► The review focuses on the Cr speciation, uses, toxicity and remediation aspects. ► Assessed amount of hexavalent Cr in soils/metallurgical/other wastes and sites. ► Chemical and bioremediation ...processes for Cr(VI) are summarised in detail. ► Strategy for bio-remediation of Cr(VI) in different solid wastes is suggested. ► Capability of microbes for reducing Cr(VI) contamination described. ► Mechanism of microbial reduction of Cr(VI) to Cr(III) is included.
Chromium is a highly toxic non-essential metal for microorganisms and plants, and its occurrence is rare in nature. Lower to higher chromium containing effluents and solid wastes released by activities such as mining, metal plating, wood preservation, ink manufacture, dyes, pigments, glass and ceramics, tanning and textile industries, and corrosion inhibitors in cooling water, induce pollution and may cause major health hazards. Besides, natural processes (weathering and biochemical) also contribute to the mobility of chromium which enters in to the soil affecting the plant growth and metabolic functions of the living species. Generally, chemical processes are used for Cr- remediation. However, with the inference derived from the diverse Cr-resistance mechanism displayed by microorganisms and the plants including biosorption, diminished accumulation, precipitation, reduction of Cr(VI) to Cr(III), and chromate efflux, bioremediation is emerging as a potential tool to address the problem of Cr(VI) pollution. This review focuses on the chemistry of chromium, its use, and toxicity and mobility in soil, while assessing its concentration in effluents/wastes which becomes the source of pollution. In order to conserve the environment and resources, the chemical/biological remediation processes for Cr(VI) and their efficiency have been summarised in some detail. The interaction of chromium with various microbial/bacterial strains isolated and their reduction capacity towards Cr(VI) are also discussed.
Industrial discharge of chromium (Cr) into environment puts serious threat on living beings due to its potent toxicity. Phytostabilization, a type of in-situ phytoremediation is aimed to immobilize ...and stabilize the toxic elements in soil using root system of metal resistant potential plants. To evaluate the phytostabilization potential of two grass species Brachiaria mutica and Leptochloa fusca, a pot study was conducted using soil spiked with different concentrations of Cr (control, 25, 50 and 100 mg kg−1). Three plants were sown in each pot with three replications and arranged following completely randomized design. After three months of growth, the plants were harvested and above and below ground plant’s parts were analyzed for various growth and physiological parameters. Data revealed that plant biomass, chlorophylls and carotenoids reduced substantially with increasing Cr concentration. Antioxidant enzymatic activity increased significantly in L. fusca as compared to B. mutica with increasing Cr levels (up to 50 mg kg−1), then reduced at maximum Cr level (100 mg kg−1) in both grasses. Leptochloa fusca performed better with maximum root Cr accumulation 93.7 μg plant−1, shoot Cr accumulation 24.7 μg plant−1, root bioconcentration factor (BCF) 2.0, shoot BCF 0.08, shoot TF 0.06 and MTI 87%. While B. mutica showed maximum root Cr accumulation 18.4 μg plant−1, shoot Cr accumulation 7.6 μg plant−1, shoot BCF 0.03, root BCF 1.28, shoot TF 0.04, and MTI 56%. These results showed that L. fusca possessed good potential with better Cr bioaccumulation, MTI, BCF and antioxidant activities compared to B. mutica. Hence L. fusca can be used as good phytostabilizing agent for the soils contaminated with lower to moderate levels of Cr.
•Brachiaria mutica and Leptochloa fusca were exploited to show their metal accumulation and growth potential under Cr stress.•Cr accumulation, root BCF and MTI results showed that L. fusca pertained better potential for growth and metal accumulation as compared to B. mutica.•Both grasses accumulate less Cr in shoot thereby above ground portion could be used as fodder for animals while keeping in view the Cr limits.•Further research at molecular level in L. fusca under Cr stress is warranted.
The oxidative dissolution of Cr(III) species (Cr2O3 and Cr(OH)3) by oxyhalide species, which produces hexavalent chromium (Cr(VI)), was studied in aqueous and frozen solution. The ...oxyhalide-induced oxidation of Cr(III) in frozen solution showed a different trend from that in aqueous solution. Cr(VI) production was higher in frozen than aqueous solution with hypochlorous acid (HOCl) and bromate (BrO3 –) but suppressed in frozen solution with hypobromous acid (HOBr) and periodate (IO4 –). In particular, bromate markedly enhanced Cr(VI) production in frozen solution, whereas it had a negligible activity in aqueous solution. On the contrary, periodate produced Cr(VI) significantly in aqueous solution but greatly suppressed it in frozen solution. Bromate was found to be much more concentrated in the ice grain boundary than periodate according to both chemical and Raman spectral analyses. The oxidative transformation of Cr(III) to Cr(VI) was accompanied by the concurrent and stoichiometric reduction of oxyhalide species. Dissolved O2 had little effect on the oxidative dissolution, but dissolved organic matter retarded the oxidation of Cr2O3 in both aqueous and frozen conditions. This study proposes that the oxyhalide-induced oxidation of Cr(III) (particularly by bromate) in frozen conditions might have a significant effect on the generation of Cr(VI) in the frozen environment.
In aqueous systems, chromium usually exists in both trivalent and hexavalent oxidation states, being Cr(VI) of particular importance and concern due to its great toxicity. Industrial sources of ...Cr(VI) are leather tanning, mining of chrome ore, production of steel and alloys, etc. The most common conventional method for Cr(VI) removal is reduction to Cr(III) at pH 2.0 and precipitation of Cr (OH)
3 with lime at pH 9–10. The disadvantage of precipitation is the disposal of the solid waste. Adsorption of Cr by different low cost materials seems to be a suitable choice for wastewater treatment. Many by-products of agriculture have proved to be suitable low cost adsorbents for Cr(VI) and Cr(III) removal from water. Lignocellulosic residues, which include both wood residues and agricultural residues, have adsorption capacity comparable to other natural sorbents, but they have the advantage of very low or no cost, great availability and simple operational process. This study is a review of the recent literature on the use of natural and modified lignocellulosic residues for Cr adsorption. The Cr maximum adsorption capacity and the adsorption mechanism under different experimental conditions are reported when possibly.
•Interaction mechanisms of Cr(III) or Cr(VI) with CAT were different.•Cr(VI) showed a stronger interaction strength with CAT than Cr(III).•Cr(III) or Cr(VI) altered the structure of CAT to different ...degrees.•The response of CAT activity to Cr(III) or Cr(VI) depends on their concentrations.
Heavy metal chromium (Cr) poses a severe health risk to humans via food chain contamination. In this study, the interactions of either trivalent chromium (Cr(III)) or hexavalent chromium (Cr(VI)) with catalase (CAT) were investigated via multi-spectroscopic studies and computational simulations. The fluorescence analysis showed that Cr(III) and Cr(VI) quenched the fluorescence of CAT through a dynamic and a static quenching mechanism, respectively. The binding constant of Cr(VI) with CAT was 3.44×104lmol−1 at 298K. Other detailed binding characterizations of the Cr(VI)–CAT complex were also obtained using spectra analysis and molecular docking. Synchronous fluorescence, UV–vis and circular dichroism (CD) spectral studies showed that either Cr(III) or Cr(VI) induced conformational changes of CAT, but the degree of influence was different. The response of CAT activity to Cr(III) or Cr(VI) was found to be variable depending on their valence states and concentrations.
The exploration of efficient broadband near-infrared (NIR) emitting materials is essential to establishing new NIR applications. In this work, an excellent NIR phosphor Mg7Ga2GeO12:Cr3+, with an ...emission band of 650–1350 nm and a full width at half maximum of 266 nm, was successfully prepared. When Ga3+ ions were replaced by In3+ ions, its emission intensity increased 4 times, and the internal and external quantum efficiency reached 86 and 37%, respectively. A NIR phosphor-converted light-emitting diode (pc-LED) component was made by combining a synthetic Mg7Ga1.84In0.07GeO12:0.09Cr3+ phosphor with a 450 nm blue luminescent chip. The vascular and skeletal distribution on human fingers and the back of the hand can be seen under the display of a commercial NIR camera, indicating that Mg7Ga1.84In0.07GeO12:0.09Cr3+ phosphors have promising applications in the field of the blood vessel and bone visualization.
As a direct consequence of the restrictions on the use of hexavalent chromium compounds, the demand for a suitable replacement has arisen. In this work the electrodeposition of thick chromium layers ...(>1 µm) from a trivalent electrolyte is investigated with the aim to identify an electrolyte composition for the deposition of hard functional coatings. These layers can be used to surface finish tribological components experiencing high wear rates or mechanical stress in applications such as coating printing cylinders, feed rollers or piston rods. The influence of different carboxylic acids (malonic acid, malic acid, glycolic acid) on the deposition has been studied. The effect of current density on the current efficiency was investigated using in-situ microgravimetry. For a technical application the electrolyte containing malonic acid was the most promising one and was further investigated regarding the properties of the deposits, such as surface morphology, crack formation, composition, thickness and hardness, aiming at properties as close as possible to those of hexavalent chromium. In comparison to hexavalent chromium, the layer of trivalent chromium showed the same properties in terms of crack formation, hardness and layer thickness (> 1 µm).
The electronic structure and ferromagnetic properties of Zn1ax M x O (M = Mn and Cr) have been investigated by using the KorringaaKohnaRostoker (KKR) method combined with the coherent potential ...approximation (CPA). The half-metal behavior is observed for different doping concentrations. The gap energies are deduced for different dilution x values. The magnetic moment of each atom and the total magnetic moment are computed. A special attention is paid to the discussion of the mechanism of ferromagnetism in these components.
In this paper, we present a theoretical study of structural, electronic and magnetic properties for zinc-blende Ga1ax TM x N(TM = Cr, Fe, Mn, V) using the full-potential augmented plane wave (FP-APW) ...method with local-spin density approximation (LSDA). We have analysed the dependence of structural parameters values on the composition x in the range of x=0.25, x=0.50. Also, the role of pad hybridisation is analysed by partial (PDOS) and total density of states (TDOS). The magnetic moment of Ga1ax TM x N has been studied by increasing the concentration of TM atom. The TM atom is the most important source of the total magnetic moment in these alloys, while the contributions from Ga and N are minor. In addition our results verify the half-metallic ferromagnetic character of TM doped GaN.
We developed a standard-free method for untreated hairs and the method has been applied to quantitative analysis of more than 30,000 hairs taken from the people concerned in order to evaluate ...exposure to some toxic elements and intakes of essential elements. Besides these analyses, we have measured nearly 2000 hairs collected from healthy people in Japan over the past 20 years. It was found that concentrations of some elements, such as vanadium, chromium, manganese, copper and mercury, keep increasing up to the present. Such tendencies were particularly notable for female, while not clearly observed for male. Concentrations of some essential elements, such as calcium, magnesium and zinc, show no obvious long-term variations. On the other hand, iron and selenium show slightly decreasing tendencies. With regard to toxic elements, it was found that arsenic, chromium and mercury are tending to increase year by year.
