Terms Of EC50 Research Articles

Toxicity of Silver Nanoparticles to Chlamydomonas reinhardtii

Silver nanoparticles (AgNP) are likely to enter the aquatic environment because of their multiple uses. We have examined the short-term toxicity of AgNP and ionic silver (Ag+) to photosynthesis in Chlamydomonas reinhardtii using fluorometry. AgNP ranged in size from 10 to 200 nm with most particles around 25 nm. As determined by DGT (diffusive gradients in thin films), by ion-selective electrode, and by centrifugal ulrafiltration, about 1% of the AgNP was present as Ag+ ions. Based on total Ag concentration, toxicity was 18 times higher for AgNO3 than for AgNP (in terms of EC50). However, when compared as a function of the Ag+ concentration,toxicity of AgNP appeared to be much higher than that of AgNO3. The ionic Ag+ measured in the AgNP suspensions could not fully explain the observed toxicity. Cysteine, a strong Ag+ ligand, abolished the inhibitory effects on photosynthesis of both AgNP and Ag+. Together, the results indicate that the interaction of these particles with algae influences the toxicity of AgNP, which is mediated by Ag+. Particles contributed to the toxicity as a source of Ag+ which is formed in presence of algae.

Toxicity and quantitative structure–activity relationships of benzoic acids to Pseudokirchneriella subcapitata

The present study presents the toxicity data of benzoic acid and its derivatives on Pseudokirchneriella subcapitata, in terms of EC50 and NOEC values. Median effective concentrations (EC50) range from 0.55 to 270.7 mg/L (based on final yield) and 1.93 to 726.3 mg/L (based on algal growth rate). No-observed-effect concentration (NOEC) is within the range of <0.0057–179.9 mg/L. From both the NOEC and EC50 values, it was found that, 2,4,6-trihydroxybenzoic acid, 4-chlorobenzoic acid, 3-bromobenzoic acid, 4-bromobenzoic acid, 2,6-dihydroxybenzoic acid, and 2,3,4-trihydroxybenzoic acid possess much higher risks to the aquatic organisms as compared to the other benzoic acids. These data are useful for risk assessment and protection of the aquatic environments, because such information is not available in the existing toxicological databases. The toxicity of halogenated benzoic acids was found to be directly related to the compound's hydrophobicity (the logarithm of the 1-octanol/water partition coefficient, log Kow). On the other hand, the number of hydroxyl groups (N OH) had a determinant influence to the toxicity of hydroxybenzoic acids. Quantitative structure–activity relationships were established to correlate the observed toxicity with log Kow and N OH values. These statistical correlations are highly significant with the predictive power Q 2 ranging from 0.896 to 0.955. Furthermore, in terms of the species sensitivity, the luminescent bacteria (Microtox) and the alga P. subcapitata appeared to be more susceptible to benzoic acids than the water flea and ciliate.

Evidence that olfactory sensitivities to calcium and sodium are mediated by different mechanisms in the goldfish Carassius auratus

The current study investigated whether the olfactory sensitivity to Ca2+ and Na+ is mediated by the same mechanism in the goldfish, a freshwater teleost. The olfactory responses, as assessed by recording the electro-encephalogram (EEG) from the olfactory bulb, to changes in external [Ca2+] and to [Na+] were recorded in the absence and presence of increasing concentrations of the other ion. Low concentrations of Na+ (0–1.0mM) had no significant effects on the olfactory response to changes in [Ca2+] in terms of EC50, Imax or Hill co-efficient (n=8). A relatively high concentration of Na+ (10mM) significantly reduced the Imax and increased the EC50. One hundred millimolars Na+ reduced the olfactory response to Ca2+ to undetectable levels. Conversely, low concentrations of Ca2+ (0.1 and 1.0mM) significantly attenuated the olfactory response to changes in environmental [Na+], reducing the amplitude of response and increasing the threshold of detection (n=7). However, a high concentration of Ca2+ (10mM) failed to attenuate the olfactory response to Na+ completely. Taken together, these results suggest that, at normal environmental concentrations of these ions, Ca2+ and Na+ are detected by distinct and separate cellular mechanisms. However, there seems to be a degree of overlap between the two mechanisms. The exact mechanisms involved, and their biological roles, remain to be established.

Hydrophilic and Lipophilic Antioxidant Capacities of Commercial Mediterranean Vegetable Soups (Gazpachos)

ABSTRACT: Gazpacho is a traditional cold Mediterranean soup consisting of 5 vegetables (tomato, cucumber, green pepper, onion, and garlic) and olive oil. Antioxidant activities of commercial gazpachos, processed by different technologies (traditional pasteurized [TP], slight pasteurized [SP], and frozen [F]), were assessed. Both lipophilic and hydrophilic DPPH* radical scavenging capacities (L-RSC and H-RSC, respectively) were determined in terms of EC50 and antiradical efficiency (AE). AE parameter takes into account not only antioxidant concentration but also antioxidant kinetic. L-RSC values were approximately 3-fold lower than the H-RSC values in all the gazpacho soups. Lycopene and total carotenoid concentration showed statistically significant correlation against L-RSC as follows: for lycopene, EC50 (r2= 0.4549, P = 0.0001) and AE (r2= 0.5982, P < 0.0001); for total carotenoid, EC50 (r2= 0.4381, P = 0.0002) and AE (r2= 0.5881, P< 0.0001). In the case of H-RSC, a correlation was found between EC50 values and total phenol content (r2= 0.1570, P = 0.0452) and vitamin C (r2= 0.1751, P = 0.0299). Also, a correlation was found between vitamin C and AE values (r2= 0.3485, P = 0.0012), suggesting a predominant role of vitamin C among others constituents in the kinetic of H-RSC. One serving (200 mL) of TP, SP, or F gazpacho soup corresponds to an intake of 16.4 ± 2.6 mg, 16.3 ± 2.1 mg, or 10.6 0.8 mg of vitamin C equivalents of H-RSC, respectively; and to an intake of 7.0 ± 1.0 mg, 6.9 ± 1.0 mg, or 5.3 ± 0.1 mg of lycopene equivalents of L-RSC, respectively.

QSAR-based toxicity classification and prediction for single and mixed aromatic compounds

Quantitative structure-activity relationships (QSARs) based on the octanol/water partition coefficient were employed to predict acute toxicities of 36 substituted aromatic compounds and their mixtures. In this study, the model developed by Verhaar et al. was modified and used to calculate octanol/water partition coefficients of chemical mixtures. To validate the model, acute toxicities of these chemicals were measured to Vibrio fischeri in terms of EC50. The results indicated that the obtained QSAR models could be used to predict toxicities of samples consisting of these substituted aromatic compounds, individually or in combinations. The obtained equations were proved to be robust enough by using the leave-one-out test method. By classifying these chemicals into two groups, polar and non-polar, the toxicities of chemical mixtures within each group can be predicted accurately from their calculated partition coefficients.

Predicting the Degree of Toxicity of Effluent from Reactive Dye Mixtures

Environmental and public health issues associated with dyes and their effluents are problematic areas for any dyehouse. If the toxicity and color of dyeing effluent can be predicted quantitatively before dyeing, one can select suitable dyes to reduce envi ronmental pollution. This study examines the acute toxicity of dyes and associated auxiliaries in terms of EC50, and these data are used to predict the toxicity of the dyeing effluent. The prediction accuracy is satisfactory when some statistical ap proaches, such as linear and nonlinear regression, are used. Furthermore, in order to make the toxicity data much easier to understand and much more directly comparable with each other, a toxicity index has been created according to the EC50 values in this study. Incorporating the toxicity information of the dyes with a computer color matching system permits the prediction of effluent toxicity generated by colorant recipes. This should assist colorists to select a "greener" formula while satisfying basic color quality requirements and will let colorists know well ahead of time the impact of toxicity from the effluent on the environment.

Effects of inoculum's mean cell volume on algal toxicity tests

The aim of the present study is to compare the effects of the mean cell volume (MCV) of algal inoculum to the sensitivity and reproducibility of the toxicity test. Two sets of experiments were conducted using inoculums with the MCV equal to 60 μm3/cell and 40 μm3/cell, respectively. The initial cell densities, however, were kept the same at 10,000 cells/mL. The results show that larger MCV of the inoculum results in greater EC50 values. Similar observations and conclusions were obtained from comparisons based on NOEC values. Thus, MCV of the inoculum significantly influences the observed toxic response in terms of EC50 and NOEC values. It is also evident that, there is a significant increase in the test variability if the MCV is not controlled properly. This study reports that standardizing the initial mean cell volume of algal culture can improve inter-laboratory and intra-laboratory precision. Furthermore, replacing the EC50 values by the calculated exposure values (EE50) can reduce the variability in data due to differences in the MCV of the inoculum.

Toxicity of Organic and Inorganic Mercury to Saccharomyces cerevisiae

In this study the effect if six different forms of mercury on the growth of the yeast Saccharomyces cerevisiae is presented. Five kinds of strains of S. cerevisiae were used. They were a wild type, a mercury-resistant type, and three mutants: mutation repair-deficient mutant, excision repair-deficient mutant, and recombination repair-deficient mutant. In terms of EC50 toward the wild-type strain, the toxicity order for the inorganic forms was Hg(NO3)2>HgSO4>HgCl2. Monovalent nitrate mercury Hg(NO3)2 was more toxic than bivalent Hg(NO3)2. The toxicity of organic mercury CH3HgCl on cell growth was two orders of magnitude higher than that of inorganic HgCl2. Between the two organic forms, CH3HgCl was more toxic than CH3HgOH. The survival rate in the presence of a certain concentration of CH3HgCl was about one-hundredth of the survival in presence of the same concentration of HgCl2. On the other hand, the concentration of CH3HgCl in the cell was about 170 times that of HgCl2. The addition of chelating agents, EDTA and methyl-penicillamine, to the medium did not reduce the toxicity of mercury. Among the three mutants tested, the one deficient in recombination repair systems was the most sensitive to mercury.

Glycosylation of asparagine 24 of the natriuretic peptide receptor-B is crucial for the formation of a competent ligand binding domain.

UV cross-linking studies of the natriuretic peptide receptor-B (NPR-B) using radiolabeled C-type natriuretic peptide (CNP) indicate that only fully glycosylated receptors are capable of binding ligand. We therefore used site-directed mutagenesis to determine which potential glycosylation sites are occupied by carbohydrate, and the relevant mutants were characterized in order to understand the function of carbohydrate addition at those sites. Our results suggest that five of seven potential N-linked glycosylation sites are modified. In addition, mutation of asparagine 24 results in a loss of approximately 90% of receptor activity. This mutant is expressed at levels comparable to the wild-type receptor, and its activity is not significantly different from that of wild-type NPR-B in terms of EC50 for CNP. Ligand binding studies on this mutant further show that although there is no change in affinity for ligand, approximately 90% of receptor binding is lost. These data suggest that many of the mutant receptors are simply not properly folded. Our results indicate that glycosylation of asparagine 24 of NPR-B receptors may be critical for the formation of a competent ligand binding domain.

Development and application of a simple procedure for toxicity testing using immobilized algae

A simple microplate technique was adopted for toxicity assessment of a number of pesticides including six herbicides (Atrazine, Dichloroprop, Glyphosphate, Chlorsulfuron, MCPA, and Simazine), an insecticide (Dimethoate) and a fungicide (Propiconazol). Growth response of free and immobilized cultures of the green chlorococcal algae Selenastrum capricornumtum to different treatments of these pesticides was tested and compared. The biotests were carried out under conditions optimal for the growth of the test alga. Algal growth was exposed in terms of dry weight, and was employed as the toxicity-response parameter. Dose-response curves were used to calculate the toxicity of the tested compounds in terms of EC50. Based on EC50 values, the responses of both immobilized and free cultures were quite similar for almost all the treatments. The technique facilitated the visual detection of the lowest toxic concentration giving no detectable algal growth (EC100). The technique is quite simple, rapid, practical, accurate, and space saving. It suggested that batteries of immobilized algae could replace free cultures in studies of toxicity testing.

Effect of selenium on the growth of some selected green and blue‐green algae

AbstractAn algal assay procedure using microplate technique was carried out to assess the effect of selenium on the growth of some green and blue‐green algae. Sodium selenite pentahydrate (Na2SeO3.5H2O) and selendioxide (Se2O4) were tested as selenium. The test algae were Selenastrum capricornutum, Scenedesmus obliquus, Chlorella sp., Monoraphidium convolutum, Monoraphidium contortum, Monoraphidium griffithii, Anabaena flos‐aquae, Micro‐cystis aeruginosa, and Oscillatoria agardhii. The blue‐green algae are toxin‐producing strains. Cell number and in vivo chlorophyll fluorescence were the growth parameters of green and blue‐green algae respectively. Dose‐response curves quantify the selenium toxicity in terms of EC50. The lowest selenium concentrations giving no detectable growth (EC100) were visually inspected. The test algae showed distinctly different responses to various selenium treatments. Selenium at concentrations &lt; 0.1 mg L−1 stimulates, to varying degrees, the growth of all the green algae with one exception: S. capricornutum was dramatically inhibited at all treatments. O. agardhii, A. flos‐aquae and M. aeruginosa showed marginal growth stimulation up to 0.1 mg Se L−1, 1.0 mg Se L−1 and 3.2 mg Se L−1 respectively. In terms of EC50, the compound selendioxide was more toxic to greens than sodium selenite. The reverse was indicated for the blue‐greens. In general, the EC50 presented a wide range (0.08–7.2 mg Se L−1), with the lowest values reported for S. obliquus and the highest for M. aeruginosa. All the test algae, except S. obliquus, maintained observable growths at higher selenium levels (EC100&gt;1.0&lt;100mg Se L−1).

水銀化合物の酵母Ｓａｃｃｈａｒｏｍｙｃｅｓ ｃｅｒｅｖｉｓｉａｅに及ぼす毒性作用と生物濃縮

It has been commonly known that mercury is one of the most toxic metals and that organic mercury is more toxic than inorganic mercury. This paper treats relationship between bioaccumulation and toxicity of various chemical forms of mercury on cell growth of the yeast Saccharomyces cerevisiae, DNA damage by mercury and effect of chelate agents on mercury toxicity.Four kinds of strains of S. cerevisiae were used. They are a wild type (AOY1) and three mutants. CA11-mutation repair-deficient mutant (rad18), CA13-exicion repair-deficient mutant (rad2) and CA15-recombination repair-deficient mutant (rad52) for DNA damage test.In terms of EC50 toward AOY1, the order of toxicity was Hg(NO3)2 > HgSO4 > HgCl2. For the same nitrate mercury, monovalent mercury(HgNO3) was more toxic than divalent mercury(Hg(NO3)2). Toxicity of organic mercury(CH3HgCl) on cell growth was two order higher than inorganic mercury(HgCl2). Comparing with the survival rate after 8 hours of inoculation and the content of both chemical forms of mercury in cells, the survival rate for CH3HgCl was about one hundredth of HgCl2, but the concentration of CH3HgCl in cells was about 170 times higher than that of HgCl2. Addition of chelate agents, EDTA and methyl penicillamine to the medium did not modify the toxicity by mercury. The mutant which is deficient in recombination repair system was most sensitive for mercury among three mutants mentioned above.

Significance of the Urogomphal Abnormality as a Criterion in the Test Method for Susceptibility to JH Mimics in Tribolium confusum12

A test method was developed to measure susceptibility of the confused flour beetle to JH mimics in terms of EC50, based on treating larvae and examining surviving adults. Persistence of the larval urogomphi is the principal adult abnormality used as a criterion of effect. This was found to be a valid indicator of the reproductive ability of the affected adults. This inhibition seems to be due to a combination of mechanical interference with the mating process and gonadal deficiencies which restrict fertilization.