Optimization of Culture Conditions for Growth Associated with Cr(VI) Removal by <Emphasis Type="Italic">Wickerhamomyces anomalus</Emphasis> M10

Chromate-resistant microorganisms with the ability of reducing toxic Cr(VI) to less toxic Cr(III), are candidates for bioremediation. An alternative culture medium to reduce Cr(VI) using Wickerhamomyces anomalus M10 was optimized. Using the Plackett-Burman design, it was determined that sucrose, K₂HPO₄ and inoculum size had significant effects on chromate removal (i.e., reduction) at 24 h. Concentrations of these significant factors were adjusted using a complete factorial design. In this case, only the K₂HPO₄ effect was significant at 12 h of culture, with greater Cr(VI) removal at low concentration (1.2 g L^?1). The optimum medium was validated at the fermenter scale level. Optimal culture conditions for complete removal of Cr(VI) (1 mM) were 400 rpm agitation and air flow of 1 vvm. Moreover, W. anomalus M10 completely removed consecutively added pulses of Cr(VI) (1 mM). These results show interesting characteristics from the standpoint of biotechnology because the development of a future remediation process using W. anomalus M10 can represent an efficient and highly profitable technology for removing the toxic form of Cr.     

Green Synthesis of Resin Supported Nanoiron and Evaluation of Efficiency for the Remediation of Cr(VI) Contaminated Groundwater by Batch Tests

In this study the fixation of nano zero valent iron (nZVI) on a polymeric matrix applying an environmentally friendly technique and the performance of this material for the treatment of Cr(VI) contaminated groundwater were evaluated. The investigated method could be applied in a pump & treat groundwater remediation system. A macroreticular cationic resin was selected as porous host material. It was found that green tea polyphenols were able to penetrate within the macroporous resin matrix and obtain the reduction of Fe(III) to the elemental state. The effectiveness of this composite material in removing Cr(VI) contaminated waters was evaluated by conducting batch tests. It was found that the reduction of Cr(VI) follows a kinetics law of first order with respect to the concentration of Cr(VI) and to the amount of nZVI per liter of solution. The kinetic constant varied between 5·10^?3 and 0.5·10^?3 per min and per mM of nZVI in the pH range 3.5–7.5.     

Adsorption of Cr(VI) and speciation of Cr(VI) and Cr(III) in aqueous solutions using chemically modified chitosan

A new type of grafting chitosan (CTS) was synthesized using 2-hydroxyethyl-trimethyl ammonium chloride (HGCTS). The adsorption of Cr(VI) on HGCTS was studied. The effect factors on adsorption and the adsorption mechanism were considered. The results indicated that the HGCTS could concentrate and separate Cr(VI) at pH 4.0; the adsorption equilibrium time was 80 min; the maximum adsorption capacity was 205 mg/g. The adsorption isotherm and kinetics were investigated, equilibrium data agreed very well with the Langmuir model and the pseudo second-order model could describe the adsorption process better than the pseudo first-order model. A novel method for speciation of Cr(VI) and Cr(III) in environmental water samples has been developed using HGCTS as adsorbent and FAAS as determination means. The detection limit of this method was 20 ng/L, the relatively standard deviation was 1.2% and the recovery was 99%~105%.     

Aqueous chemistry of airborne hexavalent chromium during sampling

Cr(III) is an essential micronutrient for the proper function of human being, while Cr(VI) is a carcinogenic chemical, which has been one of the hazardous air pollutants defined by US Environmental Protection Agency (US EPA) in 2004. Accurate measurements of atmospheric hexavalent chromium concentration are required to evaluate its toxicity. In the present study, a simulation tool using MATLAB program was developed to evaluate soluble and insoluble chromium species formed during the Cr(VI) field sampling (500 ml, 0.12 M HCO₃^? buffer, pH?=?9, 24 h, cellulose filter) which will assist us to better quantify the hexavalent chromium concentration. In this study, Cr(VI) was found to be dominant in soluble form as CrO₄^2? and in precipitated form as (NH₄)₂CrO₄, CaCrO₃, BaCrO₄, and PbCrO₄ at pH?=?9 cellulose filter. Secondly, reduction of Cr(VI) to Cr(III) was higher than the oxidation of Cr(III) to Cr(VI). Basic pH solutions retard the conversion of Cr(VI) in the presence of Fe(II) and As(III) and facilitate the precipitation of Cr(III). The presence of the NaHCO₃ as buffer on the cellulose filters and also in the filter extraction solution may add to the precipitation of Cr(VI) as NaCrO₄. This study provides new insights to improve cellulose sampling filters, and the filter extraction solutions to either prevent Cr(VI) precipitation during the wet analysis of Cr(VI) or improve the Cr(VI) analysis methods to quantify total Cr(VI) (soluble and insoluble Cr(VI)).     

Differential Uptake and Transport of Trivalent and Hexavalent Chromium by Tumbleweed (Salsola kali)

Experiments were conducted to determine the differential absorption of Cr species by tumbleweed (Salsola kali) as well as the effect of this heavy metal on plant growth and nutrient uptake. Tumbleweed seeds were grown in an agar-based media containing different concentrations of either Cr(III) or Cr(VI). The results demonstrated that the uptake of Cr was influenced by the Cr concentration in the growth medium and the speciation of this heavy metal. When supplied in the hexavalent form, the concentration of Cr in the different plant parts (2900, 790, and 600 mg kg^–1 for roots, stems, and leaves, respectively) was between 10 and 20 times higher than the amounts found when Cr was supplied in the trivalent form. In addition, it was found that in most of the experiments, Cr(III) exhibited more toxic effects on tumbleweed plants than Cr(VI). The size of roots of plants grown in 20 mg L^–1 Cr(III) were significantly smaller (p < 0.05) than those grown in 20 mg L^–1 Cr(VI). Plants exposed to 20 mg L^–1 Cr(III) produced shoots significantly shorter (p < 0.05) compared with the size of control plants and with those grown in 20 mg L^–1 Cr(VI). In addition, the absorption of macronutrients and microelements was in general lower when the plants were grown in the medium containing Cr(III). The amounts of Cr concentrated in the aerial plant parts under experimental conditions may indicate tumbleweed as a new option for the phytoremediation of Cr-contaminated soil.     

Toxicity of chromium(III) and chromium(VI) to the earthworm Eisenia fetida

The effects of Cr(III) and Cr(VI) on the survival, behavior, and morphology of the earthworm, Eisenia fetida, in water at pH 6, 7, and 8 and their toxicity in 10 different soils and an organic substrate have been assessed. A decrease in the pH of water resulted in increased toxicity of Cr to the earthworm. In water, both Cr species produced behavioral changes and morphological symptoms. The 48-h LC(50) values of Cr(III) at pH 6, 7, and 8 were 1.93, 2.55, and 2.78 mg/L, and those of Cr(VI) were 0.47, 0.61, and 0.63 mg/L, respectively. The 14-day median lethal concentrations (LC(50)) of Cr(III) and Cr(VI) for earthworm range from 1656 to 1902 mg/kg for Cr(III) and from 222 to 257 mg/kg for Cr(VI) in soil. In the organic substrate, the LC(50) values of Cr(III) and Cr(VI) were 1635 and 219 mg/kg, respectively. Stepwise multiple regression analysis predicted that clay content of soils accounted for 92% and 88% of the variation in the LC(50) values of Cr(III) and Cr(VI), respectively.     

Study on Chromium-Binding Capacity of Callitriche cophocarpa in an Aquatic Environment

The aim of the present study was to investigate the binding strength of chromium (Cr) ions to aquatic macrophyte Callitriche cophocarpa. Shoots of the plants were incubated in a natural water solution containing Cr(III) or Cr(VI) at a concentration ranging from 0.5 to 4 mM under laboratory conditions. We found that C. cophocarpa has an extremely high capacity to bind Cr. The average level of accumulation reached 28,385 or 7,315 mg kg^?1 dry weight for plants incubated with Cr(III) or Cr(VI), respectively. Shoots incubated in a 0.5 mM concentration of Cr(III) for 5 days removed almost 100 % of the metal from solution. The major pool of the bound Cr(III) ions follows the strongest mechanism of metal-binding to an organic matter. In contrast, we found that only 25 % of Cr(VI) ions are bound into the metallo-organic compounds and 57 % of Cr(VI) exists in an easily remobilizable form. Activity of a photosynthetic electron transport (as F _V/F _M) was evaluated with respect to the Cr-binding mechanism. Our results contribute to the development of knowledge on processes controlling bioremediation of heavy-metallic compounds in aquatic systems.     

Effect of available nitrogen on phytoavailability and bioaccumulation of hexavalent and trivalent chromium in hankow willows (Salix matsudana Koidz)

The effect of available nitrogen in nutrient solution on removal of two chemical forms of chromium (Cr) by plants was investigated. Pre-rooted hankow willows (Salix matsudana Koidz) were grown in a hydroponic solution system with or without nitrogen, and amended with hexavalent chromium [Cr (VI)] or trivalent chromium [Cr (III)] at 25.0±0.5 °C for 192 h. The results revealed that higher removal of Cr by plants was achieved from the hydroponic solutions without any nitrogen than those containing nitrogen. Although faster removal of Cr (VI) than Cr (III) was observed, translocation of Cr (III) within plant materials was more efficient than Cr (VI). Substantial difference existed in the distribution of Cr in different parts of plant tissues due to the nitrogen in nutrient solutions (p<0.05): lower stems were the major sink for both Cr species in willows grown in the N-free nutrient solutions and more Cr was accumulated in the roots of plants in N-containing ones. No significant difference was found in the removal rate of Cr (VI) between willows grown in the N-free and N-containing solutions (p>0.05). Removal rates of Cr (III) decreased linearly with the strength of nutrient solutions with or without N addition (p<0.01). Translocation efficiencies of both Cr species increased proportionally with the strength of N-containing nutrient solutions and decreased with the strength of N-free nutrient solutions. Results suggest that uptake and translocation mechanisms of Cr (VI) and Cr (III) are apparently different in hankow willows. The presence of easily available nitrogen and other nutrient elements in the nutrient solutions had a more pronounced influence on the uptake of Cr (III) than Cr (VI). Nitrogen availability and quantities in the ambient environment will affect the translocation of both Cr species and their distribution in willows in phytoremediation.     

An Approach to Electrokinetic Removal of Cr(VI) from Soil and Kaolin Samples

The present study examines electroremediation’s efficiency on Cr(VI) contaminated samples. Electrokinetic experiments were performed applying a DC voltage of 30 V to a cylindrical sample of 30 cm length and 4 cm diameter, using Na₂SO₄ as background electrolyte solution. The first two experiments, one with kaolin and one with soil, were carried out without applying any pH adjustment in the anode or the cathode compartment, using 0.01 M Na₂SO₄. Further experiments were carried out increasing the electrolyte’s concentration and using Mg(OH)₂ to neutralize the generated acidity in the anode. The decrease in Cr(VI) concentration in the soil samples is partly taking place because of its reduction, most likely due to the presence of organic matter. This is indicated by the mass balance calculations which were based on the analyses of treated solid samples and electrolyte solutions. ?n the kaolin samples electromigration is the main factor resulting in the accumulation of Cr(VI) in the anodic solution.     

Phosphorus Enhances Cr(VI) Uptake and Accumulation in <Emphasis Type="Italic">Leersia hexandra</Emphasis> Swartz

The effects of P supplementation on chromium(VI) uptake by Leersia hexandra Swartz were studied using pot-culture experiment. P-deficiency and zero-P addition controls were included. The Cr(VI) uptake followed Michaelis–Menten kinetics. Compare with the control, the P-supply decreased the Michaelis constant (Km) by 16.9% and the P-deficiency decreased the maximum uptake velocity (V_max) by 18%, which indicated no inhibition and competition between P and Cr(VI) uptake by L. hexandra. Moreover, there were a synergistic action between P and Cr(VI) suggests that Cr(VI) uptake by the roots of L. hexandra may be an active process. The bioconcentration factor (BCF) and the transport factor (TF′) increased with the increase in P supply. The highest BCF was 3.6-folds higher than the control, indicating that the additional P contribute to a higher ability of L. hexandra transporting Cr from root to the aboveground parts.     

Removal of Cr(VI) by Nanoscale Zero-valent Iron (nZVI) From Soil Contaminated with Tannery Wastes

The illegal disposal of tannery wastes at Rania, Kanpur has resulted in accumulation of hexavalent chromium [Cr(VI)], a toxic heavy metal in soil posing risk to human health and environment. 27 soil samples were collected at various depths from Rania for the assessment of Cr(VI) level in soil. Out of 27 samples, five samples had shown significant level of Cr(VI) with an average concentration of 15.84 mg Kg⁻¹. Varied doses of nanoscale zero-valent iron (nZVI) were applied on Cr(VI) containing soil samples for remediation of Cr(VI). Results showed that 0.10 g L⁻¹ nZVI completely reduces Cr(VI) within 120 min following pseudo first order kinetics. Further, to test the efficacy of nZVI in field, soil windrow experiments were performed at the contaminated site. nZVI showed significant Cr(VI) reduction at field also, indicating it an effective tool for managing sites contaminated with Cr(VI).     

Hexavalent Chromium Reduction by <Emphasis Type="Italic">Bacillus</Emphasis> sp. Strain FM1 Isolated from Heavy-Metal Contaminated Soil

A Cr(VI) reducing bacterial strain FM1 was isolated from heavy metal contaminated agricultural soil irrigated with tannery effluents of Jajmau, Kanpur (India), and was identified as Bacillus sp. on the basis of biochemical methods and 16S rDNA gene sequence analysis. FM1 strain was found to be resistant to some toxic heavy metals (Cr(VI), Cr(III), Cu²⁺, Co²⁺, Cd²⁺, Ni²⁺ and Zn²⁺) up to several fold concentrations to the normal levels occurring in highly polluted region. FM1 was resistant to very high concentration of Cr(VI) (1,000 mg/L) and completely reduced 100 mg/L Cr(VI) within 48 h. Factors (pH, temperature, initial Cr(VI) concentration) affecting Cr(VI) reduction under culture condition were also evaluated. Reduction was optimum at 37°C and pH 8. Cr(VI) reduction was enhanced by addition of glucose. The presence of heavy metal cations, such as Cu²⁺, Co²⁺, Cd²⁺, Ni²⁺ and Zn²⁺ showed differential effect on reduction. Since strain FM1 could grow in the presence of significant concentrations of metals and due to high Cr(VI) reduction ability, this bacterium may be potentially applicable in Cr(VI) detoxification.     

Changes in antioxidative activities induced by Fe (II) and Fe (III) in cultured vero cells

The toxicity of iron (II) and iron (III) chlorides was studied at different biochemical and cellular levels, including antioxidative and metabolic enzymes and two general indicators of cytotoxicity in Vero monkey kidney cells after 24-h exposure. Iron (II) was fourfold more toxic than Fe (III) in cell proliferation, with EC₅₀ of 5.5 and 22 mM, respectively. Metabolic markers were far more sensitive than cytotoxicity assays at these concentrations. At the highest concentrations of toxicant tested [10 mM Fe(II) and 50 mM Fe (III)], both species produced nearly total inhibition of the relative uptake of neutral red (RNRU) and phosphofructokinase activity (PFK), and stimulated intracellular specific lactate dehydrogenase activity (LDH). Succinate dehydrogenase (SDH) and hexosaminidase (HEX) activities were reduced in a dose-dependent manner, as was the antioxidative enzyme glucose-6-phosphate dehydrogenase (G-6-PDH) with both forms of iron. Glutathione reductase (GOR) and glutathione-S-transferase (GST) activities were stimulated by Fe (II) but were inhibited by the higher Fe (III) concentrations. In conclusion, the experimental model may be useful for the study of different metabolic effects induced by the two oxidation states of iron.     

Natural Hexavalent Chromium in the Pollino Massif Groundwater (Southern Apennines,Italy): Occurrence,Geochemistry and Preliminary Remediation Tests by Means of Innovative Adsorbent Nanomaterials

In this study Cr(tot), Cr(VI), major and trace elements were determined in groundwater of northern sector of the Pollino Massif (southern Italy). The investigated area is characterized by ophiolitic rocks consisting of metabasites, shales and calcschists and fractured serpentinites. Two main hydro-facies were observed, reflecting low temperature water–rock interaction. The Mg-HCO₃ hydrofacies is due to the weathering of serpentinites, Ca-HCO₃ groundwaters are linked to the interaction with calcschist and metabasites. High Cr(VI) concentrations were detected, exceeding the maximum admissible concentrations by Italian regulation, due to the release of Cr(III) from ophiolitic rocks into water and its oxidation to the hexavalent state. Remediation tests were carried out using two synthetized nanomaterials, Fe(0) and magnetite, characterized by a mean size lower than 50 nm. The experiments were conducted at fixed nanoparticles/Cr(VI) molar ratio and according to previous studies. In addition, the kinetic data were interpreted with a suitable mathematical model.

     

Occupational exposure to Cr(VI): comparison between chromium levels in lymphocytes,erythrocytes, and urine

 The relationships between chromium (Cr) levels in lymphocytes, erythrocytes, urine, and ambient air were compared among 14 chrome-platers from a metallurgic plant in Bulgaria and two groups of local controls, one from the same heavily polluted industrial town as the chrome-platers (n=11) and one from a seaside resort town 100 km away (n=6). Among the chrome-platers, the Cr concentration in peripheral lymphocytes was positively correlated with total Cr and Cr(VI) levels in ambient air and with Cr excretion in urine. As compared to the controls, the chrome-platers had mean Cr levels in lymphocytes twice as high, in erythrocytes ninefold higher, and in urine fourfold to eightfold higher. Although Cr levels in urine and lymphocytes were similar between the two control groups, levels in erythrocytes were 3 times higher among subjects from the industrial area than among those from the seaside town. The study suggests that lymphocyte Cr could be a good indicator of the Cr body burden caused by high exposures to Cr(VI), such as in electroplating operations. In these conditions, erythrocyte Cr may be less useful, possibly owing to increased toxicity due to the high affinity of erythrocytes for Cr. However, when exposure is lower, such as in most environmental situations, erythrocyte Cr should provide a better and more sensitive index than lymphocyte Cr. By contrast, urinary Cr, which provides information on total Cr exposure, including Cr(III) from dietary and environmental sources, does not seem to be of value for studying occupational exposure to Cr(VI). Received: 22 September 1995/Accepted: 2 January 1996     

Continuous Flow Process for Cr(VI) Removal from Aqueous Solutions Using Resin Supported Zero-Valent Iron

The objective of the present study was to evaluate the performance of a nanocomposite material consisting of nano zero valent iron and a cation exchange resin, for the reduction of chromate, by conducting column tests. A cationic resin, Amberlyst 15, was selected as porous host material. The synthesis of the nanocomposite material (R-nFe) was carried out using Green Tea extract to obtain the reduction of adsorbed Fe(III) to the elemental state Fe(0). Three column tests were implemented with different dimensions, corresponding to variable contact times between the aqueous solution and the resin beads loaded with Fe(0), namely 168, 744 and 1260 s respectively for columns I, II and III. The results indicated that the removal of Cr(VI) follows a first order kinetic law with a chemical constant equal to 0.0526 min⁻¹ (8.8 × 10^–4 s⁻¹).

     

Increased Solubility and Bioavailability of Hydroxy-Cr(III) Precipitates in the Presence of Hydroxamate Siderophores

Siderophores are a diverse group of low molecular weight biogenic metallophores with a particular affinity for Fe(III) but they also have potential to complex a number of other polyvalent metal cations, including Cr(III). Here we show that two hydroxamate siderophores, desferrioxamine B and rhodotorulic acid, at environmentally relevant concentrations, facilitate the dissolution of hydroxy-Cr(III) precipitates from a common layer silicate. Desferrioxamine B and rhodotorulic acid induced maximum initial Cr dissolution rates of 11.3?±?1.7?×?10^??4  and 9.03?±?0.68?×?10^??4 µmol m^??2 h^??1, respectively, yielding maximum solution Cr concentrations of 0.26?±?0.01 and 0.20?±?0.02 µmol m^??2, respectively. These data demonstrate that hydroxamate siderophores may play an important role increasing the dispersal of Cr in natural environments, thus facilitating greater bioavailability of this potential toxin.     

Biochemical and spectroscopic studies of the response of Convolvulus arvensis L. to chromium(III) and chromium(VI) stress

The objective of the present study was to determine the oxidative stress caused by hexavalent chromium (Cr[VI]), the chromium (Cr) uptake, and the Cr speciation in Convolvulus arvensis L. plants grown in hydroponics media containing either Cr(VI) or Cr(III). The results demonstrated that C. arvensis plants exposed to Cr(VI) concentrations ranging from 0 to 40 mg/L expressed higher ascorbate peroxidase specific activity in roots than in shoots. On the other hand, catalase activity monitored in plants exposed to 2 mg/L of Cr(VI) for 24 h increased in roots after a few hours of exposure. However, catalase activity in shoots revealed a decrement almost immediately after treatment was initiated. The results from x-ray absorption spectroscopic studies indicated that the oxidation state of the supplied Cr(III) remained the same in plant tissues. The supplied Cr(VI), however, was reduced to the trivalent form in plant tissues. The results of inductively coupled plasma/optical emission spectroscopy demonstrated that after 5 d, the roots of plants exposed to 40 mg/L of Cr(III) or Cr(VI) accumulated approximately 25,000 and 3,500 mg/kg dry weight of Cr, respectively. Nevertheless, shoots concentrated 1,500 and 2,000 mg/kg dry weight of Cr from Cr(III) and Cr(VI), respectively, which indicated that Cr moved faster into C. arvensis plants when supplied as Cr(VI).     

Removal of Chromium from Soils Cultivated with Maize (<Emphasis Type="Italic">Zea Mays</Emphasis>) After the Addition of Natural Minerals as Soil Amendments

The efficiency of natural minerals, i.e. zeolite, bentonite and goethite, regarding the retention of chromium, from maize was examined. Specifically, 1.0 kg of soil, 1.0 g of soil amendment and either 50 mg L^?1 Cr(III) or 1 mg L^?1 Cr(VI) were added in plant pots. Then, seeds of maize were cultivated. Each treatment was repeated three times. The statistical results of the experiments were analyzed by LSD test. Cr(III) addition in soil has shown that zeolite was the only amendment that increased the dry weight. Zeolite and bentonite reduced significantly the total chromium in plants after the addition of 50 mg L^?1 Cr(III). The addition of Cr(VI) in soil has shown that bentonite was the only amendment that increased the dry weight of biomass and the plants’ height. All soil amendments reduced to zero the total chromium concentration measured to plants after the addition of 1 mg L^?1 Cr(VI).     

Synthesis and spectroscopic studies of biologically active compounds derived from oxalyldihydrazide and benzil, and their Cr(III), Fe(III) and Mn(III) complexes

A new series of complexes have been synthesized by template condensation of oxalyldihydrazide and benzil in methanolic medium in the presence of trivalent chromium, manganese and iron salts forming complexes of the type [M(C(32)H(24)N(8)O(4))X]X(2) where M = Cr(III), Mn(III), Fe(III) and X = Cl(-1), NO(3)(-1), CH(3)COO(-1). The complexes have been characterized with the help of elemental analyses, conductance measurements, magnetic susceptibility measurements, electronic, NMR, infrared and far infrared spectral studies. On the basis of these studies, a five coordinate square pyramidal geometry has been proposed for all these complexes. The biological activities of the metal complexes have been tested in vitro against a number of pathogenic bacteria to assess their inhibiting potential. Some of these complexes have been found to exhibit remarkable antibacterial activities.