Showing papers on "Chromium published in 1981"

The carcinogenicity of chromium

Abstract: The carcinogenicity of chromium compounds is reviewed with specific attention to the gaps in knowledge for risk estimation and research needs. The most important problems at present are whether trivalent chromium compounds cause cancer, and whether there is a difference in cancer causing effects between the soluble and the slightly soluble hexavalent compounds in the practical exposure situation. Dose estimates for risk estimation based on epidemiological investigations are also lacking. Present evidence indicates that the trivalent chromium compounds do not cause cancer although high concentrations in some in vitro systems have shown genetic toxicity. Hexavalent chromium compounds cause cancer in humans, in experimental animals and exert genetic toxicity in bacteria and in mammalian cells in vitro. Epidemiological evidence and animal experiments indicate that the slightly soluble hexavalent salts are the most potent carcinogens, but proper identification and characterization of exposure patterns in epidemiological work are lacking. Workers also tend to have mixed exposures. Soluble and slightly soluble salts are equally potent genotoxic agents in vitro. Further work for establishing dose estimates for risk evaluation in epidemiological work is important. In vitro systems should be applied for further identification of the mechanism of the carcinogenic effects, and animal experiments are urgent for comparison of the carcinogenic potency of the different hexavalent salts. Hexavalent chromium salts must be regarded as established carcinogens, and proper action should be taken in all industries with regard to such exposure. At present the carcinogenic risk to the general population caused by chromium compounds seems to be negligible, chromium in cigarettes, however, is an uncertainty in this respect. The amount of chromium and the type of chromium compounds inhaled from cigarettes is not known.

Spectroscopy and photokinetics of chromium (III) in glass

Abstract: The optical absorption, emission, emission lifetime, and absolute quantum efficiency have been measured for chromium (III) in a wide variety of oxide and fluoride glasses. In all cases, the room temperature emission is dominated by inhomogeneously broadened 4T2 fluorescence, and the relaxation of this level is shown to be primarily nonradiative. Multiphonon emission to lattice modes, concentration quenching, and quenching by hydroxyl moieties is shown not to be of significance in this relaxation at low doping levels. Instead, it is proposed that the radiationless process involves primarily local modes associated with the CrX6 cluster and is sensitive to site symmetry.

Dissolved state of chromium in seawater

Abstract: The dissolved state of chromium in seawater has long been studied and in particular which species, trivalent or hexavalent, is predominant Research results are not, however, consistent, although the method used has usually been the same—using ferric hydroxide as coprecipitation carrier (Table 11–7) We have studied the coprecipitation behaviour of chromium with ferric hydroxide and other metal hydroxides in the presence of naturally existing inorganic and organic ions to attain an accurate analytical method for determining chromium content, as well as to estimate its behaviour in natural waters8,9 We report here that neither Cr(VI) nor organic species coprecipitate with ferric hydroxide in seawater; Cr(VI) can be quantitatively captured by the coprecipitation with bismuth hydroxide without any pretreatment (such as reduction); and the role of manganese oxide should be considered in addition to the amount of dissolved oxygen to understand the redox system of chromium in natural waters The inconsistency of the past research may therefore be partly because the presence of organic species was not taken into account and was analysed as either Cr(VI) or Cr(III) or overlooked entirely

The influence of thermal treatment on the chemistry and structure of grain boundaries in inconel 600

Abstract: Although it is widely accepted that certain heat treatments result in carbide precipitation accompanied by chromium depletion at the grain boundaries, no direct evidence of this phenomenon exists for Inconel 600. Using the Scanning Transmission Electron Microscope (STEM), the extent of grain boundary chromium depletion is quantitatively determined as a function of thermal treatment time at 700 °C following a 30 min solution anneal at 1100 °C. Results confirm the presence of grain boundary chromium depletion that varies in extent with time at temperature, the chromium concentration falling to values as low as 3 wt pct. The chromium depletion volume is characterized by a depletion parameter which is correlated with intergranular corrosion test results to determine a self-healing (desensitization) chromium concentration of 9 wt pct. Trace element segregation at grain boundaries is measured by Auger Electron Spectroscopy (AES) as a function of aging treatment. Results show that after thermally treating samples for various times at 700 °C, phosphorus is always present at the grain boundaries. Intergranular corrosion behavior as a function of thermal treatment appears to be governed more strongly by chromium depletion than trace element segregation.

Chromium partitioning during isothermal transformation of a eutectoid steel

Abstract: Partitioning of chromium between ferrite and cementite during the isothermal decomposition of austenite to pearlitic or pearlitic/bainitic decomposition products has been studied in a 1.4 wt pct Cr eutectoid steel using analytical electron microscopy on two-stage extraction replicas. Chromium was observed to segregate preferentially to cementite at the pearlite reaction front for temperatures in the range 730 to 550 °C. Although the extent of partitioning decreased with decreasing reaction temperature, a no-partition temperature could not be identified for the steel. It is clear that previous studies on thin foils have underestimated the temperature range over which partitioning of chromium can occur. At high reaction temperatures measured values of pearlite growth rates were found to be in excellent agreement with those calculated, using the assumption that phase boundary diffusion of chromium was rate controlling. At lower reaction temperatures models based on volume diffusion of carbon and on phase boundary diffusion of chromium both gave reasonable predictions of measured growth rates. However, it seems likely that solute drag effects influence pearlite growth at temperatures in the austenite bay region which the chromium addition produces in the T.T.T. diagram. Measurements made on upper bainite which co-existed with pearlite following transformation at 500 and 550 °C showed that preferential partitioning of chromium to cementite did not occur during this reaction.

Removal of hexavalent chromium from estuarine waters by model substrates and natural sediments

Abstract: Chromate removal from waters with a range of salinities (0-32%) was studied by using both model substrates, alumina and kaolinite, and natural estuarine sediments in order to determine possible effects of sediment on dissolved chromate in estuarine systems. The dependence of chromate removal on sediment concentrations (<1 g L/sup -1/) will be ineffective in removing dissolved chromate from the water column, though the reaction will be important in deposited sediments. Chromate removal is more effective in low- than high-salinity regimes. Removal by model substrates decreases monotonically with increasing salinity but shows a peak in the 0.1-1.0% range with estuarine sediments. This latter behavior shows similarity with the salinity dependence of chromate reduction by gallic acid, suggesting reductive adsorption by the estuarine sediments. Naturally occurring levels of phosphate ansilicate show negligible effect on chromate removal.

Differential determination of chromium(VI)-chromium(III) with poly(dithiocarbamate) chelating resin and inductively coupled plasma-atomic emission spectrometry

Abstract: This investigation has demonstrated that the poly(dithiocarbamate) resin is usable for the differential determination of Cr(VI)-Cr(III) mixtures. In this example, a concentration factor of 12.5 was obtained. However, on the basis of previous experience with the poly(dithiocarbamate) resin both large sample volumes and smaller final solution volumes can be employed in order to increase the concentration factor. The present technique is suitable for chromium determination by inductively coupled plasma-atomic emission spectrometry (ICP-AES), atomic absorption spectrometry (AAS), and other spectrochemical methods. However, the low limit of detection for chromium achieved by electrothermal atomization AAS combined with a suitable small final digested resin solution volume may allow extension of the differential analysis to low initial Cr(VI) and Cr(III) concentration-levels. Although high chloride concentration does not interfere with the Cr(VI) determination in this technique, in the total chromium procedure a chloride concentration of greater than 250 mg of Cl/L prevents complete recovery of chromium possibly through the loss of chromyl chloride. In this situation, removal of chloride by precipitation with silver nitrate may be required. This limitation is not unique to the resin approach and is common in methods requiring oxidation of Cr(III) to Cr(IV). The present technique is not affected by largemore » concentrations of alkali and alkaline earth elements or manganese because these elements do not complex with the resin. In addition, the technique is simple and provides acceptable precision.« less

Distribution and chromium binding capacity of low-molecular-weight, chromium binding substance in mice

Abstract: The distribution of low-molecular-weight, chromium-binding substance (LMWCr) and high-molecular-weight, chromium-binding substance (HMWCr) in the organ cytosol were analyzed by means of Sephadex G-25 gel filtration, after a single i.p. injection of K2Cr2O7 (280 mumol, Cr/Kg) to mice (male dd, 23 +/- 2 g). The amount of Cr in LMWCr per mouse was highest in the liver (83 micrograms), followed by those in the kidney (10 micrograms) and other organs (3-1 micrograms), with lesser amounts of Cr in HMWCr in all the organs. In these organs LMWCr was found to bind 3-28 times the amount of Cr to that in the in vivo binding after the in vitro incubation with K2Cr2O7 at 37 degrees C, showing a high Cr binding capacity of the substance. No inductive formation of LMWCr was observed in the liver even after daily repetitive administration of Cr (150 mumol/Kg, 4 days). Time course studies on the liver and the kidney of mice injected with K2Cr2O7 showed no difference in the accumulation of Cr in LMWCr and in the ratio of Cr in LMWCr to that in HMWCr between the organs at intervals of from 5 min to 24 hr after the injection. The comparative affinity of Cr(III) for LMWCr and for the serum proteins decreases in the order LMWCr, transferrin, albumin. The transfer of Cr from LMWCr to albumin and vice versa was almost negligible. However, significant amounts of the metal transfer was found from LMWCr to transferrin and vice versa, and from albumin to transferrin. These findings suggest that LMWCr is distributed widely in the body and it quickly binds invaded Cr in stable form at an organ site, especially in the liver, with participation of albumin or/then transferrin. This supports the hypothesis that LMWCr plays a large role in Cr detoxification.

Elevated Temperature Potential-pH Diagrams for the Cr-H2O, Ti-H2O, Mo-H2O, and Pt-H2O Systems

Abstract: This paper describes the potential-pH diagrams of chromium, molybdenum, titanium, and platinum in water at temperatures from 25 to 300 C. The diagrams can be utilized to predict the stability of these metals in aqueous solutions over this temperature range. A computer program written by D. D. Macdonald, et al, was utilized to perform the thermodynamic calculations and to construct the diagrams. In general, the diagrams indicate that the metals are more active at higher temperatures and that the area of the stable metal oxide domains decreases with increasing temperature.

Cytotoxic and clastogenic effects of soluble and insoluble compounds containing hexavalent and trivalent chromium.

Abstract: Cr(III) and Cr(VI) compounds of varying solubilities have been tested in vitro for their ability to inhibit cell growth and nucleic acid and protein syntheses in BHK cells, to induce alterations in the mitotic cycle in HEp cells, and to increase the frequency of chromosomal aberrations and sister chromatid exchanges (SCE) in CHO cells. All Cr(VI) compounds, and particularly those containing soluble Cr(VI), such as potassium dichromate and zinc yellow, differentially inhibit macromolecular syntheses in BKH cells, that of DNA being always the most affected. Among Cr(III) compounds, which generally have very low cytotoxicity, chromite is particularly active, and inhibits cell growth and DNA synthesis even more than the poorly soluble Cr(VI) compounds. Preincubation in growth medium, with or without metabolizing cell cultures, solubilizes considerable amounts of Cr(VI) from zinc yellow and chromite, but significant amounts are also obtained from the most insoluble Cr(VI) pigments. When BHK cells are treated with such preincubated solutions, reduction of soluble Cr(VI) to Cr(III) by cell metabolites is seen with all Cr(VI) compounds, accompanied by decreased cytotoxicity. The same differences between Cr(VI) and Cr(III) compounds apply to the cytotoxic effects on mitosis of HEp cells and the clastogenic effects on CHO cells. The activity of chromite, the only Cr(III) pigment capable of significantly increasing the frequency of SCE, is due to contamination with soluble Cr(VI). In contrast to the very low cytotoxicity of Cr(III), much higher chromium levels are detected in the cells incubated with soluble Cr(III) than with the same concentrations of soluble Cr(VI). 50% and 75% of chromium accumulated in the cells during treatments with Cr(VI) and Cr(III) respectively remains firmly bound to the cells, even when they are incubated for up to 48 h in normal growth medium. Chromium accumulated in the cells after treatment with Cr(III) is most probably bound to the cell membrane, whereas some of the Cr(VI) is transported through the cell membrane and reduced in the cell nucleus. The results of the present investigation are in agreement with those obtained with the same Cr(VI) and Cr(III) compounds in mutagenicity assays in bacteria and carcinogenicity tests in rodents. A re-evaluation of the mechanisms of chromium carcinogenisis is proposed.