Hexavalent Chromium Research Articles

Amino-Functionalized Metal–Organic Framework-Mediated Cellulose Aerogels for Efficient Cr(VI) Reduction

Industrialization activities have increased the discharge of wastewater that is polluted with hexavalent chromium (Cr(VI)), posing risks to ecosystems and humans. The photocatalytic reduction of Cr(VI) is viewed as a promising method for the removal of Cr(VI) species. However, developing photocatalysts with the desired catalytic activity, recyclability, and reusability remains a challenge. Herein, a composite aerogel was designed and fabricated with a Ti-based metal–organic framework (MIL-125-NH2) and carboxylated nanocellulose. MIL-125-NH2 presents a strong visible-light response, and the interactions between the amino groups of MIL-125-NH2 and the carboxyl groups of cellulose produce a strong interface affinity in the composites. The as-prepared aerogels exhibited a micro/macroporous structure. At an optimal MIL-125-NH2 loading of 55 wt%, the MC-5 sample showed a specific surface area of 582 m2·g−1. MC-5 achieved a photocatalytic Cr(VI) removal efficiency of 99.8%. Meanwhile, the aerogel-type photocatalysts demonstrated good stability and recycling ability, as MC-5 maintained a removal rate of 82% after 10 cycles. This work sheds light on the preparation of novel photocatalysts with three-dimensional structures for environmental remediation.

Removal of Cr(VI) from aqueous phase using dimethylaminopropylamine anchored polystyrene‐co‐divinylbenzene polymer as adsorbent

AbstractThe current investigation delves into the effectiveness of dimethylaminopropylamine tethered onto polystyrene‐co‐divinylbenzene polymer for the proficient elimination of hexavalent chromium from simulated wastewater. The resin was characterized using SEM, FT‐IR spectroscopy, EDX, elemental analysis, thermogravimetry, and solid state 13C NMR spectroscopy. The experimental investigation into sorption dynamics involved varying process parameters, including initial Cr(VI) concentration, amount of adsorbent used, solution pH, temperature, and contact between phases. The binding modes of chromate ions, either bidentate or monodentate, were observed, with their manifestation influenced by the solution's pH. Sorption capacity was found to be pH‐dependent, with removal efficiencies of 98.27%, 96.38%, and 85.52% observed at pH levels of 3, 6, and 9, respectively. PS‐DMAPA resin demonstrated robust regeneration capabilities, throughout five consecutive adsorption–desorption cycles. The Langmuir adsorption model exhibited excellent agreement with the experimental findings (R2 = 0.9994), revealing a maximum adsorption capacity of 70.15 mg g−1 at 298 K. Additionally, the experimental findings closely matched the second‐order kinetic model. The kinetics of sorption and the thermodynamic parameters were also investigated. Performance evaluating of the PS‐DMAPA resin under dynamic conditions included analyzing the Cr(VI) breakthrough curve. The 10% sodium chloride solution was employed to effectively recover the extracted Cr(VI) quantitatively.

Advancements in surface treatments for aluminum alloys in sports equipment

Abstract This review examines recent advancements in surface treatment technologies for aluminum alloys used in sports equipment. We discuss conventional methods like chemical conversion coatings and anodizing, as well as emerging techniques such as plasma electrolytic oxidation, physical vapor deposition, and laser surface modification. The replacement of toxic hexavalent chromium with eco-friendly alternatives is highlighted as a key development. We also explore the potential of smart, self-healing coatings to extend equipment lifespan. Our analysis reveals that while significant progress has been made in enhancing corrosion resistance and mechanical properties, challenges remain in scaling up advanced treatments for industrial implementation. The review concludes that continued innovation in surface treatments will be crucial for improving the performance, safety, and sustainability of aluminum alloys in sports applications, ultimately benefiting athletes and manufacturers alike.

Removal of hexavalent chromium and pentavalent arsenic from aqueous solutions by adsorption on polyethylenimine-modified silica nanoparticles.

Chromium and arsenic are commonly found in water and wastewater as hexavalent chromium, Cr(VI), and inorganic arsenic species, such as pentavalent arsenic, As(V). In aqueous media, both Cr(VI) and As(V) exist predominantly in the form of oxy-anions. In our study, we prepared a polyethylenimine-silica composite material (SiO₂-PEI) as an adsorbent to study the adsorption capacity for chromate and arsenate ions. Polyethylenimine (PEI) can effectively bind negatively charged species through electrostatic interactions. The parameters that were evaluated, regarding the adsorption capacity were the effect of pH, the effect of the initial concentration of Cr(VI) and As(V), and the presence of other anions. Also, we examined the effect of Cr(VI) and As(V) on each other by studying the simultaneous removal of chromate and arsenate ions. Isotherm, kinetic, and thermodynamic analyses on the experimental data obtained were conducted. The results showed that the pH of the solution is affecting the charge density of PEI, and at pH 4, the lower value that was examined, the SiO₂-PEI exhibited higher adsorption capacity. The presence of other anions, such as phosphate, nitrate, and sulfate ions, had an adverse effect on the adsorption capacity of the SiO₂-PEI material for both chromate and arsenate ions. The adsorption capacity of arsenate was more affected by the presence of other anions compared to the chromate, and the higher impact was observed by the sulfate ions at pH 4, on the contrary for the chromate ions the higher impact was observed by the sulfate ions at pH 7 and by the phosphate ions at pH 4. Concerning the effect of temperature, the adsorption is an exothermic process and it was more favorable at lower environmental temperature. The study of simultaneous removal of Cr(VI) and As(V) declares the material's ability to accommodate both types of ions without requiring separate treatment steps. Addressing the simultaneous removal is essential for reducing the complexity of water treatment systems, lowering operational costs, and improving the safety of treated water.

Hexavalent Chromium Adsorption on Adsorbent Derived From Biomass of Fabaceae Plant in Vietnam: Effect of Preparation Conditions on Equilibrium Adsorption Capacity

Hexavalent Chromium Adsorption on Adsorbent Derived From Biomass of Fabaceae Plant in Vietnam: Effect of Preparation Conditions on Equilibrium Adsorption Capacity

Betaine-Modified Green Carbon Dot for Cr(VI) Sensing, in Vivo Cr(VI) Imaging, and Growth Promotion in the Rice Plant.

Hexavalent chromium is a toxic environmental pollutant that damages plants due to disruption of nutrient uptake, photosynthesis metabolism, and oxidative stress, which suppresses the growth and development of the plant. In this work, we have developed a betaine-modified carbon dot (BT@CD) sensor for monitoring Cr(VI) in water and plants. Fluorescent carbon dots have been synthesized using jamun juice (Syzygium cumini) as the carbon source subjected to surface modification with betaine (BT@JCD). This BT@JCD exhibits strong blue fluorescence, which significantly decreases in the presence of Cr(VI) due to the inner filter effect in a range of 5-450 nM with a detection limit of 0.033 μM. Due to its easy translocation in the vascular bundles, these fluorescence nanosensors can be applied to detect Cr(VI) in rice plants Oryza sativa) through fluorescence confocal imaging. The treatment of rice plants with BT@JCDs in the concentration range of 0.2 to 1g/mL not only triggered photophysical parameters such as carbohydrates, chlorophyll, and carotenoids but also enhanced the antioxidant enzyme activity promoting plant growth.

Green Clay Materials Applied in Packed Bed Columns for the Hexavalent Chromium Adsorption from Aqueous Solutions

Green Clay Materials Applied in Packed Bed Columns for the Hexavalent Chromium Adsorption from Aqueous Solutions

Synthesis of Ni–FeCeO2 by mechanochemical method for high-temperature water-gas shift reaction

Hydrocarbon fuels have caused significant environmental damage, leading to a search for renewable alternatives like hydrogen. The water-gas shift reaction (WGSR) is a key process in hydrogen production, especially in ammonia synthesis. Typically, WGSR occurs in two stages: low-temperature (LT-WGSR) at 180–250 °C and high-temperature (HT-WGSR) at 310–450 °C. Traditional HT-WGSR catalysts use Fe–Cr, but the presence of carcinogenic hexavalent chromium (Cr6+) poses environmental risks, necessitating safer alternatives. This study explores the replacement of chromium with aluminum (Al) and cerium (Ce) in Fe-based catalysts, synthesized via mechanochemical methods. Characterization revealed that Fe–Ce catalysts (85:15 ratio) exhibited superior thermal stability. Additionally, varying nickel (Ni) contents were tested to improve activity, with 10% Ni offering the best performance despite some methane by-products. The study also examined the impact of reduction and calcination temperatures, GHSV, and steam/gas ratios on the catalyst's efficiency.

Preparation and characterization of β-cyclodextrin capped magnetic nanoparticles anchored on cellulosic matrix for removal of cr(VI) from mimicked wastewater: Adsorption and kinetic studies

Hexavalent Chromium (Cr(VI)) is essential in many industrial processes. However, it finds its way into water bodies, posing health problems, including lung cancer and the inhibition of DNA and RNA in biological systems. Several chemical and traditional water purification methods have been developed in the past, but most are expensive, tedious and ineffective. This study aimed to prepare and characterize a low-cost hybrid adsorbent, β-Cyclodextrin capped magnetic nanoparticles anchored on a cellulosic matrix (CNC-Fe3O4NP-CD). The characterization techniques confirmed the integration of CNCs, Fe3O4NP and CD into the prepared CNC-Fe3O4NP-CD nanocomposite adsorbent. The adsorbent was employed in batch adsorption experiments by varying adsorption parameters, including solution pH, adsorbent dosage, initial Cr(VI) concentration, and contact time. From the findings, the nanocomposite adsorbent achieved a maximum Cr(VI) removal efficiency of 97.45%, while the pseudo-second-order kinetic model best fitted the experimental data with high linear regression coefficients (R2 > 0.98). The Elovich model indicated that the adsorption process was driven by chemisorption on heterogeneous surface sites, with initial sorption rates surpassing desorption rates. These findings established that CNC-Fe3O4NP-CD presents high efficiency for Cr(VI) removal under acidic pH, offering the potential for optimization and application in real-world wastewater treatment.

Modular hydrogel selectively adsorbs phosphates and hexavalent chromium while enabling phosphate recovery

Electroplating wastewater containing high concentrations of phosphates and hexavalent chromium Cr(VI) poses serious environmental pollution. Moreover, phosphorus, as a non-renewable resource, necessitates its recovery to meet sustainable development goals. To address this issue, this study used sodium alginate as the scaffold module, synthesized lanthanum carbonate in situ within a chitosan module to serve as the phosphate adsorption module, and employed polyethyleneimine (PEI) modules to enhance the adsorption capacity for Cr(VI), successfully fabricating a modular hydrogel (LC-CSP). LC-CSP exhibits a complex porous structure and surface morphology, forming an ultra-low-density fiber network with good strength and elasticity, ensuring uniform distribution and exposure of active sites. Under optimal conditions for single-component adsorption, LC-CSP achieved adsorption capacities of 232.02 mg/g for phosphates and 474.61 mg/g for Cr(VI). Additionally, LC-CSP demonstrated excellent reusability, retaining over 83 % of its performance after five cycles. In simulated electroplating wastewater experiments with various interfering substances, LC-CSP maintained high removal efficiencies (>90.72 %) for phosphates and Cr(VI). Post-experiment, enriched water after phosphate desorption was further treated to recover phosphorus resources in complex water environments. Multiple characterization techniques elucidated the adsorption mechanisms of LC-CSP: phosphate adsorption primarily involved ligand exchange, electrostatic interactions, and hydrogen bonding, while Cr(VI) adsorption included electrostatic interactions, hydrogen bonding, and reduction reactions. Finally, fixed-bed simulated wastewater adsorption experiments validated the technical potential of LC-CSP for practical electroplating wastewater management.

Highly efficient reduction of Cr(VI) from industries sewage using novel biomass-driven carbon dots modified TiO2 under sunlight

Hexavalent chromium (Cr(VI)) pollution poses a significant global environmental challenge, with current photocatalysts exhibiting limited efficiencies under natural sunlight, especially in neutral to alkaline conditions or at high Cr(VI) concentrations. In this study, amine-rich biomass-derived carbon dots (CDs) were synthesized from peanut shells and ethylenediamine via a hydrothermal method, combined with titanium dioxide (TiO2) to form a composite with a narrower band gap. This enhanced the electrostatic interactions with Cr(VI), thus improving photocatalytic performance. The composite (1 % CDs) effectively reduced 50 mg/L of Cr(VI) within 60 min under sunlight irradiation, demonstrating stable performance across various pH levels (3, 5, 7, and 9) and Cr(VI) concentrations (10 to 60 mg/L). Even after five cycles, the reduction efficiency remained high at 96.83 %. The composite also achieved reduction rates of 90.09 % and 89.01 % for domestic and electroplating wastewater, respectively, while exhibiting antibacterial properties. Free-radical scavenging experiments confirmed that electrons and holes were the primary active species driving the reduction. This work highlights the potential of the composites for efficient and stable Cr(VI) reduction in real-world water treatment applications.

Effectiveness of Musa Balbisiana bract toward chromium removal from industrial tannery effluent: optimization, kinetics, isotherms, regeneration, and cost estimation

Eradicating chromium from industrial effluent is essential for environmental security and economic reasons. This study investigates the potency of activated Musa balbisiana bract biomass as a biosorbent to remove hexavalent chromium (Cr6+) from real industrial tannery effluent (ITE). The characterization study exemplifies the existence of irregular structures and excessive cavities, and the occurrence of functional groups (hydroxyl, carboxyl, esters, and alkynes) are benefitting the deposition of Cr6+ on the biosorbent. A maximum biosorption capacity of 42.75 ± 0.21mg/g was observed at an optimum pH of 6.5, biosorbent dosage of 0.3g, initial Cr6+ concentration of 50mg/L, and contact time of 120min. The validation experiment confirmed the removal efficiency of total chromium, trivalent chromium, and Cr6+ 92.56 ± 0.80%, 98.63 ± 0.20%, and 96.21 ± 0.50%, respectively. Among the models, Langmuir isotherm (R2: 0.9992) and pseudo-second order (R2: 0.9999) kinetic models greatly correlate with the equilibrium data. A 2-tier membrane module was examined for continuous study and reached 88.23 ± 0.60% Cr6+ removal. Statistical analysis was performed to confirm the significance of adsorption results. The likelihood of the desorption and regeneration of the treated biosorbent was investigated. The estimated cost per volume of ITE treated and unit of pollutant removal from ITE employing Musa balbisiana bract biosorbent is around $3.08/m3 and $3.75/kg.

New insights into the remediation of chromium-contaminated industrial electroplating wastewater by an innovative nano-modified biochar derived from spent mushroom substrate: Mechanisms, batch study, stability and application

To enhance the adsorption and detoxification capabilities of hexavalent chromium (Cr(VI)) using agricultural spent mushroom substrate (SMS), this study pioneered the preparation of biochar (NBC) from Lentinus edodes spent substrate. Subsequently, nano iron sulfide (FeS) particles were integrated onto NBC with carboxymethyl cellulose (CMC) as a stabilizer, resulting in a novel composite biosorption material, nFeS-BC. The adsorption and reduction potential of both NBC and nFeS-BC against Cr(VI) were evaluated through batch experiments, which identified pH as a critical factor influencing adsorption efficiency. Remarkably, nFeS-BC exhibited a superior maximum adsorption capacity (qmax) of 99.57 mg g−1 and a reduction efficiency of 68.65%, outperforming NBC by 277.73% and 211.76% under optimized conditions, respectively. Characterization techniques including Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM-EDX), Fourier Transform Infrared Spectroscopy (FT-IR), and X-ray Photoelectron Spectroscopy (XPS) elucidated the removal mechanisms, predominantly attributed to ion exchange, electrostatic attraction, functional group interaction, and redox reaction. The carbon-oxygen functional groups and nano particles were crucial in the adsorption and reduction processes. Compared with NBC, the incorporation of FeS particles increased the specific surface area and pore volume of nFeS-BC by 130.86% and 183.77%, respectively. nFeS-BC owned a shelf-life of up to ∼3 months of use and exhibited excellent performance in the processing of actual electroplating wastewater with q of 16.71 mg g−1 under 0.1 g L−1 dosage. These findings underscore the potential of nFeS-BC as an efficient material for Cr(VI) removal, presenting a novel adsorbent for the sustainable detoxification of contaminated water resources and the potential for using agricultural waste materials in environmental remediation.

Performance evaluation on the chemical looping combustion of the chromium-containing leather waste and the fate of chromium using thermodynamic analysis

Leather waste (LW) consistently contains a high content of chromium (Cr), which significantly limits its utilization due to the toxicity of hexavalent chromium formed through oxidation. To prevent this oxidation, chemical looping combustion (CLC) is employed to dispose of the chromium-rich LW. First, the gaseous and solid pollutants generated during air combustion and CLC are compared when LW is used as fuel. The results indicate that CLC is an effective way to significantly decrease the oxidation of chromium (Cr(VI)/Crtotal) at typical operating temperatures. Subsequently, various operating parameters, namely the equivalence ratio of oxygen carrier to leather waste (αOC/LW), the equivalence ratio of steam to leather waste (αS/LW), and air reactor (AR) temperature, are changed to investigate their effects on the CLC combustion and pollutant behaviors. The findings reveal that no chromium is oxidized in the fuel reactor. The oxidation in AR is associated with the presence of Na in the AR, which can react with chromium to form Na2CrO4. Increasing αOC/LW from 0.8 to 1.2 reduces the oxidation of chromium in the AR from 11.68% to 1.76%, while increasing αS/LW from 0.2 to 1.6 has the opposite effect, improving the oxidation of chromium in the AR from 3.16% to 5.18%.

Dual fillers ZrO2/BaTiO3 incorporated PVDF-HFP nanofiber composite for enhanced piezoelectric energy harvesting and piezo catalytic reduction of hexavalent chromium

A novel Piezoelectric Nanogenerator (PENG) was designed and fabricated using electrospun nanocomposite fibers of Poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP) with Barium Titanate (BaTiO3) and Zirconium Oxide (ZrO2) as dual fillers. ZrO2 fillers were incorporated at varying loadings into the PVDF-HFP polymer matrix to produce the PBZ nanocomposite fibers. The synergistic effect of BaTiO3 and ZrO2 significantly enhanced the piezoelectric performance of the resulting PBZ composite. The dual fillers also induced the nucleation of the β-phase in the nanofiber composite, which further improved its piezoelectric properties. This enhancement rendered the composite highly effective for dual applications: energy harvesting and the piezocatalytic reduction of hexavalent chromium (Cr(VI)). The PENG exhibited an open-circuit voltage of 6.3 V, a current of 0.67 µA, and a power density of 30.91 mW/m². The device was also tested in real-world scenarios, such as finger tapping and shoe sole applications, additionally it successfully powered up to five LEDs and charged a 1–2.2 μF capacitor to approximately 1–3 V under an external load of 1 N at 2 Hz. In addition to energy harvesting, the PBZ nanofibers demonstrated remarkable piezocatalytic activity by converting highly toxic Cr(VI) to Cr(III), which is biologically essential in trace amounts. The PBZ nanofiber mats achieved an impressive Cr(VI) reduction rate of up to 90.1 % under acidic conditions within 20 minutes and were recyclable for up to five cycles without loss of efficiency. Furthermore, Density Functional Theory (DFT) calculations, focusing on the Density of States (DOS), were performed to elucidate the underlying mechanisms contributing to the observed improvements in piezoelectric and piezocatalytic performance.

Advanced functional carbon electrode for ultra-sensitive detection of hexavalent chromium in water: Performance, mechanism, and application

Accurate and rapid detection of trace Cr(VI) in water is essential for environmental pollution control and human health protection. In this study, we developed a novel electrochemical sensor co-modified with polyaniline-functionalized Fe3O4 nanoparticles and a Ce-based metal–organic framework (Ce-MOF). The unique interface morphology and outstanding electrocatalytic properties of the modified electrode enabled ultra-sensitive detection of Cr(VI), with excellent linearity in the range of 1 to 1000 μg/L and a limit of detection (LOD) of 0.05 μg/L. Combined with DFT and XPS analysis, the catalytic mechanism of the Ce and Fe bimetals for Cr(VI) detection was deeply investigated. The Cr d-orbitals are hybridized with Fe d-orbitals and O p-orbitals around −5.0 eV, indicating strong electronic coupling between Cr atoms and Fe/O atoms is achieved based on the optimized model structure (Fe3O4/Ce-MOF/Cr). Additionally, Ce facilitated the valence cycling of Fe, promoting Fe2+ generation and enhancing electron donation, which in turn improved the reduction of Cr(VI). Significantly, we firstly integrated this composite with laser-induced graphene technology to create flexible integrated electrodes that meet practical requirements, breaking through the previous limitations of poor portability and expanding application scenarios. This study provides new insights for accurate, efficient, and portable on-site detection of Cr(VI) in water environments.

Ferritinophagy is involved in hexavalent chromium-induced ferroptosis in Sertoli cells

Hexavalent chromium [Cr(VI)] has significant adverse effects on the environment and human health, particularly on the male reproductive system. Previously, we observed ferroptosis and autophagy in rat testicular injury induced by Cr(VI). In the present study, we focused on the association between ferroptosis and autophagy in mouse Sertoli cells (TM4) exposed to concentrations of 2.5 μМ, 5 μМ, and 10 μМ Cr(VI). Cr(VI) exposure altered mitochondrial ultrastructure; increased intracellular iron, malondialdehyde, and reactive oxygen species (ROS) levels; decreased glutathione content; increased TfR1 protein expression; and decreased GPX4, FPN1, and SLC7A11 protein expression, ultimately resulting in ferroptosis. Additionally, we observed ferritinophagy, increased expression of BECLIN1, LC3B, and NCOA4, and decreased expression of FTH1 and P62. Inhibition of autophagy and ferritinophagy via 3-MA and small interfering RNA (siRNA)-mediated silencing of NCOA4 ameliorated changes in ferritinophagy- and ferroptosis-associated protein expression, and reduced ROS levels. Rats exposed to Cr(VI) exhibited atrophy of testicular seminiferous tubules, a reduction in germ and Sertoli cells, and the occurrence of ferritinophagy and ferroptosis in cells of the rat testes. These results indicate that ferroptosis, triggered by NCOA4-mediated ferritinophagy, is one of the mechanisms that contribute to Cr(VI)-induced damage in Sertoli cells.

Adsorption Performance for Chromium(VI) of a UiO-66-Ce Metal–Organic Framework Built by DL-Aspartic Acid

Metal–organic frameworks (MOFs) have recently received a lot of interest for their use in adsorbing and eliminating hexavalent chromium from water. Obtaining low-cost, biocompatible, and environmentally friendly MOFs for research in this field is vital. One very stable three-dimensional UiO-66-Ce(IV) MOF, Ce-asp, was synthesized with a high yield using an amino acid ligand, DL-aspartic acid. As a result, the adsorption characteristics of the MOF against hexavalent chromium ions in aqueous solution were examined. The effects of time, solution pH, MOF dose, and beginning chromium(VI) content in aqueous solution were investigated on adsorption. More crucially, the adsorption mechanism of this MOF for chromium(VI) was proposed, setting the groundwork for its future use in chromium(VI) removal in real-world waters.

Modulation of the Microstructure and Enhancement of the Photocatalytic Performance of g-C3N4 by Thermal Exfoliation

This work explores the impact of reaction temperature during thermal exfoliation treatment of bulk-g-C3N4 in the air atmosphere on the structure and performance of the resulting CN photocatalyst. The analysis conducted using XRD, FT-IR, XPS, SEM, and elements mapping tests, illustrated an increase in nitrogen-vacancy and oxygen content on the surface of the CN photocatalyst, resulting in a porous and sparse structure, changes in crystal size, and improved visible light absorption performance. The photocatalytic reduction experiments of hexavalent chromium (Cr(VI)) showed that the CN-540 showed the highest reduction rate of 96.9%, with a reaction rate constant 6.21 times that of bulk-g-C3N4. After 100 min of illumination, the photocatalytic degradation rates of CN-540 for TC-HCl and RhB were 66.7% and 60.6%, respectively. The TOC test results indicated mineralization rates of 51.5% for TC-HCl and 46.6% for RhB. Room temperature fluorescence spectroscopy (PL), transient photocurrent response (TPC), and electrochemical impedance spectroscopy (EIS) measurements confirmed the excellent photogenerated charge carrier separation and transport efficiency of CN-540. The photocatalytic mechanism for reducing Cr(VI) by CN-540 was elucidated based on the active species •OH and •O2– and Mott-Schottky (M-S) tests. This study provides experimental data for optimizing the photocatalytic performance of g-C3N4 and paves a new way for developing efficient photocatalysts. Copyright © 2024 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Carcinogenic Mechanisms of Hexavalent Chromium: From DNA Breaks to Chromosome Instability and Neoplastic Transformation.

Hexavalent chromium [Cr(VI)] is a well-established human carcinogen, yet the mechanisms by which it leads to carcinogenic outcomes is still unclear. As a driving factor in its carcinogenic mechanism, Cr(VI) causes DNA double strand breaks and break-repair deficiency, leading to the development of chromosome instability. Therefore, the aim of this review is to discuss studies assessing Cr(VI)-induced DNA double strand breaks, chromosome damage and instability, and neoplastic transformation including cell culture, experimental animal, human pathology and epidemiology studies. Recent findings confirm Cr(VI) induces DNA double strand breaks, chromosome instability and neoplastic transformation in exposed cells, animals and humans, emphasizing these outcomes as key steps in the mechanism of Cr(VI) carcinogenesis. Moreover, recent findings suggest chromosome instability is a key phenotype in Cr(VI)-neoplastically transformed clones and is an inheritable and persistent phenotype in exposed cells, once more suggesting chromosome instability as central in the carcinogenic mechanism. Although limited, some studies have demonstrated DNA damage and epigenetic modulation are also key outcomes in biopsies from chromate workers that developed lung cancer. Additionally, we also summarized new studies showing Cr(VI) causes genotoxic and clastogenic effects in cells from wildlife, such as sea turtles, whales, and alligators. Overall, across the literature, it is clear that Cr(VI) causes neoplastic transformation and lung cancer. Many studies measured Cr(VI)-induced increases in DNA double strand breaks, the most lethal type of breaks clearly showing that Cr(VI) is genotoxic. Unrepaired or inaccurately repaired breaks lead to the development of chromosome instability, which is a common phenotype in Cr(VI) exposed cells, animals, and humans. Indeed, many studies show Cr(VI) induces both structural and numerical chromosome instability. Overall, the large body of literature strongly supports the conclusion that Cr(VI) causes DNA double strand breaks, inhibits DNA repair and chromosome instability, which are key to the development of Cr(VI)-induced cell transformation.