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At least 451 records · Page 25Linked to original sources
PubMed1979

Influence of fluoride on the uptake of 51Cr-chromate by human erythrocytes.

Uptake of 51Cr-chromate by freshly collected human erythrocytes was inhibited by 90 mM sodium fluoride only in cells preincubated with fluoride. In vitro storage also increased the sensitivity of the cells: 90 mM NaF clearly inhibited the uptake of chromate in cells stored in vitro for 5 weeks. Gel chromatography revealed two forms of 51Cr within the cells, one of small molecular weight, which thin layer chromatography indicated was unchanged chromate; the other form was apparently bound to macromolecules such as hemoglobin.

Biological Transport↗
PubMed2000

Effect of Kombucha tea on chromate(VI)-induced oxidative stress in albino rats.

The effect of Kombucha tea (KT) on oxidative stress induced changes in rats subjected to chromate treatment are reported. KT feeding alone did not show any significant change in malondialdehyde (MDA) and reduced glutathione (GSH) levels, but did enhance humoral response and delayed type of hypersensitivity (DTH) response appreciably over control animals. Chromate treatment significantly enhanced plasma and tissue MDA levels, decreased DTH response considerably, enhanced glutathione peroxidase and catalase activities; however, no change in GSH, superoxide dismutase and antibody titres was noticed. KT feeding completely reversed the chromate-induced changes. These results show that Kombucha tea has potent anti-oxidant and immunopotentiating activities.

Animals↗
PubMed2001

Chromate tolerant bacteria isolated from tannery effluent.

The occurrence of metal tolerant and antibiotic resistant organisms was investigated in tannery effluent. Seventy-seven isolates comprising heterotrophs (41) and coliforms (36) which were tolerant to chromate level of > 50 microg/ml were selected for detailed study. The majority of the coliforms were resistant to higher levels of chromate (200 microg/ml) whereas around 3% of the heterotrophs were resistant to Cr6+ at a level of > 150 microg/ml. All chromate tolerant heterotrophs were also tolerant to Cu2+ (100%) whereas only 58.53% coliforms were tolerant to Cu2+. Except in the case of Cd2+ a higher number of heterotrophs were found tolerant to other heavy metals tested. Both groups of isolates were found sensitive to mercury. Resistance to cephaloridine was more abundant (P < 0.001) in coliforms as compared to heterotrophs. On the other hand a significantly higher number (P < 0.01) of heterotrophs showed resistance to streptomycin and carbencillin. All coliforms were sensitive to chloramphenicol. Around 80%) and 31.70% of coliforms and heterotrophs exhibited a relationship to the combination of metals and antibiotics. Both heterotrophs and coliforms tolerant to Hg2+ were also resistant to polymixin-B.

Bacteria↗
PubMed2006

Molecular dynamics of the Shewanella oneidensis response to chromate stress.

Temporal genomic profiling and whole-cell proteomic analyses were performed to characterize the dynamic molecular response of the metal-reducing bacterium Shewanella oneidensis MR-1 to an acute chromate shock. The complex dynamics of cellular processes demand the integration of methodologies that describe biological systems at the levels of regulation, gene and protein expression, and metabolite production. Genomic microarray analysis of the transcriptome dynamics of midexponential phase cells subjected to 1 mm potassium chromate (K(2)CrO(4)) at exposure time intervals of 5, 30, 60, and 90 min revealed 910 genes that were differentially expressed at one or more time points. Strongly induced genes included those encoding components of a TonB1 iron transport system (tonB1-exbB1-exbD1), hemin ATP-binding cassette transporters (hmuTUV), TonB-dependent receptors as well as sulfate transporters (cysP, cysW-2, and cysA-2), and enzymes involved in assimilative sulfur metabolism (cysC, cysN, cysD, cysH, cysI, and cysJ). Transcript levels for genes with annotated functions in DNA repair (lexA, recX, recA, recN, dinP, and umuD), cellular detoxification (so1756, so3585, and so3586), and two-component signal transduction systems (so2426) were also significantly up-regulated (p < 0.05) in Cr(VI)-exposed cells relative to untreated cells. By contrast, genes with functions linked to energy metabolism, particularly electron transport (e.g. so0902-03-04, mtrA, omcA, and omcB), showed dramatic temporal alterations in expression with the majority exhibiting repression. Differential proteomics based on multidimensional HPLC-MS/MS was used to complement the transcriptome data, resulting in comparable induction and repression patterns for a subset of corresponding proteins. In total, expression of 2,370 proteins were confidently verified with 624 (26%) of these annotated as hypothetical or conserved hypothetical proteins. The initial response of S. oneidensis to chromate shock appears to require a combination of different regulatory networks that involve genes with annotated functions in oxidative stress protection, detoxification, protein stress protection, iron and sulfur acquisition, and SOS-controlled DNA repair mechanisms.

Anion Transport Proteins↗
PubMedDate not supplied

The impact of a change to inhalable occupational exposure limits: strontium chromate exposure in the U.S. Air Force.

The American Conference of Governmental Industrial Hygienists has announced its intention to replace all total particulate threshold limit values (TLVs) with size-selective TLVs. Because the U.S. Air Force has adopted the TLVs as its occupational exposure limits, the impact of this change is of interest, specifically for hexavalent chromium. This article reviews historical strontium chromate sampling data in the Air Force and the impact of its reinterpretation in comparison to an inhalable TLV. Based on the measured conversion factor between the 37-mm cassette and the IOM inhalable sampler, inhalable strontium chromate exposures will continue to exceed the TLV during all aircraft priming and most sanding procedures. In addition, inhalable exposures are expected to exceed 1000 times the TLV, greater than the highest currently assigned protection factor for airline respirators, during 25% of priming procedures. Without a change in the value of the current TLV time-weighted average of 0.5 microg/m(3), the Air Force will need to reduce strontium chromate levels, either by incorporating work practices that decrease worker productivity or considering a change to nonchromated primers.

Air Pollutants, Occupational↗
PubMed1989

Effect of vitamin E on survival, glutathione reductase and formation of chromium (V) in Chinese hamster V-79 cells treated with sodium chromate (VI).

The effect of vitamin E on cytotoxicity induced by Na2CrO4 was evaluated by colony-forming assay using Chinese hamster V-79 cells. Pre-treatment with alpha-tocopherol succinate (vitamin E) for 24 h prior to exposure to Na2CrO4 resulted in a marked decrease in the cytotoxicity caused by this compound. The reduction of chromate-induced cytotoxicity was observed at all concentrations of Na2CrO4 (5-15 microM), and the protective effect increased with higher concentrations of vitamin E (5-25 microM). The level of glutathione reductase activity, which is capable of reducing chromate, was not affected by cellular pre-treatment with vitamin E. However, Na2CrO4 decreased glutathione reductase activity in a concentration-dependent fashion (5-15 microM) and pretreatment with vitamin E resulted in a significant recovery of enzyme activity suppressed by Na2CrO4, suggesting that this enzyme inhibition is linked to the cytotoxicity of this metal. Electron spin resonance studies showed that a paramagnetic chromium (V) complex was formed in cells treated with Na2CrO4, and that cellular pre-treatment with vitamin E reduced the formation of this chromium (V) intermediate. These results indicate that vitamin E protects cells from chromate-induced cytotoxicity as well as from enzyme inhibition, and also suggest that Na2CrO4-induced cytotoxicity is mediated by the generation of a reactive intermediate.

Animals↗
PubMed1991

The reduction of chromate is a prerequisite of chromium binding to cell nuclei.

Isolated calf thymus nuclei bound a chromium(III) glutathione complex in a time-dependent manner. In contrast chromium(VI) (sodium chromate) did not bind. However, when chromate was incubated with the nuclei in the presence of glutathione, chromium adducts were detected. These observations indicate that the reduction of chromate, by a reducing agent such as glutathione, is a prerequisite for the generation of bonds between the metal and constituents of the cell nuclei in vitro. Chromium adducts with nuclei are probably one cause of DNA lesions and mutations.

Animals↗
PubMed1991

Alteration in restriction enzyme digestion patterns detects DNA--protein complexes induced by chromate.

DNA--protein complexes isolated from CHO cells treated with at least 10-30 microM potassium chromate exhibited an alteration in the degradation of the DNA by restriction enzymes compared to DNA--protein complexes isolated from untreated cells. This alteration in restriction enzyme digestion of DNA--protein complexes induced by chromate was shown to depend upon the binding of trivalent chromium to the DNA and upon the protein associated with the DNA, since both EDTA pretreatment and protease K reversed the inhibition of restriction enzyme degradation of the DNA. The inhibition of restriction enzyme degradation of DNA--protein complexes may be utilized as an indirect way to detect DNA--protein complexing induced by chromate and perhaps other agents.

Animals↗
PubMed1996

Lung cancer in chromate-exposed aerospace workers.

A retrospective cohort study evaluated the risk of lung cancer in aerospace workers with minimum of 6 months' employment in jobs with chromium [VI] exposure (n = 2429). Standardized incidence ratios (SIR) estimated the risk of lung cancer by duration of employment in chromate-exposure jobs and cumulative exposure based on industrial hygiene and work-history data. The overall SIR for lung cancer was 0.8 (observed [Obs] = 15). Lung cancer risk was inversely related to estimates of cumulative chromate exposure and duration of employment as a painter. Although based on few cases, an elevated lung cancer risk was found in subjects who had worked for 5 or more years as a chrome plater or surface processor tank tender (Obs = 2, SIR = 1.9) and sander/masker or polisher (Obs = 3, SIR = 2.7). A clear association was not observed between chromate exposure and the risk of lung cancer in this population of workers.

Adult↗
PubMed1979

Reduction of chromate in cement by iron sulfate.

Cement dermatitis is connected with chromate sensitivity. It can therefore be expected that "elimination" of chromate in cement would decrease the number of cases of cement dermatitis. Iron sulfate added to cement reduces the chromate completely and the 3-valent chromium is precipitated. An amount of 0.35% (w/w) iron sulfate, FeSO4 . 7H2O, is enough to reduce 20 microgram Cr6+/g cement. There is no technical side effect to the concrete. The iron sulfate is preferably added to cement when there is an intimate contact with skin, e.g. at floor laying, repairs and hand-made casting.

Chemical Phenomena↗
PubMed1998

Contact sensitivity to chromate: comparison at a London contact dermatitis clinic over a 10-year period.

It has been argued that for chromate sensitivity to be reduced, then ferrous sulfate should be added to cement. This has not yet been done in the UK. To explore this further, we have looked at the comparative sensitization rates of patients attending the St. John's Institute of Dermatology Contact Dermatitis Clinic between the years 1982-3 and 1992-3. Patch-test-positive rates for females were not significantly different between the 2 populations studied (1982-3, 1.59% and 1992-3, 1.99% p NS). Similarly, there was no significantly different rate between the males (1982-3, 3.99% and 1992-3, 4.25% p NS) in the same time period. There was no difference in the distribution of eczema in chromate-positive subjects, nor of cobalt co-sensitization, a crude indicator of sensitization via cement. This work demonstrates no appreciable difference in the frequency of chromate sensitivity between the early 1980s and 1990s in London. Adding ferrous sulfate to cement may help to lower the frequency in the future.

Adult↗
PubMed1978

Whole blood chromium level and chromium excretion in the rat after zinc chromate inhalation.

Studies on absorption and excretion of chromium in the rat exposed to known atmospheric concentrations of zinc chromate in an inhalation chamber and the influence of diurnal variations in physical activity have been carried out. Chromium analyses were performed on samples of blood, urine and faeces using a method for determining chromium in small samples of biological material based on flameless atomic absorption spectrometry. Zinc chromate is absorbed quickly during exposure and excreted mainly via urine. An accumulation of chromium in blood was observed, followed by a slow elimination. It is suggested that chromium from zinc chromate enters the blood in the hexavalent state.

Animals↗
PubMed2001

Relationship of hydrogen bioavailability to chromate reduction in aquifer sediments.

Biological Cr(VI) reduction was studied in anaerobic sediments from an aquifer in Norman, Okla. Microcosms containing sediment and mineral medium were amended with various electron donors to determine those most important for biological Cr(VI) reduction. Cr(VI) (about 340 microM) was reduced with endogenous substrates (no donor), or acetate was added. The addition of formate, hydrogen, and glucose stimulated Cr(VI) reduction compared with reduction in unamended controls. From these sediments, an anaerobic Cr(VI)-utilizing enrichment was obtained that was dependent upon hydrogen for both growth and Cr(VI) reduction. No methane was produced by the enrichment, which reduced about 750 microM Cr(VI) in less than six days. The dissolved hydrogen concentration was used as an indicator of the terminal electron accepting process occurring in the sediments. Microcosms with sediments, groundwater, and chromate metabolized hydrogen to a concentration below the detection limits of the mercury vapor gas chromatograph. In microcosms without chromate, the hydrogen concentration was about 8 nM, a concentration comparable to that under methanogenic conditions. When these microcosms were amended with 500 microM Cr(VI), the dissolved hydrogen concentration quickly fell below the detection limits. These results showed that the hydrogen concentration under chromate-reducing conditions became very low, as low as that reported under nitrate- and manganese-reducing conditions, a result consistent with the free energy changes for these reactions. The utilization of formate, lactate, hydrogen, and glucose as electron donors for Cr(VI) reduction indicates that increasing the availability of hydrogen results in a greater capacity for Cr(VI) reduction. This conclusion is supported by the existence of an enrichment dependent upon hydrogen for growth and Cr(VI) reduction.

Anaerobiosis↗
PubMed1970

Genetic and metabolic controls for sulfate metabolism in Neurospora crassa: isolation and study of chromate-resistant and sulfate transport-negative mutants.

Mutants of Neurospora resistant to chromate were selected and all were found to map at a single genetic locus designated as cys-13. The chromate-resistant mutants grow at a wild-type rate on minimal media but are partially deficient in the transport of inorganic sulfate, especially during the conidial stage. An unlinked mutant, cys-14, is sensitive to chromate but transports sulfate during the mycelial stage at only 25% of the wild-type rate; cys-14 also grows at a fully wild-type rate on minimal media. The double-mutant strain, cys-13;cys-14, cannot utilize inorganic sulfate for growth and completely lacks the capacity to transport this anion. The only biochemical lesion that has been detected for the double-mutant strain is its loss in capacity for sulfate transport. Neurospora appears to possess two distinct sulfate permease species encoded by separate genetic loci. The transport system (permease I) encoded by cys-13 predominates in the conidial stage and is replaced by sulfate permease II, encoded by the cys-14 locus, during outgrowth into the mycelial phase. The relationship of these new mutants to cys-3, a regulatory gene that appears to control their expression, is discussed.

Biological Transport↗
PubMed1980

Follow-up study of patients with contact dermatitis caused by chromates, nickel, and cobalt.

The patch test results from 1,000 patients tested with the ICDRG standard series are analyzed for positive reactions to potassium dichromate, nickel sulphate, and cobalt chloride. Nickel appears to be the most common sensitizer, especially among women, although false-negative reactions may occur if it is tested with a 2.5% concentration in yellow petrolatum. Chromate dermatitis is generally of occupational origin among men. It is also quite common among Belgian women, probably because of the widespread use of Javel (liquid bleach), containing sodium dichromate as a colouring and stabilizing agent. Positive patch test reactions to cobalt are generally accompanied by allergic reactions to nickel or chromate. Its role as a primary allergen, however, must never be overlooked. The relationship between these metals and hand and foot eczema is evaluated. The results of a follow-up questionnaire are given. More than 70% of the patients allergic to chromates or nickel continued to suffer from contact eczema after the diagnosis had been made and therapeutic measures taken.

Adult↗
PubMed2002

Research on the utilisation of waste chromic materials in the sodium chromate production process.

The results of investigations on the utilisation of waste chromic materials for the production of sodium chromate have been presented. The optimal parameters of the sodium chromate production, which make it possible to select the best technological solutions, have been determined. A mathematical model based on a system of equations describing the process of sodium chromate production as a function of selected process parameters has been devised. This allows the values useful for a practical estimation of the process, such as mass balances, technological indicators and especially the quantity of the produced chromic waste, to be determined.

Chemical Industry↗
PubMed1994

Induction of internucleosomal DNA fragmentation by carcinogenic chromate: relationship to DNA damage, genotoxicity, and inhibition of macromolecular synthesis.

Hexavalent chromium (Cr) compounds are respiratory carcinogens in humans and animals. Treatment of Chinese hamster ovary cells with 150 and 300 microM sodium chromate (Na2CrO4) for 2 hr decreased colony-forming efficiency by 46 and 92%, respectively. These treatments induced dose-dependent internucleosomal fragmentation of cellular DNA beyond 24 hr after chromate treatment. This fragmentation pattern is characteristic of apoptosis as a mechanism of cell death. These treatments also induced an immediate inhibition of macromolecular synthesis and delayed progression of cells through S-phase of the cell cycle. Cell growth (as evidenced by DNA synthesis) was inhibited for at least 4 days and transcription remained suppressed for at least 32 hr. Many of the cells that did progress to metaphase exhibited chromosome damage. Chromate caused the dose-dependent formation of DNA single-strand breaks and DNA-protein cross-links, but these were repaired 8 and 24 hr after removal of the treatment, respectively. In contrast, Cr-DNA adducts (up to 1/100 base-pairs) were extremely resistant to repair and were still detectable even 5 days after treatment. Compared with other regions of the genome, DNA-protein cross-links and Cr adducts were preferentially associated with the nuclear matrix DNA of treated cells, which was 4.5-fold enriched in actively transcribed genes. Chromium adducts, formed on DNA in vitro at a similar level to that detected in nuclear matrix DNA, arrested the progression of a DNA polymerase in a sequence-specific manner, possibly through the formation of DNA-DNA cross-links.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗