Differential effect of chromium compounds on the immune response of the African mouth breeder Oreochromis mossambicus (Peters)

The objective of this study was to investigate the effect of trivalent (chromic chloride) and hexavalent (potassium dichromate) forms of chromium in the African mouth breeder Oreochromis mossambicus (Peters), with reference to the humoral immune response and lymphoid cells/organs. The 96 h LD50 for hexavalent and trivalent chromium was found to be 75 and 1,000microg fish(-1), respectively. Groups of fishes were injected intraperitoneally with 10, 1, 0.1 and 0.01% LD50 hexavalent and trivalent forms of chromium and subsequently immunised with bovine serum albumin (5 mg in 0.2 ml physiological saline). Both forms of chromium suppressed the antibody response, with hexavalent chromium being more suppressive than trivalent chromium. Reduction in spleen weight, splenocyte number and the percentage of blood lymphocytes was observed following administration of both forms of chromium. The possible immunological mechanisms behind the differential suppression of the antibody response and the reduction in spleen weight, splenocyte and lymphocyte counts are discussed.     

Toxicity and mutagenicity of hexavalent chromium on Salmonella typhimurium.

Four hexavalent and two trivalent chromium compounds were tested for toxicity and mutagenicity by means of the Salmonella typhimurium/mammalian-microsome test. All hexavalent compounds yielded a complete inhibition of bacterial growth at doses of 400 to 800 mug/plate, a significant increase of his(+) revertant colonies at doses ranging from 10 to 200 mug, and no effect at doses of less than 10 mug. The distinctive sensitivity of the four Salmonella strains tested (TA1535, TA1537, TA98, and TA100) suggested that hexavalent chromium directly interacts with bacterial deoxyribonucleic acid by causing both frameshift mutations and basepair substitutions. The latter mutations, which are prevalent, are amplified by an error-prone recombinational repair of the damaged deoxyribonucleic acid. On the average, 1 mumol of hexavalent chromium yielded approximately 500 revertants of the TA100 strain, irrespective of the compound tested (sodium dichromate, calcium chromate, potassium chromate, or chromic acid). The mutagenic potency of the hexavalent metal was not enhanced by adding the microsomal fraction of rat hepatocytes, induced either with sodium barbital or with Aroclor 1254. The two trivalent compounds (chromium potassium sulfate and chromic chloride), with or without the microsomal fraction, were neither toxic nor mutagenic for the bacterial tester strains.     

Differential effect of chromium compounds on the immune response of the African mouth breeder Oreochromis mossambicus (Peters)

The objective of this study was to investigate the effect of trivalent (chromic chloride) and hexavalent (potassium dichromate) forms of chromium in the African mouth breeder Oreochromis mossambicus (Peters), with reference to the humoral immune response and lymphoid cells/organs. The 96 h LD₅₀for hexavalent and trivalent chromium was found to be 75 and 1000 μg fish⁻¹, respectively. Groups of fishes were injected intraperitoneally with 10, 1, 0·1 and 0·01% LD₅₀hexavalent and trivalent forms of chromium and subsequently immunised with bovine serum albumin (5 mg in 0·2 ml physiological saline). Both forms of chromium suppressed the antibody response, with hexavalent chromium being more suppressive than trivalent chromium. Reduction in spleen weight, splenocyte number and the percentage of blood lymphocytes was observed following administration of both forms of chromium. The possible immunological mechanisms behind the differential suppression of the antibody response and the reduction in spleen weight, splenocyte and lymphocyte counts are discussed.     

Oxidation of inactive trivalent chromium to the mutagenic hexavalent form.

Soluble trivalent chromium compounds (chromium potassium sulfate, chromium nitrate, chromium chloride, neochromium and chromium alum) were inactive for Salmonella typhimurium TA100, even at milligram amounts per plate. No effect could be detected either in the absence or in the presence of rat-liver, lung or muscle microsomal fractions, of rat-muscle mitochondria (with or without ATP), of oxidized glutathione (GSSG), or of human serum, plasma or erythrocyte lysates. Conversely, addition of a strongly oxidizing agent (potassium permanganate) resulted in toxic effects in plates incorporating more than 40--80 microgram of compounds and elicited a dose-effect mutagenic response at 10--40 microgram per plate. These effects could be ascribed to oxidation of chromium from the trivalent to the active hexavalent state. Insoluble chromite, as tested in the spot test, was spontaneously mutagenic, owing to contamination of the industrial product with hexavalent chromium. The results obtained may be useful to interpret the findings of carcinogenicity tests and to predict health hazards linked to chromium.     

Potential of Live Spirulina platensis on Biosorption of Hexavalent Chromium and Its Conversion to Trivalent Chromium

Microalga biomass has been described worldwide according their capacity to realize biosorption of toxic metals. Chromium is one of the most toxic metals that could contaminate superficial and underground water. Considering the importance of Spirulina biomass in production of supplements for humans and for animal feed we assessed the biosorption of hexavalent chromium by living Spirulina platensis and its capacity to convert hexavalent chromium to trivalent chromium, less toxic, through its metabolism during growth. The active biomass was grown in Zarrouk medium diluted to 50% with distilled water, keeping the experiments under controlled conditions of aeration, temperature of 30°C and lighting of 1,800 lux. Hexavalent chromium was added using a potassium dichromate solution in fed-batch mode with the aim of evaluate the effect of several additions contaminant in the kinetic parameters of the culture. Cell growth was affected by the presence of chromium added at the beginning of cultures, and the best growth rates were obtained at lower metal concentrations in the medium. The biomass removed until 65.2% of hexavalent chromium added to the media, being 90.4% converted into trivalent chromium in the media and 9.6% retained in the biomass as trivalent chromium (0.931 mg.g^?1).     

Reduction of Toxic Chromium and Partial Localization of Chromium Reductase Activity in Bacterial Isolate DM1

Summary With advances in biotechnology, bioremediation has become one of the most rapidly developing fields in environmental restoration, utilizing microorganism to reduce the concentration and toxicity of heavy metals. Hexavalent chromium reducing bacterial culture (DM1) was isolated from the contaminated sites of chemical industries and its ability to reduce hexavalent chromium to trivalent chromium, a detoxification process in cell suspension and cell extract was examined. Based on the biochemical analysis DM1 was identified as Ochrobactrum sp. It could tolerate chromium upto a maximum concentration of 300 ppm, optimum temperature and pH being 35 °C and 7 respectively for maximum chromium reduction. Assay with the permeabilized cells (treated with toluene and Triton X-100) and cell free extract demonstrated that the hexavalent chromium reduction is mainly associated with the soluble fraction of the cell. The chromium reducing activity is inducible. The presence of an induced protein having molecular weight around 30 kDa in the presence of chromium and absence in cells without chromium points out a possible role of this protein in chromium reduction. The bacterial isolate DM1 can be exploited for bioremediation of hexavalent chromium containing wastes, since it seems to have the potential to reduce the toxic hexavalent form of chromium to its nontoxic trivalent form.     

Hexavalent Chromium Reduction in Soils Contaminated with Chromated Copper Arsenate Preservative

The toxicity and mobility of chromium in the environment greatly depends upon its speciation. The reduction of hexavalent chromium to trivalent chromium in a soil environment was examined by spiking three soil types (sandy, clayey, and organic soils) with a common wood preservative solution known as chromated copper arsenate (CCA). Chromium in the CCA preservative solution exists in the hexavalent form. The total and hexavalent chromium concentrations (mg/kg) were measured over a period of 11 months. Leachable chromium concentrations (mg/L) were assessed using the synthetic precipitation leaching procedure (SPLP). The degree and rate of hexavalent chromium reduction were similar for the sand and clayey soil, but much greater for the organic soil. Most of the chromium reduction occurred within the first month of the experiment. At the end of the experiment, approximately 50% of the hexavalent chromium was converted to the trivalent form in the sand and clayey soils. Hexavalent chromium concentrations were below detection in the organic soil at the end of the experiment. Nearly all of the chromium observed in the SPLP leachates was in the form of hexavalent chromium. Chromium leaching was thus greatest in the sand and clay soils where the hexavalent chromium persisted. The results indicate that hexavalent chromium in soils can persist for considerable time periods, in particular in soils with low organic matter content.

     

Comparative toxicity of trivalent and hexavalent chromium compounds in fig moth Ephestia cautella (Walker)

Of the trivalent (CrSO4) and hexavalent (K2Cr2O7) chromium compounds, only the hexavalent produced significant deleterious effects on development and fertility of E. cautella, when eggs were reared on laboratory medium supplemented with different concentrations of these salts.     

Effect of chromium on growth of Pseudomonas aeruginosa

Tolerance level to trivalent chromium-Cr(salen)(H2O)2+ and hexavalent chromium-K2Cr2O7 was assessed in P. aeruginosa isolated from tannery effluent soil. It could tolerate 80 and 100 ppm in liquid cultures and up to 100 and 200 ppm in plate count agar in the presence of trivalent and hexavalent chromium respectively. Unadapted cells took a longer time to grow than adapted cells in the presence of K2Cr2O7. Chromium influenced the cellular contents, morphology and respiration of P. aeruginosa. The chosen trivalent salt of chromium was more toxic than the hexavalent one.     

Toxicity and Mutagenicity of Hexavalent Chromium on Salmonella typhimurium

Four hexavalent and two trivalent chromium compounds were tested for toxicity and mutagenicity by means of the Salmonella typhimurium/mammalian-microsome test. All hexavalent compounds yielded a complete inhibition of bacterial growth at doses of 400 to 800 μg/plate, a significant increase of his⁺ revertant colonies at doses ranging from 10 to 200 μg, and no effect at doses of less than 10 μg. The distinctive sensitivity of the four Salmonella strains tested (TA1535, TA1537, TA98, and TA100) suggested that hexavalent chromium directly interacts with bacterial deoxyribonucleic acid by causing both frameshift mutations and basepair substitutions. The latter mutations, which are prevalent, are amplified by an error-prone recombinational repair of the damaged deoxyribonucleic acid. On the average, 1 μmol of hexavalent chromium yielded approximately 500 revertants of the TA100 strain, irrespective of the compound tested (sodium dichromate, calcium chromate, potassium chromate, or chromic acid). The mutagenic potency of the hexavalent metal was not enhanced by adding the microsomal fraction of rat hepatocytes, induced either with sodium barbital or with Aroclor 1254. The two trivalent compounds (chromium potassium sulfate and chromic chloride), with or without the microsomal fraction, were neither toxic nor mutagenic for the bacterial tester strains.     

Chromium reduction in Pseudomonas putida.

Reduction of hexavalent chromium (chromate) to less-toxic trivalent chromium was studied by using cell suspensions and cell-free supernatant fluids from Pseudomonas putida PRS2000. Chromate reductase activity was associated with soluble protein and not with the membrane fraction. The crude enzyme activity was heat labile and showed a Km of 40 microM CrO4(2-). Neither sulfate nor nitrate affected chromate reduction either in vitro or with intact cells.     

Insolubilization of hexavalent chromium in highly alkaline cement sludge by anaerobic bioremediation

Chemical treatment using reducing agents such as ferrous sulfate is the most popular method for remediation of hexavalent chromium–contaminated sludge. However, the use of such chemical agents poses the risk of secondary pollution through the elution of other heavy metals. Therefore, a bioremediation method was developed to remediate high-alkali cement sludge containing hexavalent chromium. When a biomediator mainly composed of lignocellulose and lignoarabinoxylan was added to hexavalent chromium–contaminated sludge under anaerobic conditions, the amount of hexavalent chromium eluted from the treated sludge decreased significantly to below the level of the environmental standard value in Japan and its pH was reduced to 8. Moreover, the oxidation-reduction potential of the treated sludge decreased and its microbiota changed. These results indicate that anaerobic microbes can facilitate the change of hexavalent chromium to an immobilized form of trivalent chromium. Nucleotide sequence analysis suggested that anaerobic microbes activated in the sludge were Exiguobacterium aurantiacum, which are known to tolerate high pH environments and produce organic acids, even in the cement sludge. Finally, treated sludge did not elute hexavalent chromium during shaking in acid or alkaline solution.     

Chromium and genomic stability

Many metals serve as micronutrients which protect against genomic instability. Chromium is most abundant in its trivalent and hexavalent forms. Trivalent chromium has historically been considered an essential element, though recent data indicate that while it can have pharmacological effects and value, it is not essential. There is no data indicating that trivalent chromium promotes genomic stability and, instead may promote genomic instability. Hexavalent chromium is widely accepted as highly toxic and carcinogenic with no nutritional value. Recent data indicate that it causes genomic instability and also has no role in promoting genomic stability.     

Toxic effects of chromium and its compounds

Chromium was discovered in 1797 by Vauquelin. Numerous industrial applications raised chromium to a very important economic element. At the same time, with the development of its uses, the adverse effects of chromium compounds in human health were being defined. Trivalent chromium is an essential trace element in humans and in animals. Chromium as pure metal has no adverse effect. Little toxic effect is attributed to trivalent chromium when present in very large quantities. Both acute and chronic toxicity of chromium are mainly caused by hexavalent compounds. The most important toxic effects, after contact, inhalation, or ingestion of hexavalent chromium compounds are the following: dermatitis, allergic and eczematous skin reactions, skin and mucous membrane ulcerations, perforation of the nasal septum, allergic asthmatic reactions, bronchial carcinomas, gastro-enteritis, hepatocellular deficiency, and renal oligo anuric deficiency. Prevention of occupational risks, biological monitoring of workers, and treatment of poisoning are also reported.     

The genotoxicity of chromium(VI) oxide in the wing spot test of Drosophila melanogaster is over 90% due to mitotic recombination.

Chromium(VI) oxide and chromium(III) chloride were tested in the wing somatic mutation and recombination test (SMART) in Drosophila melanogaster according to standard procedures. The hexavalent compound was highly genotoxic in both chronic and acute treatments whereas the trivalent one was clearly negative. Further analysis of wings carrying an inversion chromosome which eliminates all recombination events showed that over 90% of the spots induced by chromium(VI) oxide are due to mitotic recombination.     

Chromate-resistance in a chromate-reducing strain of Enterobacter cloacae

Resistance to toxic hexavalent chromium (chromate: CrO4(2)) in Enterobacter cloacae strain HO1, isolated from an activated sludge sample, was investigated under aerobic and anaerobic conditions. Decreased uptake of 51CrO4(2-) in E. cloacae strain HO1 was observed under aerobic conditions, when compared with a standard laboratory E. cloacae strain (IAM 1624). Under anaerobic conditions E. cloacae strain HO1 was able to reduce hexavalent chromium to the less toxic trivalent form. When E. clocacae strain HO1 was grown with nitrate anaerobically, the cells were observed to lose simultaneously their chromate-reducing ability and chromate-resistance under anaerobic conditions.     

Chromium reduction in Pseudomonas putida

Reduction of hexavalent chromium (chromate) to less-toxic trivalent chromium was studied by using cell suspensions and cell-free supernatant fluids from Pseudomonas putida PRS2000. Chromate reductase activity was associated with soluble protein and not with the membrane fraction. The crude enzyme activity was heat labile and showed a Km of 40 microM CrO4(2-). Neither sulfate nor nitrate affected chromate reduction either in vitro or with intact cells.     

Plasmid chromate resistance and chromate reduction.

Compounds of hexavalent chromium (chromates and dichromates) are highly toxic. Plasmid genetic determinants for chromate resistance have been described in several bacterial genera, most notably in Pseudomonas. Resistance to chromate is associated with decreased chromate transport by the resistant cells. The genes for a hydrophobic polypeptide, ChrA, were identified in chromate resistance plasmids of Pseudomonas aeruginosa and Alcaligenes eutrophus. ChrA is postulated to be responsible for the outward membrane translocation of chromate anions. Widespread bacterial reduction of hexavalent chromate to the less toxic trivalent chromic ions is also known. Chromate reduction determinants have not, however, been found on bacterial plasmids or transposons. In different bacteria, chromate reduction is either an aerobic or an anaerobic process (but not both) and is carried out either by soluble proteins or by cell membranes. Chromate reduction may also be a mechanism of resistance to chromate, but this has not been unequivocally shown.     

Chromium: a review of environmental and occupational toxicology

The following topics are covered in this brief review on the environmental and occupational toxicology of chromium: occurrence, production and uses of chromium and chromium compounds; experimental toxicology; chromium toxicity for man; hygienic and ecologic aspects of chromium contamination of the environment. The review provides a conclusive evidence which suggests that chromium, especially its hexavalent form, is both toxic and carcinogenic, but its trivalent form is physiologically essential in the metabolism of insulin. It is also emphasized that among the major sources of environmental chromium today are the cement industry and the increasingly widespread use of chromium compounds added as an anticorrosion admixture to a variety of cooling systems, e.g. in large power plants, which may greatly contribute to the overall pollution of outdoor air at the sites.     

Hexavalent-chromium reduction by a chromate-resistantBacillus sp. strain

Bacillus strain QC1-2, isolated from a chromium-polluted zone, was selected by its high ability to both tolerate and reduce hexavalent chromium [Cr(VI)] to less-toxic trivalent chromium [Cr(III)]. Cell suspensions of strain QC1-2 rapidly reduced Cr(VI), in both aerobic and anaerobic conditions, to Cr(III) which remained in the supernatant. Cr(VI) reduction was dependent on the addition of glucose but sulfate, an inhibitor of chromate transport, had no effect. Studies with permeabilized cells and cell extracts showed that the Cr(VI) reductase of strain QC1-2 is a soluble NADH-dependent enzyme.