Toxic Chromium Research Articles

Nanoceria-Templated Metal Organic Frameworks with Oxidase-Mimicking Activity Boosted by Hexavalent Chromium

The high toxicity and mobility of hexavalent chromium (Cr(VI)) allow it to easily spread and bioaccumulate, and its detection is a major part of environmental protection. In this work, an innovative method is developed for preparation of cerium oxide nanorod-templated metal-organic frameworks (CeO2NRs-MOF). The in situ growth of MOF on the surface of CeO2 nanorods (CeO2NRs) enhances its oxidase-like activity. In the presence of a trace amount of Cr(VI), CeO2NRs-MOF can significantly accelerate the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) due to Cr(VI)-boosted oxidation, resulting in a blue colored oxidation product. It can detect Cr(VI) over a range of 0.03-5 μM with high selectivity. Moreover, this method can be applied to the detection of Cr(VI) in different water environment samples with satisfactory recoveries, demonstrating the potential application of CeO2NRs-MOF for the direct monitoring of Cr(VI) in environmental water systems. Thus, this work provides a facile host-templated MOF preparation method, which could possibly be extended to other fields.

Long-term leaching characterization and geochemical modeling of chromium released from AOD slag.

The long-term leaching of chromium from AOD slag was analyzed by column percolation test (CEN/TS 14405). According to the analytical result, the eluate of the AOD slag exhibited alkaline and reductive property. Chromium released from the AOD slag was primarily presented as trivalent chromium (Cr(III)). The eluate exhibited low hexavalent chromium (Cr(VI)) concentration. As the L/S ratio increased to 115Lkg-1, the accumulated release quantity of Cr(III) and total chromium per AOD slag mass reached 1549.68 and 1613.67μgkg-1, respectively. The long-term leaching toxicity of chromium from the AOD slag was noticeable. Besides, a long-term geochemical model was built with PHREEQC software to assess the evolution of pH and chromium concentration in the eluate. The simulated pH and chromium concentrations were well consistent with those of the column percolation experiment. The result suggested that the geochemical model for chromium leaching prediction applies to the assessment of the eco-risk of AOD slag during the long-term leaching. The concentration of trivalent chromium presenting as Cr(OH)4- for instability of Cr(III) hydroxide in the alkaline eluate was regulated by the dissolution of the primary phase Cr2O3.

Glycinebetaine alleviates the chromium toxicity in Brassica oleracea L. by suppressing oxidative stress and modulating the plant morphology and photosynthetic attributes.

Anthropogenic activities are a major source for contaminating the agricultural soil with heavy metals, which can affect physiological and metabolic processes in plants. Among the heavy metals, chromium (Cr) is the most toxic pollutant that negatively affects plants' metabolic activities, growth, and yield. Chromium reduces the plant growth and development by influencing the photosynthetic performance and antioxidant enzyme activities. This study was designed to examine the promotive role of exogenously applied glycinebetaine (GB) on plant morphophysiological and biochemical attributes in cauliflower (Brassica oleracea botrytis L.) under Cr toxicity. Four levels (0, 10, 100, and 200μM) of Cr were tested under the application of GB (1mM). The results delineated that Cr stress caused a considerable reduction in plant growth, photosynthetic pigment, gas exchange parameters, and biomass production. At high concentration (200μM), chromium stress decreased the plant height (57%), root length (32%), number of leaves (45%), and leaf area (29%) as compared with controls. Due to Cr stress, the electrolyte leakage and accumulation of malondialdehyde and hydrogen peroxide increased both in the roots and leaves of cauliflower, whereas antioxidative enzyme activities (SOD, CAT, and POD) decreased both in the roots and leaves of cauliflower due to Cr stress. At 200μM of chromium treatment, root dry weight, stem dry weight, leaf dry weight, and flower dry weight declined up to 43%, 40%, 53%, and 72%, respectively. With the application of GB, dry biomass of plant increased significantly as compared with no GB treatment under chromium stress. As Cr level increased in growth media, its concentration also increased in all plant parts including roots, stem, leaves, and flowers. However, GB application efficiently alleviated the Cr toxic effects on cauliflower and maintained higher plant growth, biomass production, photosynthetic attributes, and gas exchange traits as compared with their respective controls. Exogenously applied GB decreased oxidative stress and improved antioxidative enzyme activities as compared with treatments without GB application. Furthermore, Cr concentrations taken by plants were decreased due to GB application. These findings suggest that GB can play a positive role to maintain plant morphology and photosynthetic attributes under Cr toxic conditions in cauliflower.

Modeling and optimizing parameters affecting hexavalent chromium adsorption from aqueous solutions using Ti-XAD7 nanocomposite: RSM-CCD approach, kinetic, and isotherm studies.

Due to the high toxicity of chromium, particularly as Hexavalent chromium Cr (VI), it is removed from industrial effluents before their discharge into the environment by a variety of methods, including loading catalysts onto the polymeric supports. This study focused on the removal of Cr(VI) from aqueous solutions using Amberlite XAD7 resin loaded titanium dioxide (Ti-XAD7). Ti-XAD7 was synthesized using Amberlite XAD-7 impregnated with titanium tetraethoxide. The prepared Ti-XAD7 was characterized by using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Isotherms and kinetic studies were carried out to describe the adsorption behavior of adsorbent for the removal of Cr(VI) ions. Quadratic models considering independent variables, i.e. the initial Cr(VI) concentration, adsorbent dosage, time, and pH, were evaluated and optimized to describe the behavior of Cr(VI) adsorption onto the Ti-XAD7 using RSM based on a Five-level-four-factor CCD approach. The accuracy and the fitting of the model were evaluated by ANOVA with R2 > 0.725 and P value = 5.221 × 10-5. The optimum conditions for the adsorption process were an initial Cr(VI) concentration 2750ppb, contact time of 51.53min, pH of 8.7, and Ti-XAD7 dosage of 5.05g/L. The results revealed that the Langmuir and Sips isotherm models with R2 = 0.998 and 0.999 were the best models fitting the experimental data. The adsorption capacity of Ti-XAD7 and RL constant were 2.73mg/g and 0.063-0.076 based on the Langmuir isotherm, respectively. Kinetic studies also indicated that the adsorption behavior of Cr(VI) was acceptably explained by the Elovich kinetic model with a good fitting (R2 = 0.97). Comparison of the Ti-XAD7 and XAD7 yield in chromium adsorption showed that modified XAD7 had higher removal efficiency (about 98%) compared to XAD7 alone.

Chromate separation by selective crystallization

A new paradigm to remove toxic chromate anions from aqueous solution by crystallization of chromate-water clusters with imine-linked guanidinium cationic ligands is introduced. The guanidium-based cationic ligand was easily prepared through the imine condensation of an aldehyde and aminoguanidine hydrochloride. The cationic imine-linked guanidinium ligand (BBIG-Cl) showed a high removal capacity (292.5 mg/g) in the solutions. Rapid decontamination of chromate anions from the wastewater by this cationic ligand was resulted from an instantaneous crystallization. The produced guanidium chromate salts have an extremely low solubility (Ksp,BBIG = 8.19 × 10−9). Such superior removal performance of these materials was attributed to the charge-assisted hydrogen bonding between the cationic ligand and chromate-water hydrate anions, which was revealed by the single-crystal X-ray diffraction analysis and density functional theory (DFT) calculations. In addition, the successful recovery of the guanidium-based ligand makes it more attractive for real-world applications.

Extractive continuous extractor for chromium recovery: Chromium (VI) reduction to chromium (III) in sustainable emulsion liquid membrane process

Abstract This work reports, for the first time, a detailed investigation on the Chromium (VI) reduction to Chromium (III) in a sustainable continuous emulsion liquid membrane process. This method is used in the treatment of authentic rinse electroplating wastewater containing 40 ppm Chromium (VI) concentration. The liquid membrane phase is composed of palm oil as diluent, Span 80 as surfactant, trioctylmethylammonium chloride as extractant, and acidic thiourea solution as an internal reagent. The statistical experimental design was applied in optimizing the process parameters for the removal of chromium by a sustainable continuous emulsion liquid membrane process. Recovery and enrichment of the less toxic Chromium (III) at optimum process conditions were further studied. Optimization of chromium removal was investigated using the response surface methodology. Within the range of the selected operating conditions, the optimized values of emulsion to an external feed phase ratio, agitation speed and retention time are found to be 1:5, 342 rpm and 170 s. For instance, 99% of Chromium could be extracted at the optimum process conditions. The recovered species of Chromium (VI) was efficiently stripped into the internal phase (82%) as less-toxic Chromium (III) using 2.0 M thiourea in 2.0 M sulfuric acid as the strippant. In the meantime, up to 200 ppm external feed phase concentration seems to be the best range of condition for the recovery process of chromium from rinse electroplating wastewater.

Functionalized chitosan nanocomposites for removal of toxic Cr (VI) from aqueous solution

Starting from the biopolymer chitosan, two new functionalized chitosan nanocomposities, (CTS-Cin) and (Fe3O4@CTS-Cin) were synthesised and explored for the removal of toxic chromium from aqueous solution. The two chitosan based adsorbents were prepared by co-precipitation method under N2 conditions and fully characterized by means of different analytical techniques, FT-IR, EDS, XRD, SEM, HR-TEM and VSM. Adsorption mechanism of toxic Cr (VI) was performed by batch experiments as a function of pH, adsorbent dosage, contact time and initial hexavalent chromium concentration.The adsorption isotherm and kinetics were fitted well by Langmuir and pseudo-second–order model indicating that the adsorption process is monolayer adsorption. The maximum adsorption capacity for CTS-Cin adsorbent at 298 K is 61.35 mg/g at pH = 2 and it achieved adsorption equilibrium within 35 min. However, Fe3O4@CTS-Cin adsorbent achieved adsorption equilibrium within 80 min and its maximum adsorption capacity is 58.14 mg/g at pH = 3. These results indicate that the two modified adsorbents represent promising adsorbents that would have a practical impact on wastewater treatment applications.

Biochemical tests and identification of potential indigenous bacteria from nickel post-mining land in Pomalaa

The main problem in the nickel post-mining land in Pomalaa is the toxicity of nickel and chromium. The results of the analysis of soil samples showed that nickel levels reached 11103.74 mg/kg, and chromium reached 4030.17 mg/kg. The toxicity of nickel and chromium can cause the degradation of soil fertility. Bacteria are biological agents that are environmentally friendly, which can be used to reduce heavy metal toxicity and increase soil fertility on post-mining land. This study aims to examine biochemically six indigenous bacteria resistant to 10 ppm NiCl2 and four indigenous bacteria resistant to 10 ppm CrCl2 and identification. Based on the results of biochemical tests known indigenous bacteria from the genus Bacillus sp. is gram-positive bacteria that do not have the catalase enzyme, do not have the ability to use carbohydrates and produce endospores in their life cycle while indigenous bacteria from the genus Clostridium sp. is a gram-positive bacteria which in part has the enzyme catalase, all of which have the ability to use carbohydrates and only some of them produce endospores.

Hexavalent chromium toxicity induced biochemical perturbation in Tilapia nilotica: role of Phoenix

The current study was designed to investigate the protective role of Phoenix dactylifera (date palm) water extract (DPE) against oxidative injury induced by different concentrations of hexavalent chromium (CrVI) in liver and muscles of Tilapia nilotica (Oreochromis niloticus) fish in vitro. Results demonstrated that CrVI caused a significant concentration-dependent inhibition in glutathione S-transferase, superoxide dismutase and catalase activities as well as glutathione content. In addition, inhibition in transaminases and alkaline phosphatase activities were observed. While, thiobarbituric acid reactive substances levels in liver and muscles homogenate were increased. On the other hand, homogenates treated with DPE alone improve the antioxidant status and liver function biomarkers. Moreover, homogenate pretreated with DPE then exposed to CrVI showed marked modulation in lipid peroxidation, enzyme activities and protein content as compared to their respective CrVI treated ones. Conclusively, Phoenix dactylifera might have a potential protective role against CrVI toxicity.

Effects of accelerated aging on characteristics, leaching, and toxicity of commercial lead chromate pigmented microplastics

It is of environmental significance to study the leaching performance of additives from microplastics (MPs) and further evaluate the toxicity of leachate to microalgae. Here, we investigated the effects of accelerated aging on characteristics, leaching, and toxicity of commercial lead chromate pigmented MPs. Results show that aging of MPs caused surface cracks and fragmentation, increased their surface area and carbonyl contents, and promoted the release of lead chromate pigment. Chromium (Cr) and lead (Pb) tend to leach under acidic condition, rather than neutral and alkali environment. Aging treatment facilitates the leaching performance and a high concentration of NaCl solution also favors the leaching process. Toxicology experiments demonstrate that only high concentration of leachate (>10 μg L−1) exerted significant inhibitory influence (p < 0.005) on cell photosynthesis of Microcystis aeruginosa. The growth inhibition of algal cells remarkably increased with increasing leachate concentrations. We observed more inhibiting effects on cell growth and photosynthesis using the leachates of aged MPs. Longer aging time leads to more release of Cr and Pb, rendering higher toxicity to microalgae. These novel findings will benefit us from assessing the leaching behavior of additives in MPs and their toxicological risks to aquatic organisms.

Synthesis, characterization, and application of β-cyclodextrin-based ion-imprinted polymer for selective sequestration of Cr(VI) ions from aqueous media: Kinetics and isotherm studies

Toxic chromium(VI) is a menace to the environment and humans. Its tendency to transform into chromium(III) complicates its removal. An ion-imprinted polymer (IIP) synthesized by encapsulating 1,5′-diphenylcarbazide (DPC) ligand into the β-cyclodextrin cavities then held into position by 4-vinylpyridine and ethylene glycol dimethacrylate functional monomers (γ-MPS/β-CD/DPC/VP) were employed to investigate Cr(VI) removal efficacy. The corresponding non-imprinted polymer was also prepared, but the template ion was omitted. The inclusion of DPC ligand into the polymeric matrix was responsible for the pronounced selectivity observed due to the high affinity of DPC towards Cr(VI). Characteristic peaks at 3318, 1718, 1258 and 940 cm−1 apportioned to the –OH, CO, C–N, and Si–O–CH3 functional groups were observed in the FTIR spectra. The maximum Langmuir adsorption capacity obtained at 25 °C was 15.61 mg/g for IIP. The optimum solid/liquid ratio achieved at equilibrium time (240 min) was 10 g/L. The IIP selectivity order was Cr(VI)>Cr(III)>Co(II)>Zn(II)>Ni(II).

Selenium mitigates the chromium toxicity in Brassicca napus L. by ameliorating nutrients uptake, amino acids metabolism and antioxidant defense system

The phytotoxicity of chromium (Cr) makes it obligatory for the researchers to develop strategies that seek to hinder its accumulation in food chains. While, protective role of selenium (Se) has not been discussed in detail under adverse conditions in oilseed rape. Here, our aim was to investigate the potential use of Se (0, 5 and 10 μM) in alleviating the Cr toxicity (0, 100 and 200 μM) in Brassica napus L. Results delineated that Se-supplementation notably recovered the Cr-phytotoxicity by reducing the Cr accumulation in plant tissues and boosted the inhibition in plant growth and biomass. Under Cr stress, the exogenously applied Se significantly recovered the impairment in photosynthesis related parameters (chlorophyll a, chlorophyll b, carotenoids, net photosynthetic rate, stomatal conductance, and photochemical efficiency of photosystem II), and counteracted the reduction in nutrients uptake and improved the essential amino acids (EAAs) levels. In addition, Se activated the antioxidants enzymes included in AsA-GSH cycle (SOD, CAT, APX, GR, DHAR, MDHAR, GSH, and AsA) and glyoxalase (Gly) system (Gly I and Gly II) and minimized the excessive generation of reactive oxygen species (ROS) and methylglyoxal (MG) contents in response to Cr stress. In a nutshell, Se (more effective at 5 μM) alleviated the Cr and MG induced phytotoxicity and oxidative damages by minimizing their (Cr and MG) accumulation and enhanced the plant growth, nutrients element level, nutrition quality by improving EAAs, antioxidant and Gly system. By considering the above-mentioned biomarkers, the addition of exogenous Se in Cr polluted soils might be effective approach to decrease the Cr uptake and its linked phytotoxicity in B. napus.

Removal of toxic chromium (VI) from the wastewater under the sunlight-illumination by functionalized carbon nano-rods

The minimally explored form of nano-carbon known as carbon nano-rods (CNR) has been used for removal of toxic Cr(VI) from different types of wastewater samples under the illumination of natural sunlight. The CNR was functionalized with monomeric amine molecule named as 2, 2′-(ethylenedioxy)bis(ethylamine) (EDA) to synthesize its amine functionalized water soluble version named as functionalized soluble carbon nano-rods (f-CNR). f-CNR were dialyzed to achieve most functionalized portion which was used for the sunlight-induced removal of toxic Cr(VI) from wastewater. The specific selectively for choosing toxic Cr(VI) was based on a simpler fluorescence quenching experiment, where the fluorescence emission of f-CNR was specifically quenched by Cr(VI). For practical applicability of the overall process, different types of wastewater were used such as laboratory prepared synthetic wastewater, residual wastewater collected from the undergraduate laboratory named as real wastewater, and the external spiking of Cr(VI) in unknown industrial wastewater. Compared to the dark conditions, sunlight illuminated f-CNR showed much better results for removal of toxic Cr(VI).

Alleviation of chromium toxicity in maize by Fe fortification and chromium tolerant ACC deaminase producing plant growth promoting rhizobacteria

Chromium (Cr) is becoming a potential pollutant with the passage of time. Higher intake of Cr does not only affect the productivity of crops, but also the quality of food produced in Cr polluted soils. In the past, foliar application of Fe is widely studied regarding their potential to alleviate Cr toxicity. However, limited information is documented regarding the combined use of PGPR and foliar Fe. Therefore, the current study was conducted to screen Cr tolerant PGPR and examine effect of foliar Fe with and without Cr tolerant PGPR under Cr toxicity (50 and 100 mg kg−1) in maize (Zea mays) production. Out of 15, two Cr tolerant PGPR were screened, identified (Agrobacterium fabrum and Leclercia adecarboxylata) and inoculated with 500 μM Fe. Results confirmed that Agrobacterium fabrum + 500 μM Fe performed significantly best in improving dry weight of roots and shoot, plant height, roots and shoot length and plant leaves in maize under Cr toxicity. A significant increase in chlorophyll a (51.5%), b (55.1%) and total (32.5%) validated the effectiveness of A. fabrum + 500 μM Fe to alleviate Cr toxicity. Improvement in intake of N (64.7%), P (70.0 and 183.3%), K (53.8% and 3.40-fold) in leaves and N (25.6 and 122.2%), P (25.6 and 122.2%), K (33.3% and 97.3%) in roots of maize at Cr50 and Cr100 confirmed that combined application of A. fabrum with 500 μM Fe is a more efficacious approach for alleviation of Cr toxicity and fortification of Fe comparative to sole foliar application of 500 μM Fe.

Imbalance of redox homeostasis and antioxidant defense status in maize under chromium (VI) stress

The present study assesses the toxicity of hexavalent chromium [Cr(VI)] on maize (Zea mays L.) seedlings. Three different levels of Cr stress [50, 100 and 200 mg/l CrO3] were imposed and maize seedling growth performances were monitored at 2d and 4d. Modulation of antioxidant genes expression, metabolites, membrane damage, in vivo ROS detection, foliar H2O2 and proline accumulation were studied in detail to get an overview of Cr stress response of maize. Prime stress responses included marked reduction in plant height and biomass, loss of root cell viability with decreased APX-1, Cu/Zn SOD and DHAR expression and high accumulation of Cr in roots with little translocation to shoots. Higher uptake of Evans blue by Cr challenged roots indicates loss of root cells viability. In vivo detection of superoxides and H2O2 as dark blue and deep brown spots in stressed leaves supported with CM-H2DCFDA and DHE staining of roots strongly suggest severe oxidative burst under Cr stress. Marked decline in MDAR and DHAR expression in 200 mg/l Cr challenged leaves at 4d with non-significant change in AsA/DHA ratio indicate futile recycling of ascorbate pool which might lead to disturbance in redox homeostasis. Isolated increase in GR expression coupled with high GSH/GSSG do not seem to prevent cells from oxidative damages, as evident from high foliar MDA level in Cr challenged seedlings. Moreover, enhanced proline accumulation in maize leaves does not give much protection against Cr stress. Over all, this study facilitates our understanding of the plant’s adaptive mechanisms to Cr stress.

Analysis of Local Dissolution Behavior of Intermetallic Particles on Chromate-Treated AA1050 Using Micro-Electrochemical System

Because of the high formability and high strength, Al-Fe alloys are used for ships, battery materials, and so on. The mechanical properties of Al-Fe alloys can be improved by controlling the shape and hardness of the intermetallic particles. However, it has been reported that some of the intermetallic particles become pit initiation sites. Because the electrode potential of the intermetallic particles, such as Al3Fe and Al8Fe2Si, is higher than that of Al matrix, oxygen reduction reaction readily occurs on the particles, resulting in the local alkalization. The increase in pH causes the dissolution of Al matrix around the intermetallic particles, and a trench is formed around the particle. A crystallographic pit is known to be initiated in the trench. To prevent the pitting corrosion, surface treatments are often applied. Chromate conversion coatings are employed to protect aluminum alloys in chloride environments. However, the usage is limited because of the toxicity of hexavalent chromium. To develop environmentally friendly coatings, the elucidation of the corrosion inhibition mechanism by chromates is needed. In this study, the local dissolution behaviors of chromate treated Al-Fe alloy was analyzed by in situ observation using micro-electrochemical system. A commercial Al-Fe alloy (AA1050) was used as the specimens. The cross-section of the specimen was polished by Ar+-ion sputtering (6 kV, 5h), and the intermetallic particles were characterized by an optical microscope and a field emission scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectroscopy (EDS). The existence of two types of the intermetallic particles was confirmed in the specimens. These were determined to be Al-Fe or Al-Fe-Si. There was no specific difference in color or morphology between the two particles. For the electrochemical measurements, the specimens were mechanically ground with SiC paper to 4000-grid and polished with a diamond paste (15, 6, 1, and 0.25 µm). Ethanol was used as a lubricant to minimize any water exposure. After the polishing, the specimens were cleaned ultrasonically with ethanol and dried by N2 gas. As a chromate treatment, the specimens were dipped in 10 mM CrO3 solution. Subsequently, the specimen surfaces were rinsed with pure water and dried by N2 gas, and the chromate-treated specimens were stored in ambient air for 24 h. To evaluate the electrochemical properties of the as-polished and chromate-treated specimens, open circuit potentials were measured in naturally aerated 0.1 M NaCl at 298 K. In this research, all potentials refer to the Ag/AgCl (3.33 M KCl) electrode. To elucidate the effect of the chromate treatment time in the CrO3 solution on the corrosion behavior of AA1050, the specimens were immersed in CrO3 solution for 0.06, 0.18 and 3.6 ks, and open circuit potential of each specimen was measured in 0.1 M NaCl (pH 6.0). In the case of the specimen treated for 0.06 ks, the open circuit potential started to increase from -0.81 to -0.63 V after 0.08 ks and became stable at -0.63 V after 1 ks. The open circuit potential of the specimen treated for 3.6 ks decreased to -0.83 V and started to increase to -0.63 V after 0.19 ks. The time before the increase in the open circuit potential in 0.1 M NaCl depended on the chromate treatment time, and it seemed that the most suitable chromate treatment time was 3.6 ks. In the following electrochemical measurements, the chromate-treated specimens which were immersed in the CrO3 solution for 3.6 ks were used. Open circuit potentials of the as-polished and chromate-treated AA1050 were measured for 1 ks in naturally aerated 0.1 M NaCl (pH 6.0). The open circuit potential of the as-polished AA1050 increased from -0.73 to -0.65 V and became stable at -0.65 V. For most of the intermetallic particles on the as-polished specimens, the color was changed after the immersion in naturally aerated 0.1 M NaCl. While trenches were formed around the Al-Fe-Si particles, no trench formation was observed around the Al-Fe particles. In the case of the chromate-treated AA1050, the open circuit potential decreased from -0.8 to -0.83 V in 0.05 ks. After 0.05 ks, the open circuit potential increased and became -0.72 V at 1 ks. Most of the intermetallic particles in the chromate-treated specimen showed no change in the surface color after the immersion. In the chromate-treated specimens, the number of the trenches around the particles was smaller than those on the as-polished specimens. The chromate treatment decreased the open circuit potential of AA1050 in naturally aerated 0.1 M NaCl and reduced the number of the intermetallic particles which acted as trenching sites.

Effects of Cr(VI) exposure on electrocardiogram, myocardial enzyme parameters, inflammatory factors, oxidative kinase, and ATPase of the heart in Chinese rural dogs.

Heavily chromium-polluted areas, where people are prohibited from entering, are paradises for stray dogs. In this study, stray dogs were used to study the effects of chromium exposure on the heart of dogs in severely Cr(VI)-contaminated rural areas of China. The dogs were given water (control), low dose (L, 0.92mg/kg), medium dose (M, 1.15mg/kg), and high dose (H, 1.38mg/kg) of Cr(VI). The changes of electrocardiogram (ECG), myocardial enzyme parameters, inflammatory factors, oxidative kinase, and ATPase were measured to determine the toxicity of chromium on the heart of dogs. Results showed that the ST segment of ECG increased significantly, and the amplitude of T wave increased in the experimental group. The myocardial enzyme (CK-MB, AST, CK, and LDH) content in groups M and H increased significantly over time. The values of CAT, T-SOD, IL-10, and ATPase (K+-Na+-ATPase and Ca2+-Mg2+-ATPase) decreased with the increase of Cr(VI) dose, and the content of MDA, IL-1β, IL-8, and TNF-α increased with the increase of Cr(VI) dose. Our study suggested that the heart of Chinese rural dog was damaged by Cr(VI), and Cr(VI) could cause oxidative damage and alteration of ATPase content in dogs.

Hexavalent chromium reduction ability and bioremediation potential of Aspergillus flavus CR500 isolated from electroplating wastewater

Hexavalent chromium reduction by microbes can mitigate the chromium toxicity to the environment. In the present study Cr[VI] tolerant fungal isolate (CR500) was isolated from electroplating wastewater, was able to tolerate 800 mg/L of Cr[VI. Based on the ITS region sequencing, the isolate was identified as Aspergillus flavus CR500, showed multifarious biochemical (reactive oxygen species, antioxidants response and non-protein thiol) and morphological (protrusion less, constriction and swelling/outwards growth in mycelia) response under Cr[VI] stress. Batch experiment was conducted at different Cr[VI] concentration (0–200 mg/L) to optimize the Cr[VI] reduction and removal ability of isolate CR500; results showed 89.1% reduction of Cr[VI] to Cr[III] within 24 h and 4.9 ± 0.12 mg of Cr per gram of dried biomass accumulation within 144 h at the concentration of 50 mg/L of Cr[VI]. However, a maximum of 79.4% removal of Cr was recorded at 5 mg/L within 144 h. Fourier-transform infrared spectroscopy, energy dispersive x-ray spectroscopy and X-ray diffraction analysis revealed that chromium removal also happened via adsorption/precipitation on the mycelia surface. Fungus treated and without treated 100 mg/L of Cr[VI] solution was subjected to phytotoxicity test using Vigna radiata seeds and result revealed that A. flavus CR500 successfully detoxified the Cr[VI] via reduction and removal mechanisms. Isolate CR500 also exhibited efficient bioreduction potential at different temperature (20–40 °C), pH (5.0–9.0), heavy metals (As, Cd, Cu, Mn, Ni and Pb), metabolic inhibitors (phenol and EDTA) and in sterilized tannery effluent that make it a potential candidate for Cr[VI] bioremediation.

Assessing Bioaccumulation Potentiality of Lead- and Chromium- Tolerant Bacterial Strain from Tannery Effluents of Bangladesh through Atomic Absorption Spectrophotometer

Rapid growth of industries and directly discharge of hazardous toxic effluents particularly heavy metals into water streams creating alarming circumstances for entire ecosystem. With regard to removal of heavy metals, bioaccumulation is an advantageous technique which is comparatively safer and cheaper. In this context, attempt was made to evaluate the bioaccumulation potentiality of heavy metal removing microbial flora from tannery effluents of Bangladesh. Effluent sample was collected from the drainage pipes of leather industrial zone at Hazaribagh, Dhaka, Bangladesh with proper precautions and isolation was done on mineral salt medium supplimented with different concentrations of lead and chromium separately. Antibiotic resistance pattern was checked through disc diffusion method and efficacy was determined using Atomic Absorption Spectrophotometer (AAS) furnace. Isolated bacterial colony was gram negative, rod shaped, motile, white colored morphologically. The optimum culture condition for Achromobacter sp. was found at temperature 35°C, pH 7.6 and observed as a halo-tolerant strain that could utilize upto 10% salt. Molecular identification revealed that isolated bacterium was Achromobacter sp. (85% similarity) which was also similar with the results found in morphological, biochemical and physiological tests. Isolated Achromobacter sp. was multi-drug resistant (MDR) which was confirmed against penicillin, cefuroxime, cefixime and cefotaxime and LC50 value was evaluated through probit mortality software against Artemia salina at the concentration of 93.01±0.2 μl/ml. However, isolate did not show antagonistic effect against Rhizobacteria. Highest detoxification rate of chromium and lead were 96% and 93%, respectively at 100 μg/ml concentration at day 9 of exposure. From the present study, it was clear that isolated Achromobacter sp. had remarkable biosorption efficacy of the toxic lead and chromium from tannery effluents.

Biotransformation of chromium by root nodule bacteria Sinorhizobium sp. SAR1.

The present study aims to address the problem of chromium (Cr) toxicity by providing important insights into the mechanisms involved in its bioremediation. Among the 22 Rhizobium and Sinorhizobium isolates obtained from Sesbania sesban root nodules, Sinorhizobium sp. SAR1 (JX174035.1) tolerated the maximum Cr concentration (1mM) and hence was used for further studies. The excess secretion of extra polymeric substances, as seen from scanning electron micrographs, could be a probable mechanism of adaptation to the Cr stress. The Energy dispersive X-ray spectroscopy data did not show any peaks of Cr. The biosorption studies done on the isolate gave maximum adsorption capacity as 285.71mg/g. The isotherm studies showed a better fit to Langmuir isotherm. The Weber and Morris plot established that the phenomenon of adsorption was governed by film diffusion mechanism. The FTIR analysis suggested the role of cell wall components and extracellular polymeric substances in Cr adsorption to the biomass of Sinorhizobium. On the basis of these results a compiled mechanism of Cr (VI) adsorption and its biotransformation into Cr (III) by Sinorhizobium sp. SAR1 is explained. This work outlines a comprehensive detail for the exact phenomenon of Cr biotransformation by Sinorhizobium sp. SAR1. These results may further help in developing and enhancing effective bioremediation approaches.