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Chromium Concentrations (chromium + concentration)
Selected AbstractsEffects of chromium stress on the subcellular distribution and chemical form of Ca, Mg, Fe, and Zn in two rice genotypesJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 1 2010Fanrong Zeng Abstract A hydroponic experiment was carried out to study effects of chromium (Cr) stress on the subcellular distribution and chemical form of Ca, Mg, Fe, and Zn in two rice genotypes differing in Cr accumulation. The results showed that Ca, Mg, Fe, and Zn ions were mainly located in cell walls and vacuoles in roots. However, large amounts of metal ions were transferred from the vacuole to the nucleus and to other functional organelles in shoots. Chromium concentrations in the nutrient solution of 50 ,M and above significantly decreased Ca concentrations in the chloroplast/trophoplast, the nucleus, and in mitochondria. It further increased Mg concentrations in the nucleus and in mitochondria, as well as Zn and Fe concentrations in the chloroplast/trophoplast. These Cr-induced changes in ion concentrations were associated with a significant reduction in plant biomass. It is suggested that Cr stress interferes with the functions of mineral nutrients in rice plants, thus causing a serious inhibition of plant growth. The chemical forms of the four nutrients were determined by successive extraction. Except for Ca, which was mainly chelated with insoluble phosphate and oxalic acid, Mg, Zn, and Fe were extractable by 80% ethanol, d-H2O, and 1,M NaCl. The results indicated that these low,molecular weight compounds, such as organic acids and amino acids, may play an important role in deposition and translocation of Mg, Zn, and Fe in the xylem system of rice plants. [source] Catalytic Adsorptive Stripping Voltammetric Procedure for Determination of Total Chromium in Environmental MaterialsELECTROANALYSIS, Issue 12 2006gorzata Grabarczyk Abstract A sensitive catalytic adsorptive stripping voltammetric procedure for determination of traces of total chromium in environmental samples is reported. The method is based on the preconcentration of a Cr(III)H2DTPA complex by adsorption at the HMDE from an acetate buffer solution at the potential ,1.0,V vs. Ag/AgCl. Total chromium was determined as Cr(III) after reduction of Cr(VI) to Cr(III) by NaHSO3. In order to stabilize the signal of Cr(III) the measurements were performed at 5,°C. The calibration graph for chromium for an accumulation time of 60,s was linear in the range from 5×10,10 to 5×10,8,mol L,1. The relative standard deviation for a chromium concentration of 1×10,8,mol L,1 was 3.9% (n=5). The detection limit for accumulation time of 60,s was about 8×10,11,mol L,1. The validation of the procedure was performed by the analysis of the certified reference materials. [source] Effect of carbide volume fraction on the oxidation of austenitic Fe-Cr-C alloysMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 6 2006L. B. Susanto Abstract A series of Fe-15Cr-(2-3)Mo alloys (compositions in weight percent) was produced with different carbon concentrations, to control the distribution of chromium between matrix metal and M23C6 precipitates. The alloys were oxidized in the austenitic state at 850°C in pure oxygen, with and without a pre-oxidation treatment at low oxygen potential, where no iron oxide could form. Protective, chromia-rich scaling took place if the chromium concentration at the metal-scale interface was high enough. This concentration was controlled by the original alloy matrix chromium concentration, and whether or not a high diffusivity ferrite zone developed at the surface by decarburization. Ferrite zone formation was assisted by pre-oxidation at low oxygen potentials. The value of the carbides as suppliers of additional chromium was demonstrated by comparison with the oxidation performance of carbide-free alloys of corresponding matrix chromium levels. However, because dissolution of the coarse carbides could be slow, alloys with high volume fractions of large carbides were unsuccessful. [source] Treatment of a Chromate-Contaminated Soil Site by in situ Gaseous ReductionGROUND WATER MONITORING & REMEDIATION, Issue 1 2007E.C Thornton A proof-of-concept field test for the treatment of hexavalent chromium in the vadose zone using in situ gaseous reduction was successfully completed by the U.S. Department of Energy and U.S. Department of Defense in a joint demonstration conducted at White Sands Missile Range, New Mexico. The test involved injecting hydrogen sulfide, diluted in air, into contaminated vadose zone sediment to reduce Cr(VI) to Cr(III). The gaseous mixture was injected directly into the contaminated sediment through a central injection well and vacuum extracted through the flow field with six boreholes at the site periphery over a 76-d period. Comparison of soil samples taken before and after the test indicated 70% of the total mass of hexavalent chromium originally present at the site was reduced and immobilized. The zone of highest contamination was nearly completely treated, with average Cr(VI) concentrations decreasing in this interval from an average of 8.1 mg/kg before treatment to 1.1 mg/kg after treatment. Treatment was best in higher permeability clean gypsum sands and less effective in zones containing greater amounts of silt and clay and a slightly higher iron content. All hexavalent chromium concentrations measured in the posttest samples, however, were well below the remedial goal and regulatory limit of 30 mg/kg. In addition, the field test demonstrated that vadose zone treatment of contamination can be safely conducted using diluted hydrogen sulfide gas mixtures. Ongoing development of the technology is being directed toward addressing the limitations of gaseous treatment arising from variations in sediment permeability and iron content and assessing the relationship between hydrogen sulfide consumption and reaction kinetics. [source] Four-year study of cobalt and chromium blood levels in patients managed with two different metal-on-metal total hip replacementsJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 2 2003Christian Lhotka Abstract Background: Metal-on-metal total hip prostheses will produce a certain amount of wear debris. This results in increased whole-blood metal levels, which may cause adverse effects. It is not known to what extent the problem has been overcome by advances in alloy technology. Methods: In 259 patients who with total hip replacement, blood cobalt and chromium concentrations were measured with atomic absorption spectrophotometry over a period of four years after arthroplasty. Of the patients enrolled in the study, 131 had been managed with a METASUL® cobalt-chromium alloy metal-on-metal bearing combination, while 128 had been given a SIKOMET®-SM21® cobalt-chromium alloy metal-on-metal combination. The control group consisted of 31 age- and gender-matched subjects. Results: Compared with the controls, all the patients had higher cobalt and chromium levels. Cobalt concentrations were up to 50 times higher, while chromium concentrations were up to 100 times higher. Conclusions: Both systems showed evidence, in the whole-blood samples, of wear debris production by the implants. Therefore, patients managed with metal-on-metal bearing combinations should be carefully monitored in order to ensure that any local or systemic complications are detected early on. © 2002 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved. [source] Serum Zinc, Chromium, and Iron Concentrations in Dogs with Lymphoma and OsteosarcomaJOURNAL OF VETERINARY INTERNAL MEDICINE, Issue 6 2001Kathy J. Kazmierski We compared serum concentrations of zinc, chromium, and iron in dogs with cancer to those of normal dogs. Dogs with lymphoma (n = 50) and osteosarcoma (n = 52) were evaluated. Dogs with lymphoma had significantly lower (P= .0028) mean serum zinc concentrations (mean ± SD; 1.0 ± 0.3 mg/L) when compared to normal dogs (1.2 ± 0.4 mg/L). Dogs with osteosarcoma also had lower mean serum zinc concentrations (1.1 ± 0.4 mg/L), but this difference was not significant (P= .075). Serum chromium concentrations were significantly lower in dogs with lymphoma (2.6 ± 2.6 ,g/L, P= .0007) and osteosarcoma (2.4 ± 3.1 ,g/L, P= .0001) compared to normal dogs (4.7 ± 2.8 ,g/L). Serum iron concentrations and total iron-binding capacity were significantly lower in dogs with lymphoma (110.8 ± 56.7 ,g/dL, P < .0001, and 236.6 ± 45.6 ,g/dL, P < .0001, respectively) and osteosarcoma (99.6 ± 49.3 ,g/dL, P < .0001, and 245.0 ± 43.8 ,g/dL, P= .0011, respectively) when compared to normal dogs (175.1 ± 56.7 ,g/dL and 277.1 ± 47.4 ,g/dL). Mean ferritin concentration was significantly higher in dogs with lymphoma (1291.7 ± 63.0 ,g/L) than in normal dogs (805.8 ± 291.1 ,g/L, P < .0001) and dogs with osteosarcoma (826.5 ± 309.2 ,g/L, P < .0001). Further investigation is needed to explore the clinical significance of these mineral abnormalities in dogs with cancer. [source] A comparison of two faecal collection methods for protein and amino acid digestibility coefficients of menhaden fish meal and two grades of poultry by-product meals for market-size sunshine bass (Morone chrysops × M. saxatilis)AQUACULTURE NUTRITION, Issue 1 2010S.D. RAWLES Abstract Apparent digestibility and availability coefficients for protein and amino acids in menhaden fish meal (MEN), pet-food grade (PBM-pet,) and feed-grade poultry by-product meal (PBM-feed) were determined for market-size (500 g) sunshine bass in two consecutive trials using passive netting (1.6 mm mesh) followed by manual stripping of faeces. A reference diet resembling a commercial feed was formulated to meet or exceed all known nutritional requirements of hybrid striped bass. Test diets were formulated to contain a 70 : 30 mixture of reference diet to test ingredient with chromic oxide (1%) serving as the inert marker. Diets were extruded under commercial conditions and the reference diet was fed for two weeks in order to acclimate fish to experimental conditions. Each diet was randomly assigned to triplicate tanks containing 30 fish each. Fish were fed their respective diet twice daily to apparent satiation for two weeks, with faecal collections being conducted on the 7th and 14th day, in each trial. ADC values determined in the net method were highly variable and generally lower than ADCs obtained by stripping. Consistently lower and highly variable chromium concentrations were found in the net method faecal samples and suggest that marker loss relative to nutrient content, or dilution of marker with non-faecal matter, on the net collectors influenced results in that trial. In contrast, the standard errors of ADCs determined in the strip method were less than 5 percentage points in most cases. Protein digestibility ranged from a low of 51% (PBM-feed) to a high of 87% (PBM-pet) in the net method, and from a low of 80% (PBM-feed) to a high of 99% (MEN) in the strip method. With the exception of Lys, no differences in amino acid availabilities among diets were found in the net method. In the strip method, protein digestibility and amino acid availabilities in MEN were generally greater than those found in PBM-pet or PBM-feed, whereas ADCs were not significantly different between the two poultry by-products. Based on the conditions of the present study, net collection of faecal matter can not be recommended for determining the digestibility of nutrients in feed ingredients for market-size sunshine bass. Digestibility coefficients obtained by the strip method for feed and petfood grades poultry by-product were higher than those previously reported and will be facilitate more efficient and economical diet formulations for larger sunshine bass. [source] | ||||||||||