Adsorption of Cr(VI) using cellulose microsphere-based adsorbent prepared by radiation-induced grafting

Cellulose microsphere (CMS) adsorbent was prepared by radiation-induced grafting of dimethylaminoethyl methacrylate (DMAEMA) onto CMS followed by a protonation process. The FTIR spectra analysis proved that PDMAEMA was grafted successfully onto CMS. The adsorption of Cr(VI) onto the resulting adsorbent was very fast, the equilibrium adsorption could be achieved within 15 min. The adsorption capacity strongly depended on the pH of the solution, which was attributed to the change of both the existed forms of Cr(VI) and the tertiary-ammonium group of PDMAEMA grafted CMS with the pH. A maximum Cr(VI) uptake (ca. 78 mg g^?1) was obtained as the pH was in the range of 3.0–6.0. However, even in strong acid media (pH 1.3), the adsorbents still showed a Cr(VI) uptake of 30 mg g^?1. The adsorption behavior of the resultant absorbent could be described with the Langmuir mode. This adsorbent has potential application for removing heavy metal ion pollutants (e.g. Cr(VI)) from wastewater.     

Thermodynamic analysis of sorption isotherms of chromium(VI) anionic species on reed biomass

A new sorbent material for removing Cr(VI) anionic species from aqueous solutions has been investigated. Adsorption equilibrium and thermodynamics of Cr(VI) anionic species onto reed biomass were studied at different initial concentrations, sorbent concentrations, pH levels, temperatures, and ionic strength. Equilibrium isotherm was analyzed by Langmuir model. The experimental sorption data fit the model very well. The maximum sorption capacity of Cr(VI) onto reed biomass was found to be 33 mg · g^?1. It was noted that the Cr(VI) adsorption by reed biomass decreased with increase in pH. An increase in temperature resulted in a higher Cr(VI) loading per unit weight of the adsorbent. Removal of Cr(VI) by reed biomass seems to be mainly by chemisorption. The change in entropy (ΔS^°) and heat of adsorption (ΔH^°) for Cr(VI) adsorption on reed biomass were estimated as 2205 kJ · kg^?1 · K^?1 and 822 kJ · kg^?1, respectively. The values of isosteric heat of adsorption varied with the surface loading of Cr(VI).     

Kinetics,isotherm and thermodynamics for Cr(III) and Cr(VI) adsorption from aqueous solutions by crystalline hydrous titanium oxide

The synthetic crystalline hydrous titanium(IV) oxide (CHTO), an anatase variety and thermally stable up to 300 °C, has been used for adsorption of Cr(III) and Cr(VI) from the aqueous solutions, the optimum pH-values of which are 5.0 and 1.5, respectively. The kinetic data correspond very well to the pseudo-second order equation. The rates of adsorption are controlled by the film (boundary layer) diffusion, and increase with increasing temperature. The equilibrium data describe very well the Langmuir, Redlich–Peterson, and Toth isotherms. The monolayer adsorption capacities are high, and increased with increasing temperature. The evaluated ΔG^° (kJ · mol^?1) and ΔH^° (kJ · mol^?1) indicate the spontaneous and endothermic nature of the reactions. The adsorptions occur with increase in entropy (ΔS^° = positive), and the mean free energy (E_DR) values obtained by analysis of equilibrium data with Dubinin–Radushkevick equation indicate the ion-exchange mechanism for Cr(III) and Cr(VI)-adsorptions.     

The removal of uranium (VI) from aqueous solutions onto natural sepiolite

The adsorption of uranium (VI) from aqueous solutions onto natural sepiolite has been studied using a batch adsorber. The parameters that affect the uranium (VI) sorption, such as contact time, solution pH, initial uranium(VI) concentration, and temperature, have been investigated and optimized conditions determined. Equilibrium isotherm studies were used to evaluate the maximum sorption capacity of sepiolite and experimental results showed this to be 34.61 mg · g^?1. The experimental results were correlated reasonably well by the Langmuir adsorption isotherm and the isotherm parameters (Q_o and b) were calculated. Thermodynamic parameters (ΔH° = ?126.64 kJ · mol^?1, ΔS° = ?353.84 J · mol^?1 · K^?1, ΔG° = ?21.14 kJ · mol^?1) showed the exothermic heat of adsorption and the feasibility of the process. The results suggested that sepiolite was suitable as sorbent material for recovery and adsorption of uranium (VI) ions from aqueous solutions.     

Surface-enhanced Raman studies of bradykinin using colloidal gold

In this paper, bradykinin (BK), an endogenous peptide hormone, which is involved in a number of physiological and pathophysiological processes was deposited onto the colloidal Au nanoparticles. The surface-enhanced Raman spectroscopy (SERS) was used to determine the adsorption mode of BK under different environmental conditions, including: excitation wavelengths (514.5 nm and 785.0 nm), pH of aqueous sol solutions (from pH = 3 to pH = 11), and size of the colloidal nanoparticles (10, 20, and 50 nm). The metal surface plasmon of the colloidal suspended Au nanoparticles was examined by ultraviolet-visible (UV–vis) spectroscopy. The results showed that the C-terminal part of BK plays a crucial role in the adsorption process onto the colloidal suspended Au particles. The Phe^5/8 and Arg⁹ residues of BK mainly participate in the interactions with the colloidal Au nanoparticles. At acidic pH of the solution (pH = 3), the BK COO⁻ terminal group through the both oxygen atoms strongly binds to the Au nanoparticles. The Phe⁵/Phe⁸ rings adopt tilted orientation with respect to the colloidal Au nanoparticles with diameters of 10 and 20 nm. As the particle size increases to 50 nm, the flat orientation of the Phe ring(s) with respect to the Au nanoparticles is observed.     

Thermodynamics and kinetics of adsorption of Cu(II) from aqueous solutions onto a new cation exchanger derived from tamarind fruit shell

A novel cation exchanger (TFS-CE) having carboxylate functionality was prepared through graft copolymerization of hydroxyethylmethacrylate onto tamarind fruit shell (TFS) in the presence of N,N′-methylenebisacrylamide as a cross-linking agent using K₂S₂O₈/Na₂S₂O₃ initiator system, followed by functionalisation. The TFS-CE was used for the removal of Cu(II) from aqueous solutions. At fixed solid/solution ratio the various factors affecting adsorption such as pH, initial concentration, contact time, and temperature were investigated. Kinetic experiments showed that the amount of Cu(II) adsorbed increased with increase in Cu(II) concentration and equilibrium was attained at 1 h. The kinetics of adsorption follows pseudo-second-order model and the rate constant increases with increase in temperature indicating endothermic nature of adsorption. The Arrhenius and Eyring equations were used to obtain the kinetic parameters such as activation energy (E_a) and enthalpy (ΔH^#), entropy (ΔS^#) and free energy (ΔG^#) of activation for the adsorption process. The value of E_a for adsorption was found to be 10.84 kJ · mol^?1 and the adsorption involves diffusion controlled process. The equilibrium data were well fitted to the Langmuir isotherm. The maximum adsorption capacity for Cu(II) was 64 · 10 mg · g^?1 at T = 303 K. The thermodynamic parameters such as changes in free energy (ΔG^°), enthalpy (ΔH^°), and entropy (ΔS^°) were derived to predict the nature of adsorption process. The isosteric heat of adsorption increases with increase in surface loading indicating some lateral interactions between the adsorbed metal ions.     

Étude de l’élimination du Cr(VI) par l’oxyde mixte obtenu par calcination de l’hydroxyde double lamellaire MgAl

A magnesium aluminium hydrotalcite-like compound (HT) containing carbonate anions in the interlayer space and with a final Mg/Al ratio of 2 was synthesized by the co-precipitation method. The obtained material was characterized by powder X-ray diffraction (XRD), Fourier-Transform–Infrared spectroscopy (FT–IR), thermal analysis (ATG/ATD), and surface area measurements (BET). The interaction of the clay with Cr(VI) has been studied by ultraviolet–visible (UV–vis) spectroscopy. The calcined hydrotalcite (HT-C) showed the highest capacity of removal of chromium ions, and their sorption capacities for Cr(VI) are 4.85 mmol/g. The effect of various parameters on the preparation conditions for the removal of chromium, such as the contact time, the amount of sorbent, the initial concentration of Cr(VI), and the pH values of aqueous solution were also investigated to identify their influence on Cr(VI) sorption. The characterization of the calcined hydrotalcite (HT-C) after interaction with Cr(VI) ions by FT–IR spectroscopy showed that Cr(VI) was adsorbed and intercalated by the solid.     

Chemical modification of expanded glass aggregate with N-Benzoyl-N′-(4-methylphenyl) thiourea (TTU) for the adsorptive removal of Cr(III) ion

In this study, the silylant agent 3-aminopropyl trimethoxysilane (APTES) was anchored on expanded glass aggregate (GA) to prepare a new adsorbent. N-Benzoyl-N′-(4-methylphenyl) thiourea (TTU) bonded to amino-functionalized GA adsorbent with reflux. Developed adsorbent (GA-APTES-TTU) was characterized using thermal analysis (TGA) and scanning electron microscopy (SEM). TGA and SEM studies indicated that modification of the glass aggregate (GA) surfaces was successfully performed. The adsorption studies exhibited that the GA-APTES-TTU could be efficiently used for the removal of Cr(III) from aqueous solutions. The effects of pH, adsorbent dosage, ion concentration, time, and temperature were investigated as adsorption parameters. The maximum removal of Cr(III) was observed at pH 4. The adsorption equilibrium was achieved in 120 min and adsorption of Cr(III) followed the Langmuir isotherm model. The maximum adsorption capacity for Cr(III) was 0.4305 mmol/g with GA-APTES-TTU. Thermodynamic parameters such as the standard free energy (ΔG^o), enthalpy change (ΔH°) and entropy change (ΔS°) were calculated in order to explain the mechanism of adsorption process. The thermodynamic data showed that Cr(III) adsorption was spontaneous, endothermic, and a physisorption reaction. In addition, the adsorption kinetic data fitted to the pseudo-second order model.     

Evaluation of Acacia nilotica as a non conventional low cost biosorbent for the elimination of Pb(II) and Cd(II) ions from aqueous solutions

In the present study a biomass derived from the leaves of Acacia nilotica was used as an adsorbent material for the removal of cadmium and lead from aqueous solution. The effect of various operating variables, viz., adsorbent dosage, contact time, pH and temperature on the removal of cadmium and lead has been studied. Maximum adsorption of cadmium and lead arises at a concentration of 2 g/50 ml and 3 g/50 ml and at a pH value of 5 and 4, respectively. The sorption data favored the pseudo-second-order kinetic model. Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were applied to describe the biosorption isotherm of the metal ions by A. nilotica biomass. Based on regression coefficient, the equilibrium data found were fitted well to the Langmuir equilibrium model than other models. Thermodynamic parameters such as free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) have been calculated, respectively revealed the spontaneous, endothermic and feasible nature of adsorption process. The activation energy of the biosorption (Ea) was estimated as 9.34 kJ mol⁻¹ for Pb and 3.47 kJ mol⁻¹ for Cd from Arrhenius plot at different temperatures.     

Synthesis of Faujasite type zeolite from low grade Tunisian clay for the removal of heavy metals from aqueous waste by batch process: Kinetic and equilibrium study

In this study, a faujasite type zeolite synthesized from cheap local Tunisian illitic clay and having a hierarchical porosity was used for adsorption of heavy metals. The adsorption behavior of the FAU with respect to Cu (II), Cr (III) and Co (II) has been investigated using batch experiments. The removal efficiency was determined at different contact times, initial metal concentrations, temperatures, pHs, and adsorbent amounts. Both Langmuir and Freundlich isotherms fit well with the equilibrium data. Kinetic studies showed that the adsorption followed a pseudo-second-order model. The observed selectivity was determined as follow: Cu (II) > Co (II) > Cr (III).     

Ruthenium and chromium complexes bearing pH-indicators as the η6-arene ligand: Synthesis,characterization, and protonation behavior

A series of ruthenium and chromium complexes bearing pH indicators as the η⁶-arene ligand, (η⁶-X)(ML_n)_y [X = methyl yellow, crystal violet lactone, phenolphthalein; ML_n = RuCp¹⁺, RuCl₂(L), Cr(CO)₃; y = 1, 2] is prepared and characterized by spectroscopic and crystallographic methods. Of the plural arene rings in the indicators, a specific arene ring can be successfully coordinated to the metal center in a selective manner under appropriate conditions (i.e. use of the precursors of different oxidation states and reaction with the non-protonated and protonated pH indicator). The obtained indicator complexes show halochromic behavior depending on pH as observed for the parent molecules but the transition pH ranges are shifted to the more acidic side because of the attachment of the electron-withdrawing metal fragments, which decrease the basicity of the attached pH indicators.     

Toward use of a nano layered double hydroxide/ammonium pyrrolidine dithiocarbamate in speciation analysis: One-step dispersive solid-phase extraction of chromium species in human biological samples

Chromium is a controversial element with an important essentiality and toxicity. Depending on its different species, its speciation analysis in bio-origin matrices is of utmost importance. Ammonium pyrrolidine dithiocarbamate (APDC) and layered double hydroxide (LDH) nanoparticles, with the purpose of combining their outstanding performances, were served to speciate chromium ions in human biological samples. The as-obtained sorbent (nano LDH-APDC) - after characterization by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, thermal gravimetric analysis (TGA), and scanning electron microscopy (SEM) - was used as a novel pH-sensitive adsorbent in an integrated one-step dispersive solid-phase extraction (I-OS-DSPE), which combines the benefits of the air-assisted microextraction and dispersive solid-phase extraction methods. An interesting feature of the nano LDH-APDC sorbent is that it is dissolved in an aqueous solution when the pH of the solution is lower than 4. Thus the analyte elution step, as required in most of the sorbent-based extraction methods, was obviated by dissolving the sorbent in an acidic solution after extraction and separation from the sample solution. The Cr(VI) ions were first extracted, while the Cr(III) ions remained in the aqueous solution. The extract was then directly injected into a flame atomic absorption spectrometer with a micro-sampling introduction system, and the concentration of the Cr(III) ions was calculated by its subtraction from the total chromium ions present. Several variables including the pH (5), type and amount of the nanosorbent used (30 mg of nano (Zn-Al) LDH-APDC), number of extraction cycles (15 times), and elution conditions (200 µL of 6.0 mol L⁻¹ HNO₃) were investigated to achieve the maximum extraction efficiency. Under the optimum experimental conditions, the limit of detection, linear range, consumptive index, and enrichment factor for the Cr(VI) ions were 2.4 μg L⁻¹, 8.0–640 μg L⁻¹, 0.24, and 42.5 ± 1, respectively. These findings suggested that nano (Zn-Al) LDH-APDC could be regarded as a promising adsorbent for an efficient speciation of the chromium species in the human hair, nail, saliva, plasma, and urine samples.     

Nano TiO2-based preconcentration for the speciation analysis of inorganic selenium by using ion chromatography with conductivity detection

A simple, sensitive, and cost-effective analytical method was developed for the speciation analysis of inorganic selenium by combining a nano-TiO₂ preconcentration with an ion chromatography-conductivity detection (IC-CD) system. The experimental conditions for the simultaneous adsorption and desorption of Se(IV) and Se(VI) were carefully investigated. Under the established optimum condition, the Se(IV) and Se(VI) ions could been simultaneously adsorbed onto the nano-TiO₂ surface at pH 4.0, and then effectively desorbed by 0.1 M sodium hydroxide eluent. The adsorption process was fast and reached adsorption equilibrium within 10 min. The nano-TiO₂ also exhibited high adsorption capacity with 11.3 mg g^? 1 for Se(IV) and 8.34 mg g^? 1 for Se(VI). The enrichment factors for Se(IV) and Se(VI) were calculated to be 39 and 30, respectively, with sample volume of 50 mL. The detection limits (3σ) were 0.8 μg L^? 1 for Se(IV) and 0.4 μg L^? 1 for Se(VI), which were sensitive enough for the routine analysis of water and drink samples. The relative standard deviation was calculated to be < 4% (n = 6) for detection of 30 μg L^? 1 Se(IV) and 30 μg L^? 1 Se(VI). The results of the present work confirmed that our developed nano-TiO₂-IC-CD method could be applied for the detection of inorganic selenium species in tap water and drink samples with good recoveries in the range of 82%–108%.     

Cr(VI) reduction at rutile-catalyzed cathode in microbial fuel cells

Cathodic reduction of hexavalent chromium (Cr(VI)) and simultaneous power generation were successfully achieved in a microbial fuel cell (MFC) containing a novel rutile-coated cathode. The selected rutile was previously characterized to be sensitive to visible light and capable of both non-photo- and photocatalysis. In the MFCs containing rutile-coated cathode, Cr(VI) was rapidly reduced in the cathode chamber in presence and absence of light irradiation; and the rate of Cr(VI) reduction under light irradiation was substantially higher than that in the dark. Under light irradiation, 97% of Cr(VI) (initial concentration 26 mg/L) was reduced within 26 h, which was 1.6× faster than that in the dark controls in which only background non-photocatalysis occurred. The maximal potential generated under light irradiation was 0.80 vs. 0.55 V in the dark controls. These results indicate that photocatalysis at the rutile-coated cathode in the MFCs might have lowered the cathodic overpotential, and enhanced electron transfer from the cathode to Cr(VI) for its reduction. In addition, photoexcited electrons generated during the cathode photocatalysis might also have contributed to the higher Cr(VI) reduction rates when under light irradiation. This work assessed natural rutile as a novel cathodic catalyst for MFCs in power generation; particularly it extended the practical merits of conventional MFCs to cathodic reduction of environmental contaminants such as Cr(VI).     

Sorption of chrysoidine by row cork and cork entrapped in calcium alginate beads

Azo-dyes, molecules characterised by the presence of the azo-group (–NN–), are widely used in textile, leather, rubber, plastic, and food industries. Water-soluble azo-dyes are greatly resistant to biodegradation, and are characterised by a high thermal and photo stability due to their complex structures. The release of these molecules into the environment is of crucial concern due to their toxic, mutagenic and carcinogenic characteristics. Biosorption has been demonstrated an effective method to remove pollutants from wastewaters thus solving ecological tasks, being a low cost process and the sorbent biodegradable. The main requirements of an efficient sorbent are thermal, chemical and mechanical stability, and rapid sorption.In this work, the ability of both row cork and the same sorbent entrapped in a biopolymeric gel of calcium alginate, on the removal of chrysoidine from aqueous solutions was examined.The influence on the sorption of pH, initial dye concentration, and particle size, as well as the efficiency of the entrapment, have been investigated. The maximum sorption was found for cork samples of fine particle size (FC), in both row and entrapped forms, at pH 7; conversely, at pH 4 the difference is significant (0.12 mmol/g for row cork and 0.20 mmol/g for entrapped cork), evoking a cooperation of alginate in binding the positively charged chrysoidine molecule.     

Carbon nanotubes modified with 5,7-dinitro-8-quinolinol as potentially applicable tool for efficient removal of industrial wastewater pollutants

The environmental pollution due to the industrial wastewater of four different areas in the Gulf of Suez, Red Sea, Egypt, was studied. Adsorption capacities toward the concerned heavy metal ions Cu(II), Zn(II), Fe(II), and Pb(II) by multiwalled carbon nanotubes (MWCNTs) and modified-MWCNTs with 5,7-dinitro-8-quinolinol were investigated. MWCNTs as well as the modified-MWCNTs were characterized using Fourier transform infrared (FTIR), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). Adsorption of the studied divalent metal ions was measured by atomic absorption spectrometry (AAS). The effects of solution conditions such as pH, shaking time, metal ion concentration, ionic strength and adsorbent dosage on the adsorption process were also examined. The obtained results showed that removals of the heavy metal ions under consideration by MWCNTs are obviously dependent on the experimental conditions. The maximum adsorption capacities as calculated applying Langmuir equation to single ion adsorption isotherms were found to be 142.8 mg/g for Cu(II), 250 mg/g for Zn(II), 111.1 mg/g for Fe(II), and 200 mg/g for Pb(II) using MWCNTs; meanwhile, the modified-MWCNTs exhibited higher values of the respective maximum adsorption capacities as 333.3 mg/g for Cu(II), 500 mg/g for Zn(II), 200 mg/g for Fe(II), and 333.3 mg/g for Pb(II). Kinetic studies were also performed and the experimental data followed a pseudo-second order model of the adsorption process. The obtained results suggest that the tested adsorption systems of MWCNTs and modified-MWCNTs have suitable affinity toward the metal ion under consideration. Both systems could act as potentially applicable tool in environmental protection.     

First examples of dipyrido[1,2-c:2′,1′-e]imidazolin-7-ylidenes serving as NHC-ligands: Synthesis,properties and structural features of their chromium and tungsten pentacarbonyl complexes

The first use of dipyridocarbenes as Arduengo–Wanzlick type carbene ligands for transition metal complexes is reported. The complexes M(CO)₅L (L = dipyridoimidazolinylidene, di-tert-butyldipyridoimidazolinylidene, M = Cr, W) were synthesized and their spectroscopic and structural properties compared with the literature known N-heterocyclic carbene (NHC) group 6 metal pentacarbonyl complexes. This reveals that the ¹³C NMR carbene signals of theses complexes with dipyrido carbene ligands show the strongest high-field shift ever observed for M(CO)₅(NHC) (M = Cr, W) complexes. The structural characterization shows alternating single and double bonds in the conjugated dipyrido moiety of the ligand.     

Adsorption of methyl orange on nanoparticles of a synthetic zeolite NaA/CuO

CuO supported on an NaA zeolite (CuO/NaA) was prepared with an NaA zeolite through the ion-exchange (CuO/NaA) method. The morphology and the physicochemical properties of the prepared samples were investigated by XRD, MEB, and EDS. The various parameters, such as contact time, catalyst dose, initial dye concentration, initial pH, and temperature, influencing the adsorption of methyl orange (MO) were optimized. The MO adsorption equilibrium was reached after 240 min of contact time. Removal of MO is better at neutral pH than in acidic and alkaline solutions. Among the tested models, the equilibrium adsorption data are well fitted by the Langmuir isotherm. The adsorption kinetics is best described by the pseudo-second-order model. The evaluation of the thermodynamic parameters, i.e. ΔG^o, ΔH^o, and ΔS^o, revealed that MO adsorption was spontaneous, while the activation energy (20.98 kJ/mol) indicates a physical adsorption. The photodegradation of MO decreased from 100 mg/L down to 2 mg/L when the solution is exposed to visible light.     

Reactivity of sugar cane bagasse as a natural solid phase extractor for selective removal of Fe(III) and heavy-metal ions from natural water samples

This work introduces the feasibility of using sugar cane bagasse (SCB) – a sugar cane industry waste – as a selective solid phase extractor for Fe(III). The order of metal uptake capacities in μmol g^?1 for the extraction of six tested metal ions from aqueous solution using static technique is Fe(III) > Cu(II) > Pb(II) > Zn(II) > Cd(II) > Co(II). Since SCB exhibits remarkable binding characteristics for Fe(III), special interest was devoted for optimizing its uptake and studying its selectivity properties under static and dynamic conditions. In this respect, batch experiments were carried out at the pH range 1.0–4.0, initial concentration of metal ion (10–100 μmol), weight of phase (25, 50, 75, 100, 125 and 150 mg) and shaking time (10, 30, 45, 60, 90, 120 and 150 min). FT-IR spectra of SCB before and after uptake of Fe(III) were recorded to explore the nature of the functional groups responsible for binding of Fe(III) onto the studied natural biosorbent. The equilibrium data were better fitted with Langmuir model (r² = 0.985) than Freundlich model (r² = 0.934). Moreover, Fe(III) sorption was fast and completed within 60 min. The adsorption kinetics data were best fitted with the pseudo-second-order type. As a view to find a suitable application of SCB based on its unique property as a benign sorbent, it was found that, Fe(III) spiked natural water samples such as doubly distilled water (DDW), drinking tap water (DTW), natural drinking water (NDW), ground water (GW) and Nile River water (NRW) was quantitatively recovered (>95.0%) using batch and column experiments, with no matrix interferences.     

Determination of Cr(VI) in plants by electrothermal atomic absorption spectrometry after leaching with sodium carbonate

The determination of chromium (VI) compounds in plants by electrothermal atomic absorption spectrometry (ET AAS) is proposed based on their leaching with 0.1 M Na₂CO₃. Due to the presence of relatively high amounts of Na₂CO₃ in the resulting samples, the temperature and time of pyrolysis and atomization stages must be optimized to minimize the influence of the matrix. A limit of detection (LOD) for determination of Cr(VI) in plants by ET AAS was found to be 0.024 μg g⁻¹.The concentration of Cr(VI) and total chromium in plants collected in different geographical areas (South Africa and Russia), grown on soils high in chromium was determined. The concentration of Cr(VI) and total Cr in stems and leaves of plants was in the range of 0.04–0.7 μg g⁻¹ and 0.5–10 μg g⁻¹, respectively. The limited uptake of Cr(III) by plants, in comparison to its concentration in soil, can be explained by the very low solubility of natural Cr(III) compounds.Results for the determination of Cr(VI) were confirmed by the analysis of BCR CRM 545 (Cr(VI) in welding dust) with good agreement between certified (39.5 ± 1.3 μg mg⁻¹) and found (38.8 ± 1.2 μg mg⁻¹) values. The total concentration of Cr in plants has also been determined by ET AAS after dry ashing of samples at 650 °C. Results were confirmed by the analysis of BCR CRM 281 (Trace elements in Rye Grass) with good agreement between the found (2.12 ± 0.16 μg g⁻¹) and certified value (2.14 ± 0.12 μg g⁻¹).