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PubMed1987

Effect of chromate ion on the membrane of established human cells as measured by uptake of a permeant lipophilic cation.

Cells from the established human cell line NHIK3025 concentrate the permeant lipophilic cation triphenylmethylphosphonium (TPMP+) against a concentration gradient, indicating the existence of an electrical potential across the cell membrane (interior negative). Cells exposed to potassium chromate or dichromate (7.7 mumol Cr/l) for 2 h subsequently showed reduced uptake of TPMP+, whereas similar exposure to a trivalent chromium salt (7.7 mumol/l chromic chloride) had similar uptake of TPMP+ as control cells. These preliminary results suggest that a primary effect of chromate on these cells is to reduce the electrical potential across the cell membrane.

Cell Line↗

PubMed2004

Removal of chromate anions from aqueous stream by a cationic surfactant-modified yeast.

The removal of chromate anions (CrO(4)(2-)) from aqueous solution by a cationic surfactant-modified yeast was studied in a batch system. Cetyl trimethyl ammonium bromide (CTAB) was used for biomass modification; it substantially improved the biosorption efficiency. The influences of solution pH, CrO(4)(2-) anion concentrations and biomass concentration on the biosorption efficiency were investigated. The biosorption of chromate anions by modified yeast was strongly affected by pH. The optimum pH for biosorption of CrO(4)(2-) by modified yeast was 4.5-5.5. Zeta potential values of modified and unmodified yeast were determined at various pH values. Concentrations ranging from 5.2 to 208 mg/l Cr(VI) were tested and the biosorptive removal efficiency of the metal ions from aqueous solution was more than 99.5%. Freundlich and Langmuir isotherms were used to evaluate the data and the regression constants were determined.

Adsorption↗

PubMed2006

Preparation and application of organo-modified zeolitic material in the removal of chromates and iodides.

The removal of chromates and iodides from aqueous solutions by organo-modified tuffs from the Pentolofos area (Thrace, Greece) was investigated using (51)Cr- and (131)I-labelled solutions and gamma-ray spectroscopy. The zeolitic material was modified by hexadecyltrimethyl-ammonium bromide (HDTMA-Br) and octadecyltrimethyl-ammonium bromide (ODTMA-Br) and characterized by scanning electron microscopy, FT-IR spectrometry and zeta potential measurements. Both experimental study and modelling indicated that both organo-zeolitic sorbents have a bigger affinity for iodide than for chromate. The chromium uptake did not seem to be influenced by the type of modifier but showed, as expected, a dependence on the solution pH. The maximum sorption capacity (2.27 mg/g) of Cr(VI) was achieved for the solution of initial pH 4. On the other hand, the HDTMA-modified tuff showed a lower sorption affinity for iodides than did the ODTMA-modified one (3.37 and 4.02 mg/g, respectively).

Adsorption↗

PubMed2004

Chromium is the proximate clastogenic species for lead chromate-induced clastogenicity in human bronchial cells.

Hexavalent chromium (Cr(VI)) is a well-established human lung carcinogen with potentially widespread exposure. Solubility is a key factor in the carcinogenicity of Cr(VI), with the water-insoluble or 'particulate' compounds being the more potent carcinogens. Studies have indicated that the component ions are responsible for their clastogenicity, but it is uncertain whether chromium (Cr), lead (Pb) or some combination of the two is responsible for the clastogenic effects. Accordingly, we compared the clastogenicity of lead chromate (LC) with soluble sodium chromate (SC) and lead glutamate (LG) in WTHBF-6 human lung cells. We found that 1436microM was the maximal intracellular level of Pb after exposure to clastogenic concentrations of LC. However, clastogenesis was not observed after exposure to LG, even when intracellular Pb concentrations reached 13,347microM, indicating that intracellular Pb levels did not reach clastogenic levels in WTHBF-6 cells after LC treatment. By contrast, SC was clastogenic damaging 16 and 44% of metaphase cells at intracellular Cr doses of 312 and 1262microM respectively, which was comparable to the clastogenesis observed after LC treatment. LC damaged 10, 27 and 37% of metaphases at intracellular Cr doses of 288, 926 and 1644microM, respectively. These data indicate that with respect to LC-induced clastogenicity, Cr and not Pb is the proximate clastogenic species in human lung cells.

Bronchi↗

PubMed2006

XRCC1 protects cells from chromate-induced chromosome damage, but does not affect cytotoxicity.

Hexavalent chromium Cr(VI) is a well known human carcinogen. This genotoxic metal induces DNA strand breaks and chromosome damage. However, the relationship between these lesions is uncertain. Our study focused on examining the role of XRCC1 in sodium chromate-induced cytotoxicity and chromosomal aberrations in Chinese Hamster Ovary (CHO) cells. Three different cell lines were used: AA8 (parental), EM9 (XRCC1 mutant) and H9T3 (EM9 complemented with human XRCC1 gene). Results show that concentration-dependent decreases in relative survival are similar in all three cell lines, indicating that XRCC1 is not crucial for protecting cells from sodium chromate-induced cytotoxicity. Similarly the frequency of damaged metaphase cells was not affected by XRCC1 deficiency. However, the total number of Cr(VI)-induced chromosome aberrations was exacerbated by XRCC1 deficiency and the spectrum of chromosome damage changed dramatically. Specifically, chromatid and isochromatid lesions were the most prominent aberrations induced in the cell lines and XRCC1 was essential to reduce the formation of chromatid lesions. In addition, XRCC1 deficiency caused a dramatic increase in the number of chromatid exchanges indicating that it is involved in protection from Cr(VI)-induced chromosome instability.

Animals↗

PubMed2006

Role of the Fancg gene in protecting cells from particulate chromate-induced chromosome instability.

Particulate hexavalent chromium (Cr(VI)) is a known human lung carcinogen. Cr(VI)-induced tumors exhibit chromosome instability (CIN), but the mechanisms underlying these effects are unknown. We investigated a possible role for the Fanconi anemia (FA) pathway in particulate Cr(VI)-induced chromosomal damage by focusing on the Fancg gene, which plays an important role in cellular resistance to DNA interstrand crosslinks. We used the isogenic Chinese hamster ovary (CHO) KO40 fancg mutant compared with parental and gene-complemented cells. We found that fancg cells treated with lead chromate had lower intracellular Cr ion levels than control cell lines. Accounting for differences of Cr ion levels between cell lines, we discovered that fancg cells treated with lead chromate had increased cytotoxicity and chromosomal aberrations, which was not observed after restoring the Fancg gene. Chromosomal damage was manifest as increased total chromosome damage and percent metaphases with damage, specifically an increase in chromatid and isochromatid breaks. We conclude that Fancg protects cells from particulate Cr(VI)-induced cytotoxicity and chromosome damage, which is consistent with the known sensitivity of fancg cells to crosslinking damage and the ability of Cr(VI) to produce crosslinks.

Animals↗

PubMed2004

Oxidative activation of the human carcinogen chromate by arsenite: a model for synergistic metal activation leading to oxidative DNA damage.

Human exposure to toxic metals and metalloids in the environment seldom occurs from a single pure compound. Most environmental exposure profiles are heterogeneous with co-exposure occurring coincident with multiple toxic metal species. This co-exposure to metals and metalloids in complex mixtures can result in a synergistic, additive or even depletive toxic response. The complexity of interactions presented by metal mixtures presents a need for convenient and sensitive methods to determine potential toxic responses from such co-exposure. We have studied the reaction between the two commonly associated toxic metals of chromate, Cr(VI), and arsenite, As(III), with regards to the ability of As(III) to reductively activate Cr(VI) to generate oxidative stress and DNA damage. Using a DCF-based fluorescent dye assay we have demonstrated that the redox reaction between As(III) and Cr(VI) yields high valent intermediates of chromium, Cr(V), that are highly oxidizing. This induction of oxidizing potential was dose dependent and did not occur with As(III) or Cr(VI) alone or, with the other major oxidation state of arsenic, arsenate, As(V). The mechanism of oxidation of DCFH to the fluorescent species, DCF, in this reaction was through a direct, metal-based oxidation since addition of radical scavengers did not significantly decrease oxidation of the dye in this system. The addition of a ligand that stabilizes the high valent Cr(V) oxidation state, 2-ethyl-2-hydroxybutyric acid (EHBA), to the chromate and arsenite mixture resulted in an enhancement of DCF fluorescence. The DCF fluorescence observed with the Cr(VI) and As(III) mixture was also found to correlate with oxidative DNA damage as measured by a plasmid nicking assay. These data show how metal-metal interactions in environmental mixtures could result in the synergistic induction of oxidative stress and DNA damage. Further, these data demonstrate the utility of the DCF fluorescence assay as a sensitive method for screening synergistic redox interactions in metal mixtures.

Arsenites↗

PubMed2001

Multiple effects of chromate on the photosynthetic apparatus of Spirodela polyrhiza as probed by OJIP chlorophyll a fluorescence measurements.

Chromate (Cr) decreases the growth of Spirodela polyrhiza. The fronds lost their pigments. The O2 evolution was also decreased. The Cr effect was found to be dose dependent. The toxic effects of Cr have further been studied on the photosynthetic activity of Spirodela polyrhiza by means of the chlorophyll a (Chl a) fluorescence transient O-J-I-P. The Chl a fluorescence transients were recorded in vivo with high time resolution and analyzed according to the JIP-test which can quantify the photosystem II behavior. Cr treated plants show a decrease in yield for primary photochemistry, phi Po. The performance index of PSII, PIABS, which is the combination of the indexes of three independent parameters, (1) the total number of active reaction centers per absorption (RC/ABS), (2) yield of primary photochemistry (phi Po) and (3) efficiency with which a trapped exciton can move an electron into the electron transport chain (psi 0), decreased due to Cr treatment. Chromate sensitivity varies within plant populations. In summary Cr affects several targets of PSII. More specifically, the main targets of Cr, according to the JIP-test, can be listed as a decrease in the number of active reaction centers and damage to the oxygen-evolving complex.

Araceae↗

PubMed1989

Anion-exchange high-performance liquid chromatographic determination of ascorbic acid and hexavalent chromium in rat lung preparations after treatment with sodium chromate in vitro and in vivo.

Simultaneous analysis of ascorbic acid and chromium (VI) in soluble fractions and bronchoalveolar lavage fluids of rat lungs treated with sodium chromate in vitro and in vivo was performed by anion-exchange high-performance liquid chromatography coupled to a photodiode-array detector. Absorbances at 265 and 370 nm were used for the determination of ascorbic acid and chromium (VI), respectively. The calibration graphs of standard solutions were linear in the test ranges of ascorbic acid an chromium (VI) (below 10 and 8 ppm, respectively). The detection limits of ascorbic acid and chromium (VI) were 1 and 0.5 ng, respectively. The recovery of ascorbic acid from lung tissues homogenized at pH 7.4 was 99%, and that of chromium (VI) was 96%, when tissues were homogenized under alkaline conditions (pH 11.4). Using this method, ascorbic acid levels in the soluble fractions and lavage fluids of normal rat lungs were determined. In the lung of a rat intratracheally injected with a saline solution of sodium chromate, ascorbic acid decreased to 80% of the normal level, and ca. 90% of the chromium (VI) was reduced within 4 min after injection, indicating that the ascorbic acid-related reduction of chromium (VI) is very rapid. The present method will be useful for studies of the reduction of chromium (VI) by ascorbic acid in biological systems.

Animals↗

PubMed2003

Amperometric cytochrome c3-based biosensor for chromate determination.

The chromate reductase activity of cytochrome c(3) (Cyt c(3), M(r) 13000), isolated from the sulfate-reducing bacterium Desulfomicrobium norvegicum, was used to develop an amperometric biosensor to measure chromate (CrO(4)(2-)) bioavailability. The performance of various biosensor configurations for qualitative and quantitative determination of Cr(VI) was studied. Biosensor properties depend on the technique used to immobilize the enzyme on the electrode (glassy carbon electrode). Immobilization of Cyt c(3) by entrapment in poly 3,4-ethylenedioxythiophene films denatured the enzyme, while application of an adsorption technique did not affect enzyme activity but the detection range was limited. The best results were obtained with dialysis membranes, which allowed the determination of Cr(VI) from 0.20 to 6.84 mg l(-1) (3.85-132 microM) with a sensitivity of 35 nA mg(-1) l (1.82 nA microM(-1)). No interference was observed with As(V), As(III) and Fe(III). Only a small amount of Cyt c(3) (372 ng of protein) was needed for this biosensor.

Biosensing Techniques↗

PubMed2001

Arsenate and arsenite removal by zerovalent iron: effects of phosphate, silicate, carbonate, borate, sulfate, chromate, molybdate, and nitrate, relative to chloride.

Batch tests were performed to evaluate the effects of inorganic anion competition on the kinetics of arsenate (As(V)) and arsenite (As(III)) removal by zerovalent iron (Peerless Fe0) in aqueous solution. The oxyanions underwent either sorption-dominated reactions (phosphate, silicate, carbonate, borate, and sulfate) or reduction-dominated reactions (chromate, molybdate, and nitrate) with Peerless Fe0 in the presence of As(V) or As(III), relative to chloride. Pseudo-first-order rate equations were found to describe satisfactorily both As(V) and As(III) removal kinetics in the presence of each competing anion. Of the oxyanions tested for Peerless Fe0 in the pH range from 7 to 9, phosphate caused the greatest decrease in As removal rate (7.0 x 10(-3) to 18.5 x 10(-3) h(-1)) relative to chloride (34.9 x 10(-3) to 36.2 x 10(-3) h(-1)). Silicate, chromate, and molybdate also caused strong inhibition of As removal, followed by carbonate and nitrate, whereas borate and sulfate only caused slight inhibition to As(III) removal. Present results show that Peerless Fe0 may be an excellent permeable reactive barrier medium for a suite of mixed inorganic contaminants. The anion competing effects should be considered when designing permeable reactive barriers composed of zerovalent iron for field applications to remediate As(V) and As(III).

Adsorption↗

PubMed2003

Kinetics and structural constraints of chromate reduction by green rusts.

Green rusts, ferrous-ferric iron oxides, occur in many anaerobic soils and sediments and are highly reactive, making them important phases impacting the fate and transport of environmental contaminants. Despite their potential importance in environmental settings, reactions involving green rusts remain rather poorly described. Chromate is a widespread contaminant having deleterious impacts on plant and animal health; its fate may in part be controlled by green rust. Here we examine chromate reduction by a series of green rust phases and resolve the reaction kinetics at pH 7. The overall kinetics of the reactions are well described by the expression d[Cr(VI)]/dt = -k[Cr(VI)][GR], and this model was successfully used to predict rates of reaction at varying chromium concentrations. The rates of reduction are controlled by the concentration of ferrous iron, surface area, and chemical structure of the green rust including layer spacing. On a mass basis, green rust (GR) chloride is the most rapid reductant of Cr(VI) followed by GRCO3 and GRSO4, with pseudo-first-order rate coefficients (k(obs)) (with respect to Cr(VI) concentration) ranging from 1.22 x 10(-3) to 3.7 x 10(-2) s(-1). Chromium(III)-substituted magnetite and lepidocrocite were identified as the major oxidation products. The nature of the oxidation products appears to be independent of the anionic class of green rust, but their respective concentrations display a dependence on the initial GR. The mole fraction of Fe(III) in the Cr(x),Fe(1-x)(OH)3 x nH2O reaction product ranged from 17% to 68%, leading to a highly stabilized (low solubility) phase.

Chromates↗

PubMed2005

Chromate reduction and retention processes within arid subsurface environments.

Chromate is a widespread contaminantthat has deleterious impacts on human health, the mobility and toxicity of which are diminished by reduction to Cr(III). While biological and chemical reduction reactions of Cr(VI) are well resolved, reduction within natural sediments, particularly of arid environments, remains poorly described. Here, we examine chromate reduction within arid sediments from the Hanford, WA site, where Fe(III) (hydr)oxide and carbonate coatings limit mineral reactivity. Chromium(VI) reduction by Hanford sediments is negligible unless pretreated with acid; acidic pretreatment of packed mineral beds having a Cr(VI) feed solution results in Cr(III) associating with the minerals antigorite and lizardite in addition to magnetite and Fe(II)-bearing clay minerals. Highly alkaline conditions (pH > 14), representative of conditions near high-level nuclearwaste tanks, result in Fe(II) dissolution and concurrent Cr(VI) reduction. Additionally, Cr(III) and Cr(VI) are found associated with portlandite, suggesting a secondary mechanism for chromium retention at high pH. Thus, mineral reactivity is limited within this arid environment and appreciable reduction of Cr(VI) is restricted to highly alkaline conditions resulting near leaking radioactive waste disposal tanks.

Chromates↗

PubMed2003

Properties of the reaction of chromate with metallothionein.

The reactivity of chromate or Cr(VI) with rabbit liver metallothionein (MT) was explored in this study. Zn(7)-MT reacts very slowly with Cr(VI) in a process characterized by a second-order rate constant of 3.9 x 10(-)(4) M(-)(1) s(-)(1). During the reaction, Zn(2+) was released from the protein. In contrast, apo-MT reduces chromate quicker and in this reaction is much more effective as a reducing agent, when compared to Cys or GSH. The kinetics are consistent with a reaction pathway involving an initial binding step followed by the reduction of Cr(VI). In the process, MT sulfhydryl groups were oxidized at the same rate that Cr(VI) disappeared. A Cr(V) intermediate was detected by EPR spectroscopy immediately upon mixing apo-MT with Cr(VI). The Cr(V) signal decayed during the reaction but was quite stable and could be observed for hours once the supply of thiols was depleted. The g values for the Cr(V) species were 2.014 and 1.987. The kinetics of the reaction of Cr(VI) and the concentration of the intermediate Cr(V) signal were independent of the oxygen concentration and were unaffected by the presence of superoxide dismutase, catalase, or DMSO. In the presence of oxygen, oxy radicals were generated according to ESR spin-trapping experiments with 5,5'-dimethyl-1-pyrroline-N-oxide. Superoxide dismutase decreased and catalase or DMSO largely inhibited the formation of the spin-trapped adduct. Cr(III), the presumed final species of the Cr(VI) reduction, formed a stable complex with apo-MT in the absence of oxygen with an average stoichiometry of two Cr ions bound per protein molecule. Upon addition of O(2), the complex slowly dissociated.

Animals↗

PubMed1998

Evidence for the involvement of vacuolar activity in metal(loid) tolerance: vacuolar-lacking and -defective mutants of Saccharomyces cerevisiae display higher sensitivity to chromate, tellurite and selenite.

The responses of Saccharomyces cerevisiae towards the oxyanions tellurite, selenite and chromate were investigated in order to establish the involvement of the yeast vacuole in their detoxification. Three mutants of S. cerevisiae with defective vacuolar morphology and function were used; mutant JSR180 delta 1 is devoid of any vacuolar-like structure while ScVatB and ScVatC are deficient in specific protein subunits of the vacuolar (V)-H(+)-ATPase. All the mutant strains showed increased sensitivity to tellurite and chromate compared to their parental strains. Such sensitivity of the mutants was associated with increased accumulation of tellurium and chromium. These results indicate that accumulation of both tellurium and chromium occurred mainly in the cytosolic compartment of the cell, with detoxification influenced by the presence of a functionally-active vacuole which may play a role in compartmentation as well as regulation of the cytosolic compartment for optimal expression of a detoxification mechanism, e.g. reduction. In contrast, the vacuolar-lacking mutant, JSR180 delta 1, and the defective V-H+ATPase mutant ScVatB displayed lower selenium accumulation than their parental strains. Additionally, the mutant strain ScVatB displayed a higher tolerance to selenite than the parental strain. This result suggests that accumulation of selenium occurs mainly in the vacuolar compartment of the cell with tolerance depending on the ability of the cytosolic component to reduce selenite to elemental selenium, which might, in turn, be related to activity of the V-H(+)-ATPase. These results are discussed in relation to vacuolar compartmentation and the significance of the vacuolar H(+)-ATPase in cytosolic homeostasis of H+ both of which may affect the accumulation, reduction, and tolerance to the tested metal(loids).

Chromates↗

PubMed1994

Characteristics of chromate workers' cancers, chromium lung deposition and precancerous bronchial lesions: an autopsy study.

The characteristics of lung cancers induced by inhaled chromate were studied in 13 consecutive autopsies on male ex-chromate workers. In addition to histopathology, we examined: (1) the relationship between the occurrence of lung cancer and the amount of chromium (Cr) deposited in the lung as determined by atomic absorptiometry and (2) the chronological changes in five precancerous lung lesions followed by bronchoscopy till death. Twenty-one cancers were identified, including 16 lung tumours observed either during follow-up or at autopsy. Of these 16 tumours, 13 were found in six subjects, implying a high frequency of multiple cancers. Eleven (69%) out of the 16 tumours were of squamous cell type (including carcinoma in situ), this being twice as frequent as in age-matched controls. A further characteristic was predominance in the central part of lung (69%). The lung Cr burden was very much higher [40-15,800 micrograms g-1 (dry)] in patients with lung tumours than in those without (8-28 micrograms g-1). Five of the precancerous lesions followed by bronchoscopy originated at bronchial bifurcations. Four of these cases showed a return to normal histology at autopsy even without therapy, and the other did not progress.

Aged↗

PubMed1997

A DANREF certified reference material for chromate in cement.

Two candidate reference materials for chromate in cement were produced in the DANREF network and certified in an interlaboratory study. Fifteen laboratories participated in the interlaboratory study and six different analytical methods were used. The certified values were estimated as the consensus mean of laboratory mean values (outliers excluded). Only results from laboratories using methods relying on chromate speciation were accepted. The certified values (+/- 95% confidence limits) were 0.678 (+/- 0.075) mg CrVI kg-1 dry cement for the low level and 6.04 (+/- 0.28) mg CrVI kg-1 dry cement for the high level. Methods based on total chromium determination gave on average results that were 6.5% higher (both levels). However, the difference between speciation and non-speciation results was significant at the high concentration level only.

Chromates↗

PubMed1995

Uptake of chromate in human red blood cells and isolated rat liver cells: the role of the anion carrier.

The transport of [51Cr]chromate into human erythrocytes and isolated rat hepatocytes has been investigated. It was found that uptake in both cell types could be inhibited by the established anion carrier inhibitor 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid. The uptake was very fast, and in kinetic studies a very low Km was found for both cell types, indicating either a high affinity of chromate for the carrier, and/or, more probably, an efficient intracellular reduction and trapping of 51Cr. The transport capacity, however, was of the same magnitude as for physiological substrates, such as lactate and sulfate. The uptake was temperature dependent and the activation energy was of the same magnitude as that for the physiological substrates. The uptake could be partly inhibited by high levels (mmol l-1) of lactate, pyruvate or sulfate. The uptake rate was greatly increased at lower pH (6.0 versus 7.4) which could indicate transport of the HCrO4- form or an increased intracellular rate of CrVI reduction. The results showed efficient uptake of 51CrO4(2-) by erythrocytes and hepatocytes. They were consistent with a mechanism of uptake which involved the cell membrane anion-exchange carrier in the transport and trapping of 51Cr within the cell.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗