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PubMed2004

Chromium accumulation by living yeast at various environmental conditions.

Yeast tolerance to Cr (III) and Cr (VI) as well as chromium accumulation potential were shown to depend on treatment time, metal concentration, biomass density and the phase of growth. Kinetic studies as exemplified by Pichia guilliermondii ATCC 201911 revealed a biphasic mode of Cr (III) uptake: a rapid sorption phase was followed by a slow process of accumulation, in which the contribution of the cell-bound Cr fraction increased, while the total cellular Cr level remained constant. Cr (VI) uptake was characterized by a time-dependent increase of total Cr and by a constant fractional contribution of the cell-adsorbed chromium, which suggests that the amount of cell-accumulated Cr also tended to increase over time. The resistance to Cr and metal accumulation levels were substantially elevated for a given strain when cultures were treated at high initial biomass densities (1 mg dry weight/ml) of exponentially proliferating cells. Maximum accumulation capabilities ranged between 4.0 and 13 mg Cr (III)/g dry weight and 2-6.7 mg Cr (VI)/g dry weight. The total cell-accumulated Cr contained 29.3% and 52.3% of organically bound chromium for the treatment of P. guilliermondii with Cr (III) and Cr (VI), respectively. Selected yeast strains, under specified physiological conditions, can be applied for bioremediation of environmental Cr contamination, and might be useful too for attempts to obtain chromium-enriched biomass containing biostabilized and nontoxic Cr forms for nutritional applications.

Antifungal Agents↗
PubMed2006

Chromium picolinate positively influences the glucose transporter system via affecting cholesterol homeostasis in adipocytes cultured under hyperglycemic diabetic conditions.

Since trivalent chromium (Cr(3+)) enhances glucose metabolism, interest in the use of Cr(3+)as a therapy for type 2 diabetes has grown in the mainstream medical community. Moreover, accumulating evidence suggests that Cr(3+) may also benefit cardiovascular disease (CVD) and atypical depression. We have found that cholesterol, a lipid implicated in both CVD and neurodegenerative disorders, also influences cellular glucose uptake. A recent study in our laboratory shows that exposure of 3T3-L1 adipocytes to chromium picolinate (CrPic, 10 nM) induces a loss of plasma membrane cholesterol. Concomitantly, accumulation of intracellularly sequestered glucose transporter GLUT4 at the plasma membrane was dependent on the CrPic-induced cholesterol loss. Since CrPic supplementation has the greatest benefit on glucose metabolism in hyperglycemic insulin-resistant individuals, we asked here if the CrPic effect on cells was glucose-dependent. We found that GLUT4 redistribution in cells treated with CrPic occurs only in cells cultured under high glucose (25 mM) conditions that resemble the diabetic-state, and not in cells cultured under non-diabetic (5.5 mM glucose) conditions. Examination of the effect of CrPic on proteins involved in cholesterol homeostasis revealed that the activity of sterol regulatory element-binding protein (SREBP), a membrane-bound transcription factor ultimately responsible for controlling cellular cholesterol balance, was upregulated by CrPic. In addition, ABCA1, a major player in mediating cholesterol efflux was decreased, consistent with SREBP transcriptional repression of the ABCA1 gene. Although the exact mechanism of Cr(3+)-induced cholesterol loss remains to be determined, these cellular responses highlight a novel and significant effect of chromium on cholesterol homeostasis. Furthermore, these findings provide an important clue to our understanding of how chromium supplementation might benefit hypercholesterolemia-associated disorders.

3T3-L1 Cells↗
PubMed2005

An in vitro comparison of retentive force and deformation of acetal resin and cobalt-chromium clasps.

STATEMENT OF PROBLEM: The use of metal clasps on anterior teeth may cause esthetic problems. Recently, acetal resins have been used as an alternative tooth-colored denture clasp material to improve esthetics. However, there are few studies to support acetal resin use. PURPOSE: The purpose of this in vitro study was to compare the retentive force and deformation of acetal resin and cobalt-chromium clasps after 36 months of simulated clinical use. MATERIAL AND METHODS: Forty clasps each of acetal resin (1.2 or 2.0 mm thick) and cobalt-chromium (Dentorium)(1.2 mm thick) were fabricated using half-round standard prefabricated clasp patterns. The groups were further subdivided (n=10) into the type of tooth (premolar or molar metal model) and undercut (0.25 mm or 0.50 mm). The retentive force of the clasps was measured in distilled water by a specially designed insertion-removal testing apparatus with intervals corresponding to 0, 6, 12, 18, 24, 30, and 36 months of simulated clinical use of a removable partial denture. The distance between the clasp tips (mm) was measured with a microscope before and after the insertion-removal testing procedure. Comparison of the mean values of the retentive force (gram force) of the clasps and the distance (mm) between the clasp tips was conducted with 3-way analysis of variance and a Least Significant Difference (LSD) multiple range test (alpha=.05). RESULTS: The mean values of tensile load required to dislodge acetal resin clasps with 1.2-mm thickness (111.6 g or 0.11 N) and with 2.0-mm thickness (178.4 g or 1.75 N) was significantly lower than that to dislodge Co-Cr clasps (694.1 g or 6.81 N) (P<.001). The retentive force needed to dislodge all 3 types of clasps was significantly lower for the molar than premolar models and also lower for the models with 0.25-mm undercuts than for those with 0.50-mm undercuts (P<.001). After 36 months of simulated clinical use, there was evidence of deformation in the cobalt-chromium clasps but no deformation noted for the acetal resin clasps. The retentive force of cobalt-chromium clasps (297.4 g or 2.91 N) after deformation remained significantly higher (P<.001) than the retentive force of acetal resin clasps that were 1.2 mm (110.7 g or 1.08 N) and 2.0 mm thick (177.5 g or 1.74 N), respectively. CONCLUSION: Within the limitations of this study, the results suggest that both thicknesses of acetal resin clasps evaluated required less force for insertion and removal than Co-Cr clasps over a simulated 36-month period.

Analysis of Variance↗
PubMed2005

Ameliorating effect of folic acid on chromium(VI)-induced changes in reproductive performance and seminal plasma biochemistry in male rabbits.

Chromium hexavalent (Cr(VI)) is a biologically active oxidized state of chromium. It is involved in the redox cycle, with the production of reactive oxygen species. Free radical scavenging properties and possible antioxidant activity of folic acid (FA) have been reported; therefore, the present study examined possible protective effects of FA on the reproductive toxicity of potassium dichromate (K2Cr2O7) in male New Zealand white rabbits. We monitored reproductive performance, lipid peroxidation, enzyme activities and biochemical parameters in seminal plasma. Six rabbits per treatment group (and a control group) were exposed: 8.3 microg/kg FA; 5 mg/kg potassium dichromate (contains 3.6 mg chromium(VI)) and 5 mg/kg potassium dichromate+8.3 microg/kg FA. Results showed that semen quality deteriorated following potassium dichromate exposure. Testosterone levels, body weight (BW), relative weights of testes (RTW) and epididymis (REW) all decreased. Levels of thiobarbituric acid-reactive substances increased, whereas the activities of glutathione S-transferase, transaminases and phosphatases decreased in the seminal plasma. FA alone significantly increased BW, RTW, REW, semen characteristics and seminal plasma enzymes, and decreased the levels of free radicals. Furthermore, FA can be effective in the protection of chromium-induced reproductive toxicity.

Acid Phosphatase↗
PubMed2006

Spectral studies with coordination behaviour of (NO3) and (NCS) anions and EPR parameters of chromium(III) complexes which have different chromospheres macrocyclic ligands: synthesis and electronic spectroscopy.

New macrocyclic ligands were prepared and chromium(III) stability in the marcrocyclic cavities are reported. Two of them have four-coordinate [N2O2]:[N4], third one has five-coordinate [N2O2S] and the last one has six-coordinate [N4O2] donor macrocyclic cavities. These macrocyclic ligands have been synthesized with their chromium(III) complexes which have mononuclear nature and their structural features have been discussed on the basis of: elemental analysis, magnetic moment, electronic, IR, 1H NMR, and EPR spectral studies. All the chromium(III) complexes show magnetic moments in the range of 3.74-3.80 B.M. corresponding to high-spin configuration. However, the interaction of oxygen to the chromium ion in complexes is much weaker than that of other donor atoms. The spin-orbit coupling parameter, z, gives no significance because the splitting of doublet transition lines are too large to be explained by spin-orbit coupling. The beta values (0.75-0.79) indicate the covalent character, which is due to the presence of sigma bond between the metal/ligand. lambda values indicate that the complexes under study have substantial covalent character and their g-values have also been calculated by using spin-orbital coupling constant (lambda).

Anions↗
PubMed2005

Purification of chromium(VI) finishing wastewaters using calcined and uncalcined Mg-Al-CO3-hydrotalcite.

The applicability of calcined and uncalcined hydrotalcite for the purification of industrial effluents has been studied using chromium finishing wastewaters. Using a batch method, the influence of the initial concentration of chromium (10-450mg/l), hydrotalcite (HT) dose (0.5-5g/l) and time (0.5-72h) has been evaluated. The process could be described by the Langmuir model and gave a maximum removal of chromium of 16.3mg Cr(VI)/g on uncalcined HT and 128mg Cr(VI)/g on calcined hydrotalcite (C-HT). Removal using the calcined product provided an effective system to treat chromium finishing wastewaters with the most stringent discharge limit for such industrial streams being achieved with between two and four consecutive removal cycles on C-HT at a dose of 2g/l.

Adsorption↗
PubMed2003

Effects of chromium exposure from a cement factory.

The aim of the study was to determine the chromium concentrations of soil and plant specimens taken from a rural area exposed to cement factory emissions and also to determine the blood concentrations and sensitivity conditions observed in humans residing in this rural area. The study was carried out in Cukurhisar, a town in Eskisehir-Turkey, between May 2000 and March 2001. Besides the 108 soil (36 for control) and plant specimens, which were taken from eight different directions from the cement factory, blood samples of the individuals residing in this area were taken from 258 subjects (258 for control) following a physical examination, and patch tests were also applied. The chromium concentrations of the soil and plant specimens taken from different places in different directions of the factory were higher than in the control areas. The physical examination of subjects did not reveal results different from those of the control group except for the diagnosis of contact dermatitis. The analyses of venous blood samples showed that chromium concentrations were found to be within the reference values given for both groups, but higher in the subjects (P<0.001). According to the results of patch tests, sensitivity to chromium was found to be more frequent for the subject group than the control group (P<0.05). According to these results, clinical tools revealed no toxic effects for the subjects, except contact dermatitis. However, sensitivity to patch tests showed that this subject group has been affected compared to the control group and that this effect increased with age.

Adolescent↗
PubMed2003

Determination of total and hexavalent chromium concentrations in the atmosphere of the city of Isfahan.

Airborne particulate matter was collected from the atmosphere of the city of Isfahan by a high-volume air sampler. Determination of the concentration of total chromium was carried out by graphite furnace atomic absorption spectrometry after acid digestion. The determination of hexavalent chromium was carried out by ion chromatography following the collection of Cr(vi) in an impinger. Day-to-day variations in concentrations of total and hexavalent chromium were investigated and an excellent similarity was found between them. Atmospheric levels of total and hexavalent chromium were also investigated in different months of the year, and maximum concentrations were found in October.

Air Pollutants↗
PubMed1999

Determination of total chromium in phosphate rocks by ion chromatography.

Chromium(VI) is one of seven elements which is classified in the fertilizer industry as being harmful to plants and biological systems. Phosphate rocks represent the raw material for complex fertilizer production in the world. This paper investigates for the first time the determination of total chromium in phosphate rocks by ion chromatography. The developed analytical method involves the digestion of phosphate rocks with nitric acid followed by sample treatment of the resulting solution. The digestion solution obtained was treated with an oxidising agent (potassium peroxosulphate) to convert all chromium to the hexavalent state. The analytical method developed utilizes anion-exchange ion chromatography to achieve the separation and spectrophotometric post-column reaction for detection with diphenylcarbazide. The relative standard of deviation from analytical data comparison of six different phosphate rocks with atomic absorption spectrometry and inductively coupled plasma atomic emission spectrometry techniques, and cross-analysis data against an internationally certified phosphate rock standard were between 0.58 and 1.45%. Calibration curve between 0.2 and 0.9 microgram/ml was excellent, and the method has a detection limit for Cr(VI) of 0.05 ng. The developed method offers a fast, a reliable and an alternative procedure for the determination of total chromium in phosphate rock deposits by ion chromatography.

Chromatography, Ion Exchange↗
PubMed1997

Effects of adhesive primers on bond strength of self-curing resin to cobalt-chromium alloy.

PURPOSE: This study evaluated the effects of four adhesive primers on the shear bond strength of a self curing resin to cobalt-chromium alloy. MATERIAL AND METHODS: The adhesive primers Acryl Bond (AB), Cesead Opaque Primer (COP), Metal Primer II (MPII), and MR Bond (MRB) were used. A brass ring placed over the casting alloy disk surface nonprimed or primed with each primer was filled with the self-curing methyl methacrylate polymethyl methacrylate resin. The specimens were stored in water at 37 degrees C for 24 hours and then alternately immersed in water baths at 4 degrees C and 60 degrees C for 1 minute each for up to 20,000 thermal cycles before shear mode testing at a crosshead speed of 0.5 mm/min. RESULTS: All the primers examined improved the shear bond strength between the resin and cobalt chromium alloy compared with nonprimed specimens before thermal cycling. However, after 20,000 thermal cycles, the bond strengths of resin to cobalt chromium alloy primed with COP or MPII primers were significantly greater than those of specimens primed with AB or MRB primers and nonprimed controls. CONCLUSION: This study indicated that COP and MPII are effective primers to obtain higher bond strength between resin and cobalt-chromium alloy.

Adhesives↗
PubMed1997

Comparison of titanium and cobalt-chromium removable partial denture clasps.

STATEMENT OF PROBLEM: The use of titanium alloys for removable partial dentures is an increasingly popular application. While the flexibility of titanium would allow for cast clasps to be placed in deeper undercuts than advisable with cobalt-chromium, it is possible that the retentive forces of the titanium clasp might not maintain sufficient retention after repeated flexing of the clasp arm during insertion and removal of the partial denture. PURPOSE: This study assessed the characteristics of cast clasps made of titanium and titanium alloys to determine whether these materials are suitable alternatives for removable partial denture applications. MATERIAL AND METHODS: Removable partial denture clasps at two undercut depths were fabricated from commercially pure titanium, titanium alloy (Ti-6A1-4V), and cobalt-chromium. Loss of retention force was measured as the clasps underwent 3 years of simulated clinical use. The data were subjected to ANOVA and Scheffé's tests to determine differences. Evidence of casting defects and porosity was evaluated by radiographic examination and nonparametric statistics. SEM microscopy was used to observe surface characteristics that were described qualitatively. RESULTS: For the 0.75 mm undercut specimens, there was less loss of retention for clasps made from pure titanium and titanium alloy than for cobalt-chromium clasps. Porosity was more apparent in the pure titanium and titanium alloy clasps than in those made from cobalt-chromium, but the amount of porosity did not correspond to evidence of fractures or permanent deformation. CONCLUSIONS: The long-term retentive resiliency of the pure titanium and titanium alloy clasps suggests that these materials are suitable for removable partial dentures.

Alloys↗
PubMed1998

DNA fragmentation, DNA-protein crosslinks, postlabeled nucleotidic modifications, and 8-hydroxy-2'-deoxyguanosine in the lung but not in the liver of rats receiving intratracheal instillations of chromium(VI). Chemoprevention by oral N-acetylcysteine.

An in vivo study was carried out with the objectives of evaluating (a) the localization of DNA lesions resulting from exposure to chromium(VI) by the respiratory route, (b) the molecular nature of DNA alterations, and (c) modulation of DNA damage by a known chemopreventive agent. To this purpose, Sprague-Dawley rats received intratracheal instillations of sodium dichromate (0.25 mg/kg body weight) for three consecutive days, and the day after the last treatment lung and liver were removed for DNA purification. The results showed a selective localization of DNA lesions in the lung but not in the liver, which can be ascribed to toxicokinetics and metabolic characteristics of chromium(VI). DNA alterations included DNA-protein crosslinks, DNA fragmentation, nucleotidic modifications, and 8-hydroxy-2'-deoxyguanosine. The last two endpoints were evaluated, for the first time in chromium toxicology, by means of postlabeling procedures. This methodology was adapted to the detection of the DNA damage produced by those reactive oxygen species which result from the intracellular reduction of chromium(VI). The oral administration of the thiol N-acetylcysteine completely prevented any induction of DNA lesions in lung cells.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1999

Clastogenicity of chromium contaminated soil samples evaluated by Vicia root-micronucleus assay.

Chromium compounds have been known to be highly toxic in biological systems and to some individuals act as strong allergens. A chromium processing plant in Tianjin city has been abandoned for many years and the chromium residue has been dispersed into the nearby soil. This study was designed to detect the genotoxicity of contaminated soil samples collected at various distances of 100 to 1000 m from the source using the Vicia faba root micronucleus test. Water solutions extracted from the soil samples were used to treat the roots of the Vicia beans. Micronuclei frequencies observed from the root meristems were used to determine the degree of genotoxicity. Micronuclei frequencies of the contaminated soil samples show linear dose responses to chromium contents in the soil, which were inversely proportional to the distance from the source.

Biological Assay↗
PubMed1999

Chromium levels in potable water, fruit juices and soft drinks: influence on dietary intake.

Potable water, fruit juices and soft drinks are some of the most widespread beverages in the habitual diet, and they can contribute to chromium dietary intake. We determined the concentration of chromium in 90 different samples of beverages widely consumed in Spain. Graphite furnace atomic absorption spectrometry was used to analyze samples processed with a HNO3-V2O5 acid digestion pretreatment. In water samples Cr was directly determined. We verified the sensitivity, accuracy and precision of the method and ruled out matrix interferences. In analyzed samples, chromium values ranged from not detectable to 11.80 micrograms/l in potable water, from not detectable to 17.60 micrograms/l in fruit juices and from 3.60 to 60.50 micrograms/l in soft drinks. The chromium levels we encountered are low and the contribution of non-alcoholic beverages to dietary intake of this element, have been estimated to be 0.41 microgram/day in the common Spanish diet.

Beverages↗
PubMed2001

Chromium transport, oxidation, and adsorption in manganese-coated sand.

We examine how the processes of advection, dispersion, oxidation-reduction, and adsorption combine to affect the transport of chromium through columns packed with pyrolusite (beta-MnO2)-coated sand. We find that beta-MnO2 effectively oxidizes Cr(III) to Cr(VI) and that the extent of oxidation is sensitive to changes in pH, pore water velocity, and influent concentrations of Cr(III). Cr(III) oxidation rates, although initially high, decline well before the supply of beta-MnO2 is depleted, suggesting that a reaction product inhibits the conversion of Cr(III) to Cr(VI). Rate-limited reactions govern the weak adsorption of each chromium species, with Cr(III) adsorption varying directly with pH and Cr(VI) adsorption varying inversely with pH. The breakthrough data on chromium transport can be matched closely by calculations of a simple model that accounts for (1) advective-dispersive transport of Cr(III), Cr(VI), and dissolved oxygen, (2) first-order kinetics adsorption of the reduced and oxidized chromium species, and (3) nonlinear rate-limited oxidation of Cr(III) to Cr(VI). Our work supplements the limited database on the transport of redox-sensitive metals in porous media and provides a means for quantifying the coupled processes that contribute to this transport.

Adsorption↗
PubMed2002

Concentrations of chromium, manganese, and lead in air and in avian eggs.

The expansion of urbanization introduces air pollution to wildlife areas. Some metal contaminants occurring in concentrations too small to have any measurable impact on adult birds may seriously affect embryos that are more sensitive to contaminants than the adult. Chromium, manganese, and lead are toxic and can be passed from the hen to the egg. This study relates the concentrations of these metals in eggs to their concentrations in air in three cities. Rock dove eggs were sampled and air pollution records were examined in the California cities of Riverside, Los Angeles, and San Francisco. The eggs from San Francisco did not differ from those of Los Angeles in lead concentration but the air did differ. The eggs collected in Los Angeles in 1998 had concentrations of chromium greater than in those from Riverside and from Los Angeles 1999 but the air had concentrations of chromium that did not differ among those three collections. Concentrations of manganese did not differ among the eggs but did differ among the air samples of the three cities. Exposures of embryos to chromium and manganese in this study were not at levels warranting concern. Although the concentration at which lead in eggs impairs avian health is not established, the highest concentrations found in this study exceed estimated safe concentrations. There is no indication that embryo exposure is directly related to atmospheric levels of these metals in the cities of this study.

Air Pollutants↗
PubMed2002

A comparative study of the removal of trivalent chromium from aqueous solutions by bentonite and expanded perlite.

Local bentonite and expanded perlite (Morocco) have been characterised and used for the removal of trivalent chromium from aqueous solutions. The kinetic study had showed that the uptake of Cr(III) by bentonite is very rapid compared to expanded perlite. To calculate the sorption capacities of the two sorbents, at different pH, the experimental data points have been fitted to the Freundlich and Langmuir models, respectively, for bentonite and expanded perlite. For both sorbents the sorption capacity increases with increasing the pH of the suspensions. The removal efficiency has been calculated for both sorbents resulting that bentonite (96% of Cr(III) was removed) is more effective in removing trivalent chromium from aqueous solution than expanded perlite (40% of Cr(III) was removed). In the absence of Cr(III) ions, both bentonite and expanded perlite samples yield negative zeta potential in the pH range of 2-11. The changes of expanded perlite charge, from negative to positive, observed after contact with trivalent chromium(III) solutions was related to Cr(III) sorption on the surface of the solid. Thus, it was concluded that surface complexation plays an important role in the sorption of Cr(III) species on expanded perlite. In the case of bentonite, cation-exchange is the predominate mechanism for sorption of trivalent chromium ions, wherefore no net changes of zeta potential was observed after Cr(III) sorption. X-ray photoelectron spectroscopy measurements, at different pH values, were also made to corroborate the zeta potential results.

Adsorption↗
PubMed2002

Effects of ferrous iron and molecular oxygen on chromium(VI) redox kinetics in the presence of aquifer solids.

The kinetics and stoichiometry of the reduction of hexavalent chromium (Cr(VI)) with ferrous iron (Fe(II)) were examined in systems with and without aquifer solids. Cr(VI) reduction was rapid in the absence of solids, but demonstrated slower and more complex kinetics in the presence of aquifer solids. The aquifer solids removed Fe(II) from solution and a portion of the reducing capacity of Fe(II) was transferred to the aquifer solids. The solid phases were then able to continue to remove Cr(VI). This suggests in situ treatment of Cr(VI) by Fe(II) injection would be feasible in the aquifer environment. In general, re-oxidation of reduced chromium by molecular oxygen was not observed in our systems over time periods of nearly 1 year, suggesting that the potential for chromium solubilization under these oxidizing conditions will be low. An empirical model was developed to describe the reduction kinetics of Cr(VI) in the presence of solids. The model assumes that the reaction is brought about by pseudo-species of iron that react instantaneously, rapidly and slowly with Cr(VI). A fourth pseudo-species is assumed to be non-reactive. Model coefficients were determined by non-linear regression. The model was able to describe observed concentrations of chromium well, but analysis of model errors indicated the potential existence of a distribution of species with different reaction rates rather than just three distinct species. Another model was developed to predict concentrations of different pseudo-species depending on the total amount of Fe(II) added and the amount of aquifer solids present. This model assumed that pseudo-species could result from intrinsic characteristics of the aquifer solids as well as being formed by addition of Fe(II), which could sorb to the aquifer solids.

Carcinogens, Environmental↗