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.     

Integrating photobiological hydrogen production with dye-metal bioremoval from simulated textile wastewater

The study reports production of hydrogen in photobioreactors with free (PBR_Fr) and immobilized (PBR_Imm) Nostoc biomass at enhanced and sustained rates. Before running the photobioreactors, effects of different immobilization matrices and cyanobacterial dose on hydrogen production were studied in batch mode. As hydrogen production in the PBRs declined spent biomass from the photobioreactors were collected and utilized further for column biosorption of highly toxic dyes (Reactive Red 198 + Crystal Violet) and metals (hexavalent chromium and bivalent cobalt) from simulated textile wastewater. Breakthrough time, adsorption capacity and exhaustion time of the biosorption column were studied. The photobioreactors with free and immobilized cyanobacterium produced hydrogen at average rates of 101 and 151 μmol/h/mg Chl a, respectively over 15 days, while the adsorption capacity of the spent biomass was up to 1.4 and 0.23 mg/g for metals and 15 and 1.75 mg/g for the dyes, respectively in continuous column mode.     

Biosorption of Chromium(VI) and Lead(II): Role of Spirulina platensis in the Treatment of Industrial Effluent

Biosorption is the process of removal of any chemical molecules by the treatment of biological material. Industrialization resulted in the discharge of various toxic heavy metals into water bodies, which poses serious health hazards to humans and animals. In the present study, live Spirulina platensis was used as a biosorbent for the removal of the heavy metals chromium (Cr(VI)) and lead (Pb(II)) from the aqueous samples. S. platensis were cultured in the presence of different concentrations of heavy metals. The growth of the algal cells was found to be decreased by 59% and 36% in media containing 50 ppm Cr(VI) and Pb(II), respectively. To assess the biosorption of heavy metals, at different time intervals, the spent culture media were used to detect Cr(VI) by atomic absorption spectroscopy method and Pb(II) by 4-(2-pyridylazo)resorcinol indicator method. Results suggested that there was a significant uptake of Cr(VI) and Pb(II) from the medium by S. platensis, with corresponding decrease of metals in the medium. When metal salt solutions or industrial effluent samples were passed through the column containing immobilized live S. platensis in calcium alginate beads, the concentration of Cr(VI) was found to be reduced drastically. The present study indicates the application of S. platensis for the bioremediation of heavy metals from the samples obtained from industrial effluents.     

Characterization of PGP Traits of a Hexavalent Chromium Resistant Raoultella sp. Isolated from the Rice Field near Industrial Sewage of Burdwan District,WB, India

Chromium (Cr) is the most toxic at its hexavalent state. Widespread use of chromium for various anthropogenic activities causing rapid decline of the agricultural productivity is now a major global concern. The purpose of this study was to isolate the plant growth promoting (PGP) chromium-resistant bacteria and characterize it before being applied for bioremediation. A potent Cr-resistant rhizobacterium (CrS2) was isolated from the rice field near an industrial sewage and identified as Raoultella sp. based on 16S rDNA sequence homology with some phenotypic characteristics. The strain exhibited Cr(VI) resistance up to 25 mM and also possesses some important PGP traits. The selected CrS2 strain has varied degrees of resistance to other toxic heavy metals/metalloids like arsenic, cadmium, and lead. The removal capacity of chromium was studied in broth cultures. The appropriate growth media for the strain is peptone yeast glucose media with glucose (0.5%) and peptone (1%) as carbon and nitrogen sources, respectively. The strain removed substantial amount of chromium after media optimization. The chromate reductase (EC.1.6.5.2) activity was constitutive in nature of this strain. Thus, the strain CrS2 may be exploited for bioremediation of Cr(VI) in Cr-contaminated agricultural soil, where it might also enhance plant growth promotion.     

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.     

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.     

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.     

Biosorptive removal of chromium by husk of Lathyrus sativus: Evaluation of the binding mechanism,kinetic and equilibrium study

The adsorption of tri‐ and hexavalent chromium by the husk of Lathyrus sativus (HLS), which is an agro‐waste has been investigated to find a potential solution to environmental pollution. The pH‐dependent adsorption process finds the optimum values for trivalent and hexavalent chromium ions at about pH 5.0 and pH 2.0, respectively. The process is very fast initially and attains an equilibrium within 90 min following pseudo second‐order rate kinetics. Equilibrium adsorption data can best elucidated by the Langmuir–Freundlich dual model (r² = 0.998) in comparison with other isotherm models examined indicating that both physi‐ and chemisorption are components of the binding mechanism of chromium ions on HLS. The results show that one gram of HLS can adsorb 24.6 mg Cr³⁺ and 44.5 mg Cr⁶⁺. Fourier transform infrared data and functional group modification experiments indicate that –NH₂, ‐COOH, ‐OH, ‐PO₄^3? groups of the biomass interact chemically with the chromium ions. SEM‐energy dispersive X‐ray analysis and X‐ray diffraction spectrum analysis were used to further assess the morphological changes and the mechanisms of chromium ion interaction with HLS. The analysis signified that the biosorption process involved surface morphological changes, complexation and an ion exchange mechanism. The amorphous nature of HLS facilitating metal biosorption was indicated by the X‐ray diffraction analysis.     

Removal of Heavy Metals from the Environment by Biosorption

The pollution of the environment with toxic metals is a result of many human activities, such as mining and metallurgy, and the effects of these metals on the ecosystems are of large economic and public‐healthsignificance. This paper presents the features and advantages of the unconventional removal method of heavy metals – biosorption – as a part of bioremediation. Bioremediation consists of a group of applications, which involvethe detoxification of hazardous substances instead of transferring them from one medium to another, by means of microbes and plants. This process is characterized as less disruptive and can be often carried out on site, eliminating the need to transport the toxic materials to treatment sites. The biosorption (sorption of metallic ions from solutions by live or dried biomass) offers an alternative to the remediation of industrial effluents as well as the recovery of metals contained in other media. Biosorbents are prepared from naturally abundant and/or waste biomass. Due to the high uptake capacity and very cost‐effective source of the raw material, biosorption is a progression towards a perspective method. The mechanism by which microorganisms take up metals is relatively unclear, but it has been demonstrated that both living and non‐living biomass may be utilized in biosorptive processes, as they often exhibit a marked tolerance towards metals and other adverse conditions. One of their major advantages is the treatment of large volumes of effluents with low concentrations of pollutants. Models developed were presented to determine both the number of adsorption sites required to bind each metal ion and the rate of adsorption, using a batch reactor mass balance and the Langmuir theory of adsorption to surfaces or continuous dynamic systems. Two main categories of bioreactors used in bioremediation – suspended growth and fixed film bioreactors – are discussed. Reactors with varying configurations to meet the different requirements for biosorption are analyzed considering two major groups of reactors – batch reactors and continuous reactors. Biosorption is treated as an emerging technology effective in removing even very low levels of heavy metal.     

Studies on the uptake of trivalent and hexavelent chromium by onion (Allium cepa)

Abstract

Experiments were conducted to examine the uptake and translocation of root-absorbed trivalent and hexavalent state of chromium in the onion plant (Allium cepa) grown in soil and sand culture. Chromium content in plant tissues increased with increasing amount of added chromium. Distribution of chromium in the plant in general, found to be in the order: root>>bulb>shoot. Higher uptake in the plants grown in sand from both the sources of chromium was observed as compared with the corresponding values for soil culture. Morphological and growth effects of the treatments of different oxidation state of chromium indicated that higher doses of Cr(VI) [150 and 300 μg mL^?1] were more toxic to the onion plants compared to equivalent doses of Cr(III).     

Biosorption of hexavalent chromium using biofilm of <Emphasis Type="Italic">E. coli</Emphasis> supported on granulated activated carbon

The optimization of hexavalent chromium biosorption has been studied by using three different biosorbents; biofilm of E. coli ASU 7 supported on granulated activated carbon (GAC), lyophilized cells of E. coli ASU 7 and granulated activated carbon. Supporting of bacteria on activated carbon decreased both the porosity and surface area of the GAC. Significant decrement of surface area was correlated to the blocking of microspores as a result of the various additional loads. The experimental data of adsorption was fitted towards the models postulated by Langmuir and Freundlich and their corresponding equations. The maximum biosorption capacity for hexavalent chromium using biofilm, GAC and E. coli ASU 7 were 97.70, 90.70, 64.36 mg metal/g at pH 2.0, respectively. Biosorption mechanism was related mainly to the ionic interaction and complex formation. Based on the experimental conditions, the presence of bacteria could be enhanced the capacity of activated carbon to adsorb hexavalent chromium ions from aqueous solutions.     

Bacterial Reduction of Hexavalent Chromium: Kinetic Aspects of Chromate Reduction by Enterobacter cloacae HO1

Kinetic aspects of the bacterial reduction of hexavalent chromium (chromate: CrO^2-₄) were investigated using Enterobacter cloacae strain HO1. E. cloacae strain HO1 could reduce hexavalent chromium to the trivalent form (Cr³⁺) anaerobically. High concentrations of CrO^2-₄ inhibited the reduction, and a substrate inhibition model gave a good fit to the observed data. The rate of chromate reduction was proportional to cell density. The effect of temperature on the reduction rate followed the Arrhenius equation. The rate of chromate reduction was also dependent on pH and the concentrations of carbon and energy sources in the culutre medium. Amino acids including asparagine, methionine, serine and threonine were utilized effectively as carbon and energy sources for chromate reduction.     

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.     

Biosorption Potentiality of Living Aspergillus niger Tiegh in Removing Heavy Metal from Aqueous Solution

The species of Aspergillus niger Tiegh isolated from estuarine sediments has been studied for tolerance to heavy metals such as Hg and Pb and for its capacities to uptake metals. A. niger was allowed to grow in monometal- as well as bimetal-containing media (25 mg L^?1) to determine the biosorption capacity of the organism. The effects of temperature and pH on biosorption were studied to elucidate the biosorption property and optimum growth conditions for the organism. Results revealed that 91.1% of Pb and 97.1% of Hg were removed from the monometal solutions, and there was a reduction of 96.9% of Hg and 89.3% of Pb from the bimetal solution after 92 h of fungal growth. The binding mechanism involved between metal ion and functional groups present on the cell surface of the biomass was studied using Fourier transform infrared (FTIR), which confirms the presence of amine, hydroxyl, carboxyl, and phosphate groups. The adsorption of metal ions on the biomass surface was confirmed using scanning electron microscopy–energy dispersive x-ray (SEM-EDAX) studies. The experimental study proved that A. Niger can be used as a suitable biosorption agent for removing metal ions when present in low concentration.     

Removal of chromium using Rhizobium leguminosarum

The chromium (Cr^III and Cr^VI) removal capability of Rhizobium leguminosarum was checked by estimating the amount of chromium in the medium before and after inoculation. To determine the efficiency of R. leguminosarum in removal of chromium, the influence of physical and chemical parameters such as temperature, pH and different concentrations (0.1–1.0 mM) of trivalent (Cr^III) and hexavalent (Cr^VI) chromium were studied. The chromium removal in aqueous solution by different size of active and inactivated biomass and immobilized cells of R. leguminosarum in a packed-bed column was also carried out. Results showed that in a medium containing up to 0.5 mM concentration of both Cr^III and Cr^VI, R. leguminosarum showed optimal growth. The maximum chromium removal was at pH 7.0 and 35°C. Active biomass removed 84.4 ± 3.6% of Cr^III and 77.3 ± 4.3% of Cr^VI in 24 h of incubation time. However, inactivated biomass removed maximum chromium after 36 h of incubation. Immobilized bacterial cells in a packed-bed column removed 86.4 ± 1.7% of Cr^III and 83.8 ± 2.2% of Cr^VI in 16 and 20 h of incubation time, respectively.     

Chromium ions phytoaccumulation by three floating aquatic macrophytes from a nutrient medium

In the present work, the trivalent and hexavalent chromium phytoaccumulation by three living free floating aquatic macrophytes Salvinia auriculata, Pistia stratiotes, and Eicchornia crassipes was investigated in greenhouse. These plants were grown in hydroponic solutions supplied with non-toxic Cr³⁺ and Cr⁶⁺ chromium concentrations, performing six collections of nutrient media and plants in time from a batch system. The total chromium concentrations into Cr-doped hydroponic media and dry roots and aerial parts were assayed, by using the Synchrotron radiation X-ray fluorescence technique. The aquatic plant-based chromium removal data were described by using a nonstructural kinetic model, obtaining different bioaccumulation rate, ranging from 0.015 to 0.837 l mg⁻¹ d⁻¹. The Cr³⁺ removal efficiency was about 90%, 50%, and 90% for the E. crassipes, P. stratiotes, and S. auriculata, respectively; while it was rather different for Cr⁶⁺ one, with values about 50%, 70%, and 90% for the E. crassipes, P. stratiotes, and S. auriculata.     

Microbial Waste Biomass for Removal of Chromium(VI) from Chrome Effluent

ABSTRACT

Microbial waste biomass, a by-product of the fermentation industry, was developed as a biosorbent to remove hexavalent chromium (Cr) from the acidic effluent of a metal processing industry. In batch sorption, 100% Cr(VI) removal was achieved from aqueous solution in 30 min contact at pH 4.0–5.0. The Cr(VI) sorption equilibrium was evaluated using the Langmuir and Freundlich models, indicating the involvement of ion exchange and physicochemical interaction. Fourier transform infrared (FTIR) analysis revealed the presence of amine, hydroxyl, and imine functional groups present on the surface of microbial biomass that are involved in Cr binding. In a continuous sorption system, 95 mg L^?1 of Cr(VI) was adsorbed before the column reached a breakthrough point of 0.1 mg L^?1 Cr(VI) at the column outlet. An overall biosorption capacity of 12.6 mg Cr(VI) g^?1 of dry microbial waste was achieved, including the partially saturated portion of the dynamic sorption zone. Insignificant change in metal removal was observed up to 10 cycles. In pilot-scale studies, 100% removal of Cr(VI) was observed up to 5 weeks, and the method was found to be cost-effective, commercially viable, and environmentally friendly, as it does not generate toxic chrome sludge.     

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.

     

Biosorption Performance of Multimetal Resistant Fungus Penicillium chrysogenum XJ-1 for Removal of Cu2+ and Cr6+ from Aqueous Solutions

Adsorption for heavy metals via biomaterials such as fungal biomass presents a practical remediation technique for polluted water. Among all known filamentous fungi, Penicillium chrysogenum is widespread in nature and can serve as a biosorbent for heavy metals. In the current study, the ability of P. chrysogenum XJ-1 to remove copper (Cu²⁺) and chromium (Cr⁶⁺) from water was evaluated. The maximum biosorption capacity of XJ-1 for Cu²⁺ reached 42.83 ± 0.57 mg g^?1 dry biomass at pH 5.0 after the equilibrium time of 1.5 h. The maximum biosorption capacity for Cr⁶⁺ at pH 3.0 reached 52.69 ± 1.68 mg g^?1 dry biomass after the equilibrium time of 1.5 h. The biosorption data of XJ-1 biomass were well fitted to the Freundlich isotherm model and the pseudo-second-order Lagergren kinetic model. Laundry powder-treated and HCl-treated XJ-1 biomass significantly enhanced its adsorption capacity to Cu²⁺ and Cr⁶⁺, respectively. HCl and NaOH were suitable desorbents for Cu²⁺/Cr⁶⁺ loading biomass, respectively. Fourier transform infrared spectroscopy analyses revealed that hydroxyl, amine, and sulfonyl groups on the biosorbent contributed to binding Cu²⁺ and Cr⁶⁺ and that carbonyl and carboxyl groups were also vital binding sites of Cu²⁺. Scanning electron microscopy and energy-dispersive x-ray (SEM-EDX) analyses confirmed that considerable amounts of metals were precipitated on the cell surface of XJ-1. Our results suggested that XJ-1 might be used to purify multimetal-contaminated water. This low-cost and eco-friendly biomass of XJ-1 seems to have a broad use in the restoration of metal-contaminated water.     

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.