Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “CHROMIUM”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,207 records · Page 67Linked to original sources
PubMed2004

Cloud point extraction for speciation of chromium in water samples by electrothermal atomic absorption spectrometry.

A new method based on the cloud point extraction (CPE) separation and electrothermal atomic absorption spectrometry (ETAAS) detection was proposed for the determination of chromium species. When the system temperature is higher than the cloud point extraction temperature (CPT) of selected surfactant p-octyl polyethyleneglycolphenyether (Triton X-100), the complex of Cr(VI) with dibromophenylfluorone (Br-PF) could enter surfactant-rich phase, whereas the Cr(III) remained in aqueous phase. Thus, an in situ separation of Cr(VI) and Cr(III) could be realized. Cr(VI) in surfactant-rich phase was analyzed by ETAAS and Cr(III) was calculated by subtracting of Cr(VI) from the total chromium which was directly determined by ETAAS. The main factors affecting the cloud point extraction, such as pH, concentration of Br-PF and Triton X-100, equilibration temperature and time, were investigated systematically. Under the optimized conditions, the quantitation limit for Cr(VI) as low as 0.01 microg/L was obtained by preconcentrating a 10 mL sample solution, and the relative standard deviation (n=6, c=2.0 microg/L) was 2.6%. The proposed method was applied to the speciation of chromium in different water samples and the recoveries in the range of 98.9-105.3% were obtained by spiking the real samples. In order to verify the accuracy of the method, a certified reference water sample was analyzed and the results obtained were in good agreement with the certified values.

Cations↗
PubMed2005

Studies of hexavalent chromium attenuation in redox variable soils obtained from a sandy to sub-wetland groundwater environment.

Laboratory experiments were conducted to characterize and quantify the capacity and kinetics of the combined effects of natural attenuation processes, such as adsorption, reduction, and precipitation, for hexavalent chromium [Cr(VI)] in a variable geochemical (i.e. fraction of organic carbon [foc], redox) environment of glaciated soils. Equilibrium attenuation terms: linear sorption (K(d)), estimated capacity, and non-linear Langmuir (K(L), Q) sorption parameters; varied over several orders of magnitude. The pseudo-first-order rate of disappearance of Cr(VI) from aqueous:soil slurries ranged from approximately 10(-5) to approximately 10(-1)/min. An operationally defined kinetic attenuation term, attenuation capacity (AC), describing the quantity of Cr(VI) disappearing from the slurries, ranged from 1.1 to approximately 12 microg Cr(VI)/g soil/7 days. The linear K(d)'s and estimated attenuation capacities were indirectly and directly related to increasing soil pH and foc, respectively. The AC values decreased and increased as a function of increasing soil pH and foc, respectively. The parameters determined in this work were used to evaluate the kinetics, capacity, and stability of chromium attenuation in the sub-wetland saturated soils in Hellerich (2004. A field, laboratory, and modeling study of natural attenuation processes affecting the fate and transport of hexavalent chromium in a redox variable groundwater environment. Ph.D. Dissertation, Department of Civil and Environmental Engineering, University of Connecticut-Storrs) using a statistical simulation framework.

Adsorption↗
PubMed2004

Individual susceptibility to hexavalent chromium of workers of shoe, hide, and leather industries. Immunological pattern of HLA-B8, DR3-positive subjects.

BACKGROUND: This study was designed to examine the effects of hexavalent chromium [Cr(VI)] on the immunological pattern of shoe, hide, and leather industry workers, moving from the hypothesis that some haplotypes (HLA-B8,DR3) can be important hidden risk cofactors. METHODS: Workplaces of 20 firms were monitored for total and respirable dusts and for total and hexavalent chromium. Cr(VI) on materials was also measured. Assay of chromium levels in blood and urine of 44 serological human leukocytes antigen (HLA)-typed workers (20 exposed, 15 HLA-B8,DR3-negative/5-positive and 24 non-exposed, 18 HLA-B8,DR3-negative/6-positive subjects) was performed by atomic absorption, and lymphocyte subsets (FACS-analysis), mitogen-mediate lympho-proliferation ([3H]thymidine incorporation), cytokine levels (ELISA), natural killer (NK) cytotoxic activity (51Cr-release assay) were determined. RESULTS: The environmental parameter levels are lower than threshold limit value-time-weighted average (TLV-TWA); in the materials, the Cr(VI) values exceeded the levels allowed. The peripheral blood mononuclear cells (PBMC) proliferation and the T-helper1 (TH1) cytokine pattern of subjects chronically exposed were significantly raised; addition in vitro of Cr(VI) further stimulated these parameters and in general the entire TH1 system and NK activity. The TH2 system was unaltered. In the HLA-B8,DR3-positive workers, immunologically "low responders", the addition of Cr(VI) in vitro caused a further reduction of the considered parameters in the exposed subjects with a dramatic deficit of the TH1 system. CONCLUSIONS: Results indicate the unsuitability of TLV-TWA as a line of demarcation between safe and dangerous Cr(VI) concentrations and the importance of individual genetic susceptibility for occupational and preventative medicine. In particular, the presence of the HLA-B8,DR3 alleles can represent an important cofactor of immunotoxic susceptibility consequent to chronic low-dose Cr(VI) exposure.

Carcinogens, Environmental↗
PubMed2003

A test for adequacy of chromium nutrition in humans--relation to type 2 diabetes mellitus.

When Na(2)51CrO(4) is added to blood the 51CrO(4)(2-) ions enter the erythrocytes readily, and nearly exclusively, and are reduced to 51Cr(III) ions. We have observed that a fraction of these ions becomes bound to the cell membrane in a concentration which seemingly depends on that of the dietary derived intracellular Cr(III) ions. Thus, when constant amounts of 51CrO(4)(2-) ions enter constant amounts of erythrocytes, the resulting 51Cr(III) ions become bound to the cell membrane in a concentration that varies inversely as the initial, intracellular concentration of Cr(III) ions which, in turn, depends directly on the adequacy of chromium nutrition. Therefore, we have determined an arbitrary set of conditions under which the concentration of 51Cr(III) ions bound to the erythrocyte membrane becomes an indicator of the adequacy of chromium nutrition. The application of this test to 25 Type 2 diabetes mellitus subjects and 35 normal controls, both randomly selected, indicates that the concentrations of membrane bound 51Cr(III) ions in the two groups were not significantly different. Consequently, it is concluded that the level of chromium nutrition which is normally adequate in humans has only a minor role, if any, in the genesis of Type 2 diabetes mellitus.

Adult↗
PubMed1980

Hair chromium at delivery in relation to age and number of pregnancies.

To test the hypothesis that chromium deficiency may be cumulative with age and increasing parity, hair chromium levels were measured in 432 women at delivery. Although the levels in general were lower than those found in nonpregnant women there was no correlation between hair chromium level and age or number of pregnancies. Hair zinc levels were also measured to rule out zinc deficiency as a factor.

Aging↗
PubMed1986

Rabbit lung after inhalation of hexa- and trivalent chromium.

Rabbits were exposed to aerosols of hexavalent (Na2CrO4) and trivalent chromium (Cr(NO3)3) at concentrations of 0.9 and 0.6 mg/m3 of chromium respectively for 4-6 weeks (5 days/week and 6 hr/day). Three of eight rabbits exposed to Cr(VI) and three of eight rabbits exposed to Cr(III) showed nodular accumulations of alveolar macrophages, similar to the lesions observed in previous experiments after exposure to Ni2+, Cd2+, or metallic nickel. Macrophages from rabbits exposed to Cr(III) usually contained round dark inclusions, large lysosomes, and laminated inclusions similar to the lamellar bodies in the type II cells, and most macrophages from rabbits exposed to Cr(VI) showed enlarged lysosomes. However, the total amount of phospholipids and the volume density of type II cells did not differ significantly between exposed rabbits and controls. Our findings indicate that the macrophages are directly affected by chromium. The accumulation of laminated structures in the alveolar macrophages after Cr(III) exposure might be due to an impaired catabolism of surfactant.

Administration, Inhalation↗
PubMed1989

Lung lesions after experimental combined exposure to nickel and trivalent chromium.

Rabbits were exposed to a combination of 0.7 mg/m3 of Ni2+ as NiCl2 and 1.2 mg/m3 of Cr3+ as Cr(NO3)3, to 0.6 mg/m3 of Ni2+ as NiCl2, or to filtered air for 4 months (5 days/week, 6 hr/day). Light microscopy of the lung tissue showed widespread areas with nodular accumulation of macrophages in all rabbits exposed to both metals, in two rabbits exposed to nickel alone, and in none of the controls. Electron microscopy of the lung showed attenuated septa and alveoli stuffed with surfactant-like material in the group exposed to both metals. In two of these rabbits, groups of alveoli were filled with densely packed debris and type I cell borders were obscure. The reaction in the group exposed to nickel alone was less prominent. The volume density of alveolar type II cells showed a fourfold increase after exposure to both metals and a twofold increase following exposure to nickel alone compared to controls. The lung tissue content of total phospholipids and especially phosphatidylcholines and phosphatidylinositols was significantly higher in the groups exposed to both metals than in controls or in animals exposed to nickel only. In lung tissue the molar percentage of 1,2-dipalmitoylphosphatidylcholine was significantly higher in the group exposed to both metals than in the other groups. The results indicate that trivalent chromium potentiates the effect of nickel on the type II cells resulting in an increased surfactant production; in addition, trivalent chromium probably reduces the catabolism of surfactant in alveolar macrophages. Our observations raise the concern that noxious effects might occur also in humans exposed to a combination of nickel and trivalent chromium.

Animals↗
PubMed2000

Ion-chromatographic assay of chromium(VI)-containing semiconductor etchants statistical comparison of two columns.

Semiconductor etchants are concentrated-acid mixtures that are prepared under tight specifications. Assay procedures are needed to ensure that the proportion of each component is within a small percentage (usually 10 relative percent or less) of the target concentration. One such etchant class contains chromium trioxide, usually in combination with HF and HNO3, While several ion-chromatographic columns can be used to analyze most mineral acids, chromium(VI) presents a problem. This latter species is highly retained by many separators and may also degrade the resins. This paper compares two columns that showed potential for success with these assays: the AS 11 and the AS16 separators (both from Dionex). These columns permit elution of chromium(VI) as chromate in 25 min or less. A representative mixture of HF, HNO3 and CrO3 was used in the research. Simultaneous calibration studies were conducted and the data sets analyzed statistically. Also investigated was the effect on the columns of repeated exposure to chromate.

Calibration↗
PubMed1991

Determination of dissolved hexavalent chromium in industrial wastewater effluents by ion chromatography and post-column derivatization with diphenylcarbazide.

A proposed EPA method for the determination of dissolved hexavalent chromium in drinking water, groundwater and industrial wastewater effluents was developed using existing ion chromatographic techniques. Two solid waste matrices were briefly investigated. Aqueous samples were passed through a 0.45-micron filter and the filtrate was either (1) left unadjusted, (2) adjusted to pH 8 or (3) adjusted to pH 10 prior to analysis by ion chromatography. The method detection limits were 0.3-0.4 micrograms/l. When analyzed within 24 h, the two pH levels and the unadjusted sample yielded ca. 100% recovery of spikes. No oxidation of trivalent chromium to hexavalent chromium was observed at pH 7, 8 or 10 when aqueous samples were spiked with 50 mg/l Cr(III).

Chromatography, Ion Exchange↗
PubMed1995

Deflection fatigue of cobalt-chromium, titanium, and gold alloy cast denture clasp.

The aim of this study was to determine the fatigue resistance of the cast clasps of removable partial dentures. The different commercial types of metals used included five cobalt-chromium alloys, pure titanium, one titanium alloy (Ti-6A1-4V) and one gold alloy (type IV) that was either unhardened or age-hardened (n = 5 per group). The test method used was a constant-deflection fatigue test in which the force required to deflect the clasp for 0.6 mm and the number of loading cycles required to fracture the clasp were determined. The fatigue fracture surface of the clasps was examined with a scanning electron microscope. The results revealed that a fatigue fracture occurred in the cobalt-chromium clasp after approximately 25,000 loading cycles, in the pure titanium clasps after 4500 loading cycles, in the titanium alloy clasp after 20,000 loading cycles, and in the gold alloy clasp after 21,000 loading cycles. The means differed significantly (p < 0.001). Activation of the clasp by bending it 0.5 mm increased the fatigue resistance of the cobalt-chromium alloy and gold alloy clasps but decreased the fatigue resistance of both pure titanium and titanium alloy clasps (p < 0.005). The results of this study suggest that significant differences exist in the fatigue resistance of removable denture clasps made from different commercial cast metals, which may cause loss of retention of the removable partial denture and clasp failures.

Alloys↗
PubMed1996

Duration of induction melting of cobalt-chromium alloy and its effect on resistance to deflection fatigue of cast denture clasps.

This study determined the effect of various durations of induction melting of a cobalt-chromium alloy on resistance to deflection fatigue. Commercial cobalt-chromium alloy was melted by high-frequency induction for various lengths of time before it was cast into the shape of a denture clasp. The test method used was a constant-deflection fatigue test. The fatigue fracture surface of the clasp was examined with a scanning electron microscope, and the surface hardness (Vickers hardness) of the clasps was measured. In clasps with greater fatigue resistance scanning electron microscope photomicrographs revealed a coarse grain structure. The surface hardness of the alloy was least in the group with the lowest fatigue resistance and was higher in groups with greater fatigue resistance. This study suggests that, although some porosities are formed in the middle of the clasps after the alloy is overheated, the fatigue resistance of cobalt-chromium alloy denture clasps can be increased by lengthening the induction melting period of the alloy.

Analysis of Variance↗
PubMed1997

Soldering and remelting influence on fatigue strength of cobalt-chromium alloys.

STATEMENT OF PROBLEM: For laboratory production, it would be economically advisable to reuse excess cobalt-chromium alloys in manufacturing partial denture frameworks. Furthermore, discrepancies in fit, modifications, repairs, and also economic factors could lead to soldering procedure on the metal framework. PURPOSE: This study evaluated the influence of soldering and remelting procedures on the fatigue strength of Steldent, Dentorium, and Biosil cobalt-chromium alloys, as new alloys and in a mixture of new and previously casted alloy and when submitted or not submitted to conventional soldering procedure. MATERIAL AND METHODS: The soldering procedure was conducted in rod specimens 1.7 mm in diameter made with new, or with a mixture of new and reused alloy (n = 10 per group). The results were compared with those of intact rods. The fatigue strength was carried out with a cyclic testing machine simulating the insertion and the removal of partial dentures. After failure, the fracture surface was examined with a scanning electron microscope. RESULTS: The soldered specimens revealed 1119 loading cycles before fracture. These means differed statistically from those of intact alloys, which disclosed 2733 cycles before failure (p < 0.05). Statistical analysis indicated that the soldering procedure reduced fatigue strength of all new alloys or those in a mixture of new and previously casted alloys. It was also found that the soldering procedure may cause premature failure of a removable partial denture. Photomicrographs from fracture surfaces revealed the presence of inclusions and voids. Conversely, there were no significant differences between new and reused specimens, soldered or not (p > 0.05), which suggested that it may be possible to reuse excess cobalt-chromium alloys without compromising the fatigue strength of the framework.

Chromium Alloys↗
PubMed1998

Retention of oral microorganisms on cobalt-chromium alloy and dental acrylic resin with different surface finishes.

STATEMENT OF PROBLEM: The effect of surface finish of dental materials on the subsequent contamination by microorganisms. PURPOSE: This study compared the retention of Streptococcus oralis, Actinomyces viscosus, and Candida albicans on polished, sandblasted (fine and coarse) and electrobrightened cobalt-chromium alloy and dental acrylic resin to assess in vitro the effect of such techniques on prosthesis contamination. MATERIAL AND METHODS: Standardized cell suspensions were incubated with test materials for 1 hour at 37 degrees C, after which retained cells were counted by using image analysis (percentage area of a microscopic field covered by cells). RESULTS: Retention of bacterial cells was substantial (S oralis 12% to 20% and A viscosus 9% to 16%) irrespective of surface finish. Maximal retention was observed on cobalt-chromium alloy that had undergone fine sandblasting and electrobrightening (P < .01). For C albicans, an increase in surface roughness (0.15 to 3.53 microns) resulted in an increase in retention (3% to 9%). CONCLUSION: Cell size and the type of roughening significantly affected the retention of microorganisms on surfaces. Electrobrightening of cobalt-chromium alloy did not reduce the surface roughness or subsequent cell attachment.

Acrylic Resins↗
PubMed1998

Effect of water and artificial saliva on the low cycle fatigue resistance of cobalt-chromium dental alloy.

STATEMENT OF PROBLEM: Fatigue of denture clasp alloys causes clasp failures and decreases the retention of removable partial dentures. Little information is available on how the environment (dry, water, artificial saliva) effects the fatigue behavior of cast cobalt-chromium alloy clasps. PURPOSE: This study determined the effect of water and the artificial saliva on the resistance of cast cobalt-chromium alloy to the deflection fatigue. MATERIAL AND METHODS: Test bars (n = 10) were tested either dry, in water, or in artificial saliva (Fusayama type) with a constant deflection fatigue test. The number of loading cycles before fracture was registered as resistance to fatigue. To establish whether there were indications of alloy corrosion occurring during the fatigue test, the testing liquid was analyzed retrospectively with an atomic absorbance spectroscopy. To determine elemental composition of the fracture surface, fracture surfaces of the test bars were analyzed with a scanning electron microscope and energy dispersive spectroscopy. RESULTS: The bars that were tested dry had a mean fatigue resistance of 78,000 loading cycles, whereas test specimens tested in artificial saliva had a resistance of 59,000 loading cycles and 36, 000 for those tested in water. Atomic absorbance spectroscopy revealed small amounts of cobalt (Co) in testing water and in artificial saliva. Energy dispersive spectroscopy analysis revealed differences in elemental composition of a fatigue fracture surface compared with that of a 1-bend fracture. CONCLUSIONS: The results suggest that both water and artificial saliva reduce the fatigue strength of cobalt-chromium alloy, explained by corrosion of the alloy in the wet environment.

Analysis of Variance↗
PubMed2001

Adsorption mechanism of hexavalent chromium by redox within condensed-tannin gel.

We have proposed a new recovery system of hexavalent chromium Cr(VI) that is of great toxicity utilizing condensed-tannin gels derived from a natural polymer with many polyhydroxyphenyl groups. The adsorption mechanism of Cr(VI) to the tannin molecules was clarified. The adsorption mechanism consists of four reaction steps; the esterification of chromate with tannin molecules, the reduction of Cr(VI) to trivalent chromium Cr(III), the formation of carboxyl group by the oxidation of tannin molecules and the ion exchange of the reduced Cr(III) with the carboxyl and hydroxyl groups. It was found in this recovery system that a large amount of proton was consumed accompanied with the reduction of Cr(VI) so that the acidic solution containing Cr(VI) was transferred automatically to neutral one by choosing an appropriate initial pH. The carboxyl group which was created by the oxidation of tannin molecules parallel to the reduction of Cr(VI) to Cr(III) contributed to an increase in the ion-exchange sites of the reduced Cr(III). The maximum adsorption capacity of Cr(VI) reached 287 mg Cr/g dry tannin gel under the conditions of 0.77 water content of tannin gel and the initial pH = 2. This adsorption capacity was five to ten times higher than that obtained by the ion exchange between ordinary Cr(III) and tannin molecules for the tannin gels prepared under similar conditions. The system proposed here will provide an important information on a zero-emission-oriented process because it has such advantages as higher adsorption capacity of chromium and lower volume of secondary wastes compared with conventional process.

Adsorption↗
PubMed2001

Removal of chromium from aqueous solution by complexation-ultrafiltration using a water-soluble macroligand.

A process for purifying waste waters containing heavy and toxic metal such as chromium has been studied. A batch complexation-ultrafiltration process was used to concentrate and recover chromium from sulphate solution. As the chromium ions are too small to be retained by the filter, they are first complexed with a water-soluble macroligand (polyethylene-imine). Factors affecting the rejection rate and permeate flux such as pH, concentration ligand, chloride and sulphate concentration, membrane pore size, applied pressure and extraction factor were investigated. Best operating conditions can be obtained in order to achieve high levels of removal (> 95%). Then, decomplexation is obtained so that metal can be separated from macroligand by a second ultrafiltration plant to reuse the macroligand.

Chlorides↗
PubMed2002

Equilibrium modelling of individual and simultaneous biosorption of chromium(VI) and nickel(II) onto dried activated sludge.

The biosorption of chromium(VI) and nickel(II) ions, both singly and in combination, by dried activated sludge was investigated in a batch system as a function of initial pH and single- and dual-metal ion concentrations. The working initial pH values for single chromium(VI) and nickel(II) biosorptions were determined as 1.0 and 4.5, respectively. It was observed that the co-ion effect on the equilibrium uptake became more pronounced as the co-ion concentration in solution increased and pH level increased for chromium(VI) and decreased for nickel(II). Adsorption isotherms were developed for both the single- and dual-metal ion systems at these two pH values and expressed by the mono- and multi-component Langmuir and Freundlich adsorption models and model parameters were estimated by the non-linear regression. It was seen that the mono-component adsorption equilibrium data fitted very well to both the mono-component adsorption models for both the components and the pH values studied while the multi-component Freundlich adsorption model adequately predicted the multi-component adsorption equilibrium data at moderate ranges of initial mixture concentrations for both the studied pH values.

Adsorption↗
PubMed2003

Microbiological reduction of chromium(VI) in presence of pyrolusite-coated sand by Shewanella alga Simidu ATCC 55627 in laboratory column experiments.

Hexavalent chromium (Cr(VI)) was reduced to non-toxic trivalent chromium (Cr(III)) by a dissimilatory metal reducing bacteria, Shewanella alga Simidu (BrY-MT) ATCC 55627. A series of dynamic column experiments were conducted to provide an understanding of Cr(VI) reduction by the facultative anaerobe BrY-MT in the presence of pyrolusite (beta-MnO(2)) coated sand and uncoated-quartz sand. All dynamic column experiments were conducted under growth conditions using Cr(VI) as the terminal electron acceptor and lactate as the electron donor and energy source. Reduction of Cr(VI) was rapid (within 8 h) in columns packed with uncoated quartz sand and BrY-MT, whereas Cr(VI) reduction by BrY-MT was delayed (57 h) in the presence of beta-MnO(2)-coated sand. The role of beta-MnO(2) in this study was to provide oxidation of trivalent chromium (Cr(III)). BrY-MT attachment was higher on beta-MnO(2)-coated sand than on uncoated quartz sand at 10, 60, and 85.5 h. Results have shown that this particular strain of Shewanella did not appreciably reduce Mn(IV) to Mn(II) species nor biosorbed Cr and Mn during its metabolic activities.

Adsorption↗