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Funding Information: This project received funding from the COST Action CA18218 European Burden of Disease Network, supporting the first author with a Short-Term Scientific Mission to the National Food Institute, Technical University of Denmark, with the aim of improving knowledge and applying the appropriate methodology on burden of disease on this project.The authors would like to thank the researchers from the Research Group for Risk Benefit from the National Food Institute, Technical University of Denmark for raising questions to improve the robustness of the research project, as well as the COST Action CA18218 European Burden of Disease Network for funding and supporting the project, and to the researchers Carla Martins from NOVA National School of Public Health and Ricardo Assunção from Egas Moniz Cooperativa de Ensino Superior for contributing to the initial brainstorming on the disease pathology. Publisher Copyright: © 2023 The Authors Background: Exposure to hexavalent chromium [Cr(VI)] occurs widely in occupational settings across the EU and is associated with lung cancer. In 2025, the occupational exposure limit is set to change to 5 μg/m3. Current exposure limits are higher, with 10 μg/m3 as a general limit and 25 μg/m3 for the welding industry. We aimed to assess the current burden of lung cancer caused by occupational exposure to Cr(VI) and to evaluate the impact of the recently established EU regulation by analysing different occupational exposure limits. Methods: Data were extracted from the literature, the Global Burden of Disease 2019) study, and Eurostat. We estimated the cases of cancer attributable to workplace exposure to Cr(VI) by combining exposure-effect relationships with exposure data, and calculated related DALYs and health costs in scenarios with different occupational exposure limits. Results: With current EU regulations, 253 cases (95%UI 250.96–255.71) of lung cancer were estimated to be caused by Cr(VI) in 2019, resulting in 4684 DALYs (95%UI 4683.57–4704.08). In case the welding industry adopted 10 μg/m3, a decrease of 43 cases and 797 DALYs from current values is expected. The predicted application of a 5 μg/m3 limit would cause a decrease of 148 cases and 2746 DALYs. Current costs are estimated to amount to 12.47 million euros/year (95%UI 10.19–453.82), corresponding to 39.97 million euros (95%UI 22.75–70.10) when considering costs per DALY. The limits implemented in 2025 would lead to a decrease of 23.35 million euros when considering DALYs, with benefits of introducing a limit value occurring after many decades. Adopting a 1 μg/m3 limit would lower costs to 1.04 million euros (95%UI 0.85–37.67) and to 3.33 million euros for DALYs (95%UI 1.89–5.84). Discussion: Assessing different scenarios with different Cr(VI) occupational exposure limits allowed to understand the impact of EU regulatory actions. These findings make a strong case for adapting even stricter exposure limits to protect workers’ health and avoid associated costs. publishersversion published

The article is devoted to the neutralization of the harmful effects of aluminochrome catalyst sludge. Catalyst sludge is a waste product from petrochemical production and poses a serious threat to the environment and humans because of the toxic hexavalent chromium it contains. The emissions of Russian petrochemical enterprises’ alumochrome sludge is 10,000–12,000 tons per year. In this paper, research related to the possibility of reducing the harmful effects of sludge by converting hexavalent chromium to a less dangerous trivalent state is presented. The reduction of hexavalent chromium was carried out with different reagents: Na2SO3, FeSO4, Na2S2O3, and Na2S2O5. Then, a comparative analysis was carried out, and sodium metabisulfite was chosen as the most preferred reagent. The peculiarity of the reducing method was carrying out the reaction in a neutral medium, pH = 7.0. The reduction was carried out in the temperature range of 60–85 °C and under standard conditions. The maximum recovery efficiency of chromium from the catalyst sludge (100%) was achieved at 85 °C and 10 min. This method did not involve the use of concentrated sulfuric acid, as in a number of common techniques, or additional reagents for the precipitation of chromium in the form of hydroxide.

Biochar adsorption has emerged as a favorable and environmentally friendly approach for removing metals such as chromium (Cr) from wastewater. However, the use of pristine biochar (PBC) is limited due to its finite adsorptive capacity, selectivity, and potential for secondary pollution. In this study, a novel bifunctionalized magnetic biochar (BMBC) was fabricated by incorporating cystamine as a ligand and glutaraldehyde as a crosslinker into alkali-treated magnetic biochar (MBC). This chemical modification introduced numerous amino groups and disulfide bonds onto the surfaces of BMBC. The biochar adsorbents’ surface morphologies, crystal structures, and texture properties were characterized using SEM, XRD, and N2 adsorption-desorption techniques. The specific surface area was determined using the BET method. Furthermore, the surface functional groups and elemental compositions before and after adsorption were analyzed using FTIR and XPS, respectively. The results demonstrated higher Cr(VI) removal efficacy of BMBC (100%) than MBC (72.37%) and PBC (61.42%). Optimal conditions for Cr(VI) removal were observed at a solution pH of 2, a temperature of 50 °C, a reaction time of around 1440 min, and an initial adsorbate concentration of 300 mg/L. The sorption process followed a chemical mechanism and was controlled by monolayer adsorption, with a maximum adsorption capacity of 66.10 mg/g at 50 °C and a pH of 2, as indicated by the larger fitting values of the pseudo–second-order and Langmuir models. The positive ∆Ho and ∆So values and negative ∆G0 values suggested a spontaneous and endothermic Cr(VI) adsorption process with high randomness at the solid/liquid interface. The removal of Cr(VI) was attributed to the reduction of Cr(VI) into Cr(III) facilitated by the introduced amino acids, sulfur, and Fe(II), electrostatic interaction between Cr(VI) in the solution and positive charges on the adsorbent surface, and complexation with functional groups. The presence of co-existing cations such as Cu(II), Cd(II), Mn(II), and K(I) had little effect on Cr(VI) removal efficiency. At the same time, the co-existence of anions of Cl−, NO3−, SO42−, and HPO42− resulted in a 7.58% decrease in the Cr(VI) removal rate. After five consecutive adsorption/desorption cycles, BMBC maintained a high Cr(VI) removal rate of 61.12%. Overall, this novel BMBC derived from rice straw shows great promise as a biosorbent for treating Cr(VI) in wastewater.

Environmental and occupational exposure to hexavalent chromium, Cr(VI), causes female reproductive failures and infertility. Cr(VI) is used in more than 50 industries and is a group A carcinogen, mutagenic and teratogenic, and a male and female reproductive toxicant. Our previous findings indicate that Cr(VI) causes follicular atresia, trophoblast cell apoptosis, and mitochondrial dysfunction in metaphase II (MII) oocytes. However, the integrated molecular mechanism of Cr(VI)-induced oocyte defects is not understood. The current study investigates the mechanism of Cr(VI) in causing meiotic disruption of MII oocytes, leading to oocyte incompetence in superovulated rats. Postnatal day (PND) 22 rats were treated with potassium dichromate (1 and 5 ppm) in drinking water from PND 22–29 and superovulated. MII oocytes were analyzed by immunofluorescence, and images were captured by confocal microscopy and quantified by Image-Pro Plus software, Version 10.0.5. Our data showed that Cr(VI) increased microtubule misalignment (~9 fold), led to missegregation of chromosomes and bulged and folded actin caps, increased oxidative DNA (~3 fold) and protein (~9–12 fold) damage, and increased DNA double-strand breaks (~5–10 fold) and DNA repair protein RAD51 (~3–6 fold). Cr(VI) also induced incomplete cytokinesis and delayed polar body extrusion. Our study indicates that exposure to environmentally relevant doses of Cr(VI) caused severe DNA damage, distorted oocyte cytoskeletal proteins, and caused oxidative DNA and protein damage, resulting in developmental arrest in MII oocytes.

Conversion of hexavalent chromium (Cr(VI)) to trivalent chromium (Cr(III)) is an effective way to reduce its environmental risk, especially via photoreduction process. However, over a wide range of pH values, it is still a great challenge to achieve a high removal rate, and the disposal of produced Cr(III) should be concerned. In this work, we implemented a high removal rate at 98% for Cr(VI) and total chromium (Cr(T)) over a wide pH range (4–10) through the synergistic effect of adsorption, photoreduction and immobilization on the surface of BiOBr0.25I0.75. The substitution of bromine by iodine reduced the adsorption energy of Cr(VI) on BiOBr0.25I0.75, promoting the adsorption of Cr(VI). Meanwhile, the introduced iodine upshifted the conduction band (CB), enhancing the reduction ability for Cr(VI) to Cr(III). The negative surface of BiOBr0.25I0.75 can capture Cr(III), achieving a high removal rate for Cr(T). The pH-independent feature for Cr(VI) and Cr(III) removal make BiOBr0.25I0.75 a potential material for chromium-containing wastewater treatment. This work provides an effective strategy for removing chromium over a wide pH range.

A novel Cr (VI) removal material was designed and produced comprising multi-walled carbon nanotubes (MWCNTs) as a support with a high specific surface area and the loaded Fe–Ni bimetallic particles as catalytic reducing agents. Such a design permits the composite particle to perform the adsorption, reduction, and immobilisation of Cr (VI) quickly and efficiently. Due to MWCNTs’ physical adsorption, Cr (VI) in solution aggregates in the vicinity of the composite, and Fe rapidly reduces Cr (VI) to Cr (III) catalysed by Ni. The results demonstrated that the Fe–Ni/MWCNTs exhibits an adsorption capacity of 207 mg/g at pH = 6.4 for Cr (VI) and 256 mg/g at pH 4.8, which is about twice those reported for other materials under similar conditions. The formed Cr (III) is solidified to the surface by MWCNTs and remains stable for several months without secondary contamination. The reusability of the composites was proven by retaining at least 90% of the adsorption capacity for five instances of reutilization. Considering the facile synthesis process, low cost of raw material, and reusability of the formed Fe–Ni/MWCNTs, this work shows great potential for industrialisation.

Iron-modified biochar adsorbent shows its promise for removing Cr(VI) from water. However, the traditional dry-grinding modification methods to prepare iron-modified biochar (DFeBC) usually result in the aggregation of iron oxide particles, thus impeding the adsorption capacity. Herein, blue-green algae waste derived biochar modified in a wet process by K2FeO4 (WFeBC) was developed, and it showed well-distributed iron oxide on the surface of the biochar. As a result, WFeBC displayed a larger theoretical adsorption capacity of 66.22 mg/g than that of DFeBC (48.54 mg/g). It was found that the uniform-distributed iron oxide and abundant oxygen functional groups of WFeBC played an important role in the removal process of Cr(VI). In the adsorption process, the reduction of Cr(VI) to Cr(III) by Fe(II) promoted the removal of hexavalent chromium. The Cr(VI) will be attracted by protonated oxygen functional groups through electrostatic interaction and complexation in an acid environment. All the results show that the wet modification of biochar by K2FeO4 can effectively improve the removal ability of WFeBC to Cr(VI).

Photoelectrochemical (PEC) sensors show great potential for the detection of heavy metal ions because of their low background noise, high sensitivity, and ease of integration. However, the detection limit is relatively high for hexavalent chromium (Cr(VI)) monitoring in addition to the requirement of an external bias. Herein, a CuO film is readily synthesized as the photoactive material via reactive sputtering and thermal annealing in the construction of a PEC sensing photocathode for Cr(VI) monitoring. A different mechanism (i.e., Signal-Weakening PEC sensing) is confirmed by examining the electrochemical impedance and photocurrent response of different CuO film photoelectrodes prepared with the same conditions in contact with various solutions containing concentration-varying Cr(VI) for different durations. The detection of Cr(VI) is successfully achieved with the Signal-Weakening PEC response; a drop of photocathode signal with an increasing Cr(VI) concentration from the steric hindrance effect of the in situ formed Cr(OH)3 precipitates. The photocurrent of the optimized CuO film photocathode linearly declines as the concentration of Cr(VI) increases from 0.08 to 20 µM, with a detection limit down to 2.8 nM (Signal/Noise = 3) and a fitted sensitivity of 4.22 µA·μM−1. Moreover, this proposed sensing route shows operation simplicity, satisfactory selectivity, and reproducibility.

The rapid progress of modern industry not only brings convenience to people’s lives, but also brings negative effects. Industrial development produces a large amount of waste metal, which brings harm to the environment and human health. Carbon nitride (g-C3N4) was successfully prepared using the thermal-polymerization method and petal-like g-C3N4 (CA-g-C3N4) was impregnated with citric acid (CA). Compared with g-C3N4, CA-g-C3N4 showed extremely high photocatalytic activity because the petal-like g-C3N4 (CA-g-C3N4) had a larger specific surface area, which increased the active sites on the surface of the photocatalyst and improved the photocatalytic activity. After citric acid treatment, the removal of hexavalent chromium (Cr(VI)) by g-C3N4 increased from 48% to 93%. The photocatalytic materials were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) and UV-vis diffuse reflectance spectra (UV-vis). In summary, this study confirmed that citric acid can improve the photocatalytic activity of g-C3N4 by increasing its specific surface area and the active site of the photocatalytic material so as to achieve the purpose of removing hexavalent chromium from water.

Iron species can act as electron donors, electron acceptors or serve as a sorbent to co-precipitate contaminants. These properties, along with its relatively low cost as a material, make iron an ideal compound for environmental applications in the removal of pollutants from water and wastewater. This study assesses the use of metallic iron as a reductant for the removal of toxic Cr(VI) from aqueous solutions, as well as the use of hexavalent iron (ferrates) for the removal of organic compounds, turbidity and biological contaminants from water and wastewater. Laboratory-scale experiments show that the Cr(VI) removal efficiency of metallic iron filling materials, such as scrap iron fillings, via reduction to Cr(III) and the subsequent precipitation/filtration of aggregates can reach values over 99.0%. Moreover, the efficiency of ferrates, in situ synthesized via a low-cost Fe0/Fe0 electrochemical cell, in the removal of organic compounds, turbidity and biological contaminants from high-strength industrial wastewater, biologically treated wastewater and natural water can also reach values over 99.0%. The results showed that iron species can be applied in low-cost and environmentally friendly technologies for natural water remediation and wastewater treatment. Furthermore, the study showed that the challenge of an iron material’s surface passivation, as well as of ferrates’ procurement cost and stability, can be resolved via the application of ultrasounds and via in situ ferrate electrosynthesis.

Due to its excellent textural features, non-toxicity, low cost and high uptake capacity, biochar has been synthesized from various biomasses and utilized as a biosorbent to remove hexavalent chromium (Cr6+) from contaminated water. Herein, activated eucalyptus biochar (AEB) was prepared via a pyrolysis-chemical activation process and then used as a less expensive biosorbent to adsorb Cr6+ ions from an aqueous solution. Proximate, ultimate, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) analyses were employed in appraising the biosorbent characteristics. Furthermore, response surface methodology (RSM) and adaptive neuro-fuzzy inference system (ANFIS) were applied to establish the best operating conditions. Based on the results obtained, there was little discrepancy between the observed data and the data predicted by RSM and ANFIS approaches. In terms of prediction accuracy, ANFIS (MAE = 2.512 andR2=0.9200) was superior to RSM (MAE = 2.512 andR2=0.9002). Under best-optimized conditions (initial Cr6+ concentration = 38.14 mg/L, biosorbent dosage = 1.33 g/L and pH = 4.35), which were offered by the ANFIS–ACO technique, the maximum percentage removal of 99.92±0.18% was achieved. The AEB performed exceptionally well due to its better textural characteristics, well-developed porous framework, and dominance of active surface functional groups, which were confirmed by BET, SEM, and FTIR analyses. The comparison of RSM, ACO and GA for process parameter optimization has not been reported in the open literature for Cr6+ adsorption by AEB and hence has been shown in this study.

Funding Information: The recently completed EU human biomonitoring initiative (HBM4EU, www.hbm4eu.eu/about-hbm4eu/), was a European Joint Programme that aimed to harmonise the collection and use of biomonitoring data to better understand human exposure to chemicals in the environment, in occupational settings and through the use of consumer products to improve chemical risk assessment and management efforts, and to support policy making (Ganzleben et al., 2017). Within the context of the HBM4EU project several priority substances were selected for investigation based on the most important needs of policy makers and risk assessors, as well as common needs of participating countries and a broad range of other stakeholders including trade unions (Ougier et al., 2021). Many of the priority substances, along with having an important economic role, also pose health risks for workers due to their occupational use. One of the priority substances was hexavalent chromium (Cr(VI)), which was the main focus of the first of a series of three different HBM4EU occupational studies (Santonen et al. 2019a, 2022), the other two being focussed on electronic waste (E-waste) and diisocyanates exposures (Jones et al., 2022; Scheepers et al., 2021). In addition to Cr(VI), it was recognised that in chrome plating activities there may also be exposure to another group of HBM4EU priority chemicals, per- and polyfluoroalkyl substances (PFASs). PFASs, including PFOS (perfluorooctane sulfonate), have been used as mist suppressants in chrome plating baths to prevent the evaporation of Cr(VI) vapours (Blepp et al., 2017; Gluge et al., 2020). Although PFOS has now been largely replaced in the EU, many of its substitutes in chrome plating activities are also PFASs which may cause similar health and environmental concerns.Occupational exposure to Cr(VI) has been associated with an increased risk of lung and sinonasal cancers and is suspected to lead to gastrointestinal tract cancers (den Braver-Sewradj et al., 2021; ECHA 2013; IARC 2012). In addition, it is a common cause of occupational asthma, allergic dermatitis and there is a concern for adverse effects on reproductive health (Sun and Costa 2022). Exposure to Cr(VI) may occur in several occupational activities, e.g., in welding, Cr(VI) electroplating and other surface treatment processes such as paint application and removal of old paint containing Cr(VI) (SCOEL 2017). In order to limit the workers’ exposure to Cr(VI) in the EU, Cr(VI) is currently regulated under both the European regulation (EC 1907/2006) on the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) and the EU Directive 2004/37/EC on the protection of workers from the risks related to exposure to carcinogens, mutagens or reprotoxic substances at work (CMRD) (EU 2004). The current binding Occupational Exposure Limit (OEL) set under the EU Directive 2004/37/EC is 10 μg/m3 (8-h time-weighted average (8-h TWA)) until January 17, 2025. After that period, the OEL (8-h TWA) will be reduced to 5 μg/m3. For welding, plasma-cutting processes and similar work processes that generate fumes, there is a derogation with an OEL of 25 μg/m³ (8-h TWA) until January 2025; after that date the OEL (8-h TWA) of 5 μg/m3 will be applicable. France, the Netherlands and Denmark already have stricter limits, with an OEL of 1 μg/m3 (8-h TWA) for Cr(VI) in all uses (Beskæftigelsesministeriet 2020; Ministère du travail, 2012; MinSZW 2016). In the US, the American Conference of Governmental Industrial Hygienists (ACGIH) has published, for inhalable Cr(VI) compounds, a threshold limit value (TLV) of 0.2 μg/m3 (8-h TWA) and a TLV Short-Term Exposure Limit (STEL) of 0.5 μg/m3 (ACGIH 2021). No EU-wide biological limit values (BLVs) for Cr(VI) are available, however some Member States have set BLVs for occupational exposure to Cr(VI), measured as urinary chromium (U–Cr). For example, France and Finland have derived BLVs of 2.5 μg/L and 10 μg/L corresponding to their respective OELs of 1 μg/m3 and 5 μg/m3 for Cr(VI) (ANSES 2017; STM 2020). The German Research Foundation (DFG 2020) has established biological exposure equivalents for carcinogenic substances (EKA values), ranging from 12 to 40 μg/L for U–Cr. These correspond to exposures ranging between 30 and 100 μg/m3 soluble alkaline chromate and/or Cr(VI) containing welding fumes over an 8-h work shift (Bolt and Lewalter 2012). Since these current national BLVs are mainly based on studies from plating workers, they include uncertainties especially concerning their applicability to workplaces other than the electroplating industry. One of the main aims of the HBM4EU chromates study was to provide EU relevant data on the current occupational Cr(VI) exposure to support the regulatory risk assessment and decision-making process. In addition, exposure to PFASs was evaluated in a subset of workers performing chrome plating activities.This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 733032 and received co-funding from the author's organizations and/or Ministries. The project team would like to thank all the companies and workers who participated in the HBM4EU chromates study and all the experts who have contributed to the conduct of the study. Participants of the HBM4EU chromates study workshop and policy questionnaires are also acknowledged. Mr. Jouko Remes and Dr. Kia Gluschkoff (Finnish Institute of Occupational Health) are acknowledged for their assistance with the statistical analyses and figures. Funding Information: This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 733032 and received co-funding from the author's organizations and/or Ministries. Publisher Copyright: © 2022 The Authors Within the EU human biomonitoring initiative (HBM4EU), a targeted, multi-national study on occupational exposure to hexavalent chromium (Cr(VI)) was performed. Cr(VI) is currently regulated in EU under REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) and under occupational safety and health (OSH) legislation. It has recently been subject to regulatory actions to improve its risk management in European workplaces. Analysis of the data obtained within the HBM4EU chromates study provides support both for the implementation of these regulatory actions and for national enforcement programs and may also contribute to the updating of occupational limit values (OELs) and biological limit values for Cr(VI). It also provides useful insights on the contribution of different risk management measures (RMMs) to further reduce the exposure to Cr(VI) and may support the evaluation of applications for authorisation under REACH. Findings on chrome platers’ additional per- and polyfluoroalkyl substances (PFAS) exposure highlight the need to also pay attention to this substance group in the metals sector. A survey performed to evaluate the policy relevance of the HBM4EU chromates study findings supports the usefulness of the study results. According to the responses received from the survey, the HBM4EU chromates study was able to demonstrate the added value of the human biomonitoring (HBM) approach in assessment and management of occupational exposure to Cr(VI). For future occupational studies, we emphasise the need for engagement of policy makers and regulators throughout the whole research process to ensure awareness, relevance and uptake of the results in future policies. publishersversion published

Electrocatalytic reduction of Cr(VI) to less toxic Cr(III) is deemed as a promising technique. Conventional electrocatalytic reduction is always driven by a constant cathodic potential, which exhibits a repelling action to Cr(VI) oxyanions in wastewater and consequently suppresses reduction kinetics. In order to remarkably accelerate Cr(VI) electrocatalytic reduction, we applied a pulsed potential on an Fe2+-NiFe LDH/NF electrode synthesized by in situ growth of Fe2+-doped NiFe LDH nanosheets on Ni foam using a spontaneous redox reaction. Under anodic potential section, HCrO4– anions are adsorbed on the electrode surface and reduced to Cr(III) by Fe2+. Then, Cr(III) ions are desorbed from the electrode surface under coulombic force. The regeneration of Fe2+ and direct reduction of Cr(VI) are achieved under cathodic potential section. The pulsed potential can achieve complete elimination of Cr(VI) within 60 min at an initial concentration of 10 mg L−1, and the removal efficiency shows a 60% increase with respect to that under constant cathodic potential.

All-solid-state Z-scheme photocatalysts, containing Cu2O, TiO2 (rutile), and Au as the electron mediator, were prepared and applied to the reduction of Cr(VI) in aqueous solutions. The Cu2O–Au–TiO2 composites were prepared by loading Au core–Cu2O shell hemisphere particles on TiO2 (rutile) nanorods using a two-step photocatalytic deposition process. Under ultraviolet–visible (UV–vis) light illumination, the Cu2O–Au–TiO2 composites exhibited higher photocatalytic Cr(VI) reduction activities than those exhibited by single TiO2 (rutile) and Cu2O. In this reaction, a precipitate containing Cr, which was considered to be Cr(OH)3, was deposited site-selectively on the Au core–Cu2O shell particles of the composites, indicating that the reduction site of the composite was Cu2O, and the reaction proceeded according to the Z-scheme. The Cu2O–Au–TiO2 composites also exhibited photocatalytic activity under visible light illumination. The oxidation state of Cu in the Cu2O–Au–TiO2 composite gradually changed from Cu(I) to Cu(II) during the photocatalytic Cr(VI) reduction. However the composite maintained its high photocatalytic performance even after oxidation. The role of Au in the Cu2O–Au–TiO2 composite was examined by comparing the properties of the Cu2O–Au–TiO2 composite with those of the Cu2O–TiO2 composite prepared via direct Cu2O deposition on TiO2.

Nowadays, the scientific interest is focused more and more on the development of new strategies in recycling of waste products as well as on the development of clean technologies due to the increased environmental pollution. In this work we studied the valorization of an expired cheese-tomato flavor corn snack, which is polysaccharide food product, by producing advanced hybrid magnetic materials for environmental remediation purposes. The carbonization-chemical activation of this snack using potassium hydroxide leads to a microporous activated carbon with high surface area (SgBET ~800 m2/g). The magnetic hybrid material was synthesized via an in-situ technique using iron acetate complex as the precursor to produce iron based magnetic nanoparticles. The resulting material retains a fraction of the microporous structure with surface area SgBET ~500 m2/g. Such material consists, of homogenously dispersed magnetic isolated zero valent iron nanoparticles and of iron carbides (Fe3C), into the carbon matrix. The magnetic carbon exhibited high adsorption capacity in Cr(VI) removal applications following a pseudosecond order kinetic model. The maximum adsorption capacity was 88.382 mgCr(VI)/gAC at pH = 3. Finally, oxidation experiments, in combination with FT-IR, Mössbauer, and VSM measurements indicated that the possible Cr6+ removal mechanism involves oxidation of iron phases and reduction of Cr6+ to Cr3+.

Piezocatalysis, driven by mechanical energy and piezoelectric effect, is of great potential in addressing the environmental issues. In this work, a piezoelectric catalyst was fabricated by growing few-layer MoS2 nanosheets onto CuS, for the piezocatalytic degradation of Rhodamine B (RhB), methylene blue (MB) and hexavalent chromium (Cr (VI)). The excellent removal efficiency of Cr (VI) and RhB can be reached 100% within 180 s, through the piezocatalysis of CuS/MoS2-0.6 driven by mechanical stirring in the dark. Impressively, the piezoelectric current of CuS/MoS2-0.6 is 48 and 35.7 times higher than that of pure CuS and MoS2, respectively. The significantly enhanced piezocatalytic performance can be ascribed to the formation of CuS/MoS2 heterojunction and the piezoelectric field generated by MoS2 nanosheets, which promotes the efficient separation of electrons and holes. This study provides insights into strategies to improve catalytic performance through utilizing mechanical energy and opens a new horizon for environmental remediation.

Current technologies for removal of Cr(VI) are generally fit for acidic wastewater. In this study, a new ferrite process for removal and recycling of Cr(VI) from alkaline wastewater to produce the valuable chromium ferrite has been developed. The results show that this new ferrite method is a one-step process which can be divided into two successive reactions including Cr(VI) reduction to form coprecipitation (Cr0.25Fe0.75(OH)3) and subsequently magnetic conversion of Cr0.25Fe0.75(OH)3 induced by Fe2+ under the same alkaline condition. The total Fe/Cr mole ratio of 5:1 is at least required for the chromium ferrite transformation. Increasing temperature and pH can enhance the interaction of Fe2+ with Cr0.25Fe0.75(OH)3 and further promote the formation of chromium ferrite, while suppressing the generation of nonmagnetic by-product goethite. Almost pure chromium ferrite is formed under proposed optimum conditions (Fe/Cr = 7:1, 65 °C and pH of 9) with Cr(VI) removal ratio around 100%. The Cr(VI) remained in the filtrate can be reduced to 0.01 mg/L which is much lower than the limits concentration for surface water (≤0.05 mg/L). The chromium ferrite product whose molecular formula can be expressed as Cr0.5-xFe2.5+xO4 (where 0 ≤ x

To efficiently remove high concentrations of hexavalent chromium (Cr(VI)), calcium–aluminum-layered double hydroxide (CaAl-LDH, denoted as CAL), and polypyrrole-modified CAL (CAL-PPy) were prepared by hydrothermal and in situ polymerization methods, respectively. The chemical structure, morphology, and elemental results indicated that the chain-like polypyrrole was decorated with hexagonal CAL. The specific surface area of CAL-PPy increased from 8.746 m2/g to 24.24 m2/g. The adsorption performances of CAL and CAL-PPy for aqueous Cr(VI) were investigated using batch equilibrium experiments. The decontamination process of aqueous Cr(VI) (100 mg/L) reached the equilibrium state within 50 min, and the kinetic data met the pseudo-second-order kinetic equation. The Langmuir model described the isothermal data properly, and the obtained theoretical adsorption capacity of CAL for Cr(VI) at 318 K was 34.06 mg/g, while that of CAL-PPy was 66.14 mg/g. The removal mechanisms involved electrostatic attraction, surface complexation, anion exchange, and reduction to low-toxicity Cr(III). Therefore, CAL and CAL-PPy have underlying applications in treating real wastewater containing Cr(VI).

Heterojunction engineering has been regarded as a promising strategy to sufficiently utilizing photogenerated charge carriers, thus benefiting the improvement of photocatalytic performance. Herein, Ag3PO4/WO3 S-scheme heterojunction was synthesized via a simple deposition-precipitation process, and its photocatalytic activity was evaluated by monitoring water splitting and pollutant degradation under visible light. As a result, Ag3PO4/WO3 with optimized ratio photocatalyst showed enhanced photocatalytic activity in oxygen production (306.6 μmol·L-1·h-1) relative to pure Ag3PO4 (204.4 μmol·L-1·h-1). Additionally, it also exhibits rapid toxicity elimination efficiency over hexavalent chromium ions (Cr6+) and ciprofloxacin (CIP) with degrading rate of 72% and 83% within 30 min, respectively. According to a series characterization, a possible S-scheme photocatalytic mechanism of Ag3PO4/WO3 was demonstrated in detail, which endowed the heterojunction with strong redox abilities to provide powerful diving force towards the photocatalytic reaction. This work presents an innovative perspective to construct Ag3PO4-based S-scheme heterojunctions for boosting photocatalytic performance for various applications.

A low-temperature hydrothermal process was developed to synthesize erdite adsorbent from a solid waste sludge contained 10.2% Fe, 6.2% Al and 1.4% Si, alongside 59.5% water content. At 90℃, adding Na2S and NaOH could convert it into erdite nanorods with a diameter of 80 nm and a length of 100 nm. In the sludge, only Fe oxyhydroxide was involved in the formation of erdite, and the other Al/Si-bearing compounds were dissolved in an alkaline medium. The dissolved Al/Si-bearing compounds were further removed, forming faujasite so that the used medium was purified and then entirely recycled into the next conversion stage. No secondary waste was generated in the pilot-scale conversion, and the adsorption efficiency of the prepared products to wastewater with a high initial Cr(VI) concentration of 1000 mg/L was more than 99.5%. The adsorption data complied with the pseudo-second-order kinetics. During the wastewater treatment, hexavalent chromium anion diffused to erdite surface and replaced -OH/-SH groups of adjacent structural Fe to form a stable complex ligand. In addition, the redox reaction between hexavalent chromium and the -SH group occurred to generate a trivalent chromium complex on the Fe/S-bearing flocs surface.

The present study investigates ameliorative effect of silicon nanoparticles (SiNPs) and indole acetic acid (IAA) alone and in combination against hexavalent chromium (CrVI) toxicity in rice seedlings. The results of the study revealed protective effects of SiNPs and IAA against CrVI toxicity. The 100μM of CrVI imposed toxic effects in rice seedlings at morphological, physiological and biochemical levels which coincided with increased level of intracellular CrVI and declined level of endogenous nitric oxide (NO). The CrVI enhanced levels of superoxide radicals (SOR) (59.51% and 50.1% in shoot and root, respectively) and H2O2 (19.5% and 23.69% in shoot and root, respectively). However, when SiNPs and IAA were applied to plants under CrVI stress, they enhanced tolerance and defence mechanisms as manifested in terms of increased biomass, endogenous NO, photosynthetic pigments, and antioxidants level (ascorbate-glutathione cycle). It was also noticed that CrVI arrested cell cycle at G2/M phase whereas growth was restored as compared to control when SiNPs and IAA were supplemented. Thus, the hypothesis that combined application of SiNPs and IAA will be effective in alleviating CrVI toxicity is validated from the results of this study. Moreover, in SiNPs and IAA-mediated mitigation of CrVI toxicity, endogenous NO has a positive role. The importance of the study will be that the combination of SiNPs and IAA can be utilized against heavy metal stress and even when supplied alone, they will enhance the crop productivity parameters with and without stress conditions.

This paper aims to synthesis a recyclable adsorbent from solid waste using a clean and environmentally friendly method to deal with Cr(VI) water pollution. Magnetic zeolite/chitosan composites (ZFA/MCS) were prepared by the neutralization method. The adsorption properties of ZFA/MCS, prepared by the neutralization method for Cr(VI) ions under different conditions especially cross-linking, were investigated in detail. The results showed that cross-linked ZFA/MCS generally showed higher adsorption capacity than uncross-linked ones. The uncross-linked ZFA/MCS and cross-linked ZFA/MCS showed a saturated adsorption capacity of 25.67 mg·g−1 and 28.47 mg·g−1 at pH = 3 and 30 °C, respectively. The experimental values were followed Langmuir adsorption equations and pseudo-second-order kinetic model, indicating that the adsorption was probably monolayer coverage and chemical adsorption, respectively. The effect of temperature proved that the adsorption was spontaneous and endothermic. Therefore, the adsorbent with excellent recyclability and adsorbability was successfully fabricated via a green synthetic strategy.

Hexavalent chromium [Cr(VI)] is a heavy metal pollutant in the environment released through leather tanning. In this context, the present study was envisaged to isolate and identify chromium reducing bacteria in order to employ them towards detoxification of chromium. In general, bacteria are ecofriendly and cost-effective which can be efficiently used in bioremediation processes. The collected tannery effluents yielded considerable Bacillus species. These isolates demonstrated well for their resistance which showed exceptional Cr(VI) reduction within 48 h under aerobic conditions. Mostly, chromium resistance confers through Chromate transporters which involves metabolic reduction of toxic Cr(VI) to non-toxic Cr(III). Distribution of chr genes in Bacillus species were identified from their genome through UniProt. Treatment of raw tannery effluent employing these isolates individually or as a consortia reduced Cr(VI) significantly. Thus, these bacterial strains, could evolve as a potential organisms to reduce toxic Cr(VI) to its non-toxic Cr(III) form in chromium contaminated sites.

In this article, low-molecular-weight organic acids were applied to remediate the hexavalent chromium [Cr(VI)]-contaminated soil. The influence of different parameters (washing concentration, solid...

The ecosystems and human health were seriously threatened by hexavalent chromium (Cr(VI)) in wastewater. In this article, using the idea of the highly matched energy band structure between indium sulfide (In2S3) and MIL-53(Fe), a Type-II heterojunction has been constructed by loading In2S3 on MIL-53(Fe) microrod to overcome the fault like high recombination rates of photogenerated electron-holes of In2S3. The composite with 20:1 mass ratio of In2S3 to MIL-53(Fe) (IM-2) was adopted as an optimal sample for efficient photocatalytic Cr(VI) reduction under visible light. Various characterization techniques were used to verify the characteristics of composites and delved into the structure-effect relationship between this heterojunction and its activity. Results showed that the reaction rate constants of the photoreduction process over IM-2 was ~ 4 and 26 times higher than those of pure In2S3 and MIL-53(Fe), respectively, and the catalyst could maintain superior removal efficiency (88.6%) and steady crystal structure after four cycles. First-principles calculations further illustrated that the heterostructure formed between In2S3 and MIL-53(Fe) could effectively accelerate the separation of photogenerated electrons and holes, thus improving the photocatalytic reduction performance. Moreover, the active species analyses revealed that the superoxide radicals and electrons were mainly involved in the reduction of Cr(VI).

Graphical abstract, Highlights • Cr(VI) can induce inflammatory, oxidative stress, and apoptosis in rat liver. • Cr(VI) induces inflammatory response in the liver by inhibiting deacetylation. • Oxidative stress caused by Cr(VI) is related to the inhibition of deacetylation. • Cr(VI) aggravates hepatocyte apoptosis by inhibiting deacetylation in rats. • Cr(VI) induces liver injury via inhibition of the deacetylation of Sirt1., Introduction Hexavalent chromium (Cr(VI)), one of the toxic heavy metals, poses a serious threat to human and animal health. Protein acetylation regulates the structure and function of most proteins in a variety of ways. However, the hepatotoxicity of Cr(VI) and whether it is related to deacetylation remains largely unknown. Objectives We aimed to explore the link between the deacetylation of silent information regulator two ortholog 1 (Sirt1) and hepatotoxicity induced by Cr(VI) exposure, and to better clarify the biological mechanism of liver injury induced by Cr(VI). Methods We established a model of liver injury of K2Cr2O7 by injecting rats intraperitoneally for 35 days continuously and adding resveratrol (Res) to further explore the link between deacetylation and hepatotoxicity. Results The results revealed that Cr(VI) induced inflammatory response and apoptosis in hepatocytes. Furthermore, Cr(VI) reduced Sirt1 expression and inhibited the deacetylation of Sirt1 to downstream key transcription factors, including nuclear factor erythroid 2-related factor 2 (Nrf2), Forkhead box O3 (FOXO3), and nuclear factor-kappa B (NF-κB). Conversely, when Res was administered as an activator of Sirt1, the deacetylation of Sirt1 was enhanced, and inflammatory response and apoptosis were significantly alleviated. Conclusion In summary, this work firstly demonstrates that Cr(VI) induces liver injury in rat by inhibiting the deacetylation of Sirt1, which is of positive significance for protecting the natural environment and animal health from chronic Cr poisoning.

Comprehensive utilization of stainless-steel slag (SSS) is restrained due to the risk of Cr6+ leaching. Based on the studying the microstructure of synthetic slag (SS) containing Cr2O3 with XRD, SEM-EDS, and Image pro, the effect of binary basicity on the chromium occurrence in SSS was investigated. The results indicated that the binary basicity had a significant impact on the properties of spinel crystals. There was a positive correlation between the calcium content in spinel crystals and the SS basicity. The size of spinel crystals varied from large to small and the precipitation occurrence changed with the basicity increase. Furthermore, the chromium occurrences changed with the basicity. The chromium was produced in spinel crystals at lower basicity, but as the basicity increased to 3.0, the chromium precipitated as calcium chromate. In view of the relationship between the chromium leaching behavior and its occurrence, increasing basicity raised the Cr6+ leaching.

Department of Chemical Engg, Haldia institute of technology. Haldia -721657, India Department of Chemical Engg, Meghnath Saha Institute of Technology, Haldia Associate Manager , Linde India Limited., Kolkata Email Corresponding Author : radha.das6@gmail.com, Effluents from various industries like electroplating, leather tanning, cement, petrochemicals, dye etc, contains significant amount of toxic hexavalent chromium, Cr(VI) with concentration of 10th to 100th ppm level. To avoid the health hazard from long term exposure of Cr(VI) , there is high high demand of feasible cost effective technologies which would eventually save aquatic & human lives from the carcinogenic effect of Cr+6. In this work activated Neem leaf powder (NLP) and Neem saw dust (NSD) were selected as cost effective adsorbent for elimination of chromium (VI) compound from synthetic waste water using adsorption process at various pH, concentration , time and temperature. It was observed that the reduction of Cr+6 increases with the increase of time of contact and adsorbent amount but decreases with higher solute concentration. Determination of free Cr+6 ions concentration in the effluent has been determined Spectro-Photometrically at 542 nm wavelength. The results show that 98 - 99.88 % reduction of Cr+6 may be achieved successfully depending on pH and nature of adsorbents, temperature and concentration of solution. The rate constants of these sorption processes were observed using pseudo first order and pseudo second order reaction kinetic models. Freundlich Isotherm and rearranged Langmuir model were used to find out the applicability of these isotherms for both adsorption processes. Results also show that the performance efficiency of activated NLP was slightly higher compared to the NSD at the same sorption conditions. The maximum adsorption of Cr(VI) was obtained as 55.86 and 40.0 mg/gm using NLP and NSD respectively .

In this study, CTS-GSH was prepared by grafting thiol (–SH) groups onto chitosan (CTS), which was characterized through Fourier Transform Infrared (FT-IR) spectra, Scanning Electron Microscopy (SEM) and Differential Thermal Analysis–Thermogravimetric Analysis (DTA-TG). The performance of CTS-GSH was evaluated by measuring Cr(VI) removal efficiency. The –SH group was successfully grafted onto CTS, forming a chemical composite, CTS-GSH, with a rough, porous and spatial network surface. All of the molecules tested in this study were efficient at removing Cr(VI) from the solution. The more CTS-GSH added, the more Cr(VI) removed. When a suitable dosage of CTS-GSH was added, Cr(VI) was almost completely removed. The acidic environment at pH 5–6 was beneficial for the removal of Cr(VI), and at pH 6, the maximum removal efficiency was achieved. Further experimentation showed that with 100.0 mg/L CTS-GSH for the disposal of 5.0 mg/L Cr(VI) solution, the removal rate of Cr(VI) reached 99.3% with a slow stirring time of 8.0 min and sedimentation time of 3 h; the presence of four common ions, including Mg2+, Ca2+, SO42− and CO32−, had an inhibitory effect on CTS-GSH’s ability to remove Cr(VI) from the aqueous solution, and more CTS-GSH was needed to reduce this inhibiting action. Overall, CTS-GSH exhibited good results in Cr(VI) removal, and thus has good potential for the further treatment of heavy metal wastewater.

In order to reduce the content of Cr(VI) in the soil of the relocated chromium salt factory, the rice straw-derived hydrothermal carbon was prepared by hydrothermal method and loaded with nano zero-valent iron generated by liquid phase reduction, which effectively alleviated the self-aggregation problem of nano zero-valent iron (nZVI) in the treatment of Cr(VI) and improved the Cr(VI) reduction rate without changing the soil structure. The reduction effect of Cr(VI) in soil by key influencing factors such as carbon-iron ratio, initial pH value, and initial temperature was investigated. The results showed that nZVI modified hydro-thermal carbon composite (named RC-nZVI) had a good reduction effect on Cr(VI). Scanning electron microscope (SEM) and energy spectrum analysis showed that nZVI was evenly distributed on the surface of hydrothermal carbon, which effectively reduced the agglomeration of iron. Under the conditions of C/Fe = 1:2, 60 °C, with pH of 2, the average Cr(VI) content in soil decreased from 182.9 mg kg−1 to 21.6 mg kg−1. Adsorption kinetics of Cr(VI) by RC-nZVI fit well with the pseudo-second-order model, and the kinetic velocity constant revealed that Cr(VI) reduction rate decreased with increasing initial Cr(VI) concentration. Cr(VI) reduction by RC-nZVI was mainly dominated by chemical adsorption.

Raw data of scanning electron images obtained within the framework of the NFFA-Europe Pilot Transnational Access Activity, proposal ID262

In this study, a flower–like BiVO4/MIL–101–NH2 composite is synthesized by a facile and surfactant–free process. The –COO−–Bi3+ ionic bond construction was conductive to enhance the interface affinity between BiVO4 and MIL–101–NH2. Due to the highly efficient light capture and sufficient electron traps induced by oxygen vacancies and the formation of a heterostructure, the improved separation and transportation rates of charge carriers are realized. In addition, the MIL–101–NH2/BiVO4 composite is favorable for Cr(VI) photocatalytic removal (91.2%). Moreover, FNBV–3 (Fe/Bi = 0.25) also exhibited an excellent reusability after five cycles.

As a carcinogenic pollutant, hexavalent chromium (Cr(VI)) in the ambient air has serious influences on public health. Due to its instability and difficulty in chemical analysis, few studies have been conducted on the regional concentration level of environmental Cr(VI), especially in China. The pollution levels of Cr(VI) in ambient PM2.5 were determined in two sampling sites of Beijing and Qingdao from September to December 2020. The concentrations of Cr(VI) were determined using Ion Chromatography-inductively coupled plasma mass spectrometry(IC-ICP-MS), and the Cr concentrations were simultaneously analyzed by Inductively Coupled Plasma-atomic emission spectrometry(ICP-AES). The main results are as follows: (1) Based on the analysis of samples collected at the sampling sites of Beijing and Qingdao, the concentrations of Cr(VI) in PM2.5 were (0.140 ± 0.065) ng/m3 and (0.091 ± 0.073) ng/m3, respectively; (2) During the sampling period, the mean ratio of Cr(VI) to Cr was (0.0623 ± 0.0969). The ratio of Cr(VI)/Cr in Beijing and Qingdao were 0.076 ± 0.104 and 0.041 ± 0.039, respectively. In conclusion, compared with other countries, the concentration of Cr(VI) at the sampling sites of Beijing and Qingdao showed lower values. The average concentration of Cr(VI) estimated by the ratio of this research in China is lower than that in South Korea and similar to those in Canada and Australia.

Herein, three types of graphene oxides (GOs, GO-M1, GO-M2 and GO-M3) have been successfully prepared from graphite by three different methods and utilized for the removal of Cr(VI) from aqueous solutions. Further, the effects of initial concentration and pH, adsorbent dosage, contact time and temperature on the adsorption performance of GOs were investigated by batch adsorption experiments. Furthermore, the adsorption mechanisms for Cr(VI) adsorption by GOs are mainly the redox reaction and electrostatic attraction, while there are also pore filling, ion exchange and complexation involved in these adsorption processes. The adsorption kinetic and isotherm data indicate that these adsorption processes of GOs on Cr(VI) are dominantly monolayer chemisorption and equilibrium can be reached in 30 min. The saturation adsorption capacities (Qm, 298.15 K) of GO-M1, GO-M2 and GO-M3 for Cr(VI) are estimated to be 3.5412 mg⋅g−1, 2.3631 mg⋅g−1 and 7.0358 mg⋅g−1, respectively. Moreover, the adsorption thermodynamic study showed that these adsorption processes of Cr(VI) by the three types of GOs at 298.15 K to 323.15 K are endothermic, entropy-driven and thermodynamically spontaneous and feasible. Overall, these findings provided vital insights into the mechanism and application of Cr(VI) removal by GOs.

Due to the adverse effects of hexavalent chromium (Cr6+) on human health and the quality of the environment, the scientific community has invested a lot of effort to solve this pollution problem. Thus, implementing sustainable alternatives for Cr6+ elimination by exploiting the capacity of microbial biomass to retain heavy metals by biosorption is considered an economic and eco-friendly solution, compared to the conventional physico-chemical processes. However, the ability of microorganisms to remove Cr6+ from liquid effluents can strongly be affected by biotic and abiotic factors. With these issues in mind, the main purpose of this paper was to investigate Cr6+ biosorption on Bacillus megaterium and Rhodotorula sp. biomass inactivated by thermal treatments, exploring the effects of some factors such as: pH, biosorbent dose, initial concentration of the metal in solution, temperature and contact time between the biosorbent and the metal ions on process effectiveness. The results showed that Cr6+ removal by biosorption on the selected microorganisms was strongly influenced by the pH of the solution which contains chromium, the reduction being the principal mechanism involved in hexavalent chromium biosorption. Equilibrium and kinetic studies were also performed, together with SEM-EDX and FTIR spectra, to explain the mechanisms of the biosorption process on the selected biomasses. Maximum uptake capacities of 34.80 mg/g biosorbent and 47.70 mg/g biosorbent were achieved by Bacillus megaterium and Rhodotorula sp., respectively, at pH 1, biosorbent dosage of 8 g/L, 25 °C, after a contact time of 48 h and an initial Cr6+ concentration in solution of 402.52 mg/L. The experimental results showed that Cr6+ biosorption by selected microorganisms followed the Elovich model, the values of the correlation coefficients being 0.9868 and 0.9887, respectively. The Freundlich isotherm model best describes the Cr6+ biosorption by Bacillus megaterium and Rhodotorula sp., indicating that a multilayer biosorption mainly controls the process and is conducted on heterogeneous surfaces with uniformly distributed energy., info:eu-repo/semantics/publishedVersion

Within the EU human biomonitoring initiative (HBM4EU), a targeted, multi-national study on occupational exposure to hexavalent chromium (Cr(VI)) was performed. Cr(VI) is currently regulated in EU under REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) and under occupational safety and health (OSH) legislation. It has recently been subject to regulatory actions to improve its risk management in European workplaces. Analysis of the data obtained within the HBM4EU chromates study provides support both for the implementation of these regulatory actions and for national enforcement programs and may also contribute to the updating of occupational limit values (OELs) and biological limit values for Cr(VI). It also provides useful insights on the contribution of different risk management measures (RMMs) to further reduce the exposure to Cr(VI) and may support the evaluation of applications for authorisation under REACH. Findings on chrome platers’ additional per- and polyfluoroalkyl substances (PFAS) exposure highlight the need to also pay attention to this substance group in the metals sector. A survey performed to evaluate the policy relevance of the HBM4EU chromates study findings supports the usefulness of the study results. According to the responses received from the survey, the HBM4EU chromates study was able to demonstrate the added value of the human biomonitoring (HBM) approach in assessment and management of occupational exposure to Cr(VI). For future occupational studies, we emphasise the need for engagement of policy makers and regulators throughout the whole research process to ensure awareness, relevance and uptake of the results in future policies. Highlights: Potential policy impact of the HBM4EU chromates study is presented and discussed; Surveyed policy makers confirmed policy relevance of biomonitoring results; Study considered to support national enforcement and further lowering of OELs; Added value of HBM in the management of occupational exposure to Cr(VI) was demonstrated; Close co-operation with regulators to support policy uptake is emphasised. Funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 733032 and received co-funding from the author's organizations and/or Ministries. info:eu-repo/semantics/publishedVersion

In order to enhance the slag resistance of Al2O3-spinel castables, (Al,Cr)2O3 is added into Al2O3-spinel system as a pre-synthesized micro-powder. Firstly, (Al,Cr)2O3 micro-powder is synthesized by sintering under reduction conditions to prevent the formation of hexavalent chromium. The Al2O3-spinel castables are prepared using tabular alumina, fused spinel, α-Al2O3 micro-powder, calcium aluminate cement and (Al,Cr)2O3 micro-powder as the raw materials. The bulk density, porosity, mechanical properties, and slag resistance of the samples are tested. Afterward, the effects of (Al,Cr)2O3 micro-powder (0–3 wt%) on the slag resistance and microstructures of the Al2O3-spinel castables are assessed by X-ray diffraction (XRD) and energy-dispersive (SEM-EDS) analysis. The results show that the addition of (Al,Cr)2O3 micro-powder can could inhibit the deteriorating effects of Cr3+ on the mechanical properties of the samples. The microstructure results also shows that with the addition of the (Al,Cr)2O3 micro-powder, a secondary solid solution of Ca(Al,Cr)12O19 formed, causing the unit cell to become larger. In the slag erosion area, CA6 crystals formed with network-like interwoven structures, high density, and greater thickness. These characteristics significantly reduce the erosion and permeability indices of the castables, and improve the slag erosion resistance of the material.

Cr-refractories usually contain Cr(III) compounds that can convert into carcinogenic Cr(VI) compounds such as CaCrO4 and Ca4Al6CrO16 under alkaline and oxygen-rich conditions. Literature provides insight into the characteristics, thermal stability, and aqueous solubility of CaCrO4, while there is hardly any data available on Ca4Al6CrO16. The present paper comprehensively studied high-temperature stability and leaching kinetics and other characteristics of Ca4Al6CrO16 by using high-temperature XRD, TG-DSC, XPS, Raman, and TRGS 613. XPS confirmed that chromium in Ca4Al6CrO16 is present in the +6 oxidation state. Ca4Al6CrO16 is thermally stable up to 1500 °C in the air but decomposes in nitrogen above 1258 °C to form the Cr3+-containing phases CaCr2O4 and Ca6Al4Cr2O15. The Ksp of Ca4Al6CrO16 in deionized water is 1.0381 × 10−22, 4.5723 × 10−21 and 2.3489 × 10−20 at 12, 25, and 40 °C, respectively. The leaching process of Ca4Al6CrO16 is chemical reaction controlled, with an apparent activation energy of 58.78 kJ/mol.

Cadmium (Cd), lead (Pb), and hexavalent chromium (Cr(VI)) are often found in soils and water affected by metal smelting, chemical manufacturing, and electroplating. In this study, synthetic iron sulfide nanoparticles (FeS NPs) were stabilized with carboxymethyl cellulose (CMC) and utilized to remove Cr(VI), Cd, and Pb from an aqueous solution. Batch experiments, a Visual MINTEQ model, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectrometer (XPS) analysis were used to determine the removal efficiencies, influencing factors, and mechanisms. The FeS NP suspension simultaneously removed Cr(VI), Cd, and Pb from an aqueous solution. The concentrations of Cr(VI), Cd, and Pb decreased from 50, 10, and 50 mg·L-1 to 2.5, 0.1, and 0.1 mg·L-1, respectively. The removal capacities were up to 418, 96, and 585 mg per gram of stabilized FeS NPs, respectively. The acidic conditions significantly favored the removal of aqueous Cr(VI) while the alkaline conditions favored the removal of Cd and Pb. Oxygen slightly inhibited the removal of Cr(VI), but it had no significant influence on the removal of Cd and Pb. A potential mechanism was proposed for the simultaneous removal of Cr(VI), Cd, and Pb using FeS NPs. The interactions of the three heavy metals involved a cationic bridging effect on Cr(VI) by Cd, an enhanced adsorption effect on Cd by [Cr,Fe](OH)3, precipitation of PbCrO4, and transformation of PbCrO4 to PbS. Therefore, FeS NPs have a high potential for use in the simultaneous removal of Cr(VI), Cd, and Pb from contaminated aqueous solutions.

Hexavalent chromium (VI) is a potent carcinogen for humans, while trivalent chromium (III) is an important element in glucose metabolism. In atmospheric water droplets, oxidation of Cr(III) to Cr(V...

Soil microbial communities connect to the functional environment and play an important role in the biogeochemical cycle and waste degradation. The current study evaluated the distribution of the core microbial population of garden soil in the Varanasi region of Uttar Pradesh, India and their metabolic potential for mitigating toxic hexavalent chromium from wastewater. Metagenomes contain 0.2 million reads and 56.5% GC content. The metagenomic analysis provided insight into the relative abundance of soil microbial communities and revealed the domination of around 200 bacterial species belonging to different phyla and four archaeal phyla. The top 10 abundant genera in garden soil were Gemmata, Planctomyces, Steroidobacter, Pirellula, Pedomicrobium, Rhodoplanes, Nitrospira Mycobacterium, Pseudonocardia, and Acinetobacter. In this study, Gemmata was dominating bacterial genera. Euryarchaeota, Parvarchaeota, and Crenarchaeota archaeal species were present with low abundance in soil samples. X-ray photoelectric spectroscopy (XPS) analysis indicates the presence of carbon, nitrogen–oxygen, calcium, phosphorous, and silica in the soil. Soil-derived bacterial consortia showed high hexavalent chromium [Cr (VI)] removal efficiency (99.37%). The bacterial consortia isolated from garden soil had an important role in the hexavalent chromium bioremediation, and thus, this study could be beneficial for the design of a heavy-metal treatment system.

Hexavalent chromium (Cr(VI)) is recognized to be carcinogenic and toxic and registered as a contaminant in many drinking water regulations. It occurs naturally and is also produced by industrial processes. The reduction of Cr(VI) to Cr(III) has been a central topic for chromium remediation since Cr(III) is less toxic and less mobile. In this study, fermentative Fe(III)-reducing bacterial strains (Cellu-2a, Cellu-5a, and Cellu-5b) were isolated from a groundwater sample and were phylogenetically related to species of Cellulomonas by 16S rRNA gene analysis. One selected strain, Cellu-2a showed its capacity of reduction of both soluble iron (ferric citrate) and solid iron (hydrous ferric oxide, HFO), as well as aqueous Cr(VI). The strain Cellu-2a was able to reduce 15 μM Cr(VI) directly with glucose or sucrose as a sole carbon source under the anaerobic condition and indirectly with one of the substrates and HFO in the same incubations. The heterogeneous reduction of Cr(VI) by the surface-associated reduced iron from HFO by Cellu-2a likely assisted the Cr(VI) reduction. Fermentative features such as large-scale cell growth may impose advantages on the application of bacterial Cr(VI) reduction over anaerobic respiratory reduction.

Biochar-harbored zero-valent iron (ZVI/BC) has been extensively used to detoxify hexavalent chromium (Cr(VI)). However, the role played by biochar in promoting electron transfer of ZVI and Cr(VI) reduction was not fully uncovered. Herein, three biomass modeling components (cellulose, hemicellulose, and lignin) and their blends were utilized to synthesize ZVI/BC via co-pyrolysis with hematite. X-ray diffraction analysis showed that hematite was successfully reduced to ZVI in nitrogen ambience. Batch sorption experiment showed that mass ratio (hematite to lignocellulosic component) of 1:20 is most optimal for reduction of Cr(VI) by ZVI/BCs. ZVI supported by BC derived from cellulose, hemicellulose, and their binary mixture demonstrated better Cr(VI) removal capacity (23.8–38.3 mg g−1) owing to higher ordered and graphitic carbon structure as revealed by Raman spectrum. In addition, lower Tafel corrosion potentials and smaller electrochemical impedance arc radiuses were observed based on electrochemical analysis, suggesting their higher electrical conductivity and faster electron transfer, whereas the BCs derived from lignin and lignin-containing hybrids were not conducive to electron transfer of ZVI due to lower degree of graphitization, thus compromising Cr(VI) removal by ZVI/BC (7.7–17.7 mg g−1). As per X-ray photoelectron spectroscopy analysis, reduction, complexation, and co-precipitation were the main mechanisms for Cr(VI) removal. The present study provided a scientific evidence for screening plant-derived biomass feedstock with high contents of cellulose and hemicellulose and low lignin content to fabricate ZVI/BC to achieve high Cr(VI) removal.

Two Bacteria were isolated from heavy metal contaminated soil with high concentration of total chromium (ca. 2300 mg/L) showed their significant ability of chromate reduction. The bacteria were identified as Ochrobactrum sp. and Microbacterium sp., and were designed as Ochrobactrum sp. strain 71 and Microbacterium sp. strain 73, respectively according to their 16S rRNA gene sequence analysis. The ability of the two isolates to reduce hexavalent chromium in actively growing cells as well as in resting cells was examined. The results showed both strains were able to reduce Cr(VI) to trivalent chromium Cr(III) very rapidly when grown in LB medium containing chromate (in the form of K2Cr2O7, 5 mg/L and 50 mg/L). Reduction of Cr(VI) to Cr(III) in the phosphate buffer containing chromate was insignificant when using resting cells collected from exponential growth phase. However, when supplemented with electron donor (ex. acetate, citrate or NADH), resting cells also showed significant ability to reduce Cr(VI) to Cr(III). Reduction of the toxic Cr(VI) to the less toxic Cr(III) is a promising bioremedial process in detoxification of Cr(VI)-contaminated environment. Therefore, traits of chromate reduction by these two indigenous isolates showed significant potential in helping in situ Cr(VI) bioremediation efforts.

Identification of the factors controlling the migration of hexavalent chromium (Cr (VI)) in soil can provide valuable information for pollution control and risk assessment. In this study, we assessed the processes of transportation and migration of Cr (VI) in soil by batch and column experiments. Breakthrough curves were used to examine the mobility of Cr (VI) in soil columns. Most of them could be described by a typical S-shaped curve. The Yoon–Nelson model and Thomas model were applied to predict the behavior of Cr (VI) in soil and obtained parameters to characterize the rate and capacity of adsorption. It was observed that all obtained parameters changed along with soil properties. Moreover, stepwise multiple regression and grey correlation analysis were used to determine the main control factors by evaluating the relationship between soil properties and dynamic or static parameters. The results showed Fe oxide content was the key factor no matter in static or dynamic adsorption while soil texture had a great influence on the transportation of Cr (VI) in soil columns. Also, in the actual situation, the external input condition should not be ignored. Our research provides meaningful information for authorities to develop better soil management and remediation strategies.

In this study, the removal of hexavalent chromium from the aqueous solution using birds' feathers amended by polyaniline is investigated. Firstly, various bird feathers and polyaniline composites are synthesized and used in batch experiments to separate hexavalent chromium. Results show optimal performance of polyaniline and bird feathers composite in chromium removal. Among the bird's feather and polyaniline composites, the polyaniline/ostrich feathers/polyethylene glycol composite has the most optimal performance with a removal percentage of about four times more than that of activated carbon (87.36 %), at pH = 6 and the contact time of about 30 min. Analysis of cavities size as well as analysis of BET specific surface shows that specific surface area of polyaniline/ostrich feathers/polyethylene glycol composite with 36.22 m2/g is higher than other composites. Scanning electron microscope (SEM) images taken from the surface of the composites show better and more uniform coverage of polyaniline on the ostrich feather in the polyaniline/ostrich feather/polyethylene glycol composite. The XRD analysis and FTIR analysis confirm the synthesis of aniline on the resulted composite and it is declared that the structure of the achieved composite is amorphous.

In the present study, an innovative carbon self-doped g-C3N4 (CCN) loaded with ultra-low CeO2 (0.067–0.74 wt%) composite photocatalyst is successfully synthesized via a facile one-pot hydrothermal and calcination method. The CeO2/CCN exhibits superior photocatalytic performance for tetracycline degradation (78.9% within 60 min), H2O2 production (151.92 μmol L-1 within 60 min), and Cr(VI) reduction (99.5% within 40 min), which much higher than that of g-C3N4, CCN, CeO2, and CeO2/g-C3N4. The enhanced photocatalytic performance is originated from the fact that the doping of C can efficaciously broaden the utilization range of solar light and improve the reduction ability of photogenerated electrons. Meanwhile, the ultra-low loading of CeO2 can effectually promote the migration of photogenerated electrons and enhance the specific surface area. Besides, the experiments of pH effect and cycle ability indicate that CeO2/CCN has excellent durability and stability. Finally, the photocatalytic mechanism of CeO2/CCN is systematically discussed. This work proves that combining element doping and semiconductor coupling is a promising strategy to design high-efficiency g-C3N4-based photocatalysts.

Cr(VI) is a type of dangerous effluent that has caused great harm to human health and the environment. Recognition and perception of Cr(VI) by artificial receptors has attracted extensive attention. A novel fluorescent chemical sensor based on the 5,7-dihydroxyflavone skeleton was designed and synthesized for the selective recognition of Cr(VI). As confirmed by fluorescence technology, the fluorescent probe 4-dimethylaminobenzyl chrysin ester-Zn (DBC-Zn) showed high sensitivity and selectivity for dichromate and a fast response (less than 30 sec) recognition. The fluorescence intensity of DBC-Zn varies linearly with the concentration of Cr(VI) in the range 0.1-1 μM. The detection limit of Cr2 O7 2- by DBC-Zn is 2.3 nM, which is far lower than the national safe drinking water standard stipulated by the US Environmental Protection Agency (1.9 μM). The quenching mechanism of the probe can be attributed to the interaction of the dynamic quenching effect and the fluorescence internal filtration effect. In addition, the probe has good stability in both neutral and alkaline environments, and the accuracy of quantitative analysis of Cr2 O7 2- in lake water or tap water is more than 80%. The test paper based on DBC-Zn can effectively detect Cr2 O7 2- at the concentration of 100 ppb. This shows that the probe has a certain practical application value.