Chromium In Natural Waters Research Articles

The Chemical Transformations of Chromium in Natural Waters – A Model Study

A hybrid chemical kinetic and equilibrium model has been developed to quantitatively assess the dynamic oxidation-reduction (redox) transformations of chromium in natural waters. Simulations are conducted to examine the effects of 11 chemical and environmental parameters on the redox cycle between trivalent [Cr(III)] and hexavalent [Cr(VI)] chromium. Based on the model results, it is found that natural water serves as a reductive environment for chromium under typical conditions, since the common oxidants of Cr(III) (e.g., hydroxyl radical and manganese) do not convert chromium to Cr(VI) at significant rates because of their extremely low levels or slow oxidation kinetics. At low pH ( 6.0), ferrous iron [Fe(II)] becomes the predominant reductant. However, at pH greater than 8.0 and in the presence of dissolved oxygen (DO), Cr(VI) reduction by Fe(II) is greatly suppressed due to the rapid oxidation of Fe(II) by DO. Other reactive species such as hydroperoxyl radical (HO2•/O2•-) and hydrogen peroxide (H2O2) present in sunlit waters can indirectly affect the chromium redox cycle through their reactions with iron and S(IV). pH appears to be an important parameter, as it affects both chemical speciation and reaction kinetics. Chelating agents in natural waters should not significantly affect chromium redox transformations due to their usually low concentrations and generally weak interactions with Fe(II).

Synthesis and characterization of a new resin functionalized with 2-naphthol-3,6-disulfonic acid and its application for the speciation of chromium in natural water

A polystyrene divinyl benzene (8%) copolymer has been functionalized by coupling it through NN group with 2-naphthol-3,6-disulfonic acid (NDSA). The resulting resin has been characterized by elemental analysis, thermogravimetric analysis and infrared spectra. The hydrogen ion, water regain and metal ion capacities of the resin have been determined. Two forms of chromium show different exchange capacities at different pH values, viz. Cr(III) selectively retained at pH 6.5 whereas Cr(VI) retained at pH 1.5. Hence complete separation of the two forms of chromium is possible. The kinetic studies show that the exchange of Cr(III) and Cr(VI) follows second-order kinetics. The metal ion concentration was measured by flame atomic absorption spectrometry. The method has been successfully applied for the speciation of chromium in natural water samples.

Determination of Cr(III) and Cr(VI) species in natural waters by catalytic cathodic stripping voltammetry

A technique for determining the speciation of chromium in natural waters is presented to distinguish Cr(VI), active inorganic Cr(III) and non-active organic Cr(III) complexes. The technique is based on catalytic cathodic stripping voltammetry with adsorption of Cr(III)-DTPA complexes (CCSV-DTPA). Organic-Cr(III) complexes are not electrochemically active, whereas free aqua Cr 3+ and its hydroxyl ions active. According to different behaviors of Cr(VI) and active Cr(III) in buck solution and at electrode interface, a new calibration for [Cr(III)] active and an entire protocol for Cr speciation are proposed. Peak currents for active Cr(III) decreased and could be fitted exponentially. Following the fitting curve for first 10–20 min, the extrapolated peak current at time zero ( i p t0 ) was used as a measure of [Cr(III)] active. [Cr(VI)] was measured 60 min after DTPA addition with a stable peak current when Cr(III)-DTPA complexes were all converted to a non-active species. The operational conditions for CCSV-DTPA were optimized. The detection limit and the recovery of [Cr(VI)] and [Cr(III)] active were, respectively, 0.1 nM and (100±3)% at 10 nM level in the presence of organic ligands. The speciation procedure was applied to natural samples collected from Swiss rivers, lakes, soil drainage, and landfill leachate. The [Cr] total measured by GF-AAS and by CCSV-DTPA is close in nanomolar. The results indicate occurrence of non-active organic-Cr(III) complexes in natural waters. The fractions of [Cr(III)] were substantial in some samples from pollutant small rivers and soil leachates. Further application of the technique with evaluation of species alteration would facilitate studies related to chromium transportation, transformation and remediation in natural and contaminated environments.

Preconcentration by coprecipitation of chromium in natural waters with Pd/8-quinolinol/tannic acid complex and its direct determination by solid-sampling atomic absorption spectrometry

A sensitive and accurate method for the determination of chromium at the ultra-trace levels has been investigated and applied to river water and seawater. Chromium was pre-concentrated by coprecipitation with a combination of 8-quinolinol, palladium as a carrier element and tannic acid as an auxiliary complexing agent, and the coprecipitates obtained were directly measured by graphite furnace atomic absorption spectrometry (GFAAS) using the solid sampling technique. The coprecipitation conditions for chromium with Pd/8-quinolinol/tannic acid complex, such as the effects of the pH, amounts of palladium and tannic acid, were examined in detail. It was found that chromium is coprecipitated quantitatively with Pd/8-quinolinol/tannic acid complex in the pH range of 5.1–5.3. The detection limit for chromium, which was defined as the concentration calculated from three times of the standard deviation of the procedural blanks, is 20 ng/l for 300 ml portions of water samples in the proposed method.

Catalytic‐adsorptive stripping voltammetric determination of chromium in environmental materials

AbstractTrace levels of chromium in natural water, soil and plants can be determined directly after accumulation of the chromium(III)‐2,2‐bipyridine complex on a hanging mercury drop electrode, coupled with the catalytic effect of the adsorbed complex on the reduction of nitrite. The adsorptive‐catalytic characteristic of the complex provides the needed sensitivity and selectivity for direct determination of ultratrace concentrations of chromium in environmental samples. The effect of various experimental parameters on the catalytic current was investigated. Under optimal conditions, the adsorptive‐catalytic stripping voltammetric procedure produces a detection limit of 20 pM (1.0 ppt) chromium and a linear catalytic current‐chromium concentration relationship up to 50 nM, following 5 s of accumulation. Most of the coexisting metals do not interfere with the measurements.

Preconcentration of chromium(III) from sea-water by adsorption on silica and voltammetric determination

CrIII generally forms only a minor part of total dissolved chromium in natural waters. However, it is interesting to determine the concentration of CrIII as its ratio with CrVI can be used as an indicator of the redox potential of natural waters and disequilibria thereof as a result of photochemical and biological processes. CrVI and total dissolved chromium in natural waters, including sea-water, can be determined accurately and sensitively by cathodic stripping voltammetry, but the concentration of CrIII is close to the limit of detection. A method is presented to preconcentrate CrIII from sea-water by selective adsorption on silica particles. The adsorbed CrIII is recovered by re-oxidation to CrVI by UV digestion of the re-suspended silica in water in the presence of excess of dissolved oxygen. The concentration of the desorbed CrVI is determined using cathodic stripping voltammetry. A very low analytical limit of detection (approximately 1 pmol l–1) is obtained by this method when the CrIII is preconcentrated from a 100 ml sample of sea-water; however, the limit of determination was higher at 0.03 nmol l–1 CrIII owing to a reagent blank. The silica preconcentration method was used successfully to determine CrIII in sea-water samples from the NE Atlantic.

Monitoring, sampling, and automated analysis

Monitoring, sampling, and automated analysis

Reduction of low concentration Cr(VI) in acid solutions

The speciation of chromium in natural waters presents problems of sampling, transport and storage, especially when the species are in low concentration. Typical sampling procedures involve filtration of aliquots of the water into acid-cleaned polyethylene bottles and storage at pH 2 for subsequent speciation. This study shows that, at low concentration, 51Cr(VI) is reduced to 51Cr(III) in acid solution at rates which depend strongly on both the chromium concentration and on the acid concentration. Thus, 20% of 10−6 mol/l 51Cr(VI) is reduced in 1 10 days at pH 4 while 45% is reduced at pH 2. More than 10% of 51Cr(VI) is reduced in day at pH 2 and in 1 h at pH 1. However, if the 51Cr(VI) concentration is 10−4 mol/l or higher, only very small amounts are reduced in one day at ambient temperatures. All reductions produce a mixture of 51Cr(III) products, as shown by ion exchange chromatography. Such results suggest that Cr(VI)/Cr(III) speciation measurements of sampled waters may be compromised at very low chromium concentrations by the storage procedures commonly adopted and that alternative procedures should be considered for accurate speciation at low concentrations.

Differential determination of chromium(VI) and total chromium in natural waters using flow injection on-line separation and preconcentration electrothermal atomic absorption spectrometry.

A rapid, sensitive and selective method for the differential determination of CrIII and CrVI in natural waters is described. Chromium(vi) can be determined directly by flow injection on-line sorbent extraction preconcentration coupled with electrothermal atomic absorption spectrometry using sodium diethyldithiocarbamate as the complexing agent and C18 bonded silica reversed-phase sorbent as the column material. Total Cr can be determined after oxidation of CrIII to CrVI by potassium peroxydisulfate. Chromium(III) can be calculated by difference. The optimum conditions for sorbent extraction of CrVI and oxidation of CrIII to CrVI are evaluated. A 12-fold enhancement in sensitivity compared with direct introduction of 40 microliters samples was achieved after preconcentration for 60 s, giving detection limits of 16 ng l-1 for CrVI and 18 ng l-1 for total Cr (based on 3 sigma). Results obtained for sea-water and river water reference materials were all within the certified range for total Cr with a precision of better than 10% relative standard deviation in the range 100-200 ng l-1. The selectivity of the determination of CrVI was evaluated by analysing spiked reference materials in the presence of CrIII, resulting in quantitative recovery of CrVI.

Speciation of Cr(VI)/Cr(III) by electrothermal atomisation AAS after electrodeposition on a L'vov platform

The pyrolysed graphite L'vov platform of a tube furnace is considered as an electrode for the electrodeposition and speciation of chromium by electrothermal atomisation atomic absorption spectrometry (ETA-AAS). Firstly, a preliminary study of the Cr(VI)/Cr(III) voltammetric behavior at pH 4.70 on a glassy-carbon electrode is carried out. Secondly, the L'vov platform is used as a cathodic macro-electrode for the selective preconcentration of Cr(VI)/Cr(III) on a mercury film. Speciation of Cr(VI)/Cr(III) is carried out on the basis of the electrolysis potential (Ee): at pH 4.70 and Ee=−0.30 V, only Cr(VI) is reduced to Cr(III) and accumulated as Cr(OH)3 by adsorption on a mercury film; at Ee=−1.80 V both Cr(VI) and Cr(III) are accumulated forming an amalgam with added mercury(II) ions. Once the film has been formed, the platform is transferred to a graphite tube to atomise the element. The reliability of the method was tested for the speciation of chromium in natural waters and it proves to be highly sensitive thanks to the electroanalytical step. In all samples, the Cr(VI) concentration was less than the detection limit (0.15 ng ml−1), and the concentration of Cr(III) agrees with those of total chromium. The analytical recovery of Cr(VI) added to water samples [3.50 ng ml−1 of Cr(VI)] was 105±6.2%.

Chromium (III) interactions in seawater through its oxidation kinetics

The rates of oxidation of chromium(III) to chromium(VI) with H2O2 have been measured in NaCl and the major sea salts at pH 8 and 25°C. The effect of aging the chromium(III) solutions before the addition of H2O2 has also been investigated for the same solutions. Borate was the only major component of seawater found to affect the oxidation in seawater. Like OH−, an increase in the B(OH)4− concentration causes the rates of oxidation to increase. The rate-determining steps in seawater involve two chromium (III) species Cr(H2O)5OH2++H2O2→KOH products Cr(H2O)4(OH) [B(OH)4] + + H2O2→KB products and the rate equation is given by dCr(III)/dt = −k3[H2O2] [OH−] [B(OH)4−]0.3 where k3=k1/[H2O2][OH−][B(OH)4−]0.3 (k1 is the pseudo-first-order rate constant). Aging of the solutions causes the rates of oxidation to decrease and is affected by the concentration of borate, carbonate and magnesium ions. Borate causes a reduction of the aging effect, while carbonate and magnesium produce an increase of the aging effect. The Mg2+ influence is much stronger than CO32− when these ions are present at their seawater levels in individual Na-Mg-Cl and Na-Cl-CO3 solutions. When CO32− and Mg2+ are present at the same time, the combined aging effect is less than that found in simple Na-Mg-Cl solutions. Since the aging effect is related to the precipitation of chromium(III), magnesium and carbonate ions will probably affect the solubility of chromium in natural waters.

An overview of chromium in the marine environment

Chromium concentrations in natural waters range from 2 to 5 nmol kg−1 in open ocean water up to 100 nmol kg−1 in freshwater. Its oceanic behavior is complicated by the occurrence of two important oxidation states with very different properties and possible organically bound species. Cr(III) has a significant affinity for suspended particulate matter and is readily adsorbed to it in the water column and in the sediment. Cr(VI), as the thermodynamically stable form in sea water, is the dominant species. It is also known to be of much higher toxicity than Cr(III), which is generally accepted as an essential trace element. Sources for chromium in the oceans are mineral weathering processes and riverine and atmospheric input. The possibility of conversion between different species impedes the determination and classification of chromium compounds particularly when preliminary separation and preconcentration steps are necessary to determine the very low levels of chromium in natural waters.

The effect of organic matter and colloidal particles on the determination of chromium(VI) in natural waters

The chromium(VI) contents of two water samples, a river water and a sea-water, were determined by means of solvent extraction with APDC (ammonium pyrrolidinedithiocarbamate) into chloroform and by co-precipitation with iron(III) hydroxide. The analytical results depended on the separation method used, possibly because of differences in the behaviour of the chemical species of chromium in natural waters. Various chromium species, including simple inorganic ions, organic complexes, Cr(III) adsorbed on inorganic colloids and Cr(III) combined with organic polymers, were prepared, and their analytical characteristics were investigated.

Dissolved state of chromium in seawater

The dissolved state of chromium in seawater has long been studied and in particular which species, trivalent or hexavalent, is predominant. Research results are not, however, consistent, although the method used has usually been the same—using ferric hydroxide as coprecipitation carrier (Table 11–7). We have studied the coprecipitation behaviour of chromium with ferric hydroxide and other metal hydroxides in the presence of naturally existing inorganic and organic ions to attain an accurate analytical method for determining chromium content, as well as to estimate its behaviour in natural waters8,9. We report here that neither Cr(VI) nor organic species coprecipitate with ferric hydroxide in seawater; Cr(VI) can be quantitatively captured by the coprecipitation with bismuth hydroxide without any pretreatment (such as reduction); and the role of manganese oxide should be considered in addition to the amount of dissolved oxygen to understand the redox system of chromium in natural waters. The inconsistency of the past research may therefore be partly because the presence of organic species was not taken into account and was analysed as either Cr(VI) or Cr(III) or overlooked entirely.

Chemical forms of chromium in natural water

The interaction of chromium (III) with humic substances obtained from pond sediment was experimentally studied using electrophoresis combined with ultrafiltration. The results show that within the neutral pH range chromium (III) in the presence of humic substances and some organic acids forms uncharged and/or negatively charged organic complexes of various molecular weights. A part of the chromium(III)-humic or -fulvic acid complexes having a negative charge was of lower molecular weight. Chromium (III) spiked in fresh water exists as various soluble anionic and/or uncharged species, and the molecular weights of these anionic complexes correspond to those of chromium(III)-humic and -fulvic complexes. These complexes may remain as stable dissolved forms for 10 days. The significance of the occurrence of chromium(III)-organic complexes in natural water in the geochemical cycle of chromium in the hydrosphere is discussed.

Determination of chromium in natural waters and sewage effluents by atomic-absorption spectrophotometry using an air-acetylene flame

A simple method for the determination of chromium in natural waters and sewage final effluents by atomic-absorption spectrophotometry using an air-acetylene flame is described. The sample is concentrated by evaporation by a factor of five. Interference effects were minimised by the addition of ammonium perchlorate and were further reduced by working with a flame on the verge of luminosity rather than a distinctly luminous flame.

Ion-exchanger colorimetry—II microdetermination of chromium in natural waters

Ion-exchanger colorimetry for chromium(VI) with 1,5-diphenylcarbohydrazide has been developed for the determination of chromium at μg/l. concentrations in natural water samples. About 90% of the chromium(VI) in a 1-litre sample solution is concentrated in 200–400 mesh Dowex 50W-X4 resin within half an hour. It is possible to obtain higher sensitivity by employing a larger amount of sample solution. Total chromium can be determined by oxidizing chromium(III) to chromium(VI) with ceric sulphate.

Analysis of chromium in natural waters by gas chromatography

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAnalysis of chromium in natural waters by gas chromatographyR. J. Lovett and G. Fred. LeeCite this: Environ. Sci. Technol. 1976, 10, 1, 67–71Publication Date (Print):January 1, 1976Publication History Published online1 May 2002Published inissue 1 January 1976https://doi.org/10.1021/es60112a004RIGHTS & PERMISSIONSArticle Views68Altmetric-Citations24LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (515 KB) Get e-Alerts Get e-Alerts

Rapid determination of chromium in natural waters by chemiluminescence with a centrifugal fast analyzer

The centrifugal fast analyzer was adapted for luminescence measurements by designing an improved transfer disk which mixes solutions more efficiently and by reprogramming the dedicated computer for rapid data acquisition. The modified analyzer system was applied to the chemiluminescent determination of chromium( III) and, after reduction, chromium(VI), by catalysis of the luminol-peroxide reaction in basic medium. From 50 to 600 p.p.b. of chromium in water samples were determined with a relative standard deviation of 1–2%. Sensitivity can be increased if necessary. The method is very rapid—as many as 11 samples can be analyzed in 2.5 s—and only a small sample, 0.3 ml, is required. Since this. method is selective for uncomplexed chromium(III) ions, comparison of results with analyses for total chromium and chromium(VI) by other methods provides information concerning the chromium species present in a sample and the presence or absence of complexing agents.

Potential transformations of chromium in natural waters

A study has been conducted on the transformation of Cr(III) and Cr(VI) in simulated natural water conditions. It has been found that these forms are readily interconvertible under natural water conditions. The results of this study indicate that Cr(VI) is reduced by Fe(II), dissolved sulfides, and certain organic compounds with sulfhydryl groups, while Cr(III) is oxidized by a large excess of MnO2 and at a slow rate by Oz under conditions approximating those in natural waters. Based on the results of these studies, water quality standards for Cr should be based on total Cr rather than on Cr(VI), as has been frequently done in the past.