Nutritional role of chromium

Chromium is an essential trace element required for normal carbohydrate metabolism. The biological function of chromium is closely associated with that of insulin and most chromium-stimulated reactions are also insulin dependent. Proper chromium nutrition leads to a decreased requirement for insulin and also an improved blood lipid profile. Most fresh foods and minimally processed foods are good sources of dietary chromium. Inorganic chromium does not potentiate insulin action and must be converted to an organic biologically active form. An organic form of chromium capable of potentiating insulin action has been isolated from brewer's yeast and was shown to contain: Cr, nicotinic acid and a combination of amino acids. Synthetic insulin potentiating organic chromium complexes containing chromium, nicotinic acid, glycine, cysteine, and glutamic acid or chromium, nicotinic acid and glutathione have been prepared. These complexes have not been purified to homogeneity since they dissociate during purification. Suitable analytical bioassays are available to measure total chromium and the organic biologically-active forms of chromium, respectively.     

Analytical chemistry of chromium

The determination of chromium in most biological materials is extremely difficult because of the very low levels present. Easily accessible samples, for example biological fluids such as serum, urine, etc., usually have chromium concentrations well below 1 ng g-1. The only widely available analytical method with sufficient sensitivity is graphite furnace atomic absorption spectrometry (GFAAS), yet values reported in the early literature were wildly divergent. Man appeared to be excreting several times the amount of chromium he was absorbing from his diet. This dilemma was resolved in 1978 when it was shown that all previous chromium analytical results were probably wrong (too high), due to limitations of the instrumentation used up until then. Subsequent instruments with improved background correction capabilities have removed this limitation. However, making determinations at the sub-parts-per-billion level remains a formidable task in terms of contamination control.     

Environmental chemistry of chromium

The processes that control the environmental chemistry of chromium include redox transformation, precipitation/dissolution, and adsorption/desorption reactions. Commonly occurring reductants, such as ferrous iron and organic material, can transform Cr(VI) to Cr(III), but manganese oxides are the only inorganic oxidants found in the environment that cause the rapid oxidation of Cr(III) to Cr(VI). In the trivalent state, chromium readily forms compounds such as Cr(OH)3 and (Cr,Fe)(OH)3. These solids show amphoteric solubility behavior, with hydroxo complexes being the dominant aqueous species of Cr(III). The relatively low solubilities of Cr(OH)3 and (Cr,Fe)(OH)3 limit Cr(III) concentrations to less than the drinking water limit over much of the pH range of environmental interest. In the hexavalent state, the formation of the Ba(S,Cr)O4 solid solution controls the dissolved chromium concentrations in environments that contain BaSO4. In the absence of solubility-controlling Cr(VI) solids, Cr(VI) concentrations in acidic to slightly alkaline conditions are expected to be limited by adsorption. Iron oxides are the most important absorbents for aqueous Cr(VI) species in most soil environments. Although these processes are complex and interrelated, each must be considered to predict the aqueous concentrations, mobility, and toxicity of chromium in the environment.     

Inorganic chemistry of chromium and its speciation in Whetlerite

Chromium compounds are among the impregnants that enhance the ability of carbon air filters to absorb and destroy toxic agents such as CK and AC. The possibility of inhaling chromium-containing carbon dust from such filters has caused concern because, in addition to being an essential nutrient, chromium has been identified as a chemical carcinogen in humans. The essentiality or carcinogenicity of chromium depends upon its chemical speciation. Solubility and oxidation state are particularly important factors in assessing the potential hazards associated with the possible inhalation of chromium-containing dusts from these impregnated carbons or Whetlerites. The chemical speciation of the chromium in Whetlerite was found to be: from 0.6 to 1.3% insoluble trivalent chromium; from 1.0 to 1.3% insoluble hexavalent chromium; and from 0.7 to 0.9% soluble hexavalent chromium. The impregnation process, and the resulting speciation of chromium in Whetlerite, is consistent with the inorganic chemistry of chromium.     

Essentiality of chromium in humans

Chromium is an essential nutrient required for normal sugar and fat metabolism. Insufficient dietary chromium is associated with maturity-onset diabetes and/or cardiovascular diseases. Dietary chromium intake in the U.S. and other developed countries is roughly half of the minimum suggested intake of 50 micrograms. Well controlled studies involving human subjects have demonstrated beneficial effects of supplemental chromium on fasting glucose, glucose tolerance, blood lipids, insulin binding, and hypoglycemic blood glucose values and symptoms. Since chromium is a nutrient and not a therapeutic agent, it will only benefit those people whose signs and symptoms are due to marginal or overt chromium deficiency. Stresses including high sugar diets, strenuous exercise, physical trauma, infection and certain diseases exacerbate the signs and symptoms associated with marginal intakes of dietary chromium. While excessive levels of chromium are usually limited to industrial settings, marginal dietary chromium intake is widespread in the general population and may lead to serious health problems.     

Mutagenicity and disposition of chromium

Hexavalent chromium was administered to rats at doses of 20-240 mumol kg-1 for several periods of time, from 2 to 14 days. Lung, liver and blood contained the highest amounts of chromium, as detected by atomic absorption or by ICP, 24 h after cessation of treatment. A maximum of 40% of the dose was recoverable in organs along with feces and urine at this same time period, and chromium in soil (5.6% Cr) was absorbed better than equimolar amounts of the hexavalent chromates of calcium or sodium. The contaminated chromium-containing soil was found to have 30-35% of the chromium in the hexavalent state. The mutagenicity of chromium as tested in the bacterial strain of Salmonella typhimurium (strain TA 104) was decreased when tested without metabolic activation with the addition of leachate (of inexact analysis) from a waste site. When studied by alkaline elution, chromium (5-20 microM) caused single strand breaks as well as DNA-protein crosslinks in A549 lung cells, while with L1210 mouse leukemia cells, only DNA-protein crosslinks were found. Chromium(III) compounds caused no damage to DNA.     

Kinetics of chromium during peritoneal dialysis

This study describes investigations on the possible mechanisms involved in the transfer of Cr from the dialysate to the blood during peritoneal dialysis. The ability of Cr(III) compounds to penetrate across a membrane at physiological pH seems rather questionable, as it is well known that Cr(III) tends to form polymeric chains. Therefore, a systematic study was undertaken to describe the pathways involved in this transport. The characteristics during 'in vitro' dialysis were compared to the behaviour of Cr during acute 'in vivo' experiments on anesthetized rabbits. It appeared that lactate, a common substance of the dialysate, plays an extremely important role in the mobility and subsequent transfer of Cr(III) across the peritoneum.     

Environmental chemistry of phosphonates

Phosphonates are anthropogenic complexing agents containing one or more C-PO(OH)(2) groups. They are used in numerous technical and industrial applications as chelating agents and scale inhibitors. Phosphonates have properties that differentiate them from other chelating agents and that greatly affect their environmental behavior. Phosphonates have a very strong interaction with surfaces, which results in a significant removal in technical and natural systems. Due to this strong adsorption, little or no remobilization of metals is expected. No biodegradation of phosphonates during water treatment is observed but photodegradation of the Fe(III)-complexes is rapid. Aminopolyphosphonates are also rapidly oxidized in the presence of Mn(II) and oxygen and stable breakdown products are formed that have been detected in wastewater. The lack of information about phosphonates in the environment is linked to analytical problems of their determination at trace concentrations in natural waters. Further method development is urgently needed in this area, including speciation of these compounds. With the current knowledge on speciation, we can conclude that phosphonates are mainly present as Ca and Mg-complexes in natural waters and therefore do not affect metal speciation or transport.     

Effects of pH and oxidation state of chromium on the behavior of chromium in the activated sludge process

The behavior of chromium (Cr) in the activated sludge process (ASP) was evaluated in laboratory-scale, fill-and-draw activated sludge experiments. Both pH and the oxidation state of chromium were confirmed as critical parameters in the ASP for evaluating the behavior of chromium. More than 55% of chromium was removed when trivalent chromium [Cr(III)] was introduced into the influent while less than 60% was removed when hexavalent chromium [Cr(VI)] was added over a pH range from 5 to 9. As pH was increased, the removal increased when Cr(III) was introduced but the reverse occurred with Cr(VI). Introduction of Cr(VI) into the influent resulted in less than 80% of chromium associated with solids; however, with Cr(III), more than 90% of chromium was bound with solids. These results suggest that the ASP is capable of controlling the transport of Cr(III) to the environment but such is not case for Cr(VI).Theoretical consideration based on thermodynamics predicted that no reduction of Cr(VI) into Cr(III) should occur and the only redox reaction should be the oxidation of Cr(III) into Cr(VI). However, no oxidation of Cr(III) into Cr(VI) was observed; some Cr(VI) was reduced into Cr(III). Kinetic constraints may have impeded the oxidation of Cr(III). Under the conditions of this study, Cr(III) may have been removed through adsorption rather than precipitation as Cr(OH)₃. Cr(VI) might be adsorbed on the bacterial surface through specific adsorption.     

Kinetics of chromium transformations in the environment

Kinetics of chromium transformations under typical environmental conditions were systematically investigated using batch, microcosm and column experiments. Oxidation and reduction rates were evaluated in single phase water systems and in two phase water-solid systems. Natural and reference waters, sediments and soils representing a broad range of characteristics were used. Some of the investigated reactions, such as the reduction of Cr(VI) by S2- or Fe2+ ions under anaerobic conditions, were instantaneous and the experimental results exactly followed the stoichiometric and equilibrium calculations. Other reactions, such as the reduction of Cr(VI) by organics in sediments and soils, or the oxidation of Cr(III) by MnO2, were much slower and clearly exhibited kinetic controls. Reduction of Cr(VI) by organics was dependent on both the type and amount of organic material. Dissolved oxygen by itself did not induce measurable oxidation of Cr(III), spiked to the experimental waters, after 128 days. Slow Cr(III) oxidation to Cr(VI) was only noted in one of the natural waters and sediments with half-lives ranging from 2 to 9 years. In all cases the extent of Cr(III) oxidation did not exceed 15% of the initial Cr(III) present. The overall results indicate that the transport and transformation of chromium can be predicted using kinetics data derived from a simplified laboratory experiment, the Eh-pH data and the aquatic system characteristics. Results of the microcosm and laboratory experiments were in good agreement with the predicted concentrations.     

Toxic effect of chromium on cellular metabolism

The cytotoxic action of Cr(VI) in intact mammalian cells is strictly related to its carrier-mediated transport across the plasma membrane and its reduction to Cr(III) inside the cell. A marked decrease in the ratio of reduced/oxidized glutathione in rat thymocytes treated with dichromate indicates an involvement of glutathione in the reduction of Cr(VI) to Cr(III) in these cells. Intracellular chromium is shown to interfere with specific steps of cellular energy metabolism in that it produces severe unbalance of purine ribonucleotide pools in hamster fibroblast cultures and inhibition of mitochondrial oxygen consumption in rat thymocytes at micromolar concentrations. To what extent the effects caused by Cr(VI) are directly related to the reduction process or to the subsequent binding of Cr(III), and possibly of Cr(V), to biological molecules playing a critical role in cell physiology, remains to be elucidated.     

Acute and chronic systemic chromium toxicity

Although chromium and compounds containing it have been recognized as having potential severe adverse effects on health for more than 160 years, understanding of the systemic toxicology and true hazard of these compounds is still not complete. A review of the current state of knowledge is attempted in this paper, with appropriate attention given to the complications of multiple valence states and solubility. Selected chromium compounds, particularly hexavalent ones, are carcinogens, corrosives, delayed contact sensitizers, and have the kidney as their primary target organ. But chromium is also an essential element for humans. The body clearly possesses some effective detoxification mechanisms for some degree of exposure to hexavalent chrome compounds. The significant features of acute and chronic chromium toxicity are presented in view of these considerations.     

废水处理中脱除铬的步骤

简要介绍了铬的形态和特性,并对废水处理中脱除铬所采用的材料方法及步骤进行了详细阐述,指出采用NaHSO3减小pH值,使在中性条件下难溶的Cr3+进一步沉淀,为通过pH和ORP传感器的反应进行自动控制提供了可行性。     

Determination of total chromium in environmental water samples

It is often desirable to quantify both dissolved Cr(VI) and total Cr in samples accurately. Various protocols are now being utilized to quantify the amount of total chromium in natural waters and each of these has possible interferences. This study describes the shortcomings of each method when particulate iron is present in a water sample, and a more rigorous digestion protocol is tested. Data from bench studies as well as a field survey of 21 water utilities are presented. Additionally, field data from several hundred water utility samples are presented to illustrate the potential for incomplete recovery of total chromium using accepted protocols.     

Experimental copper and chromium deficiency and additional molybdenum supplementation in goats. II. Concentrations of trace and minor elements in liver, kidneys and ribs: haematology and clinical chemistry

Since the mid-1980s a previously undescribed disease has affected moose in south-western Sweden. Investigations made to reveal evidence of a viral aetiology have proved unsuccessful. Trace element studies in apparently healthy moose shot during regular hunting suggested a trace element imbalance, with excessive molybdenum uptake causing secondary copper deficiency. The results also indicated a possible chromium deficiency. To verify this hypothesis, an experimental study was performed in male goats fed a semi-synthetic diet for 1.5 years. The animals were kept and treated in four groups: Controls, Cu-deficient group (group 1), Cr-deficient group (group 2), and combined Cu- and Cr-deficient group with additional supplementation of tetrathiomolybdate for 10 weeks at the end of the study (group 3). The present paper presents tissue contents of trace and minor elements, haematology and clinical chemical parameters. Feed consumption and weight development, as well as pathological and histopathological investigations, were also performed in this study, but these results are presented elsewhere. Changes in trace element concentrations were determined by comparing groups 1, 2 and 3 with the control group. Increased concentrations were observed for Al, Ca, Co, Fe, Mo, Pb, Se in the liver; for Al, Cd, Co, Cr, Mo in the kidneys; and for Mn and Mo in the ribs. Considerable accumulation of Mn in ribs seems to be a useful way to determine oxidative stress. Decreases in Mg and P in all organs and blood serum is characteristic of Cu deficiency and molybdenosis. Also the ratio of Ca/Mg was increased as the result of tissue lesions causing an intracellular increase in Ca and decrease in Mg. The trace element changes observed in group 1 were enhanced by the Mo supplementation in group 3, resulting in characteristic patterns, 'spectra' of changes. The alterations were not as remarkable in group 2 as in the two other groups. However, Cr deficiency considerably influenced Al, Co, V and to a smaller extent also Mn in ribs. In groups 1 and 2, only a few minor changes were detected in the haematological parameters, probably caused by increased adrenal activity after transportation of the animals. In group 3, severe anaemia was present but also a leukopenia. For the different clinical chemical parameters measured, all three groups showed changes, explained mainly by the altered activity of enzymes induced by trace element deficiencies and imbalance. Impaired carbohydrate and lipid metabolism was seen in groups 1 and 3, with increased concentrations of glucose, lactate and triglycerides in serum. Increased concentrations of total bilirubin were measured in all three groups (bile stasis was also seen post mortem). A considerably increased concentration of serum urea was found in group 3, although there were no indications of renal insufficiency or dehydration. Regarding hormones, a substantial decrease was seen in thyroxine (T4) in group 3 as a result of the molybdenosis, but a minor decrease was also seen in group 1. Insulin on the other hand showed increased levels in group 3--and especially in group 2 due to the Cr deficiency but also affected by the molybdenosis. As could be expected, Cu deficiency (groups 1 and 3) caused low levels of caeruloplasmin, secondarily affecting the Fe metabolism in these animals. Protein abnormalities, detected as altered electrophoretic patterns of serum proteins, were also seen mainly in group 3. The findings were also confirmed by multivariate data analysis, where PCA revealed the overall impact of the deficiencies, and PLS regression coefficients indicated the influence on the various analytes.     

谈镀铬车间的设计方法

针对镀铬车间的特殊性,探讨了镀铬车间防腐设计的方法,介绍了该车间选址过程中的注意事项,着重对工程的材料要求、结构选型、基础设计等进行了分析研究,为类似工程的设计与施工积累了经验。     

The kinetics of hexavalent chromium reduction by metallic iron

The rate reduction of hexavalent chromium (Cr(VI)) by metallic iron under a range of conditions was studied in batch systems. The chemical variables studied were the Cr(VI) concentration, hydrogen ion concentration and surface area of iron. The influence of ionic strength and mixing rate was also examined. The reaction kinetics were found to be dependent on hydrogen ion concentration, hexavalent chromium concentration and iron surface area and to adhere to the following kinetic expression.

Full-size image (1K)

.The rate constant was evaluated and found to have a value of 5.45 × 10⁻⁵ 1 cm⁻² min⁻¹ over a wide range of conditions.The rate constant was found to increase as mixing rate increased up to a maximum value beyond which the rate was essentially independent of mixing. Increases in ionic strength were found to result in a rapid decrease in the rate constant at ionic strengths below 0.1 M. Further increases in ionic strength had no detectable impact on the rate constant. All rate determination studies were run in the mixing and ionic strength independent regions of these systems.Reaction stoichiometry was found to be, with one exception, independent of environmental conditions. In general, 1.33 mol of iron dissolved for each mol of Cr(VI) reduced. This highly efficient utilization of iron in the reduction suggests that hydrogen generated during iron dissolution may be acting as a reductant for the Cr(VI). The single parameter which influenced the reaction stoichiometry was the initial Cr(VI) concentration. The ratio of Cr(VI) reduced to iron dissolved increased rapidly as the Cr(VI) concentration increased. This observation was taken as being consistant with a surface interaction between the hexavalent chromium and some metastable hydrogen species at the iron surface.     

Selected toxicological aspects of chromium(VI) compounds

Chromium(III) is thought to be an essential element in mammals, its toxicity being very low. On the contrary, chromium (VI) is highly toxic to man, even if its effects are generally local, involving the respiratory tract and the skin. Once absorbed, chromium(VI) is quickly reduced to the trivalent form which accounts for all of this element present in the blood stream or taken up by tissues. As a result, any differences in systemic toxicity can only be attributed to differential solubilities and absorption rates. The kidney should be regarded as the critical organ, although tubular damage following occupational exposure is mostly due to acute absorption and transient in nature. Sensitive immunochemical techniques for the measurement of specific proteins in the urine have been used for the early detection of kidney damage, a possible threshold having been indicated at exposure levels yielding 15 micrograms/g creatinine in urine. Such a threshold has been confirmed by using monoclonal antibodies to reveal antigens from the brush-border of proximal tubules. Two main features of kidney damage were, however, apparent. The first one is the lack of dose-effect/response relationships, i.e. the lack of any progression toward more severe impairments when the exposure intensity increases. The second one is that the recent absorption rate more than the cumulated dose is responsible for the observed nephrotoxic effects.     

高铬合金铸球在水泥磨机的应用

概述了高铬合金铸球在水泥磨机中应用的试验情况,通过试验结果来说明：应用高铬合金铸球可有效提高磨机的经济效益;阐明它的推广价值。     

Development of the revised drinking water standard for chromium

Comprehensive regulations are being developed to limit human exposure to contamination in drinking water by the United States Environmental Protection Agency (EPA) under the authority of the Safe Drinking Water Act (SDWA). These regulations are being developed in several phases and include synthetic organic chemicals, inorganic chemicals, microbiological contaminants and radionuclides. This paper addresses the fundamental concepts and approaches used by EPA in setting drinking water regulations and how EPA is using these concepts to revise the drinking water standard for chromium.