Showing papers on "Chromium published in 1994"

The Biological and Environmental Chemistry of Chromium

Abstract: Chemical and physical properties of chromium current recommendations on chromium exposure and intake determination of chromium in environmental and biological materials (sample collection) manufacture, use and distribution of chromium and its compounds the environmental fate of chromium and its compounds toxicology of chromium the role of chromium as an essential micronutrient (importance of chemical speciation).

Environmental biochemistry of chromium.

Abstract: Chromium (Cr) was first discovered in Siberian red lead ore (crocoite) in 1798 by the French chemist, Vauquelin. Named for the bright colors of its compounds, Cr has since found an extremely wide variety of industrial uses that exploit these colors, as well as various other characteristics of Cr, such as strength, hardness and corrosion resistance of the metal, and the oxidizing capabilities of certain Cr species. Not surprisingly, large volumes of Cr waste in various chemical forms are generated from industrial processes and discharged into the environment. While Cr, in trace amounts, is essential for human life, exposure to some Cr compounds can pose a major health risk to all forms of life. This review will discuss some of the environmental impacts of chromium, including novel bioremediation techniques currently under development for detoxifying Cr-contaminated water and soils.

Method for producing an unsaturated carboxylic acid

Abstract: A method for producing an unsaturated carboxylic acid, which comprises subjecting an alkane to a vapor phase catalytic oxidation reaction in the presence of a catalyst containing a mixed metal oxide comprising, as essential components, Mo, V, Te, O and X wherein X is at least one element selected from the group consisting of niobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium, manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium, platinum, antimony, bismuth, boron, indium and cerium, wherein the proportions of the respective essential components, based on the total amount of the essential components exclusive of oxygen, satisfy the following formulas: 0.25

Reaction of chromium(VI) with ascorbate produces chromium(V), chromium(IV), and carbon-based radicals.

Abstract: Reaction of potassium dichromate with sodium ascorbate was studied by EPR spectroscopy at room temperature, in 0.10 M N-[2-hydroxyethyl]piperazine-N'-[2-ethanesulfonic acid] (HEPES), phosphate, cacodylate, and tris(hydroxymethyl)aminomethane hydrochloride (Tris.HCl) buffers at pH 7.0, in the presence of 0.10 M spin trap [5,5-dimethyl-1-pyrroline 1-oxide or 2-methyl-N-(4-pyridinylmethylene)-2-propanamine N,N'-dioxide]. Chromium(V), ascorbate radical, CO2-, and other carbon-based spin trap-radical adducts were observed. Chromium(V), CO2-, and the carbon-based radicals were observed at low ratios of ascorbate to chromium, and ascorbate radical was observed at high ratios of ascorbate to chromium. The presence of Cr(IV) was detected indirectly by reaction with Mn(II) and a subsequent decrease in the Mn(II) EPR signal. More Cr(IV) was found for the higher reaction ratios of ascorbate to Cr(VI). The only buffer effect observed was a relative decrease of the Cr(V) signal in Tris.HCl vs HEPES, phosphate, and cacodylate buffers, no change in the radical adducts was observed. There was no evidence for reactive oxygen species an intermediates in this reaction. Addition of the singlet oxygen trap 2,2,6,6-tetramethyl-4-piperidone hydrochloride showed no 2,2,6,6-tetramethyl-1-piperidinyloxy radical formation. The Cr(V) species did not react with dioxygen, and dioxygen did not affect the formation of carbon-based radicals. A mechanism consistent with these observations is discussed.

Mechanisms of chromium(III) sorption on silica. 1. Chromium(III) surface structure derived by extended x-ray absorption fine structure spectroscopy

Abstract: Metal ion reactions at the solid/solution interface are important in an array of disciplines and are of environmental significance as such reactions can greatly affect the risk imposed by metals. The structural environment of metals at the solid/water interface determines their potential for remobilization to the aqueous environment and the physical/chemical modifications of the sorbent. In this study, extended X-ray absorption fine structure (EXAFS) spectroscopy was used to discern the local structural environment of Cr(III) sorbed on silica. Chromium(III) formed a monodentate surface complex on silica, with a Cr-Si distance of 3.39 A. At the surface coverages investigated, a polynuclear chromium hydroxide surface phase occurred with Cr-Cr distances of 2.99 A, indicative of edge-sharing Cr octahedra. Crystallographic parameters resulting from the measured atomic distances dictate that the surface phase was most likely of the [gamma]-CrOOH-type local structure. Environmental considerations of Cr(III) remobilization must therefore consider the chemical/physical properties of the monodentate surface-complexed Cr(III) and surface-nucleated chromium hydroxide. 32 refs., 6 figs., 2 tabs.

Reduction of hexavalent chromium by Pseudomonas fluorescens LB300 in batch and continuous cultures

Abstract: Batch and continuous cultures of Pseudomonas fluorescens LB300 were shown to reduce hexavalent chromium, Cr(VI), aerobically at neutral pH (pH 7.0) with citrate as carbon and energy source. The product of Cr(VI) reduction was previously shown and confirmed in this work to be trivalent chromium, Cr(III), by quantitative reoxidation to Cr(VI) with KMnO4. In separate batch cultures (100 ml) containing initial Cr(VI) concentrations of 314.0, 200.0 and 112.5 mg Cr(VI) L−1, the organism reduced 61%, 69% and 99.7% of the Cr(VI), respectively. In a comparison of stationary and shaken cultures, the organism reduced 81% of Cr(VI) in 147 h in stationary culture and 80% in 122 h in shaken culture. In continuous culture, the organism lowered the influent Cr(VI) concentration by 28% with an 11.7-h residence time, by 39% with a 20.8-h residence time and by 57% with a 38.5-h residence time. A mass balance of chromium in a continuous culture at steady state showed an insignificant uptake of chromium by cells of P. fluorescens LB300.

Diffuse reflectance spectroscopy study of the thermal genesis and molecular structure of chromium-supported catalysts

Abstract: The diffuse reflectance spectra of a series of chromium-supported silica aluminas, with varying SiO2 content, have been investigated before and after drying and after calcination, successive CO reductions, and recalcination The molecular structure of chromium before drying is influenced by the isoelectric point (IEP) of the supports It is concluded that the lower the IEP of the support, the higher the amount of surface dichromate After calcination at 720 degrees C, Cr is anchored to the surface without changing the chromate:dichromate ratio Reduction results in the formation of octahedral Cr3+, pseudooctahedral and pseudotetrahedral Cr2+ A higher silica content of the support, a higher reduction temperature, and a higher calcination temperature result in a deeper reduction of the supported Cr Recalcination restores the initial chromate:dichromate ratio on each support; however, small quantities of Cr3+ remain in the samples This deeper reduction and reversibility can be explained by the low OH content of the supports calcined at 720 degrees C

C-H Bond Activation by Metal Oxo Species: Oxidation of Cyclohexane by Chromyl Chloride

Abstract: Chromyl chloride (CrO 2 Cl 2 ) reacts with cyclohexane solvent at 75 o C to give a dark precipitate along with chlorocyclohexane and a small amount of cyclohexene (in 10.0 and ca. 0.3% yields based on chromium). Hydrolysis of the precipitate, or treatment with a coordinating organic solvent such as acetonitrile, yields cyclohexanone (8.0%) and chlorocyclohexanone (2.5%). Spectroscopic studies of the precipitate indicate that the ketone products are present intact as σ-only ligands. Iodometric titrations of the complex show the average chromium oxidation state to be 3.41. The observed organic products account for only 26% of the chromium oxidizing equivalents used in the reaction; the remainder are most likely consumed in the formation of ring-opened products such as adipic acid

Effects of chromium picolinate supplementation on body composition, strength, and urinary chromium loss in football players

Abstract: The effects of 9 weeks of daily chromium supplementation (200 microgram Cr as picolinate) were investigated in a double-blind design in football players during spring training. Testing was done pre-, mid-, and postsupplementation on the following criterion measures: urinary chromium excretion, girth and skinfold measures, percent body fat and lean body mass, and isometric and dynamic strength. With the exception of 2 variables (of 65 variables analyzed), no significant group by trials interactions were found (based on a repeated measures ANOVA). The two exceptions were unrelated and inconsequential. For 27 of the 38 subjects, average urinary chromium loss at pre was 0.36 microgram/24 hr, whereas it was undetectable (<0.1 microgram/24 hr) for 10 subjects and excessive in 1 subject (2.4 micrograms/24 hr). Subjects receiving chromium supplements demonstrated urinary chromium losses five times greater than those in the placebo group at mid and post. Chromium picolinate supplementation was ineffective in bringing about changes in body composition or strength during a program of intensive weight-lifting training.

Base-specific arrest of in vitro DNA replication by carcinogenic chromium: relationship to DNA interstrand crosslinking

Abstract: We have previously shown that trivalent chromium can bind to purified DNA and form lesions capable of obstructing DNA replication in vitro. Trivalent chromium is not, however, carcinogenic to humans. Rather, it is the end product of the intracellular reduction of hexavalent chromium, which is carcinogenic. The process of chromium reduction yields several reactive intermediates which may also interact with DNA, perhaps producing different lesions than those generated when trivalent chromium binds DNA. The present study was undertaken to determine whether the treatment of DNA with hexavalent chromium in the presence of ascorbate (the intracellular reductant responsible for most in vivo chromium reduction), would also generate DNA lesions capable of obstructing replication. Using increasing chromium concentrations and a constant ascorbate:chromium ratio of 0.5:1 to generate biologically relevant adduct levels, a DNA polymerase arrest assay revealed that polymerase arresting lesions were formed and were indistinguishable from those generated by trivalent chromium, in that the most prominent arrests sites were one base upstream of guanine residues on the template strand. Measurement of the amount of chromium bound to template DNA in relation to the number of arrests demonstrated that only a subset (18.5%) of the chromium adducts were capable of causing polymerase arrest. Arrest assays performed with increasing ratios of ascorbate to chromium showed that high ratios (> or = 5:1) resulted in decreased polymerase arrests. DNA interstrand crosslinks in the arrest assay template were detected by renaturing agarose gel electrophoresis, and were shown to decrease markedly with increasing ascorbate to chromium ratios, whereas chromium binding levels remained unchanged. These results strongly implicate DNA interstrand crosslinks as the polymerase arresting lesion. The present study confirms and extends our previous study with trivalent chromium, and suggests that while the initial chemical nature of the DNA lesions formed by either trivalent chromium or reductive intermediates of hexavalent chromium may differ, their effect on DNA replication is the same.

Factors affecting chemical and biological reduction of hexavalent chromium in soil

Abstract: Hexavalent chromium [Cr(VI)] is a common environmental pollutant that is mobile in soils and is a known mutagen The trivalent form [Cr(III)] has no known mutagenic properties and is highly insoluble and immobile above pH 5 5 Reduction to the trivalent state thus represents an effective mechanism for detoxification and immobilization of Cr(VI) in soil/water systems In this study, we conducted experiments to examine various parameters involving aerobic reduction of Cr(VI) in a field soil We found that organic matter content, bioactivity, and oxygen status were important factors Under optimum conditions, the soil reduced 96% of added Cr(VI) under aerobic, field moist conditions The pH of the system was shown to have little effect Both biological and nonbiological processes were influential, and, of 20 chromate resistant bacterial cultures isolated from soils, 9 were found to actively reduce Cr(VI) to Cr(III) in liquid media Our study suggests that organic amended soils can readily reduce Cr(VI) and could promote excellent removal efficiency either as a primary treatment technique, or in conjunction with bioreactor type wastewater treatment systems

High-temperature corrosion of Cr2O3-forming alloys in CO-CO2-N2 atmospheres

Abstract: The corrosion of Fe−28Cr, Ni−28Cr, Co−28Cr, and pure chromium in a number of gas atmospheres made up of CO−CO2(−N2) was studied at 900°C. In addition, chromium was reacted with H2−H2O−N2, and Fe−28Cr was reacted with pure oxygen at 1 atm. Exposure of pure chromium to H2−H2O−N2 produced a single-phase of Cr2O3. In a CO−CO2 mixture, a sublayer consisting of Cr2O3 and Cr7C3 was formed underneath an external Cr2O3 layer. Adding nitrogen to the CO−CO2 mixture resulted in the formation of an additional single-phase layer of Cr2N next to the metal substrate. Oxidizing the binary alloys in CO−CO2−N2 resulted in a single Cr2O3 scale on Fe−28Cr and Ni−28Cr, while oxide precipitation occurred below the outer-oxide scale on Co−28Cr, which is ascribed to the slow alloy interdiffusion and possibily high oxygen solubility of Co−Cr alloys. Oxide growth followed the parabolic law, and the rate constant was virtually independent of oxygen partial pressure for Fe−28Cr, but varied between the different materials, decreasing in the order chromium >Fe−28Cr>Ni(Co)−28Cr. The formation of an inner corrosion zone on chromium caused a reduction in external-oxide growth rate. Permeation of carbon and nitrogen through Cr2O3 is thought to be due to molecular diffusion, and it is concluded that the nature of the atmosphere affects the permeability of the oxide.

Removal of hexavalent chromium from wastewater by adsorption

Abstract: Removal of chromium (VI) from aqueous waste was investigated using adsorbents based on bagasse and coconut jute. The effects of solution pH, Cr (VI) concentration, adsorbent dosage and contact time were studied in a batch experiment. The removal was in general most effective at low pH (≤2) values and low chromium (VI) concentrations. Activated coconut jute carbon was the most active among the four adsorbents studied. It was fairly stable even at higher pH. Removal of Cr (VI) of around 97% was observed with coconut jute carbon at natural pH, whereas other conventional adsorbents showed much lower activities. The data for all the adsorbents fit well to the Freundlich isotherm.

Effects of chromium on dna replication in vitro

Abstract: Chromium is an environmentally significant human carcinogen with complicated metabolism and an unknown mechanism of mutagenesis. Chromium(VI) is taken up by cells as the chromate anion and is reduc...

Chromium‐induced micronuclei in fish

Abstract: An investigation of the cytogenetic effects of chromium (Cr(VI) and Cr(III)) in Prussian carp (Carassius auratus gibelio) was made. For detecting cytogenetic damage, micronuclei induction in fish erythrocyte cells was employed. Fish were investigated 100 m above and 400 m below the discharge of leather waste products into the river Ljubljanica, and by exposing fish to three doses of chromium (Cr(VI) and Cr(III)) in the laboratory. The exposure of fish to various concentration levels (sub-lethal) of chromium under laboratory and field conditions caused an increase in the frequency of micronuclei compared with the control groups.