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Growth, lipid peroxidation, H2O2 produciton and the response of the antioxidant enzymes and metabolites of the ascorbate glutathione pathway to oxidative stress caused by two concentrations (50 and 100µM) of Cr(III) and Cr(VI) was studied in 15 day old seedlings of sorghum (Sorghum bicolor(L.) MoenchcvCO 27) after 10 days of treatment. Cr accumulation in sorghum plants was concentration and organ dependant. There was no significant growth retardation of plants under 50µM Cr(III) stress. 100µM Cr(VI) was most toxic of all the treatments in terms of root and leaf growth and oxidative stress. 50µM Cr(VI) treated roots exhibited high significant increase in superoxide dismutase (SOD), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) (p<0.01) and significant increases in catalse (CAT), ascorbate peroxidase (APX) and monodehydroascorbate reductase (MDHAR) (p<0.05). A high increase in ascorbic acid (AA) level was seen in roots of 50µM Cr(VI) treated plants in comparison with control. Levels of reduced glutathione (GSH) showed a varied and complex response in all the treatments in both plant parts. GSH/GSSG ratio was not affected by Cr(III) treatment in leaves, in contrast, roots exhibited significant reduction in the ratio. Results indicate that GSH depletion increased sensitivity to oxidative stress (Cr(VI) roots and leaves and Cr(III) 100µM roots) and AA in tandem with APX compensated for GSH depletion by acting directly on H2O2 and the mechanism of defensive response in roots as well as leaves varied in its degree and effectiveness due to the concentration dependant differences observed in translocation of the element itself, reactive oxygen species (ROS) generation and enzyme inhibition based on the oxidation state supplied to the plants. [ABSTRACT FROM AUTHOR]

The catalytic adsorptive stripping voltammetry (CAdSV) has been applied to physico-chemical chromium speciation study in the upper Dunajec catchment, severely polluted by the tannery wastewater. The method is based on the adsorptive preconcentration of the Cr(III)–diethylenetriammine-N,N,N′,N″,N″-pentaacetic acid (DTPA) complex and the utilization of the catalytic reaction in the presence of nitrate. Under optimized conditions the CAdSV enables the oxidation state speciation study of Cr content by direct determination of Cr(VI) in the presence of the predominant Cr(III) concentration with the detection limit for chromium(VI) of 0.08 nM and the linearity range from 0.1 to 80 nM obtained for 20 s of accumulation, as well as the determination of total Cr after UV oxidation of Cr(III) to Cr(VI). Due to the difference in the chemical properties of different chromium species the CAdSV method makes possible a speciation study of Cr(III) and Cr(VI) oxidation state. The RSD of the determination of Cr(VI) and Cr(III) varies from 0.5 to 5%. It has been proved that in natural water in which strong complexants of Cr(III) such a humid acids are presented, Cr(VI) can be determined accurately in the presence of high excess of Cr(III). Fractionation of selected water samples with tangential flow filtration (TFF, cut-off 10 and/or 1 kDa) provides insight into physical Cr speciation, i.e. partitioning of the Cr(VI) and Cr(III) between the colloidal and the dissolved fractions. It has been shown that the content of the Cr species in the Dunajec river depends on the season, and is significantly higher in autumn and winter during the most intensive tanneries production processes. The concentration of total Cr exceeds occasionally the legally admissible level. A large fraction of total Cr(III) concentration is associated with the colloidal material, while Cr(VI) occurs solely in the truly dissolved form. [Copyright &y& Elsevier]

The development of a new method for chromium speciation using capillary electrophoresis-electrothermal atomic absorption spectrometry (CE-ETAAS) is described For that propose a simple capillary electrophoresis device enabling simultaneous separation and concentration of different chromium species has been designed and constructed The device proved suitable for separating Cr(III) and Cr(VI) in aqueous samples The sample amounts were sufficient for off-line collection and subsequent oil-line detection with ETAAS The influence of sample and background electrolyte pH values on the analytes' sepmation and recovery was investigated The separation time and sample zone length were optimized The limit of detection for both analyses was 1 ng/mL RSD of the experiments was about 10%. [ABSTRACT FROM AUTHOR]

Two methods coupling ion chromatography with inductively coupled plasma -- optical emission spectroscopy (ICP-OES) were developed for the simultaneous separation and determination of Cr(III) and Cr(VI) species. In the first method, anion chromatography with sodium bicarbonate/carbonate solution as the eluent was utilized. Cr(III) species were protected from precipitation by complexation with ethylenediaminetetra-acetic acid (EDTA) prior to analysis. The detection limits were determined experimentally as 0.05 mg L-1 for both species. Most of the common cations were found to interfere with the accurate determination of Cr(III) when present in excess of 50 mg L-1 . In the second method using cation chromatography, a guard column was employed in conjunction with a stepwise elution programme to elute the chromium species. The detection limits were experimentally determined as 0.1 mg L-1 for both species. [ABSTRACT FROM AUTHOR]

Detailed surveys of intertidal sediments have been performed along the north and south shores of the Inner Clyde estuary, UK. Surface sediment data reveal significant spatial variation in Cr content and an association with major sediment characteristics and location within the estuary. Depth variation for Cr and other heavy metals cannot be explained by variation in major geochemical controls such as grain size and organic matter and highlights the impact of historical contamination on sediment quality. These elevated levels at depth may still have environmental impact through redox-reactivity, in association with iron and manganese. Sequential extraction of sediments and pore water analysis of Cr(VI) and Cr(III) provide detailed information on release potential from the sediments. The implication of Cr mobility for biota in the estuary has been assessed by the analysis of a common marine bivalve, Mytilus edulis (Blue Mussel) and a burrowing polychaete, Nereis diversicolor (rag worm) from a number of survey sites. Bioconcentration factors for Mytilus indicate that the weakly held portion of sediment Cr is available for uptake and in the case of Nereis, bioaccumulation appears to be inhibited by sediment organic matter. [ABSTRACT FROM AUTHOR]

Speciation of chromium has attracted a great deal of interest in view of the toxic properties of Cr6+ compared with the much less toxic Cr3+. A freshwater plant, duckweed which is uniquely suitable for aquatic toxicity tests is utilized to study the growth responses and accumulation of chromium in the presence of copper and zinc. Speciation analysis was carried out by using differently activated alumina. Metal ion concentrations in the plant were determined by FAA spectrometry. Results of the present study revealed that the oxidation state of chromium as well as its concentration in media controlled the growth and the metal accumulation in duckweed. Regarding this, Lemna minor (common duckweed species) accumulated Cr3+ in smaller quantities and it resulted in relatively larger growth responses, whereas Cr6+ was accumulated in larger quantities and it yielded relatively smaller growth responses. Different types of metal interactions among chromium, copper, and zinc ions were evident. These interactions were classified as synergistic, antagonistic, and additive and they were strictly dependent on the oxidation state of the chromium ion. [Copyright &y& Elsevier]

Chromium exists in nature in two oxidation state, +3 and +6. It is a bioelement in +3 state but mutagenic in +6 state. Therefore, the speciation of chromium in the contaminated environments becomes very important to understand its fates and exposure. Used techniques are based on the determination of Cr (VI) and total chromium, and then Cr (III) is determined by difference. Cr (VI) is measured spectrophotometricall, as Cr (VI)- diphenylcarbazide complex, and total chromium after oxidation Cr (III) to Cr (VI) with H2O2 and KOH. The method was applied to the analysis chromium speciation in water, sediments and plants from "TABACARIE" Lake, Constantza District, Romania. It was noticed that the sediments contain generally, Cr (VI) and Cr (III) species in higher concentration that plants, and in the water exist smaller quantities. [ABSTRACT FROM AUTHOR]

In this approach a fluorometric technique has been developed to study chromium speciation, based on optimised conditions using chemometric methods of experimental design and central composite design. Full and fractional factorial design was used for evaluation of the effective factors in determination of Cr(VI) by fluorometric using Rhodamine-6G in the presence of H2SO4. Theory and methodology of a central composite design as a chemometric method for the optimisation of analytical procedures were developed in this approach. It was found that the analytical performance for measurement at the point of optimum in this technique is superior and more accurate than that of one variable at a time. Cr(VI) and Cr(III) were measured in a wastewater sample using the proposed technique. The results confirm the selective determination and speciation of Cr(VI)/Cr(III). [Copyright &y& Elsevier]

The article presents analytical characterisation of solid and solution-phase chromium species at chromite ore processing residue (COPR)-contaminated sites. The solid phases present in COPR from three of the sites investigated were identified and quantified using X-ray powder diffractometry and scanning electron microscopy combined with energy dispersive X-ray microanalysis. The valency of the constituent ions is not obtained directly from the electron microprobe analysis but is derived from the stoichiometry and the known mineral structures.

A new analytical procedure for the speciation of chromium (Cr) in plants by high performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS) was developed using a strong anion-exchange Mono Q column for the separation of the Cr species. To optimize the analytical procedure, Cr complexes were first synthesized from Cr-nitrate with the addition of an excess of ligand (90°C). Cr-oxalate, Cr-malate, Cr-citrate, Cr-aconitate and Cr-quinate complexes and Cr-nitrate (pH 6.5) were chromatographically separated from Cr(VI) by applying linear gradient elution from 100% water to 100% NH 4 Cl at a flow rate of 1.5 ml min -1 in 10 min. The column recoveries ranged from 100 to 104%. The exception was Cr-aconitate (column recovery 33%), where a quantitative synthesis was not possible. Good repeatability of the measurements (relative standard deviations better than ± 3%) and low limits of detection (below 0.37 ng ml -1 Cr) were achieved for the individual Cr species. The developed analytical procedure was applied to Cr speciation for dandelions ( Taraxacum officinale ) grown in soil with a high Cr content and a study of the uptake and metabolism of Cr species in dandelions grown in soil with a low Cr content treated with solutions of Cr(VI) or Cr-nitrate (5000 ng ml -1 Cr, pH 6.5) for 48 h. The separated Cr species were quantified by post-column isotope dilution ICP-MS, while the identification was based on retention times and was also supported by mass spectra obtained with high resolution mass spectrometry (HR-MS). The data indicate that for dandelions grown in Cr-rich soil and that treated with Cr-nitrate (pH 6.5), the Cr was mainly accumulated in the roots, while in plants treated with Cr(VI) (pH 6.5), the Cr was evenly distributed between the roots and the leaves. The Cr species found in dandelion roots and leaves were Cr-aconitate, Cr-malate, and Cr-quinate. The results revealed that Cr(VI) was completely reduced and metabolized to Cr(III) complexes. LA-ICP-MS data showed that the Cr in a leaf of dandelion grown in Cr-rich soil was localized mainly at the apex of the leaf., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Marković, Levstek, Žigon, Ščančar and Milačič.)

The chromium (Cr) isotope system is an important redox proxy for understanding Earth's oxygenation history. However, quantitative application of this proxy is hindered by a lack of clear understanding of the global Cr isotope mass balance. Estuarine environments potentially play important roles in influencing the global oceanic Cr mass balance because riverine Cr derived from continental weathering must first travel through estuaries before entering the open ocean. We collected water, suspended particulate matter, and sediment samples across a salinity gradient in the Mobile Bay Estuary located in the Northern Gulf of Mexico, with a purpose of evaluating whether Cr behaves conservatively in estuarine environments. A simple conservative mixing model between the fresh Mobile River water and Gulf of Mexico seawater alone was insufficient to explain the Cr concentration and isotope data, suggesting that Cr behaves non-conservatively in this estuary system. A model incorporating conservative mixing, partial Cr(VI) reduction and partial scavenging of the produced Cr(III) is developed to reproduce the observed data. Our data and modeling exercise suggest that up to 60% of Cr(VI) is reduced to Cr(III) in the Mobile Bay Estuary with a Cr isotope fractionation factor of −1.2‰, and 40% of the produced Cr(III) is removed from solution. Although these parameters may not be the sole solution to the system of equations involved, they are consistent with previous estimates. Future redox-specific Cr isotope data in estuarine environments are needed to place finer constraints on these parameters in estuaries, which is critical for estimating global marine Cr isotope mass balance using riverine Cr concentration and isotope data. [ABSTRACT FROM AUTHOR]

Thermal decomposition is a promising technology for tannery sludge disposal, as through thermal decomposition, the energy in tannery sludge could be recovered, and the abundant harmful metal chromium (Cr) could be fixed in the solid residues, which might be recycled as the chromium-rich mineral for further use. In order to provide objective evaluation on the various thermal decomposition technologies for tannery sludge disposal from safety perspective, in this study, different thermal decomposition processes of tannery sludge in typical reactors were simulated on a bench-scale equipment in laboratory, and the transformation characteristics of Cr species in tannery sludge during the processes were systematically investigated. Through characterization of the solid products of decomposition, only Cr (III) species of Cr 2 O 3 and MgCr 2 O 4 were determined in the pyrolysis product, while both Cr (III) species of Cr 2 O 3 and Cr (VI) species of CaCrO 4 were detected in the incineration product. For the processes of simulating gasification, when the final stage was combustion, Cr (III) species of Cr 2 O 3 and MgCr 2 O 4 and Cr (VI) species of CaCrO 4 were observed, while when the final stage was reduction, only Cr (III) species of Cr 2 O 3 , MgCr 2 O 4 and CaCr 2 O 4 were observed. It was found that the Cr (III) species of MgCr 2 O 4 generated in the pyrolysis stage has high stability and is difficult to be oxidized in the combustion stage, while Cr (VI) species of CaCrO 4 produced in the combustion stage can be removed in the subsequent reduction stage. Based on the results, among the various thermal decomposition technologies to dispose of tannery sludge, pyrolysis is the safest, while incineration presents a huge risk. The adoption of downdraft gasifier is safer than that of updraft gasifier. Therefore, employing pyrolysis or downdraft gasification technology to dispose of tannery sludge is expected to fix Cr in the form of non-toxic Cr (III) in the solid residue, and then reuse it as tannery agent, so as to achieve the goal of cleaner production. • Typical thermal decomposition processes for tannery sludge disposal were simulated. • Only Cr (III) existed in the product of tannery sludge pyrolysis. • Both Cr (III) and Cr (VI) existed in the product of tannery sludge incineration. • MgCr 2 O 4 generated in the pyrolysis is difficult to be oxidized through combustion. • CaCrO 4 generated in the combustion stage can be reduced by H 2 at high temperature. [ABSTRACT FROM AUTHOR]

• First report on Cr(III) and Cr(VI) speciation analysis in bread and breakfast cereals using SS-ID and HPLC-ICP-MS (primary analysis method). • Cr(VI) was not detected in bread and breakfast cereals samples while total Cr consisted of Cr(III) solely. • Consumption of bread and breakfast cereals products in France and Denmark showed no significant to Cr in both countries. This study reports the development and validation of a analytical approach for simultaneous Cr(III) and Cr(VI) speciation analysis in bread and breakfast cereals using species specific isotope dilution (SS-ID) and high-performance liquid chromatography (HPLC) coupled to inductively coupled plasma-mass spectrometry (ICP-MS). The species were extracted by sequential complexation of genuine Cr(III) with ethylenediaminetetraacetic acid (EDTA) and subsequently of Cr(III) originating from reduction of Cr(VI) with 1,5-diphenylcarbazone (DPCO) in the same analytical run. Efficient HPLC separation of Cr(III)-EDTA and Cr(III)-DPCO complexes was carried out by anion exchange HPLC in less than 3 min. The method was validated by means of the accuracy profile approach by carrying out 3 measurement series in duplicate on 5 different days over a timespan of one month. The quantification limits were 0.014 μg kg−1 for Cr(III) and 0.047 μg kg−1 for Cr(VI), respectively. The measurement bias ranged from 0.31 to 0.49 %, whereas the coefficient of variation in terms of repeatability (CV r) varied from 1.3–4.4 % for Cr(III) and from 0.6–7.9% for Cr(VI). Similarly, the coefficient of variation in terms of intermediate reproducibility (CV R) ranged from 1.3–4.4% for Cr(III) and from 2.0–8.9% for Cr(VI), respectively. The method was successfully applied to the analysis of a selection of bread and breakfast cereals samples. Cr(VI) was not detected in any of these samples while Cr(III) levels ranged between 5.2 and 176 μg kg−1 for bread samples and between 23.8 and 350 μg kg-1 for breakfast cereals. These results were comparable with the levels of total Cr analysed in the same samples by ICP-MS. The method developed in this study on the basis of SS-ID and sequential species complexation is a powerful analytical tool for accurate and precise quantification of Cr(III) and Cr(VI) at trace levels and allows for correction of any species interconversion during sample preparation. [ABSTRACT FROM AUTHOR]

Herein, modified Fe 3 O 4 magnetic nanoparticles by ZrO 2 (MNPZs) were prepared by co-precipitation method. Prepared MNPZs were characterized with XRD, SEM, EDX, TEM, FTIR and VSM techniques. In addition, a modified magnetic carbon paste electrode (CPE) by MNPZ was prepared, and its interaction with Cr(III) and Cr(VI) ions was investigated in the presence of [Fe(CN) 6 ]3-/4- and PBQ/H 2 Q redox probes via CV and EIS. An electrochemical technique based on observed behavior of redox probes with accumulated each forms of chromium was developed for speciation of Cr(III) and Cr(VI) in this work. Accumulated Cr(III) on CPE/MNPZ showed electrostatic attraction toward [Fe(CN) 6 ]3-/4- redox probe and accumulated Cr(VI) showed a blocking behavior toward PBQ/H 2 Q redox probe. According to different behaviors of Cr(III) and Cr(VI) at electrode interface in the presence of redox probes, a new calibration for each forms of chromium ions and an entire protocol for Cr speciation are proposed based on voltammetry and impedimetry. After optimization of affecting experimental parameters on the electrode response, linear calibration curves from 1.0 × 10-9 to 1.0 × 10-3 M with sensitivity as 3.41 μA/M and detection limit (DL) as 8.1 × 10-10 M, and from 1.0 × 10-9 to 1.0 × 10-6 M with sensitivity as 4.07 kΩ/M and DL as 6.9 × 10-11 M, were obtained for Cr(III) by using [Fe(CN) 6 ]3-/4- as a redox probe in CV and EIS methods, respectively. Also, linear calibration curves from 5.0 × 10-9 to 1.0 × 10-4 M with sensitivity as 1.79 μA/M and DL as 5.3 × 10-10 M, and from 1.0 × 10-9 to 5.0 × 10-5 M with sensitivity as 7.05 kΩ/M and DL as 4.5 × 10-10 M, were observed for Cr(VI) when use PBQ/H 2 Q as redox probe in CV and EIS methods, respectively. [ABSTRACT FROM AUTHOR]

The production of reference materials for quality control of Cr(III) and Cr(VI) speciation in environmental samples is described. It concerns in the first place two lyophilized solutions containing Cr(III) and Cr(VI) at different concentrations, respectively representative for drinking water and filter leaching solutions, and in the second place filters loaded with welding dust. Twenty-four laboratories with experience in the field participated in an intercomparison exercise organized to validate the suitability of the reference materials and to gauge the state-of-the-art of Cr speciation throughout Europe. The outcome of this exercise is discussed. [ABSTRACT FROM AUTHOR]

A simple and robust field sampling technique has been developed for the determination of chromium (III) and chromium (VI) in rivers. Water samples, on collection, were immediately passed through microcolumns of activated alumina to isolate and retain the desired species. Microcolumns were then returned to the laboratory and inserted into a FI-ICP-ES system for elution/ quantitation. Field sampling performed at 2 stations in S. Yorkshire over a 1 month period yielded elevated concentrations of chromium (III) (8-20μg/1) and chromium (VI) (1.1-4.5 μg/1) and, for each data set, the sum of the two fractions matched the total chromium concentration. [ABSTRACT FROM AUTHOR]

An analytical method derived from the coupling of frontal chromatography (FC) with Inductively Coupled Plasma – Mass Spectrometry (ICP-MS) is proposed for the fast determination of Cr(VI) ultra-traces. The insertion of a short, homemade column filled with a strong cationic exchange resin in the flow-path of a commercial ICP-MS allows on-line trapping of cationic Cr(III) and elution of anionic Cr(VI). As a result, only the Cr(VI) front reaches the detector. This separation mechanism enables the highly selective quantification of Cr(VI) ultra-traces (LOD = 0.026 µg/kg - defined as 3 s of 10 replicated measurements of a 0.050 µg/kg solution) over a wide linearity range (tested up to 1024 µg/kg), even in the presence of Cr(III) concentration as high as 50 mg/kg. Key advantages of the proposed method are the extremely short analysis time (one minute), together with the simplicity and cost-effectiveness of the modifications applied over a commercial ICP-MS instrumental configuration. No time- or chemical-consuming pretreatments are needed: it is only necessary to acidify the sample prior Cr(VI) determination, as normally performed for common ICP-MS analysis. The applicability of the method was demonstrated over mineral water samples and toy migration solutions. [Display omitted] • A frontal chromatography-ICP-MS derived method for Cr(VI) analysis is developed. • The implementation of the separation system to ICP-MS is very simple and cheap. • Cr(VI) ultra-traces are determined in the presence of 50 mg/kg of Cr(III). • Cr(VI) determination requires only 1 min, without specific sample pretreatments. [ABSTRACT FROM AUTHOR]

• Nickel oxide/nickel ferrite/Ni-Al layered double hydroxide nano-composite was synthesized. • The synthesized nanocomposite indicated high extraction capability towards Cr(VI) anion. • The nanocomposite was used as a nano-sorbent for magnetic solid-phase extraction of Cr(VI). • The Cr(III) cation was extracted and pre-concentrated after its oxidation to Cr(VI) anions. • The method was applied for the speciation of Cr(VI) and Cr(III) species in water samples. A facile hydrothermal method was used to prepare a magnetic nanocomposite (MNC) based on nickel oxide/nickel ferrite/Ni-Al layered double hydroxide (NiO/NiFe 2 O 4 /LDH). The synthesized NiO/NiFe 2 O 4 /LDH MNC was characterized using various techniques, including X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, and vibrating sample magnetometry. After evaluation of its capability to selective extraction of Cr(VI) ions, an efficient magnetic solid-phase extraction method was developed for the pre-concentration and speciation of chromium species (Cr(III) and Cr(VI)) using the as-prepared NiO/NiFe 2 O 4 /LDH MNC as an adsorbent and flame atomic absorption spectrometry. Due to owning positively charged surface, the LDH can establish selective electrostatic interaction with Cr(VI) species in the form of CrO 4 2- or HCrO 4 -. Numerous important parameters influencing the extraction efficiency were studied and optimized. Based on the method validation applying the optimized extraction conditions, the calibration curve was linear in the range of 0.5 to 120 ng mL−1 with a correlation coefficient of 0.9983. The limit of detection was estimated to be 0.14 ng mL−1, and the method intera- and inter-day precisions were 1.47% and 3.19%, respectively. The presented method was validated by the analysis of the certified reference material NIST SRM 1643e, and applied for the speciation of Cr(VI) and Cr(III) species in various water and industrial wastewater samples. [ABSTRACT FROM AUTHOR]

• MA/IT-SPME was firstly introduced to perform chromium speciation. • A new adsorbent was prepared and acted as extraction phase of MA/IT-SPME. • The application of magnetic field assisted the extraction efficiencies obviously. • The reliability of current on-line method was evidenced by confirmatory experiments. In the present study, a new method for chromium speciation was proposed by on-line coupling of magnetism-assisted in-tube solid phase microextraction (MA/IT-SPME) with high-performance liquid chromatography-diode array detector (HPLC-DAD). Firstly, Cr(III) and Cr(VI) were coordinated with ammonium pyrrolidinedithiocarbamate (APD) to form Cr(III)/APD and Cr(VI)/APD complexes, separately. After that, a microextraction column based on porous monolith doped with magnetic nanoparticles was in situ fabricated in a capillary. The microextraction column was twined with a magnetic coil which was employed to engender changeable magnetic fields during extraction period. Various main factors influencing the extraction performance were inspected in detail. Results well indicated that the implementation of the magnetic field could assist the enhancement of extraction efficiency for Cr(III)/APD (80.4%) and Cr(VI)/APD (86.2%) complexes. Under the optimized parameters, the limits of detection for Cr(III) and Cr(VI) in water sample were 0.0059 μg/L and 0.0020 μg/L, respectively, and the corresponding values in soil sample were 0.47 μg/kg and 0.057 μg/kg, separately. The enrichment factors were 59 and 72 for Cr(III) and Cr(VI), respectively. The successful quantification of Cr(III) and Cr(VI) at trace levels in environmental water and soil samples well demonstrated the reliability and practicality of the proposed on-line approach for chromium speciation. [ABSTRACT FROM AUTHOR]

Amino-immobilized (poly(4,9-dioxadodecane-1,12-guanidine, polydiallyldimethylammonium, hexadimethrin bromide, polyhexamethylene guanidine) silicas were proposed for chromium speciation for the first time. Adsorbents surface was characterized by TGA-DSC, FT-IR, CHN, XRD and SEM analysis. Polyamines were strongly fixed on the silica surface and were not washed off with solutions of 3М HNO 3 and 20 g L−1 NaCl. Аmino-immobilized silica quantitatively removed (R ≥ 99%) Cr(VI) from solutions at pH 4–7. Cr(III) was not recovered in this pH range, which makes it possible to separate Cr(VI) from Cr(III). The separation factor (К Cr(VI)/Cr(III)) was ≥ 1∙104. Silica-based adsorbents layer-by-layer immobilized with polyamines and 2-(1,8-dihydroxy-3,6-disulfo-2-naphthylazo)benzenearsonic acid were proposed for quantitative removal of Cr(III) from aqueous solutions with pH 4–6 at 90 °C. A system of sequentially connected columns filled with selective adsorbents was used to separate the chromium species in stream at рН= 5 and a flow rate of 1 mL min−1. Chromium was determined after its elution with 5 mL of 2 M HNO 3 at a flow rate of 1 mL min−1 using ICP-OES or ICP-MS. The pre-concentration factors for Cr(VI) and Cr(III) was 60. A two-column system was used for chromium speciation in technological solutions. The efficiency of chromium speciation was confirmed by state standard procedure. ga1 • Ammine-immobilized silicas were proposed for the preconcentration of Cr(VI) and separation it from Cr(III). • The separation factor (K Сr(VI)/Сr(III)) was 1∙104. • The maximum adsorption capacity of SiO 2 -PA was 147 μmol Сr(VI) g−1. • Silica layer-by-layer immobilized with polyamines and ArsI quantitatively recovered Сr(III). • Sequentially connected columns were used to separate the chromium species in the flow prior to their determination. [ABSTRACT FROM AUTHOR]

This study presents the development, validation and application of a new analytical approach for the simultaneous speciation analysis of Cr(III) and Cr(VI) in meat and dairy products by high-performance liquid chromatography (HPLC) coupled to inductively coupled plasma mass spectrometry (ICP-MS) and double spike species specific-isotope dilution (SS-ID). The species extraction was achieved by sequential complexation of Cr(III) with ethylenediaminetetraacetic acid (EDTA) and of Cr(VI) with 1,5-diphenylcarbazide (DPC) in the same analytical run. The HPLC separation of complexed species was carried out using a short (5 cm) microbore anion-exchange HPLC column and a mobile phase consisting of 0.01 mol L−1 HNO 3 + 2.5% (v/v) MeOH + 0.30 mol L−1 EDTA (pH = 2) in isocratic elution mode with excellent baseline separation achieved in less than 3 min. The method was validated by means of the accuracy profile approach by carrying out 6 measurement series in duplicate on (six) different days over a timespan of two months. The quantification limit was 0.013 μg kg−1 for Cr(III) and 0.049 μg kg−1 for Cr(VI), respectively. The measurement bias corresponding to the validity domain ranged from 0.01 to 0.11%, whereas the coefficient of variation in terms of repeatability (CV r) varied from 2.9 to 11.6% (depending on the analyte level) for Cr(III) and from 6.7 to 11.8% for Cr(VI). Similarly, the coefficient of variation in terms of intermediate reproducibility (CV R) ranged from 6.8 to 13% for Cr(III) and from 6.8 to 25.9% for Cr(VI), respectively. The method was successfully applied to the analysis of a selection of food samples such as baby and semi-skimmed milk and steak beef samples. Cr(VI) was not quantified in any of these samples while Cr(III) levels ranged between 2.7 and 4.7 μg kg−1, which were comparable with the levels of total chromium analysed in the same samples by ICP-MS (accredited method). The method presented here with combined use of species specific isotope dilution and sequential species complexation is a powerful analytical tool for accurate and precise quantification of Cr(III) and Cr(VI) at trace levels and allows for correction of any species interconversion during sample preparation. Image 1 • New analytical approach for simultaneous speciation analysis of Cr(III)-Cr(VI) in food by HPLC-ICP-MS and double spike SS-ID. • Single run selective complexation/derivatisation of Cr(III) and Cr(VI) by EDTA and 1,5-diphenylcarbazide, respectively. • The method was validated by means of the accuracy profile, one of the most robust approaches for this purpose. • Cr(VI) was not quantified in the milk/beef samples analysed here whereas Cr(III) levels were highly comparable with total Cr. [ABSTRACT FROM AUTHOR]

• δ 53 Cr values are not modified by estuarine redox reactions in the Beaulieu estuary. • Anoxic weathering and organic reactions influence riverine δ 53 Cr values. • δ 53 Cr of marine endmember is controlled by shelf sea biogeochemical cycling. Rivers are the principal source of chromium (Cr) to seawater and the Cr isotopic signatures of ancient marine sediments are widely considered to provide a record of the presence or absence of oxidative weathering processes on land. This assumes, however, that the δ 53 Cr value of river water is faithfully transferred to the oceans and is not modified in the estuarine mixing zone. To test this assumption we have determined the concentration and δ 53 Cr values of inorganic Cr (Cr(III) + Cr(VI)), and also Cr speciation for water samples collected within the estuarine mixing zone of the Beaulieu River, UK. The δ 53 Cr values of dissolved inorganic Cr ranged from −0.59 to 1.68‰, Cr(VI) concentrations from 0.39 to 1.83 nmol kg−1 and Cr(III) concentrations from 0.11 to 3.21 nmol kg−1. Both Cr(VI) concentrations and δ 53 Cr values increased linearly as a function of salinity, while Cr(III) concentrations decreased linearly with salinity. Thus δ 53 Cr, Cr(III) and Cr(VI) all showed conservative behaviour in the estuarine mixing zone, and the δ 53 Cr signature of Beaulieu River water was modified only by mixing between the river and seawater endmembers. The calculated average δ 53 Cr value of the river water endmember (−0.39 ± 0.08‰) was, however, lower than the range that has been observed in other rivers, which we attribute to input of organically-bound Cr(III) released by anoxic weathering processes. This is supported by the fact that Cr recovered by UV irradiation was found to have low δ 53 Cr values (−0.11 to −0.75‰). While input of Cr from anoxic weathering processes is unlikely to be an important source of Cr to the oceans today, this suggests that processes other than oxidative weathering may have an influence on the δ 53 Cr values of estuarine and coastal waters on the local scale. The δ 53 Cr value of the coastal seawater endmember (1.6 ± 0.4‰) was also higher than the range observed in the deep open ocean, due to in situ biogeochemical cycling of Cr. These factors need to be considered in the interpretation of marine sedimentary δ 53 Cr records. [ABSTRACT FROM AUTHOR]

As a hazardous waste, the disposal of chromium enriched tannery sludge has attracted increasing public concern due to its potential adverse risks towards the environment. And incineration is considered to be an effective method to stabilize heavy metals, like Cr, in solid phase during tannery sludge treatment. In this study, real chromium enriched tannery sludge without pre-treatment was incinerated at 300°C–1200 °C under air atmosphere to investigate the transformation of chromium speciation. Here detailed thermal behavior, phase transformation and chromium speciation were characterized by TG-DSC, XRD and XPS, respectively. Experimental results show that content of Cr(VI) increases gradually with the increase of temperature from 300 °C to 500 °C and reaches a maximal level of 46% total Cr at 500 °C, with different Cr(VI) species of CaCrO 4 , MgCrO 4 and Cr 5 O 12. However, the content of Cr(VI) decreases gradually with the further increase of temperature, with only about 5% Cr(VI) at high temperature of 1200 °C, due to formation of Cr(III) species of Cr 2 O 3 crystallite and MgCr 2 O 4 spinel. Besides, a growing number of hexagonally shaped flake-like crystallite Cr 2 O 3 can be discovered from characterization results of XRD and SEM. Finally, the reduction of CaCrO 4 to Cr 2 O 3 in the presence of SiO 2 is thermodynamically feasible over 700 °C, indicating possible transformation of Cr(VI) to Cr(III) through controlled incineration temperature. • Chromium-rich tannery sludge was incinerated under air atmosphere without any pretreatment. • Cr(VI) content reaches a maximal level of 46% of total Cr at 500 °C. • Most of Cr(VI) is gradually reduced to Cr(III) with the temperature increasing over 500 °C. • SiO 2 presented in tannery sludge can induce the reduction of Cr(VI) to Cr(III) above 700 °C. • Main Cr-containing crystalline phases are CaCrO 4 , MgCrO 4 , MgCr 2 O 4 , Cr 5 O 12 and Cr 2 O 3. [ABSTRACT FROM AUTHOR]

Abstract: We are operating a superconducting tunnel junction detector for high-resolution soft X-ray spectroscopy at the Advanced Biological and Environmental X-ray Facility at the Advanced Light Source synchrotron. We have recently upgraded the instrument from 9 to 36pixels for increased sensitivity. We have also acquired a new digital signal readout to increase the total count rate capabilities to ∼106 counts/s while maintaining a high peak-to-background ratio. We report on the performance of the spectrometer, and discuss speciation measurements of chromium in welding aerosols as a typical application of the instrument in environmental science. [Copyright &y& Elsevier]

Bioremediation of Cr(VI) contamination using microorganisms is a promising method for reducing its environmental risks. The objective of this study was to clarify Cr(VI) removal by Penicillium oxalicum SL2 in terms of indirect Cr(VI) reduction by metabolites, interaction sites, and form transformation of chromium. Strain SL2 could sequentially remove Cr(VI) in the bioreactor. Oxalic acid produced by the fungus contributed to Cr(VI) reduction. Scanning transmissiony X-ray microscop (STXM) analysis suggested strain SL2 could partly reduce Cr(VI) to Cr(III) in the cell. Amine, carboxyl, and phosphate groups were related to Cr(VI) removal. Chromium K-edge X-ray absorption near edge structure (XANES) analysis implied Cr(III)-Cys potentially acted as an intermediate for the formation of chromium oxalate complexes during the process of treatment. This study would support the application of strain SL2 in Cr(VI) bioremediation and expand knowledge on the interaction of chromium with fungus., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

A chromium speciation and preconcentration method was developed for graphite furnace atomic absorption spectrometry (GFAAS). This method was based on a continuous liquid-liquid extraction technique. For the separation and enrichment of the chromium species, an ion-pair forming quaternary ammonium compound was used. The sample and chloroform with the ion-pair forming agent were introduced into a patented extraction glass device. After the extraction, the Cr(VI) content of real water samples was determined by GFAAS. The optimized extraction conditions were as follows: the detection limit (S/N = 3) of 0.01 μg L−1, linear range of 0.04–5.00 μg L−1 and precision (RSD, n = 3) ≤ 3.0%. The advantages of this method are its simplicity, cost efficiency, the high enrichment factor of chromium species and easy usage with the GFAAS technique. Thus, the concentration of the chromium species can be determined at sub μg L−1 level. • A simply, cost-effective chromium speciation method had been developed. • 0.01 μg L−1 limit of detection can be achieved for Cr(VI). • Easy usage, quick measurement • High degree of enrichment can be achieved through liquid-liquid extraction. [ABSTRACT FROM AUTHOR]

This paper presents the results of determination of hazardous metal (Cd, Cu, Cr, Hg, Mn, Ni, Pb, Zn) and metalloid (As, Sb) levels in toys available in the Polish market. Two independent sample preparation methods were used to determine the concentration and content of the metals and metalloids. The first one is defined by the guidelines of the EN-71 standard and undertook extraction in 0.07 mol/L HCl. This method was used to conduct speciation analysis of Cr(III) and Cr(VI), as well as for the determination of selected metals and metalloids. The second method conducted mineralization in a HNO3 and H2O2 mixture using microwave energy to determine the content of metals and metalloids. Determination of chromium forms was made using the high-performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS) method, while those of metals and metalloids were made using the ICP-MS technique. Additionally, in order to determine total content of chromium in toys, an energy dispersive X-ray fluorescence spectrometer (EDX) was used. The results of the analyses showed that Cr(VI) was not detected in the toys. In general, the content of heavy metals and metalloids in the studied samples was below the migration limit set by the norm EN-71. [ABSTRACT FROM AUTHOR]