Showing papers on "Chromium published in 1989"

Isolation and Characterization of an Enterobacter cloacae Strain That Reduces Hexavalent Chromium under Anaerobic Conditions.

Abstract: An Enterobacter cloacae strain (HO1) capable of reducing hexavalent chromium (chromate) was isolated from activated sludge. This bacterium was resistant to chromate under both aerobic and anaerobic conditions. Only the anaerobic culture of the E. cloacae isolate showed chromate reduction. In the anaerobic culture, yellow turned white with chromate and the turbidity increased as the reduction proceeded, suggesting that insoluble chromium hydroxide was formed. E. cloacae is likely to utilize toxic chromate as an electron acceptor anaerobically because (i) the anaerobic growth of E. cloacae HO1 accompanied the decrease of toxic chromate in culture medium, (ii) the chromate-reducing activity was rapidly inhibited by oxygen, and (iii) the reduction occurred more rapidly in glycerol- or acetate-grown cells than in glucose-grown cells. The chromate reduction in E. cloacae HO1 was observed at pH 6.0 to 8.5 (optimum pH, 7.0) and at 10 to 40°C (optimum, 30°C).

Effect of chromium on properties of Fe3Al

Abstract: The effects of the addition of chromium on several properties of Fe3Al, including tensile strength and ductility, fracture behavior, and slip and dislocation characteristics, were studied. Alloying with up to 6 at. % chromium results in an increase in room temperature ductility from approximately 4% to 8–10%. Along with this increase in ductility, the addition of chromium produces a change in fracture mode from transgranular cleavage to a mixed mode of intergranular-transgranular cleavage, and a change in slip behavior from coarse straight slip to fine wavy slip. These phenomena are discussed in terms of the effect of chromium on the antiphase boundary energies and dislocation characteristics.

The effects of heat treatment on the chromium depletion, precipitate evolution, and corrosion resistance of INCONEL alloy 690

Abstract: A series of heat treatments were performed to study the sensitization and the stress corrosion cracking (SCC) behavior of INCONEL Alloy 690. The microstructural evaluation and the chromium depletion near grain boundaries were carefully studied using analytical electron microscopy (AEM). The measured chromium depletion profiles were matched well to the calculated results from a thermodynamic/kinetic model. The constant extension rate test (CERT) was performed in the solution containing 0.001 M sodium thiosulfate (Na2S2O3) to study the SCC resistance of this alloy. The Huey test was also performed in a boiling 65 pct HNO3 solution for 48 hours to study the intergranular attack (IGA) resistance of this alloy. Both tests showed that INCONEL 690 has very good corrosion resistance. It is believed that the superior IGA and SCC resistances of this alloy are due to the high chromium concentration (≈30 wt pct). It is concluded in this study that INCONEL 690 may be a better alloy than INCONEL 600 for use as the steam generator (S/G) tubing material for pressurized water reactors (PWR's)

Internal-external transition for the oxidation of Fe-Cr-Ni austenitic stainless steels in steam

Abstract: Several Fe-Cr-Ni austenitic stainless steels (Cr wt.%: 13–25, Ni wt.%: 15) were oxidized in steam for 1000 hr at 500–900°C. The oxide scales were examined and categorized with respect to the chromium concentration and the grain size of the base metal. Experiments showed three conditions for the critical bulk Cr concentration and the oxidation temperature at which the oxidation behavior changed drastically. Metallographic examination showed that two of these three conditions resulted from the internal-external transition of Cr2O3 either on the metal surface or along the grain boundaries of the base metal. Attempts were made to interpret these conditions from the available oxidation theories. Atkinson's treatment was employed with some modification to incorporate the grain-boundary diffusion of Cr in the base metal. The calculation basically explained the internal-external transition for the oxidation of these steels.

Role of chromium(V), glutathione thiyl radical and hydroxyl radical intermediates in Chromium(VI)‐induced DNA Damage

Abstract: In vitro chromium(VI) is unreactive toward DNA under physiological conditions. Therefore, the ability of chromium(VI) to damage DNA depends on the presence of cellular components capable of forming “reactive intermediates”; upon reaction with chromium(VI). We have examined the role of glutathione and hydrogen peroxide in chromium(VI)‐induced DNA damage in vitro. Reaction of glutathione with chromium(VI) produced significant levels of two chromium(V) complexes and glutathione thiyl radical, whereas reaction of chromium(VI) with hydrogen peroxide produced hydroxyl radical without producing detectable levels of chromium(V). Reaction of DNA with chromium(VI) in the presence of glutathione resulted in Cr‐DNA adducts with little DNA strand breakage. Reaction of DNA with chromium(Vl) in the presence of hydrogen peroxide produced the 8‐hydroxydeoxyguanosine adduct and extensive DNA strand breakage in the absence of significant Cr‐DNA adduct formation. These results suggest that the nature of chromium(VI)...

Early stages of the hydrolysis of chromium(III) in aqueous solution. 4. The stability constants of the hydrolytic dimer, trimer, and tetramer at 25 DegC and I = 1.0 M

Abstract: Identification et evolution des differentes especes etudiees au moyen de la pHmetrie et a partir d'une separation chromatographique. Diagrammes de distribution du chrome(III) dans les differents oligomeres en fonction du pH

Generation of PM2 DNA breaks in the course of reduction of chromium(VI) by glutathione.

Abstract: The carcinogen chromate is efficiently taken up and reduced to chromium(III) compounds by various biological systems. To test the possible DNA damage induced in the course of chromium(VI) reduction, we used a combination of chromate with the reductant glutathione (GSH) as well as a green complex of chromium(V), which is formed in the reaction of chromate with GSH. The combination of chromate and glutathione was found to cause single-strand breaks in supercoiled circular DNA of the bacteriophage PM2. The green chromium(V) complex Na4(GSH)4Cr(V).8H2O, prepared from chromate and glutathione, also cleaved supercoiled PM2 DNA. No DNA-degrading effects were observed with either chromate or the final product of the reaction with GSH, a purple anionic chromium(III) GSH complex. The nature of the buffering agents revealed a strong influence on the extent of DNA strand breaks produced by chromate and GSH. A variation of the GSH concentration in the reaction with chromate and PM2 DNA, performed in sodium phosphate-buffered solutions showed an initial increase in the number of strand breaks at GSH concentrations up to 1 mM followed by a decline at higher GSH concentrations. Since neither chromate, when administered individually, nor the final product of chromium(VI) reduction, the purple chromium(III) GSH complex, produced any detectable DNA cleavage, the critical steps leading to DNA strand breaks occur in the course of the conversion of chromium(VI) to chromium(III) by GSH, the most abundant intracellular low molecular thiol. Moreover, the demonstration that DNA cleavage is induced in the presence of the chromium(V) complex identifies chromium(V) as the oxidation state of the metal, which is involved in the steps leading to DNA-damaging effects of chromate.

Chromium(VI) Toxicity: Uptake, Reduction, and DNA Damage:

Abstract: Much recent data supports the “uptake-reduction” model explaining the carcinogenicity of chromium(VI) compounds and the lack of carcinogenicity of chromium(III) com pounds. Cr(VI) readily enters ce...

Differential effects of chromium(VI) on constitutive and inducible gene expression in chick embryo liver in vivo and correlation with chromium(VI)-induced DNA damage.

Abstract: The effect of DNA damage induced by the carcinogen chromium(VI) on the function of DNA as a template for transcription of constitutive and inducible genes was examined in chick embryo liver in vivo. Changes in gene expression, determined using solution hybridization and northern blot analyses to measure steady-state mRNA levels and a nuclear run-off assay to measure gene transcription rates, were compared to chromium-DNA binding and to chromium(VI)-induced DNA damage as previously measured by DNA alkaline elution. Chromium(VI) treatment had little or no effect on either the steady-state mRNA levels or the transcription rates of the constitutively expressed genes for albumin, conalbumin (avian transferrin), or beta-actin. In contrast, chromium(VI) treatment had significant but opposite effects on the basal and drug-inducible expression of 5-aminolevulinate synthase and cytochrome PB1 P450. The changes in steady-state expression of these two inducible genes were similar to the changes in transcription rate, indicating that the effects of chromium were principally transcriptional. Chromium(VI) treatment increased the basal expression of both inducible genes four- to fivefold at maximum, and the time course of this effect was similar to the time course for chromium(VI)-induced DNA damage and repair. In contrast, chromium(VI) pretreatment suppressed by 60-70% at maximum the subsequent induction of these genes by glutethimide, a phenobarbital analog, and the time course of this effect also corresponded to that of chromium(VI)-induced DNA damage and repair. The time courses of the changes in expression of these genes were bimodal, with the second peak corresponding closely to that of chromium(VI)-induced DNA cross-links. However, the first peak occurred during a period when no DNA cross-links or strand breaks were detectable by alkaline elution, although significant levels of chromium were bound to DNA. This suggests that chromium(VI), like cisplatin, may initially produce a DNA monoadduct that subsequently leads to DNA cross-link formation and that both types of chromium(VI)-induced lesions have a significant effect on the expression of targeted genes.

Mechanism of chromium(VI) carcinogenesis. Reactive intermediates and effect on gene expression.

Abstract: Since chromium(VI) is unreactive toward DNA under physiological conditions in vitro, the ability of carcinogenic chromium(VI) compounds to damage DNA depends on the presence of cellular redox components that reduce chromium(VI) to reactive species capable of interacting with DNA. We have examined the role of glutathione and hydrogen peroxide in chromium(VI)-induced DNA damage in vitro. Upon reaction with chromium(VI), glutathione produced chromium(V) and glutathione thiyl radical reactive intermediates, whereas hydrogen peroxide produced chromium(V) and hydroxyl radical. Reaction of DNA with chromium(VI) in the presence of glutathione resulted in binding of chromium and glutathione to DNA with little or no DNA strand breakage. Reaction of DNA with chromium(VI) in the presence of hydrogen peroxide produced the 8-hydroxydeoxyguanosine adduct and extensive DNA strand breakage in the absence of significant Cr-DNA adduct formation. These results suggest that the nature of chromium(VI)-induced DNA damage will be strongly dependent on reactive intermediates such as chromium(V), glutathione thiyl radical, and hydroxyl radical, produced by cellular components active in chromium(VI) metabolism. In order to assess the ability of chromium(VI)-induced DNA damage to affect the normal template function of DNA, we investigated the effects of chromium(VI) on steady-state mRNA levels of various genes in chick embryo liver in vivo, and compared the effects to the levels of DNA damage observed. Chromium(VI) induced DNA-protein and DNA interstrand cross-links in chick embryo liver in vivo and suppressed the induction of 5-aminolevulinic acid synthase and cytochrome P-450 mRNA expression by porphyrinogenic drugs.(ABSTRACT TRUNCATED AT 250 WORDS)

Removal of chromium from aqueous solutions by treatment with porous carbon electrodes: electrochemical principles

Abstract: The possibility of removing hexavalent chromium from waste water by electrochemical treatment using a graphite felt electrode and synthetic electrolytes is investigated. It is suggested that the process proceeds in two steps: electrochemical reduction of the hexavalent chromium to chromic ion followed by the formation of an insoluble chromic hydroxide in an electrochemically generated high pH environment. The chromic hydroxide adheres to the electrode surface as a charged colloidal particle. The electrochemical dissolution of the hydroxide layer by potential inversion is also discussed as a possible regeneration procedure.

Chromium cross-links glutathione and cysteine to DNA

Abstract: The formation of chromium-DNA adducts, and chromium-mediated peptide-DNA or amino acid-DNA cross-links was measured after treatment of calf thymus DNA and defined DNA polynucleotides in vitro with potassium dichromate in the presence of glutathione or cysteine. The level of chromium bound to DNA after reaction with chromium(VI) in the presence of glutathione increased with increasing glutathione concentration to a level of approximately 1.4 x 10(-2) chromium per nucleotide. Glutathione and chromium were associated with the DNA in a 1:1 ratio. Reaction of chromium(VI) with DNA in the presence of cysteine led to a maximal level of chromium binding that was 10-fold lower than that measured with glutathione, with 2-4 cysteine bound per chromium. The thiol-chromium-DNA complexes were stable to dialysis at room temperature against diethylenetriaminepentaacetic acid, orthophenanthroline and ethylenediaminetetraacetic acid. However, when the chromium-DNA complexes were dialyzed against ethylenediaminetetraacetic acid at 37 degrees C to chelate bound chromium, equivalent amounts of chromium and thiol were lost from the DNA, suggesting that thiol was associated with the DNA-bound chromium. These results suggest that chromium mediates cross-linking of cysteine and glutathione to DNA, to form glutathione-chromium-DNA and (cysteine)2-4-chromium-DNA complexes. In order to probe the DNA base and sequence specificity of glutathione-chromium-DNA adduct formation, chromium and glutathione binding to polynucleotides of defined composition was determined. Preferential binding of chromium to guanine-containing polynucleotides was observed. These results suggest that the interaction of chromium with thiol-containing amino acids and peptides may be important in chromium genotoxicity, and indicate that the thiol-activated chromium may target guanine bases in DNA.

Cytotoxic and neoplastic transforming effects of industrial hexavalent chromium pigments in Syrian hamster embryo cells

Abstract: Twenty eight moderately water-soluble to insoluble chromium (VI) compounds, such as zinc and lead chromate, industrial and laboratory synthesized pigments, and the analytical reagents strontium, barium and calcium chromate, were physicochemically characterized and studied for cytotoxicity and morphological transformation in cultured Syrian hamster embryo (SHE) cells. In vivo validation of malignancy of transformed SHE cells was performed. A high physicochemical diversity among the complex chromium pigments was revealed. The solubility of the compounds was greatly increased after incubation in a complete medium and even higher under cell culture conditions. The cytotoxic effects appeared to be due principally to extracellular solubilized chromium because the most solubilized compounds. Zn, Ca and Sr chromates, were equitoxic at about the same Cr concentration treatment and 8-fold more cytotoxic than less soluble compounds such as some Pb chromates and Ba chromate. However, certain physicochemical properties of lead chromate pigments could also influence their cytotoxic activity. All test compounds were, in a dose-dependent manner, efficient in inducing morphological transformation of SHE cells. Many of the Cr pigments, although physicochemically different, were similarly effective in transformation induction. Nevertheless, compounds among Zn and Pb chromates had various transforming potencies. Ba chromate was the least active in inducing transformation. Certain physicochemical properties could mediate the transforming activity but no particular relationship could be established between any one of the physicochemical parameters and the transforming potency. Cloned morphologically-transformed colonies of SHE cells were grown in soft agar medium and showed true neoplastic behaviour by tumour formation in syngeneic animals. These results show that various chromate pigments containing either Zn or Pb, of medium to very low aqueous solubility, induced neoplastic transformation of SHE cells.