EC50 Levels Research Articles

Assessment of toxicity thresholds in aquatic environments: Does benthic growth of diatoms affect their exposure and sensitivity to herbicides?

Benthic diatoms evolved in a biofilm structure, at the interface between water and substrata. Biofilms can adsorb toxicants, such as herbicides, but little is known about the exposure of biofilm organisms, such as benthic diatoms, to these adsorbed herbicides. We assessed the sensitivity of 11 benthic diatoms species to 6 herbicides under both planktonic and benthic conditions using single-species bioassays. The concentration that reduced the growth rate of the population by 10% (EC10) and 50% (EC50), respectively, varied depending on the species, the herbicides, and the growth forms involved. As a general trend, the more hydrophobic the herbicide, the more species were found to be sensitive under benthic growth conditions. Statistical differences (alpha<5%) were observed between the sensitivities under planktonic and benthic growth conditions for many hydrophobic herbicides. A protective effect of the biofilm against herbicides was observed, and this tended to decrease (at both the EC10 and EC50 levels) with increasing hydrophobicity. The biofilm matrix appeared to control exposure to herbicides, and consequently their toxicity towards benthic diatoms. For metolachlor, terbutryn and irgarol, benthic thresholds derived from species sensitivity distributions were more protective than planktonic thresholds. For hydrophobic herbicides, deriving sensitivity thresholds from data obtained under benthic growth seems to offer a promising alternative.

Combination effects of bisphenol A and isobutylparaben on the green macroalga Ulva pertusa

Endocrine related disorders have increased in human and wildlife due to the exposure of the endocrine disruptors (EDs). Estrogenic EDs can generate combination effects when they are present in a mixture at a concentration that does not individually induce observable effects. Therefore, this study was performed to characterize the reproductive toxicity of bisphenol A (BPA) and isobutylparaben (IBP) exposed to Ulva pertusa (U. pertusa), and also to determine the combined effects of BPA and IBP in U. pertusa. The median sporulation inhibition concentrations (EC50) of individual BPA and IBP exposure in U. pertusa showed 23.84 mg/L and 15.65 mg/L, respectively. The inhibition on sporulation of U. pertusa to a mixture of BPA and IBP at EC50 level was observed to be higher when compared to individual exposure. In conclusion, reproduction inhibition to a mixture of BPA and IBP exposure at EC50 levels was relatively greater than individual exposure to U. pertusa.

Fate and distribution of nitrogen in soil and plants irrigated with landfill leachate

Landfill leachate contains a high concentration of ammoniacal substances which can be a potential supply of N for plants. A bioassay was conducted using seeds of Brassica chinensis and Lolium perenne to evaluate the phytotoxicity of the leachate sample. A soil column experiment was then carried out in a greenhouse to study the effect of leachate on plant growth. Two grasses ( Paspalum notatum and Vetiver zizanioides) and two trees ( Hibiscus tiliaceus and Litsea glutinosa) were irrigated with leachate at the EC50 levels for 12 weeks. Their growth performance and the distribution of N were examined and compared with columns applied with chemical fertilizer. With the exception of P. notatum, plants receiving leachate and fertilizer grew better than those receiving water alone. The growth of L. glutinosa and V. zizanioides with leachate irrigation did not differ significantly from plants treated with fertilizer. Leachate irrigation significantly increased the levels of NH x –N in soil. Although NO x –N was below 1 mg N L −1 in the leachate sample, the soil NO x –N content increased by 9-fold after leachate irrigation, possibly as a result of nitrification. Leachate irrigation at EC50 provided an N input of 1920 kg N ha −1 over the experimental period, during which up to 1050 kg N ha −1 was retained in the soil and biomass, depending on the type of vegetation. The amount of nutrient added seems to exceed beyond the assimilative capability. Practitioners should be aware of the possible consequence of N saturation when deciding the application rate if leachate irrigation is aimed for water reuse.

Predicting hormesis in mixtures.

Figure 1. Selected concentration–response relationships for the inhibition of root length of Lactuca sativa. The figures, adapted from Belz et al. (2008), illustrate how both the dose range and the size of the maximal response is approximately proportional to the mixture ratio of 50:50%, both for mixtures between 2 hormetic compounds (a) and between a hormetic and a nonhormetic compound (b). L e a rn e d D ico u se PREDICTING HORMESIS IN MIXTURES

P019 Perception and reproduction of whole body rotation in standing subjects

Metal-based engineered nanomaterials (ENMs) are known to affect bacterial processes and metabolic activities. While testing their negative effects on biological components, studies traditionally rely on initial exposure concentrations and thereby do not take into consideration the dynamic behavior of ENMs that ultimately determines exposure and toxicity (e.g. ion release). Moreover, functional responses of soil microbial communities to ENMs exposure can be caused by both the particulate forms and the ionic forms, yet their relative contributions remain poorly understood. Therefore, we investigated the dynamic changes of exposure concentrations of three different types of ENMs (nano-ZnO, -Cu and -Pb) and submicron particles (SMPs) in relation to their impact on the capacity of soil bacterial communities to utilize carbon substrates. The different ENMs were chosen to differ in dissolution potential. The dynamic exposures of ENMs were considered using a time weighted average (TWA) approach. The joint toxicity of the particulate forms and the ionic forms of ENMs was evaluated using a response addition model. Our results showed that the effect concentrations of spherical nano-ZnO, -Cu and SMPs, and Pb-based perovskites expressed as TWA were lower than expressed as initial concentrations. Both particulate forms and ionic forms of spherical 18 nm, 43 nm nano-ZnO and 50 nm, 100 nm nano-Cu contribute to the overall response at the EC50 levels. The particulate forms for 150 nm, 200 nm and 900 nm ZnO SMPs and rod-shaped 78 nm nano-Cu mainly affected the soil microbial metabolic potential, while the Cu ions released from spherical 25 nm nano-Cu, 500 nm Cu SMPs and Pb ions released from perovskites mainly described the effects to bacterial communities. Our results indicate that the dynamic exposure of ENMs and relative contributions of particles and ions require consideration in order to pursue a naturally realistic assessment of environmental risks of metal-based ENMs.

Selective Feeding of Helicoverpa armigera (Hübner) and Spodoptera litura (Fabricius) on Meridic Diet with Bacillus thuringiensis Toxins

Laboratory experiments were conducted to evaluate the behavior of Helicoverpa armigera (Hubner) and Spodoptera litura (Fabricius) larvae on meridic diet with different concentrations of Bt spray formulation Delfin or isolated Cry1Ac protein or the foliage and bolls from transgenic cotton, Bollgard hybrid RCH-317 Bt. Both insect species selectively fed on nontreated diet compared with the diet treated with Delfin. While H. armigera exhibited concentration response with Cry1Ac, this protein did not affect S. litura larvae. In general Helicoverpa selected diet with low concentrations (EC20 and EC50 levels) of Cry1Ac compared with higher concentrations of Cry1Ac. In order to develop appropriate management strategies, a thorough understanding of the behavioral mechanisms leading to the responses of insects to the proteins in transgenic varieties is required. Thus, based on results of the insects fed individually on the leaf discs or bolls from transgenic cotton plants alone or under choice situation with meridic diet revealed that H. armigera larvae preferred meridic diet to transgenic leaves or bolls expressing Cry1Ac protein. H. armigera larvae preferred meridic diet to plant material; more than 70% larvae were seen on the meridic diet, and average larval weight gain was in the range of 121.7–130.5 mg. However, in case of S. litura the larvae showed no significant discrimination between meridic diet and the leaf discs. In fact more than 60% larvae preferred leaf discs for feeding, though Cry1Ac expression in leaf discs was in the range of 0.9–2.18 μg/g. Thus differences in behavioral response could potentially impact the level of efficacy of crop cultivars that have been genetically engineered to produce these proteins.

Unified Basis for the Respirometric Evaluation of Inhibition for Activated Sludge

This paper explores the merit of the oxygen uptake rate (OUR) profile obtained by means of respirometry as the basic mechanistic instrument for evaluating activated sludge inhibition. Experimental OUR data are generated using the synthetic peptone-based substrate and inhibition is tested with 60 mg/L hexavalent chromium and 33 mg/L nickel additions, corresponding to EC50 levels determined using the standard ISO 8192 procedure. Experimental results are evaluated by model calibration using ASM1 modified for dual hydrolysis and ASM3 modified for simultaneous growth. Model evaluations indicate that inhibition affects not only growth, but also other significant microbial mechanisms such as substrate storage and hydrolysis, leading to conclude that the proposed approach will enable to visualize the overall impact of the inhibitory compound on every stage of substrate biodegradation, through inspection and evaluation of the entire OUR profile.

Phytotoxicity data safeguard the performance of the recipient plants in leachate irrigation

Leachates from an operating and a closed landfill were examined for their phytotoxicity by seed germination/root elongation tests using seeds of Brassica chinensis and Lolium perenne. Their EC50s ranged from 3% to 46% v/v, which varied remarkably with the operating status of the landfills. Seedlings of twelve tree species were grown in pots, which were irrigated with landfill leachate at the EC50 levels, with tap water as control. No tree mortality or growth inhibition was observed after 90 days of leachate application. Chlorophyll fluorescence measurement also showed that plants receiving leachate did not suffer from a decline in photosynthetic efficiency. Litsea glutinosa and Hibiscus tiliaceus had remarkable growth, and other non-N-fixers were not inferior to the N-fixing Acacia auriculiformis. Leachate irrigation improved soil N content, though P deficiency is still a problem. The seed bioassay provided a conservative estimate of the phytotoxicity of landfill leachate. Plants irrigated can be protected from growth inhibition when the leachate irrigation plan is designed with reference to phytotoxicity data.

Assessment of the estrogenicity of isoflavonoids, using MCF-7-ERE-Luc cells.

In the current study, our research focused on the estrogenic activity of isoflavonoids, mainly genistein, biochanin A and daidzein. Genistein enhanced the reporter gene expression of MCF-7-ERE-Luc cells, at a concentration as low as 10 nM, with a concentration of 100 nM the achieved gene expression effects were similar to those of 10 pM 17beta-estradiol, Based on the estrogenic activities of biochanin A and daidzein, hydroxyl groups at the 4' and 5 positions are needed for the maximal effect of the genistein. The estrogenic effects of these isoflavonoids were inhibited by the concomitant treatment with tamoxifen. The data showed that the estrogenic effects of isoflavonoids were mediated through estrogen receptors. When the isoflavonoids were tested as mixtures, the estrogenic effects were lower than the arithmetic sum of those induced by each individual isoflavonoid. The estrogenic potency of each isoflavonoid was presented at EC50 levels with a 17beta-estradiol equivalent concentration (EEQ) based on the dose response of each chemical. The EC50s and EEQs of genistein, biochanin A and daidzein were 4.15, 0.89 and 0.18 microM, and 15.0, 5.12 and 1.83 microM/M, respectively. Our data clearly demonstrated that the pERE-luciferase reporter gene assay was suited for the sensitive and quantitative measurement, and large scale screening, of the estrogenicity of chemicals in vitro.

Combination Effect of Light and Toxicity in Algal Tests

The sensitivity of Scenedesmus subspicatus against potassium dichromate is positively correlated to the photon flux density during the algal growth inhibition test. Low photon flux densities led to significantly reduced maximum effects and higher EC50 levels. To improve the testing of colored substances, we distinguished between the toxic effect (chemical part, represented by potassium dichromate) and the shading effect (physical part, simulated by reduced light intensities during the test) of a hypothetical light absorbing substance. The contribution of these single effects to the total inhibition varied greatly. At high concentrations of potassium dichromate (1.6 and 3.2 mg L(-1)) the physical part never exceeded 25% of the total inhibition, not even at strongest light reduction, while at low concentrations (0.2 and 0.4 mg L(-1)) the physical effect became more prominent when halving the amount of available light. Further, the combination effect of the chemical and the physical effect could be calculated well only by using the concept of independent action. Thus, if chemical and physical effects are measured in combination, as is the case in tests with dye-stuffs, the current test protocol for the algal growth inhibition test may lead to incorrect estimations of the toxic potential.

Combination Effect of Light and Toxicity in Algal Tests

The sensitivity of Scenedesmus subspicatus against potassium dichromate is positively correlated to the photon flux density during the algal growth inhibition test. Low photon flux densities led to significantly reduced maximum effects and higher EC50 levels. To improve the testing of colored substances, we distinguished between the toxic effect (chemical part, represented by potassium dichromate) and the shading effect (physical part, simulated by reduced light intensities during the test) of a hypothetical light absorbing substance. The contribution of these single effects to the total inhibition varied greatly. At high concentrations of potassium dichromate (1.6 and 3.2 mg L−1) the physical part never exceeded 25% of the total inhibition, not even at strongest light reduction, while at low concentrations (0.2 and 0.4 mg L−1) the physical effect became more prominent when halving the amount of available light. Further, the combination effect of the chemical and the physical effect could be calculated well only by using the concept of independent action. Thus, if chemical and physical effects are measured in combination, as is the case in tests with dyestuffs, the current test protocol for the algal growth inhibition test may lead to incorrect estimations of the toxic potential.

Identification of a cardiac sodium channel insensitive to synthetic modulators.

DPI 201-106 (DPI) was the first synthetic compound showing cardioselective modulation of voltage-gated sodium channels (VGSCs) resulting in a positive inotropic effect. Currently, the exact mode of action for this class of compounds is not known. Effects of different natural and synthetic sodium channel modulators were investigated in cardiac tissue of several species with conventional electrophysiologic methods. In electrically driven cardiac tissues, all compounds investigated increased force of contraction (FC) and action potential duration (APD) with increasing concentrations except for DPI in cattle trabecular muscle, which demonstrated no effect. Interestingly, calculation of EC50 levels at 30% repolarization demonstrates that natural VGSC-ligands were highly potent in prolonging the APD in cattle whereas no positive trends could be obtained for DPI and SDZ 211-939 (SDZ) in cattle. These results demonstrate that the binding site for DPI and SDZ is distinct from sites 2 or 3 of the VGSC alpha-subunit. Moreover, this is the first time that these compounds show no effect or even shortening of APD. This finding will enable the characterization of the mode of action and probably the binding site for synthetic VGSC-modulators.

Comparison of changes evoked by GABA (γ-aminobutyric acid) and anoxia in [K+]o, [Cl-]o, and [Na+]o in stratum pyramidale and stratum radiatum of the guinea pig hippocampus

Ion-selective microelectrode recordings were made to assess a possible contribution of extracellular gamma-aminobutyric acid (GABA) accumulation to early responses evoked in the brain by anoxia and ischemia. Changes evoked by GABA or N2 in [K+]o, [Cl-]o, [Na+]o, and [TMA+]o were recorded in the cell body and dendritic regions of the stratum pyramidale (SP) and stratum radiatum (SR), respectively, of pyramidal neurons in CA1 of guinea pig hippocampal slices. Bath application of GABA (1-10 mM) for approximately 5 min evoked changes in [K+]o and [Cl-]o with respective EC50 levels of 3.8 and 4.1 mM in SP, and 4.7 and 5.6 mM in SR. In SP 5 mM GABA reversibly increased [K+]o and [Cl-]o and decreased [Na+]o; replacement of 95% O2 -5% CO2 by 95% N2 -5% CO2 for a similar period of time evoked changes which were for each ion in the same direction as those with GABA. In SR both GABA and N2 caused increases in [K+]o and decreases in [Cl-]o and [Na+]. The reduction of extracellular space, estimated from levels of [TMA+]o during exposures to GABA and N2, was 5-6% and insufficient to cause the observed changes in ion concentration. Ion changes induced by GABA and N2 were reversibly attenuated by the GABA(A) receptor antagonist bicuculline methiodide (BMI, 100 microM). GABA-evoked changes in [K+]o in SP and SR and [Cl-]o in SP were depressed by > or =90%, and of [Cl-]o in SR by 50%; N2-evoked changes in [K+]o in SP and SR were decreased by 70% and those of [Cl-]o by 50%. BMI blocked delta [Na+]o with both GABA and N2 by 20-30%. It is concluded that during early anoxia: (i) accumulation of GABA and activation of GABA(A) receptors may contribute to the ion changes and play a significant role, and (ii) responses in the dendritic (SR) regions are greater than and (or) differ from those in the somal (SP) layers. A large component of the [K+]o increase may involve a GABA-evoked Ca2+-activated gk, secondary to [Ca2+]i increase. A major part of [Cl-]o changes may arise from GABA-induced g(Cl) and glial efflux, with strong stimulation of active outward transport and anion exchange at SP, and inward Na+/K+/2Cl- co-transport at SR. Na+ influx is attributable mainly to Na+-dependent transmitter uptake, with only a small amount related to GABA(A) receptor activation. Although the release and (or) accumulation of GABA during anoxia might be viewed as potentially protectant, the ultimate role may more likely be an important contribution to toxicity and delayed neuronal death.

Toxicity of beta-blockers in a rat whole embryo culture: concentration-response relationships and tissue concentrations.

Beta-adrenoceptor blockers are widely used drugs for the treatment of cardiovascular diseases. Since beta-blockers cross the placenta, it is essential to consider possible adverse effects on the embryo. Six beta-adrenoceptor blockers were tested at various concentrations (10-5000 microM) in a rat whole embryo culture. Although inducing a very similar pattern of dysmorphogenetic effects (incomplete flexure, disturbed development of the neural tube, the head, the heart and the tail bud), the compounds exhibited a wide range of embryotoxic potency. Estimation of the EC50 (median-concentration producing dysmorphogenesis in 50% of the embryos) for the six compounds revealed differences of more than two orders of magnitude: propranolol 25 microM, alprenolol 30 microM, metoprolol 100 microM, pindolol 150 microM, acebutolol 500 microM, atenolol 4000 microM. Measurements of the concentrations of the various drugs in the cultured embryos at corresponding EC50 levels showed differing values: metoprolol 4.5 microM, propranolol 5.2 microM, alprenolol 8.4 microM, pindolol 9.0 microM, acebutolol 12.5 microM and atenolol 77.0 microM. With regard to the EC50 and the degree of substance transfer to the embryo it can be stated that propranolol and metoprolol show a much higher intrinsic potency to interfere with normal in vitro embryonic development than, e.g. atenolol.

Comparison of cromakalim-induced relaxation of potassium precontracted rabbit, cat, and rat isolated cerebral arteries

The effects of cromakalim were investigated in KCl-precontracted cat, rabbit, and rat isolated cerebral arteries with intact endothelium. Potassium induced contraction of all cerebral arteries studied, but exhibited marked vessel and species variation with no spasm to 20 or 30 mmol/l KCl in the rat basilar artery or 20 mmol/l KCl in the rabbit middle cerebral artery. On sustained tension to 20 mmol/l KCl, cromakalim induced concentration-related relaxation in the rabbit basilar artery and the cat basilar and middle cerebral arteries with Hill coefficients greater than unity. Cromakalim was more potent in the rabbit basilar artery precontracted with 20 or 30 mmol/KCl than in the rabbit middle cerebral artery or the cat basilar or middle cerebral artery. Elevation of the KCl concentration to 50 mmol/l inhibited cromakalim-induced relaxation and produced a decrease in the Hill coefficient. Preincubation of cerebral arteries with glibenclamide (100 nmol/l-1 mumol/l) produced concentration-related inhibition of the cromakalim-induced relaxation in the rabbit basilar, cat basilar, and cat middle cerebral arteries precontracted with 20 mmol/l KCl. The degree of rightward shift of concentration-effect curves by glibenclamide was calculated at the EC25, EC50, and EC75 levels. A good correlation was observed between the shifts at the EC50 and EC75 levels. However, the shift in concentration-effect curves for cromakalim produced at the EC25 level was markedly less than the EC50 or EC75 levels in the presence of 1 mumol/l glibenclamide. The pA2 values for glibenclamide calculated at the EC50 level were 6.6 +/- 0.09, 7.1 +/- 0.1, and 6.5 +/- 0.5 in the rabbit basilar, cat basilar, and cat middle cerebral artery, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of immunosuppressive chemicals on lymphoid development in foetal thymus organ cultures.

A murine foetal thymus organ culture system was employed to screen a number of immunotoxic chemicals for direct thymus toxicity. The toxic effects caused by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and its congeners on the system used had previously been shown to be similar to those caused in vivo on lymphoid development. The most potent compound tested was the corticosteroid fluocinolone acetonide, which caused a 50% inhibition of lymphoid development (EC50) at a concentration of 5 x 10(-11) M. The EC50 of TCDD was around 5 x 10(-10) M while that of 4 beta-phorbol 12-myristate 13-acetate (TPA) was ca 10(-7) M. TCDD and its congeners are believed to act via binding to the Ah receptor. Other known or presumed ligands of this receptor, which are potent inducers of P1-450 (P-448) -dependent polysubstrate monooxygenase activities, were considerably less toxic with EC50 levels varying between 10(-5) M (7,12-dimethylbenz(alpha-) antracene, alpha-naphthoflavone, benzo(alpha)pyrene) and 10(-4) M (beta-naphthoflavone and 3-methylcholantrene). Dinaphtho/2,3-b,5,6-b/dioxin and indolo/2,3-b/carbazole showed toxicity at 5 x 10(-6)-10(-5) M and 5 x 10(-5) M respectively. TCDD, TPA, and fluocinolone showed additive effects when added two by two in different combinations. Thus fluocinolone, known to counteract the toxicity and epidermal growth factor (EGF) cell-surface receptor-decreasing activity caused by TPA in other cell types, failed to decrease TPA toxicity in the thymus culture system.