Showing papers on "Chromium published in 1999"

A Critical Assessment of Chromium in the Environment

Abstract: This article reviews the emissions, environmental fate and transport, analytical chemistry, uptake and metabolism, toxicology, and human epidemiology of chromium Chromium is unique among regulated toxic elements in the environment in that different species of chromium, specifically chromium (III) and chromium (VI), are regulated in different ways, in contrast to other toxic elements where the oxidation state is not distinguished In both industrial and environmental situations chromium (III) and chromium (VI) can inter-convert, with reduction of chromium (VI) to chromium (III) generally being favored in most environmental situations Chromium released into the air, water, and soil can be transported among the various environmental media through various intermedia transport processes Once in the environment, chromium can be taken up by human and other ecological receptors Chromium (III) is generally absorbed through cell membranes albeit to a significantly lesser degree than chromium (VI) Because most

Influence of Mineral Surfaces on Chromium(VI) Reduction by Iron(II)

Abstract: Chromium(VI) is a priority pollutant of some soils and natural waters in industrial areas. Iron(II), an important natural reductant of Cr(VI), is an option in remediation of contaminated sites, transforming Cr(VI) to essentially nontoxic Cr(III). After kinetics and pathways of this redox reaction had been reported to depend strongly on pH and organic ligands, this study investigated the influence of mineral surfaces. Kinetic measurements with UV−vis in mineral and soil suspensions at pH 5 showed that all minerals tested, except Al2O3, accelerated the Cr(VI) reduction by Fe(II), in the order of α-FeOOH ≈ γ-FeOOH ≫ montmorillonite > kaolinite ≈ SiO2 ≫ Al2O3. Similar kinetics were observed with soil from the E and BFe horizons of a Podzol. The reactions appear to be driven by the high reactivity of adsorbed Fe(II). Whereas adsorbed Cr(VI) was reducible by Fe(II), the sparingly soluble BaCrO4 was largely protected from reduction. This is of environmental relevance since in many polluted soils, Cr(VI) is partl...

Indication of Chromium Oxide Hydroxide Evaporation During Oxidation of 304L at 873 K in the Presence of 10% Water Vapor

Abstract: The oxidation of type 304L stainless steel wasinvestigated at 873 K in the presence of O2and O2 + 10% H2O. Oxidation timevaried between 1 and 672 hr. The oxidized samples wereinvestigated by a number of surface-analytical techniques includinggrazing-angle XRD, SEM/EDX, auger spectroscopy, SIMS andXPS. Oxidation in dry oxygen results in the formation acorundum-type oxide (Me2O3) withadditional formation of spinel oxides after prolonged exposure. Theoxide layer contained mainly chromium, with smalleramounts of Fe and Mn. Oxidation in the presence of watervapor results in an oxide that contains more Fe and less Cr, the outer part of the oxide beingdepleted in Cr. In the presence of water vapor, a massloss is detected after prolonged exposure. We show thatthe mass loss is caused by chromium evaporation. The volatile species is suggested to beCrO2(OH)2.

The nutritional supplement chromium(III) tris(picolinate) cleaves DNA.

Abstract: Chromium(III) tris(picolinate) [Cr(pic)3] is currently a very popular nutritional supplement; however, its safety has recently been questioned, especially with regard to its ability to act as a cla...

Chromium, Nickel and Cobalt in Environmental Samples and Existing Legal Norms

Abstract: This paper presents the occurrence, properties and origin of chromium, nickel and cobalt in environmental samples soil, water and the atmosphere. Methods of determining the above-mentioned elements and ways of preparing environmental samples for chemical analyses are presented. The content of chromium, nickel and cobalt in the atmosphere, naturally occurring waters, and soil is shown, along with the permissible concentrations of the above elements in the three divisions of the environment legally required in Poland and other countries.

Laboratory Studies on Remediation of Chromium-Contaminated Soils

Abstract: Soil washing processes and in-situ immobilization techniques have been often-suggested technologies for remediation of soils contaminated with heavy metals such as chromium. Laboratory batch extraction studies were conducted with synthetically contaminated soils [with Cr(VI)] to determine the ability of extractants such as 0.12 M Na4P2O7, 0.1 M NaF, and 1.0 M HCl to remove chromium from three types of soils with varying soil pH (5.8–8.1), organic matter (1.0–5.0%), and clay content (10–35%). Up to 73% of the total chromium present in the synthetically contaminated soil was removed by 0.12 M Na4P2O7. The synthetically contaminated soils were also treated with FeSO4 and NaOH solutions to immobilize chromium and investigated for leachability of Cr by Cr-free water. Up to 80% of the chromium could be retained in the soil following the immobilization process. The presence of soil organic matter and clay content enhanced the immobilization of chromium in both chromium flushing and immobilization experiments.

Use of X-ray absorption spectroscopy and esterification to investigate Cr(III) and Ni(II) ligands in alfalfa biomass

Abstract: Previously performed studies have shown that alfalfa shoot biomass can bind an appreciable amount of nickel(II) and chromium(III) ions from aqueous solution. Direct and indirect approaches were applied to study the possible mechanisms involved in metal binding by the alfalfa biomass. The direct approach involves investigations of the metal-bound alfalfa shoot biomass by X-ray absorption spectroscopic analysis (XANES and EXAFS). Results from these studies suggest that nickel(II) and chromium(III) binding mostly occurs through coordination with oxygen ligands. Indirect approaches consist of chemical modification of carboxylate groups that have been shown to play an important role in metal binding to the alfalfa biomass. An appreciable decrease in metal binding resulted after acidic methanol esterification of the biomass, indicating that carboxyl groups are entailed in the metal binding by the alfalfa biomass. In addition, base hydrolysis of the alfalfa biomass increased the binding of these metals, which further indicates that carboxyl groups play an important role in the binding of these metal ions from solution. Therefore, by combining two different techniques, our results indicate that carboxylate groups are the major ligands responsible for the binding of nickel(II) and chromium(III) by alfalfa biomass.

Reversal of corticosteroid-induced diabetes mellitus with supplemental chromium

Abstract: Summary Aims To determine if the stress of corticosteroid treatment increases chromium (Cr) losses and if corticosteroid-induced diabetes (steroid diabetes) can be reversed by supplemental chromium. Methods The effects of corticosteroid treatment on chromium losses of 13 patients 2 days prior to steroid administration and the first 3 days following treatment were determined. Since steroid-induced diabetes was associated with increased chromium losses and insufficient dietary chromium is associated with glucose intolerance and diabetes, we treated three patients with steroid-induced diabetes with 600 μg per day of chromium as chromium picolinate. Results Urinary chromium losses following corticosteroid treatment increased from 155 ± 28 ng/d before corticosteroid treatment to 244 ± 33 ng/d in the first 3 days following treatment. Chromium supplementation of patients with steroid-induced diabetes resulted in decreases in fasting blood glucose values from greater than 13.9 mmol/l (250 mg/dl) to less than 8.3 mmol/l (150 mg/dl). Hypoglycaemic drugs were also reduced 50% in all patients when given supplemental chromium. Conclusions These data demonstrate that corticosteroid treatment increases chromium losses and that steroid-induced diabetes can be reversed by chromium supplementation. Follow-up, double-blind studies are needed to confirm these observations. Diabet. Med. 16, 164–167 (1999)

Hydrogen in Chromium: Influence on the High-Temperature Oxidation Kinetics in H2O, Oxide-Growth Mechanisms, and Scale Adherence

Abstract: The effects of hydrogen and Y_2O_3 on high-temperature oxidation of Cr in 20 mbar O2 have been studied at 900°C. Oxidation- and O2-dissociation rates were determined from gas-phase measurements. Hydrogen in Cr leads to breakdown of the oxide scale. The oxide scale on Cr–1%Y2O3 charged with hydrogen for 4 hr (resulting in Cr–1%Y2O3 with approximately 10 ppm hydrogen) is adherent to the metal substrate. The oxidation rate is similar for Cr with ≤1 ppm hydrogen and Cr–1%Y2O3 with ≤1 ppm hydrogen, but significantly lower for 4-hr H-charged Cr–1%Y2O3. The oxidation rate of Cr–5%Fe–1%Y2O3–25 ppm H is also lower than the oxidation rate of Cr–5%Fe–1%Y2O3–≤1 ppm H. This indicates that unless hydrogen is present, there are virtually no effects of the addition of 1% Y2O3 to Cr. Using labeled oxygen, 16,16O2 and 18,18O2, was found that at 900°C the dissociation rate of O2 is higher on Y2O3 than on Cr2O3. It is suggested that the well-known improvement of the oxidation resistance of Cr as an effect of additions of Y or Y2O3 is related to an increase in the dissociation rate of O2 and that there is a synergetic effect in combining Y2O3 and hydrogen.

Corrosion of CrN and TiAlN coatings in chloride-containing atmospheres

Abstract: Chromium and titanium–aluminium nitrides were deposited, by physical vapour deposition techniques, on stainless steel substrates and their corrosion behaviour was studied in two different environments: a gaseous environment containing HCl at a temperature of 350°C and a 1 M HCl aqueous solution environment, at room temperature. X-ray photoelectron spectroscopy was used to study the mechanism of the reactions that occurred in the gaseous environment. This analysis shows an oxidation of the surface caused by the substitution of nitrogen by oxygen. Open circuit potential and potentiodynamic polarisation measurements were performed in the aqueous solution environment. The aqueous corrosion behaviour of the nitride coatings is strongly dependent on the microdefect density of the coating.

The role of goethite in the formation of the protective corrosion layer on steels

Abstract: The corrosion products formed on carbon and weathering steels exposed in marine, industrial and rural environments in the United States for 16 years have been investigated using Mossbauer spectroscopy, Raman spectrometry and chemical analysis. Mossbauer spectroscopy was used to measure the fraction of each oxide in the corrosion coatings and micro-Raman spectrometry was used to locate and map the oxides to 2 µm spatial resolution. Mossbauer spectroscopy identified the corrosion products in the weathering steels as 75% goethite, 20% lepidocrocite and 5% maghemite. Raman analysis showed that the corrosion products generally formed as alternating layers containing different oxides. For the weathering steels the protective inner-layer closest to the steel substrate consisted of nano-sized goethite ranging in size from 5–30 nm and having a mean particle size of about 12 nm. The outer-layer close to the coating surface, consisted of lepidocrocite and goethite with the former oxide being most abundant. Electron probe micro-analysis measured significant chromium in the goethite close to the steel substrate. Comparison of the goethite in the corrosion products was made with synthetic chromium substituted goethite with nearly identical microstructural characteristics being recorded. It is concluded that chromium inclusions in the goethite are important for formation of a nano-phase oxide layer which may help protect the weathering steel from further corrosion.

Comparative studies of the reduction behavior of chromium(VI) by humic substances and their precursors

Abstract: Hexavalent chromium (Cr[VI]) is reduced by dissolved organic carbons (DOCs) such as humic substances, tannic acid (TA), and gallic acid (GA). The kinetic constants and the resulting chemical species after the reduction were compared with each other. The kinetic constants for GA and TA, which are model precursors of humic substances, were two to three orders of magnitude larger than those for the humic substances when these kinetic constants were expressed as a function of the molar concentration of the reductive functional group (F[sub red]) in various DOCs. After the reduction of Cr(VI), the percentages of the species complexed with GA and TA were higher than those with the humic substances. This appears to be due to the formation of high molecular weight compounds by polymerization during the reduction of Cr(VI) and complexation of Cr(III) with the polymerized compounds. The UV-vis spectrophotometric data and gel permeation chromatography support this view.

Chromium mobilization and plant availability — the impact of organic complexing ligands

Abstract: Pot experiments were conducted to investigate the effect of various organic acids (carboxylic and amino acids) on the uptake and translocation of root-absorbed trivalent chromium by tomato ( Lycopersicum esculentum) plants grown in sand and soil culture Statistically significant increases in chromium accumulation from Cr(III) treated plants in the presence of increasing concentrations of organic acid suggest the existence of Cr(III) — organic acid interactions in the soil-plant system However, the amino acids have been less effective in the mobilization of chromium compared to carboxylic acids The results are discussed on the basis of the potential of organic acids to form complexes with Cr(III)