeruginosa but CPs do not. The stimulatory effect of hormesis is linked with accelerated replication of DNA, which is considered to stem from the moderate rise in intracellular reactive oxygen species (ROS). Joint toxicity tests reveal that both QNs & CPs mixtures and DECs & CPs mixtures show hormetic effects on M. aeruginosa, but QNs & DECs mixtures show no hormetic effect. QNs & DECs mixtures exhibit synergistic toxic actions, which may be caused by a sharp rise in intracellular ROS simultaneously produced by the agents. Joint toxic actions of both QNs & CPs, and DECs & CPs shift from addition to antagonism as concentration increases, and this shift may mainly depend on the influence of CPs on cell membrane hydrophobicity of M. aeruginosa. This study provides data and toxic mechanisms for the hormetic phenomenon of single and joint HOPs on M. aeruginosa. The hormetic effects of HOPs may benefit the proliferation of M. aeruginosa in the aquatic environment, aggravating the formation of algal blooms. This study also reflects the important role of hormesis in environmental risk assessment of pollutants.

A simple judgment method for joint action of antibacterial agents on bacterial resistance

The severe pollution of bacterial resistance induced by the wide and even indiscriminate use of antibacterial agents has posed serious threats to human health and ecological safety. Furthermore, the combined effects of antibacterial agents have a closer relationship with the pollution of bacterial resistance than single antibacterial agent. However, there is little information regarding how multiple antibacterial agents interplay to induce bacterial resistance. Here, we developed a simple judgment method with five basic procedures for the joint action of antibacterial agents on bacterial resistance, involving toxicity determination, mutation frequency determination, conjugative transfer frequency determination, dose-response relationship fitting, key parameters obtaining, and joint resistance action judgment. This proposed approach was validated through investigating the joint resistance action between silver nanoparticle (AgNP) and 1-pyrrolidino-1-cyclohexene (1P1C, a kind of quorum sensing inhibitors). According to the procedures, the mutation unit and conjugative transfer unit for the AgNP-1P1C mixture were calculated to be 64.27 and 5.10, respectively, indicating the antagonism for their joint resistance action. This method can not only benefit the mechanistic explanation for how mixed antibacterial agents stimulate the bacterial resistance, but also guide the environmental risk assessment and clinical use of combined antibacterial agents in the related fields.• We present a novel method to judge the joint resistance action of antibacterial agents, taking the emergence and dissemination of antibiotic resistance genes into account.• Toxicity determination can help to design the mixtures of antibacterial agents and confirm the appropriate test concentration range of antibacterial agents used in mutation frequency and conjugative transfer frequency determination.• The mutation unit and conjugative transfer unit were proposed according to the toxic unit in the judgment of joint toxic action.

Effects of natural organic matter on the joint toxicity and accumulation of Cu nanoparticles and ZnO nanoparticles in Daphnia magna

Various modern products have metallic nanoparticles (MNPs) embedded to enhance products performance. Technological advances enable nowadays even multiple hybrid nanoparticles. Consequently, the future co-release of multiple MNPs will inevitably result in the presence of MNP mixtures in the environment. An important question is if the responses of mixtures of MNPs can be dealt with in a similar way as with the responses of biota to mixtures of metal salts. Moreover, natural organic matter (NOM) is an important parameter affecting the behavior and effect of MNPs. Herein, we determined the joint toxicity and accumulation of copper nanoparticles (CuNPs) and zinc oxide nanoparticles (ZnONPs) in Daphnia magna in the absence and presence of Suwannee River natural organic matter (SR-NOM), compared to the joint toxicity and accumulation of corresponding metal salts. The results of toxicity testing showed that the joint toxicity of CuNPs + ZnONPs was greater than the single toxicity of CuNPs or ZnONPs. The joint toxic action of CuNPs + ZnONPs was additive or more-than-additive for D. magna. A similar pattern was found in the toxicity of the mixtures of Cu- and Zn-salts from the literature data. The presence of SR-NOM had no significant impact on the joint toxicity of CuNPs + ZnONPs. The calculated component-specific contribution to overall toxicity indicated that SR-NOM increased the relative contribution of dissolved ions released from the MNPs to the toxicity of the binary mixtures at high-effect concentrations of individual MNPs. Moreover, dissolved Zn-ions released from the ZnONPs were found to dominate the joint toxicity of CuNPs + ZnONPs in the presence of SR-NOM. Furthermore, the results of the accumulation experiment displayed that the presence of SR-NOM significantly enhanced the accumulation of either CuNPs or ZnONPs in D. magna exposed to the MNP mixtures.

Toxicity of Quaternary Mixture of Formulated Glyphosate and Phenols on Providencia vermicola Dehydrogenase Activity

Aims: To assess the toxicity of glyphosate (as an active ingredient in drysate), three phenols (2,4-dichlorophenol, 4-chlorophenols and phenol) and quaternary mixtures of glyphosate, 2,4-dichlorophenol, 4-chlorophenol and phenol on the dehydrogenase activity (DHA) of P. vermicola.
 Study Design: The glyphosate, 2,4-dichlorophenol, 4-chlorophenol and phenol mixture ratios (%) were designed as: 25%:25%:25%:25%; 30%:20%:20%:30%, 40%:10%:10%: 40%; 50%:5%:30%:15% and 20%:20%:10%:50% for the respective mixtures in the concentration range of 0-1000 mg/L.
 Place and Duration of Study: Silver Press Laboratory, Owerri Nigeria between July, 2016 and August, 2019.
 Methodology:A laboratory scale study was carried on four toxicants using dehydrogenase inhibition test. The inhibition of dehydrogenase activity of the isolate by toxicant was calculated relative to the control. The percentage inhibition data generated was fitted into a logistic dose response model and Weibulleum to obtain their respective IC50.
 Results:The results revealed that the median inhibitory concentrations (IC50) of the mixtures on the Providencia vermicola were 247.17 ±10.20, 163.44 ± 8.18, 251.33 ± 45.25, 267.30 ± 8.76 and 178.93 ± 45.53 mg/L, respectively. Toxicity index (TI) model was used to evaluate the joint action toxicity of the mixtures on the test organism and was 60 % antagonistic.
 Conclusion: Thus, these synergistic and additive interactions of formulated glyphosate with the intermediates of 2,4-D was possible against the dehydrogenase activity of Providenciavermicola an important plant growth promoting bacterium. The dynamics of the toxic effects thus would depend on the concentration of the compounds.

Joint Toxic Action of Spinosad with Fenpropathrin and Chlorpyrifos and its Latent Effect on Different Egyptian Field Populations of Spodoptera littoralis

Joint Toxic Action of Spinosad with Fenpropathrin and Chlorpyrifos and its Latent Effect on Different Egyptian Field Populations of Spodoptera littoralis

The effects of complex metal oxide mixtures on three soil invertebrates with contrasting biological traits

For regulatory purposes, the concentration addition model is the default first tier for assessing joint-action toxicity of metal mixtures. Although many researchers have evaluated binary and ternary mixtures, fewer have investigated joint-action toxicity in more complex mixtures, where deviations from additivity are more likely due to the greater number of potential interactions. In this study, we tested fixed ratios of five metals (lead, copper, nickel, zinc, cobalt) as metal oxide mixtures on three soil invertebrate species (Enchytraeus crypticus, Folsomia candida, Oppia nitens) at different dose effect levels (EC10-EC90) in an acid sandy forest and a loamy soil. Total metal concentrations for mixture ratios in soil did not explain or correlate with species responses. For F. candida, toxicity was linked to metal solubility, while for O. nitens and E. crypticus, toxicity did not correlate with total or extractable metals. In O. nitens and E. crypticus, however, soil ingestion could be an important route of exposure. Analysing the joint effect of metal mixtures, F. candida response was globally additive, while E. crypticus and O. nitens both presented synergistic effects at low-dose effect levels. Estimations at the EC50 level underestimated the deviations from additivity which were larger at higher and especially lower effect levels. Testing across different effect concentrations (EC10-EC90) was an important tool allowing the identification of these larger deviations from additivity outside the EC50 threshold. Considering most protection thresholds are set below the EC50 level, and it was in this low effect range where the highest synergisms were observed, risk assessment schemes should test additivity at the target protection level using representative test organisms.

Toxic Effects of Four Plant Essential Oils alone and in Combination with Controlled modified Atmosphere on the Cowpea Beetle Callosobruchus maculatus (Fabricius.) (Coleoptera: Bruchidae) under Laboratory Conditions

Four plant essential oils alone as repellent and fumigant, and in combination with the controlled modified atmospheres against the adult of cowpea weevil, Callosobruchus maculatus Fabricius (Coleoptera: Bruchidae) were assessed in the laboratory. These essential oils were extracted from the leaves of four source plants: Prunus amigdalus, Moringa oleifera, Simmondsia chinensis, and Ricinus communis. The repellency test indicated that C. maculatus adults were repelled by four essential oils. Of these essential oils, the P. amigdalus oil was most effective followed by M. oleifera, S. chinensis, and R. communis. The average repellency of the P. amigdalus oil against C. maculatus adults was significantly higher than the other three tested oils after 7 days. These essential oils had a high level of toxicity in the fumigation assay against C. maculatus adults. The results showed that P. amigdalus oil gave the highest toxicity at LC50 (2.08 ppm) and R. communis gave the lowest value of LC50 (55.05ppm). In results of the effectiveness of the four essential oils when combined with two controlled atmospheres concentrations, 12.5- 25% CO2, the toxicity of plant oils was enhanced significantly against C. maculatus adults. The results of joint toxic action indicated that at concentration 10 ppm of the four essential oils under modified atmospheres of 12.5 % CO2 produced an additive effect at all exposure periods, while in case of M. oleifera and S. chinensis gave additive effect at 3 and 5 days exposure periods. The same trend was found at the highest concentration 20 ppm of three essential oils P. amigdalus, M. oleifera, and S. chinensis under modified atmospheres of 12.5-25% CO2 and produced an additive effect at all exposure periods, while Co-toxicity values of 20 ppm R. communis essential oil after the various exposer periods showed antagonism effect against C. maculatus adults. In conclusion, the present study revealed that the combination of the four tested essential oils with CO2 enhanced its fumigant toxicity to stored product insect, cowpea beetle.

Salinity Influence on Copper Sulphate and Lead Nitrate Combined Toxicity Against <i>Oreochromis niloticus</i>

Brackish water ecosystems characterized by fluctuating physicochemical parameters are more susceptible to the toxic effects of heavy metals acting singly or jointly. This study investigated the effect of salinity variations on the joint action toxicity of copper sulphate (CuSO4) and lead nitrate Pb(NO3)2 against fingerlings of Oreochromis niloticus. Fingerlings were exposed to binary mixtures of CuSO4 and Pb(NO3)2 (ratios 1:1 and 1:4) at varying salinities (0‰, 2‰, 12‰ and 18‰) in laboratory bioassays. The binary mixtures of the heavy metals were least toxic to the fish at 12‰ with 96 h LC50 values of 115.558 mg l-1 and 198.274 mg l-1 compared to 8.465 mg l-1 and 16.884 mg l-1 for 0‰, 46.084 mg l-1 and 69.843 mg l-1 for 2‰ and 13.196mg l-1 and 100.567 mg l-1 for 18‰ at ratios 1:1 and 1:4 respectively. Analysis using the Synergistic Ratio Model (SR) showed that both heavy metals were less toxic to the fish species when acting jointly irrespective of ratio than when acting singly at 12‰. Therefore, the need to consider the fluctuating salinity and joint interaction of heavy metals in setting ecologically safe limits for the discharge of effluents containing heavy metals into the aquatic ecosystems is important.
 Key words: Salinity, Heavy Metals, Toxicity, Oreochromis niloticus

Differential toxicities of anionic and nonionic surfactants in fish

This study investigated the differential toxicities of anionic and nonionic surfactants commonly used as active ingredients in household cleaning agents. The acute toxicity of the surfactants against Clarias gariepinus were investigated using static bioassays while the sublethal effects on the biochemical parameters and the histopathology of liver and gills of the fish were investigated for a period of 28days using a static renewal bioassay. The anionic surfactants were found to be more acutely toxic against the fish than the nonionic surfactants. The evaluation of the joint action toxicity of the surfactants against the test species using the concentration-addition model showed antagonistic interactions when the surfactants are present in mixtures. The two groups of surfactants also had varying degree of effects on the antioxidant stress enzymes and the liver function enzymes of the fish. However, only the anionic surfactants caused changes in the histopathology of the gills of the fish. The results obtained from this study have shown that anionic surfactants are more toxic to fish compared to nonionic surfactants. Anionic surfactants are the most commonly used surfactants in cleaning agents, there is a need for stricter regulations governing the use of this class of surfactants in cleaning agents.