Trivalent Chromium Research Articles

New insights into the cooperative adsorption behavior of Cr(VI) and humic acid in water by powdered activated carbon

Chromium and humic acid often co-exist in wastewater and source waters, and the removal of chromium through sorption by activated carbon may be greatly influenced by humic acid. In this study, we systematically evaluated concurrent adsorption of humic acid (HA) and hexavalent chromium (Cr(VI)) in water by powdered activated carbon (PAC) and further, the effect on conversion to trivalent chromium (Cr(III)). Adsorption of both HA and Cr(VI) was significantly enhanced in the dual adsorbate system as compared to treatments with HA or Cr(VI) alone. The removal of HA increased by 16.0% in the presence of 80 mg/L Cr(VI), while the removal of Cr(VI) similarly increased with increasing levels of HA. However, the promotion effect of HA was found to decrease with increasing pH. With HA at 20 mg/L, removal of Cr(VI) increased from 40.09% to 70.12% at pH 3, which was about twice the increase at pH 10. The cooperative adsorption mechanism was explored using scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), Raman spectroscopy, Fourier transform infrared spectrometer (FTIR), and X-ray photoelectron spectroscopy (XPS). Comprehensive analysis of spectra suggested that the mutual promotion between HA and Cr(VI) adsorption was attributable to the formation of Cr(VI)-HA and Cr(III)-HA complexes that were readily adsorbed on the PAC surfaces. The higher HA concentrations increased the reduction of Cr(VI) to Cr(III), which was likely due to the electron transfer provided by the functional groups such as -CO, -OH and -COOH in both PAC and HA. At pH 3, 99.1% of Cr adsorbed on the PAC surface was in the form of Cr(III). These findings imply that the interactions between Cr(VI) and HA in the process of water treatment by PAC provides additional and synergistic benefits, leading to a greater removal of chromium.

Bi2S3-sensitized TiO2 nanostructures prepared by solution process for highly efficient photoreduction of hexavalent chromium ions in water under visible light

The release of hexavalent chromium ions (Cr (VI)) in water can pose critical intimidations to the ecological environments and highly hazardous impacts on health. This study demonstrates the construction of nanostructured Bi2S3/TiO2 as a visible-light active photocatalyst for the rapid reduction of Cr(VI) to trivalent chromium ions (Cr(III)). Mesostructured TiO2 was grown by surfactant-assisted sol-gel process. The Bi2S3 of 8.3 nm in size were anchored the 19.4 nm TiO2 rhombohedra by coprecipitation at 1.0–4.0 wt%, as proved by TEM, XPS, and XRD explorations. The absorption of visible light was enhanced as a result of bandgap reduction to ∼2.5 eV for the 3.0% Bi2S3/TiO2. This developed Bi2S3-sensitized TiO2 achieved a fast photocatalytic reduction of Cr(VI) at 284.2 μmol min−1 within just 30 min by adjusting dose at 2.0 gL−1. In addition, this developed photocatalyst showed magnificent reproducibility for five runs. This promoted photoactivity is ascribed to the efficient interfacial charge separation by Bi2S3 sensitization as inveterate by photoluminescence and photocurrent measurements. This work opens the door for plenty of metal chalcogenide-based oxide nanostructured photocatalysts for heavy metal remediation under visible light.

Chromium Speciation and Agricultural Soil Contamination in the Surrounding Tannery Regions of Walajaphet, Vellore District, Southern India

The emerging environmental problem in the tanning industry is the disposal of chromium-contaminated sludge in the soil. In the Walajapet Taluk of the Vellore District, the distribution and mobility of chromium in the soils and sludge surrounding the tannery waste disposal region were explored. This paper presents soil contamination of agricultural lands located in the SIPCOT Industrial complex near Walajapet in Vellore District, India. 64 soil samples were collected from 15 different villages, and the soil samples were analyzed for pH, EC, total chromium, hexavalent, and trivalent chromium. Studies were carried out to find the chromium contamination of the agricultural lands due to industrial effluents. It is found that 75 % of the agricultural soil samples were highly contaminated, posing a risk to agricultural lands, based on the comparison of chromium in the soil with WHO standards. The majority of the soil samples (>80%) from the locations exhibited high Cr (>200 mg kg-1) concentrations that exceeded the maximum permissible limit. Furthermore, soil samples taken near tanneries revealed that tannery effluent has a significant impact. The facts strongly demonstrate the existence of hazardous chromium, resulting in severe deterioration of agricultural land. As a result, developing an effective plan and implementing a suitable remediation technique to address the heavy metals contamination problem is critical.

Heteroleptic mer-[Cr(N∩N∩N)(CN)3] complexes: synthetic challenge, structural characterization and photophysical properties.

The substitution of three water molecules around trivalent chromium in CrBr3·6H2O with the tridentate 2,2′:6′,2′′-terpyridine (tpy), N,N′-dimethyl-N,N′-di(pyridine-2-yl)pyridine-2,6-diamine (ddpd) or 2,6-di(quinolin-8-yl)pyridine (dqp) ligands gives the heteroleptic mer-[Cr(L)Br3] complexes. Stepwise treatments with Ag(CF3SO3) and KCN under microwave irradiations provide mer-[Cr(L)(CN)3] in moderate yields. According to their X-ray crystal structures, the associated six-coordinate meridional [CrN3C3] chromophores increasingly deviate from a pseudo-octahedral arrangement according to L = ddpd ≈ dpq ≪ tpy; a trend in line with the replacement of six-membered with five-membered chelate rings around CrIII. Room-temperature ligand-centered UV-excitation at 18 170 cm−1 (λexc = 350 nm), followed by energy transfer and intersystem crossing eventually yield microsecond metal-centered Cr(2E → 4A2) phosphorescence in the red to near infrared domain 13 150–12 650 cm−1 (760 ≤ λem ≤ 790 nm). Decreasing the temperature to liquid nitrogen (77 K) extends the emission lifetimes to reach the millisecond regime with a record of 4.02 ms for mer-[Cr(dqp)(CN)3] in frozen acetonitrile.

Effects of Tannic Acid on the Transport Behavior of Trivalent Chromium in Soils and its Mechanism

Effects of Tannic Acid on the Transport Behavior of Trivalent Chromium in Soils and its Mechanism

Effect of electrode modification on the production of electrical energy and degradation of Cr (Ⅵ) waste using tubular microbial fuel cell

<abstract> <p>Carcinogenic hexavalent chromium is increasing worldwide due to the increased electroplating, welding and textile industry. On the other hand, molasses, the sugar factory's byproduct with high organic compounds (sugars), may pollute the environment if it is not processed. However, microbial fuel cell (MFC) seems to be a promising technology due to its ability to produce electrical energy from pollutant degradation using microbes while reducing hexavalent chromium to trivalent chromium with less toxicity. Carbon felt was used at both electrodes. This research aimed to determine the effect of modifying the anode with rice bran and cathode with Cu catalyst towards electricity generation and pollutant removal in molasses and reducing Cr (Ⅵ) into Cr (Ⅲ) using tubular microbial fuel cells. Moreover, the effect of mixing Sidoarjo mud and <italic>Shewanella oneidensis</italic> MR-1 as electricigen bacteria toward electrical energy production and pollutant removal was determined. Experiments revealed that the S/CM/AM variable, which only used <italic>Shewanella oneidensis</italic> MR-1 as an electricigen bacteria with both modified electrodes, produced the highest total power density of 530.42 mW/m<sup>2</sup> and the highest percentage of Cr (Ⅵ) reduction of 98.87%. In contrast, the highest microbial population of 66.5 × 10<sup>10</sup> cells/mL, 61.28% of Biological Oxygen Demand (BOD<sub>5</sub>) removal and 59.49% of Chemical Oxygen Demand (COD) were achieved by SSi/CM/AM variable, mixing <italic>Shewanella oneidensis</italic> MR-1 and Sidoarjo mud as an electricigen bacteria with both modified electrodes. Therefore, this study indicates that double chamber tubular microbial fuel cells may be a sustainable solution for managing molasses and carcinogen hexavalent chromium.</p> </abstract>

Establishment of Tissue Biodistribution and Blood Clearance Rates of Intravenously Administered Radioactive 51Cr3+ in New Zealand White Rabbits

HIGHLIGHTS Tissue biodistribution of intravenously administered trivalent chromium. Blood clearance rates of intravenously administered trivalent chromium. Faster systemic blood clearance is through renal excretion. Understanding of the above parameters is relevant for its diagnostic applications.

Magnetoelectric reduction of chromium(VI) to chromium(III)

Toxic heavy-metal pollution represents one of the most pressing environmental challenges that humankind faces today. The conventional approaches for removing highly toxic and carcinogenic heavy metals are currently unsuitable for practical applications. The reduction of harmful heavy metals, such as hexavalent chromium (Cr(VI)) into less harmful trivalent chromium Cr(III), has been gaining considerable interest. In response to this, UV light based photocatalysts have been comprehensively investigated for the reduction of various problematic heavy metals. However, for practical applications, using light as a solution can be highly inefficient owing to poor light absorption in murky or colored heavy metal contaminated water. Here, we demonstrate that wireless magnetic fields can induce the reduction of toxic heavy metals. Core-shell magnetoelectric CoFe2O4@BiFeO3 nano-octahedral particles were fabricated and used for the catalytic reduction of Cr(VI) via the magnetoelectric effect. We have conducted trapping experiments to propose a mechanism behind the magnetoelectric-effect catalytic reduction. We have achieved reduction of 86% of toxic Cr(VI) using a scavenger for singlet oxygen. In addition, we show the concomitant reduction of Cr(VI) and degradation of an organic pollutant, methylene blue, in a synergistic manner, where the presence of methylene blue accelerates the reduction of Cr(VI) to Cr(III).

Divalent (Cr2+), trivalent (Cr3+), and tetravalent (Cr4+) chromium ion-doped tunable solid-state lasers operating in the near and mid-infrared spectral regions

Divalent (Cr2+), trivalent (Cr3+), and tetravalent (Cr4+) chromium ion-doped tunable solid-state lasers operating in the near and mid-infrared spectral regions

Palladium Nanoparticles Supported on Activated Carbon (C) for the Catalytic Hexavalent Chromium Reduction

Hexavalent chromium is widely used in industry and causes human health and environmental problems due to its extremely toxic properties. On the contrary, trivalent chromium is necessary for living ecosystems. Therefore, reducing hexavalent chromium to trivalent chromium is the best strategy for detoxifying hexavalent chromium. Pd(0)@C nanocatalyst was prepared by a simple impregnation-reduction method in solution under mild conditions at 298 K and was identified by XPS, XRD, TEM, TEM–EDX, HR-TEM, and ICP-OES analyses. TEM results showed that very well-dispersed Pd nanoparticles were formed on the C surface (mean particle sizes 3.98 ± 0.24 nm). The catalytic performance of Pd(O)NPs impregnated on cheap and easily available commercial activated carbon were tested as heterogeneous nanocatalysts in the catalytic reduction of hexavalent chromium in the medium of formic acid, which is a good reducing agent, and sodium formate as the promoter at 298 K. It was determined that the formed Pd(0) nanoclusters could successfully reduce Cr(VI) to Cr(III) with high selectivity (~ 97%) in formic acid and sodium formate solution under mild conditions. It was also observed that the Pd(0)@C catalyst retained a significant (> 75%) initial activity even after the 5th use. In addition, the kinetic studies of the catalytic reduction reaction of Cr(VI) catalyzed by Pd(0)@C nanoparticles were investigated depending on the substrate [Cr2O72−], catalyst [Pd(0)@C], sodium formate [HCOONa], formic acid [HCOOH] concentrations, and temperature parameter. From the rich kinetic data obtained, the nature of the velocity equation was explained, and the activation parameters were calculated.

Efficient removal of Cr (VI) by modified sodium alginate via synergistic adsorption and photocatalytic reduction

Conventional photocatalytic removal of hexavalent chromium (Cr (VI)) suffers from low metal uptake capacity, expensive photocatalysts, and slow desorption of trivalent chromium from the catalyst surface. In this study, calcium chloride and iron(III) nitrate were used to cross-link with polyethyleneimine grafted sodium alginate (SA) to acquire two materials, named as SPC and SPF, respectively, for the efficient removal of Cr (VI) from aqueous solutions via adsorption and photocatalytic reduction. FT-IR, DFT, and XPS results indicated that polyethyleneimine was successfully grafted onto the SA matrix and could electrostatically attractted hexavalent chromium anions in solution. Fe (III) cross-linking forms a highly porous structure at ambient temperature, which could overcome the polysaccharide collapse in the dehydration process. The UV–vis DRS, EIS, and photocurrent density characterizations of SA, SPC, and SPF suggested that SPF has smaller charge transfer resistance and is conducive to the separation of photogenerated charges, thus SPF exhibited superior performance in the photocatalytic reduction of Cr (VI). As a result, SPF is an efficient photocatalyst for the removal of Cr (VI) and provides new sights on polysaccharide-based photocatalysts applications.

Palladium nanoparticles supported on multı-walled carbon nanotube (MWCNT) for the catalytic hexavalent chromium reduction

Chromium (VI) is widely accepted as an acute toxic contaminant in living ecosystems, while the trivalent Chromium form (III) is thought to be an important element for living beings. This study showed that zero palladium (Pd0) metal nanoparticles supported onto a multi-walled carbon nanotube (MWCNT) catalyst (Pd@MWCNT) effectively catalyzed the reduction reaction of Chromium (VI) to Chromium (III) using HCOOH (formic acid) as a reducing agent. The catalyst (Pd@MWCNT) was prepared reproducibly in the aqueous mixture at room conditions through the impregnation-reduction technique and identified using some analytical characterization techniques (HRTEM, DR/UV–vis, TEM-EDX, TEM, XPS, ICP-OES, and P-XRD). The results of the characterization studies show that the palladium(0) nanoparticles (demean = 2.20 ± 0.25 nm) are very well dispersed onto the MWCNT support material surface. The stability and activity of catalytic performance of Pd(0) metal nanoparticles were investigated in the reactions of Chromium (VI) to Chromium (III) in HCOOH solution. The results show that the Pd@MWCNT catalyst exhibited excellent activity (TOF = 281 mol Cr2O72−/mol Pd min), even after 5 times of reuse (<86%) in the reduction reaction of Chromium (VI) to Chromium (III) at 298K. In addition, this study includes very rich kinetic data depending on [Pd@MWCNT], [HCOOH], [HCOONa], [Cr2O72−] concentrations and temperature parameters to determine the nature of the reduction rate and activation parameters of Cr(VI) catalyzed by Pd@MWCNT nanocatalyst in the formic acid medium as a reducing agent.

Analysis of Hydrogeochemical Characteristics and Origins of Chromium Contamination in Groundwater at a Site in Xinxiang City, Henan Province

Hexavalent chromium contamination in groundwater has become a very serious and challenging problem. Identification of the groundwater chemical characteristics of the sites and their control mechanisms for remediation of pollutants is a significant challenge. In this study, a contaminated site in Xinxiang City, Henan Province, was investigated and 92 groundwater samples were collected from the site. Furthermore, the hydrogeochemical characteristics and the distribution patterns of components in the groundwater were analyzed by a combination of multivariate statistical analysis, Piper diagram, Gibbs diagram, ions ratio and hydrogeochemical simulation. The results showed that the HCO3-Cl-Mg-Ca type, SO4-HCO3-Na type, and HCO3-Mg-Ca-Na type characterize the hydrogeochemical composition of shallow groundwater and HCO3-Cl-Mg-Ca type, HCO3-Na-Mg type, and HCO3-SO4-Mg-Na-Ca type characterize the hydrogeochemical composition of deep groundwater. Ion ratios and saturation index indicated that the groundwater hydrogeochemical characteristics of the study area are mainly controlled by water–rock action and evaporative crystallization. The dissolution of halite, gypsum and anhydrite, the precipitation of aragonite, calcite and dolomite, and the precipitation of trivalent chromium minerals other than CrCl3 and the dissolution of hexavalent chromium minerals occurred in groundwater at the site. The minimum value of pH in groundwater at the site is 7.55 and the maximum value is 9.26. The influence of pH on the fugacity state of minerals was further investigated. It was concluded that the saturation index of dolomite, calcite, aragonite and MgCr2O4 increases with the increase of pH, indicating that these minerals are more prone to precipitation, and the saturation index of Na2Cr2O7, K2Cr2O7 and CrCl3 decreases with the increase of pH, implying that Na2Cr2O7, K2Cr2O7 and CrCl3 are more prone to dissolution. The saturation index of the remaining minerals is less affected by pH changes. The study can provide a scientific basis for groundwater remediation.

Camelina Meal and Chromium Picolinate Effects on Broiler Thigh Meat Nutritional Properties

Abstract The aim of this study was to evaluate the combined effects of trivalent chromium and camelina meal on proximate composition, mineral content and fatty acids profile of broiler chicken thigh meat. An experiment with 2 x 3 factorial arrangement was performed on 240 Ross 308 broiler chicken aged 14 days. Six dietary treatments were elaborated as follows: 0 and 3% inclusion rate of Camelina meal and 0, 200 and 400 μg/kg chromium picolinate (CrPic). Supplementation of broiler diets with 3% Camelina meal led to significantly (P&lt;0.05) increased crude fat concentrations in thigh samples compared to control group or with single chromium supplemented groups. In thigh samples, Zn and Fe concentrations increased under CrPic influence and fatty acids profile was influenced by Camelina meal presence in the diets. In Camelina meal supplemented groups, were registered significantly increased omega 3 fatty acids concentrations compared to control group or single chromium supplemented groups. The results of the present study found that Camelina meal and chromium picolinate supplements in broilers diets improved the nutritional properties of thigh meat, especially essential minerals content and fatty acids profile.

Resource-saving processing of technological solutions and wastewater by electrochemical method (methods overview)

The paper summarizes the data on the wastewater formation from a number of plants of chemical, engineering, energy and leather industries and its processing in electrolyzers of various designs to obtain the substances that can be used in various production processes. In the ethylenediamine production, wastewater occurs at the stages of amines rectification and of ethylenediamine dihydrochloride neutralization. Recycling of effluents generated during the amine rectification in a two-chamber electrolysis cell allows the ethylenediamine and ammonia to be returned to the production process. The processing of ethylenediamine dihydrochloride solution in the membrane electrolyzers saves alkali for the neutralization process. Electrochemical processing of distilled liquid in soda production makes possible to obtain calcium hydroxide, sodium hydroxide and hydrochloric acid or chlorine, which can be used in various industrial processes. Wastewater generated during the demineralized water production contains a significant amounts of sodium sulfates and chlorides. The processing of these effluents in a membrane electrolyzer yields sulfuric acid and alkali, which are suitable for the regeneration of ion-exchange filters. After processing in an electrodialysis apparatus the wastewater generated during the chromium and nickel coatings, is concentrated to values that allow them to be used to prepare an electrolyte adjustment. The leather industry effluents contains an amount of trivalent chromium and sulphides. Electrochemical processing of these effluents leads to almost complete extraction of chromium and sulfides.

Coupled Mn(II) and Cr(III) Oxidation Mediated by Ascomycete Fungi.

Manganese (Mn) oxides are considered as the primary oxidant of trivalent chromium [Cr(III)] in the environment. Microbial activities are responsible for the majority of Mn oxide formation in nature, thus likely influencing Cr(III) oxidation. Previous studies have been limited to Cr(III) oxidation by bacterial Mn oxides. Herein, we report coupled Mn(II) and Cr(III) oxidation in the presence of three Mn(II)-oxidizing Ascomycete fungi. In contrast to the previously reported inhibitory effect of Cr(III) on bacterial Mn(II) oxidation, varying effects of Cr(III) on fungal Mn(II) oxidation were observed, which may be linked to their Mn(II)-oxidation mechanisms. Under the concentrations of Mn(II) and Cr(III) applied in this study, Cr(III) promoted Mn(II) oxidation if it was mediated by hyphae-associated processes, but inhibited Mn(II) oxidation if it was achieved via extracellular enzymes/metabolites. The Cr(III) oxidation rate and extent were affected by Cr(III) speciation, Cr(VI) removal capacity (i.e., adsorption/reduction) of fungi, and organic content. The morphology and spatial relationship of Mn oxides with fungi varied, depending on fungal species and Cr(III) presence. Our findings highlight the importance of Mn(II)-oxidizing fungi in biogeochemical cycles of Mn and Cr and have significant implications for the origin of geogenic Cr(VI) and stability of reduced chromium in contaminated environments.

High efficient adsorption and photocatalytic removal of hexavalent chromium over three-dimensional grapheneoxide aerogel under visible light

<p indent="0mm">Heavy metal ions such as hexavalent chromium (Cr(VI)) existed in wastewater have caused serious pollution problems.Cr(VI) is teratogenic and carcinogenic, while trivalent chromium (Cr(III)) is an essential nutrient for humans and animals. Adsorption method can transfer Cr(VI) from liquid phase to absorbent surface, but it needs follow-up treatment to remove Cr(VI). Photocatalysis technique can reduce Cr(VI) to Cr(III), so as to decrease its toxicity, but the adsorption capacity towards Cr(VI) is always small due to poor surface area of some traditional semiconductor oxide photocatalysts. Therefore, a new material with both good adsorption capacity and photocatalytic activity is needed for Cr(VI) removal. As an emerging kind of carbon materials, graphene oxide (GO) has attracted particular attention in the catalysis field. Graphene oxide aerogel (GOA), a three dimensional nanomaterial, possesses numerous adsorption sites and superior ability to accept and transport photogenerated electrons, would thus present good adsorption capacity and high photocatalytic performance simultaneously. So far, most studies on GO-base material are towards investigating its co-catalyst role (adsorption enhancement or electron shuttle) in improving efficiency of metal or semiconductor photocatalysts. Only a few studies have applied GO-base material as a sole photocatalyst. In this study, combined with the cross-linking method and the supercritical CO₂ fluid extraction method, three-dimensional porous and recyclable GOA with large specific surface area and defect sites was prepared by using GO as the precursor. The physicochemical properties were characterized by SEM, XRD, Raman spectroscopy and nitrogen adsorption methods. The adsorption behavior and photocatalytic reduction performance of GOA towards Cr(VI) under visible light were investigated. GO was hydrothermally reduced during the preparation process, and many defects were generated on GO sheets. Melamine and cyanuric acid were used as crosslinking agents to increase the interlayer spacing, and at the same time providing GOA a large specific surface area and a rich porous structure. When the mass ratio of GO, melamine, and cyanuric acid was 3:3:3 and the GO concentration was 6 mg L⁻¹, GOA exhibited the largest specific surface area and defect density. This kind of GOA, i.e., GOA_333-6 presented the best adsorption capacity and photocatalytic efficiency of Cr(VI). The adsorption behavior of GOA on Cr(VI) fits to the quasi-second-order kinetic model and the Langmuir adsorption isotherm model, indicating that the adsorption process was a single-layer chemical adsorption, in which the intra-particle diffusion in the initial adsorption stage was the rate-limiting step. The three-dimensional graphene oxide aerogel GOA obtained in this study exhibited large adsorption capacity, high photocatalytic removal efficiency for high concentration Cr(VI) under visible light, and good repeatability. Single GOA material has potential application in removing heavy metal ions from polluted wastewater.

Chromium induced neurotoxicity by altering metabolism in zebrafish larvae

BackgroundRecently, both trivalent chromium Cr (III) and hexavalent chromium Cr (VI) have been reported to produce neurotoxicity. However, the underlying mechanisms of the neurotoxicity caused by different chemical valence of chromium remain unclear. ObjectiveThe purpose of this study was to investigate the mechanism of neurotoxicity induced by exposure to chromium with different valence states based on metabolic disturbance in zebrafish larvae. MethodsZebrafish embryos were exposed to 1 mg/L Cr (III) and 1 mg/L Cr (VI) for 120 hpf respectively. The related indexes of neural development were observed by stereoscope and behavior analysis system. 8OH-dG were detected using enzyme-linked immunosorbent assay. The generation of reactive oxygen species was detected using an oxidant-sensing probe 2',7'-dichlorodihydrofluorescein diacetate. AChE activity was determined by a colorimetric assay based on hydrolysis of acetylcholine. The expression levels of neurodevelopmental genes and methyltransferase genes in juvenile zebrafish was analyzed by real-time PCR. The methylation status of neurogenin1 and neurod1 genes was detected by bisulfite sequencing PCR. The binding of H3K27me3 was detected by chromatin immunoprecipitation-qPCR. Metabolic profiles and one carbon metabolic analysis were performed by UPLC-MS. ResultsThere were no significant differences in survival rate, hatching rate and spontaneous movement of zebrafish in both Cr-exposed groups compared to the control. The malformation rate in Cr (VI) -exposed group was obviously increased compared to the control and Cr (III) -exposed group. At 48hpf and 72hpf of exposure, the embryonic heart rate in Cr (III)-exposed group was significantly higher than that of Cr (VI)-exposed group and the control. At 120hpf, zebrafish in both Cr-exposed groups exhibited decreasing changes in swimming distance and disturbance of sensitivity to light and dark. 8OH-dG in Cr (VI)-exposed group were significantly higher than that in the control. The generation of ROS in both Cr -exposed groups was significantly higher than that in the control. The activity of AchE was significantly decreased in both Cr-exposed groups compared to the control. Most of early neurogenesis related genes, such as α-tubulin, elavl3, gap43, sox19b, neurogenin1 and neurod1 in Cr-exposed groups were significantly up-regulated compared to those in the control. The expression of dnmt1 and dnmt3 genes was significantly down-regulated in both Cr-exposed groups. BSP-PCR results showed that genic sequences in the neurogenin1 and neurod1 genes have lower levels of DNA methylation in both Cr-exposed groups, especial in Cr (VI)-exposed group. ChIP analysis showed that there was a decrease in H3K27me3 binding within the corresponding region of neurogenin1 in both Cr-exposed groups and that of neurod1 in Cr (III)-exposed group. Untargeted metabolomic analysis showed that significant changes in metabolites induced by Cr exposure were associated with differences in primary bile acid biosynthesis, phospholipid biosynthesis (phosphatidylcholine biosynthesis and phosphatidylethanolamine biosynthesis), linoleic acid metabolism, arachidonic acid metabolism, amino acid metabolism, purine metabolism, betaine metabolism, spermidine and spermine biosynthesis, and folate metabolism, the last four of which are related to one carbon metabolism. Targeted analysis of one carbon metabolites (5-MT, Gly, Met, SAH and Hcy) related with folate cycle and methionine metabolism were significantly decreased upon Cr exposure. The elevated SAM to SAH ratio in both Cr- exposed group indicated the decreasing capacity for methylation reaction. ConclusionCr (III) and Cr (VI) can induce neurotoxicity by interfering with one carbon metabolism and affecting DNA methylation and histone methylation to regulate the expression of neuro-related genes. Cr exposure also influenced primary bile acid biosynthesis and phospholipid biosynthesis, which are associated with neuroprotective effects and need to be further validated.

Sulfur-doped carbon dots synthesis under microwave irradiation as turn-off fluorescent sensor for Cr(III)

This study synthesized a facile and high sensitive fluorescent probe based on sulfur-doped carbon dots (S-CDs) using a one-step microwave irradiation method. The probe exhibited a strong blue emission and a high quantum yield (QY) of 36.40%. In the detection, the presence of trivalent chromium (Cr(III)) strongly quenched the PL intensity of S-CDs by the inner filter effect (IFE) quenching mechanism of Cr(III) on the S-CDs. The S-CDs exhibited good sensitivity to turn-off Cr(III) detection with a linear range concentration of 0–45 μM and a detection limit of 0.17 μM. Furthermore, the proposed method has been successfully applied for Cr(III) detection in natural water samples with the 93.68–106.20% recoveries.

Nanocrystalline erdite from iron-rich sludge: Green synthesis, characterization and utilization as an efficient adsorbent of hexavalent chromium

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.