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.     

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.     

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.     

Chromosomal aberrations and sister-chromatid exchanges in Chinese hamster cells treated in vitro with hexavalent chromium compounds.

Chinese hamster cells (CHO line) were treated in vitro for 30--39 h with hexavalent chromium compounds (K2Cr2O7 and Na2CrO7), at concentrations ranging from 0.1 to 1.0 microgram of Cr6+ per ml, in medium containing BUdr. Chromosomal aberrations and sister-chromatid exchanges were scored on BUdr-labelled 2nd division metaphases, collected at the end of treatment and stained with Giemsa. Treatment with mitomycin C 0.009--0.030 microgram/ml) was carried out as a control for the responsiveness of the cell system to chromosomal damage. Both chromium compounds induced marked mitotic delays. Chromosomal aberrations were increased about 10-fold by exposure to Cr6+ (1.0 microgram/ml). The principal aberrations observed were single chromatid gaps, breaks and interchanges, whose frequencies increased proportionally to the concentration of chromium. Dicentric chromosomes, isochromatid breaks, chromosome and chromatid rings were also induced. The frequenyc of sister-chromatid exchanges was hardly doubled 30 h after exposure to Cr6+ at 0.3 microgram/ml, whereas it was trebled 39 h after treatment, in the cells whose division cycle had been slowed down by chromium.     

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.     

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.     

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).     

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.     

Comparative toxicity of trivalent and hexavalent chromium to rabbits. III. Biochemical and histological changes in testicular tissue.

The administration of trivalent and hexavalent chromium compounds produced inhibition of the activity of succinic dehydrogenase, adenosine triphosphatase and acid phosphattase accompanied by cellular degeneration with complete absence of spermatocytes in the testis of rabbits. The biochemical and histological changes were more marked in the animals treated with the trivalent chromium than those exposed to hexavalent chromium and were progressive with the duration of exposure.     

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.     

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.     

Mutagenicity of nitrovin--a nitrofuran feed additive.

Nitrovin, a nitrofuran feed additive, is shown to be directly mutagenic in Salmonella typhimurium TA 98 and TA 100 between 0.1 and 2.5 microgram per plate (0.09--2.3 micrometer). Addition of a rat-liver homogenate reduces the mutation rates. Nitrovin inhibits growth of the same bacteria in suspension cultures at concentrations above 0.09 micrometer.     

Effects of the trivalent and hexavalent chromium on the physicochemical properties of mammalian cell nucleic acids and synthetic polynucleotides

The effects of trivalent (chromium chloride) and hexavalent (potassium dichromate) chromium have been studied on the nucleic acids of cultured mammalian cells (BHK hamster fibroblast line), commercial DNA and RNA, and synthetic polynucleotides of known base composition. Modifications of UV absorption spectra and alterations of thermal denaturation and renaturation patterns have been observed by directly treating purified nucleic acids, as well as by examining nucleic acids extracted from cells treated with chromium compounds.Cr(III) interacts with nucleic acid bases, mostly guanine and cytosine, but also with phosphate groups, leading to deprotonation of bases as well as intramolecular cross-links, sandwich complexes between bases and chelation between bases and phosphates. Such interactions destabilize the DNA structure. On the contrary, stabilization of RNA, due to intramolecular metal bonds between nitrogen bases in GC-rich regions, is mainly produced. The kind of interaction of Cr(III) with nucleic acids is not significantly different when intact BHK cells are treated.Cr(VI) interacts similarly with DNA and RNA giving instead different effects when purified nucleic acids or intact cells are treated. Treatment of purified DNA produces breakages in the polynucleotide chain due to the oxidizing power of Cr(VI). In intact cell treatments, changes in the properties of DNA are observed. These could result from the combined action of Cr(III), produced by the intracellular reduction of Cr(VI) and the oxidizing activity of residual Cr(VI).The relevance of Cr(VI) and Cr(III) interactions to the mechanisms of chromium (carcino)genic action is summarized. It is stressed that Cr(VI), if not completely reduced to Cr(III) by extracellular and endoplasmic constituents, can reach the cell nucleus and directly interact with DNA.     

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.     

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.     

Comparing metabolic effects of six different commercial trivalent chromium compounds

Recent reports provide cogent evidence that the average individual becomes chromium deficient with age. Unfortunately, chromium deficiency is strongly associated with many aspects of the Metabolic Syndrome, including insulin resistance and type 2 diabetes. Since replacement of chromium, per os, often ameliorates many deleterious manifestations associated with insulin resistance and diabetes, it is not surprising that many different, commercial trivalent chromium compounds are available on the market. However, previous reports have shown that the form of trivalent chromium (negative charges) can influence effectiveness markedly. We compared various commercial forms of trivalent chromium commonly used alone or in formulations, to examine whether they are equally effective and non-toxic. In the first study, five different chromium products were examined - citrate, amino acid chelate (AAC), chelavite, polynicotinate (NBC), and nicotinate. In the second study, effects of NBC and picolinate were assessed. Results demonstrated that only chelavite and NBC improved insulin sensitivity, and only NBC decreased systolic blood pressure (SBP) significantly. In the second study, both picolinate and NBC significantly decreased SBP compared to control. NBC and picolinate decreased malonyldialdehyde concentrations (free radical formation) and DNA fragmentation in hepatic and renal tissues. No evidence of adverse effects was noted with any of the compounds tested. In conclusion, while all the trivalent chromium compounds tested seem safe, only three enhanced insulin sensitivity (NBC, chelavite, and picolinate) and only two decreased SBP significantly (NBC and picolinate). Furthermore, both NBC and picolinate were protective in lessening free radical formation and DNA damage in the liver and kidneys.     

Elucidation of the percutaneous absorption of chromium compounds by functional proteomics

Chromium compounds are known to be associated with cytotoxicity and carcinogenicity when applied via a skin route. The aim of this study was to evaluate the skin permeability and toxicological profiles of four chromium species. Chromium permeation across the skin, as determined by an in vitro Franz cell, decreased in the order of sodium chromate>potassium chromate>potassium dichromate>chromium nitrate. The uptake of chromium species within the skin generally showed a contrary trend to the results of permeation, although differences among the various compounds were not large. Levels of in vivo skin deposition of the four compounds showed no statistically significant differences. Potassium chromate produced the greatest disruption of the skin structure as determined by HE staining, followed in order by sodium chromate, potassium dichromate, and chromium nitrate. This indicates that hexavalent chromium elicited greater toxicity to the skin compared to trivalent chromium. A similar result was observed for the viability of skin fibroblasts. To improve our understanding of the molecular mechanisms leading to functional changes in proteins, proteomic tools, including 2‐DE and MS techniques combined with sequence database correlations, were applied to identify target proteins altered by pathologic states. Eight protein spots, corresponding to cutaneous enzymes involved in energy metabolism and chaperon proteins, which were identified and discussed in this study, were associated with skin cytotoxicity, immunity, and carcinogenesis. In addition, functional proteomics of skin tissues may provide a promising tool for developing therapeutic strategies and can serve as the basis for further research.     

Bacterial interactions with chromate

Hexavalent chromium compounds (chromates and dichromates) are highly toxic and are considered as mutagens and carcinogens. These compounds are discharged frequently to the environment as a result of diverse industrial processes. Some microorganisms are able to reduce hexavalent chromium to the less toxic trivalent form. Chromate pollution has promoted the selection of bacterial strains possessing chromate resistance determinants, usually carried by plasmids. Strains combining both abilities, i.e. resistance to and reduction of chromate, are potentially useful for detoxifying chromate polluted waste waters.     

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.     

Effect of Rhamnolipids on Chromium-Contaminated Kaolinite

Hexavalent chromium Cr(VI) is a common environmental pollutant that is treated by its reduction to the trivalent form Cr(III). The latter can be re-oxidized to the toxic form, Cr(VI), under specific conditions. A study was conducted on the removal of Cr(III) to eliminate the hazard imposed by its presence in soil as there has been some evidence that organic compounds can decrease its sorption. The effect of addition of negatively-charged biosurfactants (rhamnolipids) on chromium contaminated kaolinite was studied. Results showed that the rhamnolipids have the capability of extracting 25% portion of the stable form of chromium, Cr(III), from the kaolinite, under optimal conditions. The removal of hexavalent chromium was also enhanced compared to water by a factor of 2 using a solution of rhamnolipids. Results from the sequential extraction procedure showed that rhamnolipids remove Cr(III) mainly from the carbonate and oxide/hydroxide portions of the kaolinite. The rhamnolipids had also the capability of reducing close to 100% of the extracted Cr(VI) to Cr(III) over a period of 24 days. This study indicated that rhamnolipids could be beneficial for the removal or long–term conversion of chromium Cr(VI) to Cr(III).