A new method of evaluation of element pollutant mobility in sediments

The application of a strong chelating agent for the screening test of element mobility in sedimentary systems was investigated. Single-step and sequential extraction procedures were applied to four sediment samples collected from an industrially polluted region of Eastern Slovakia. A sequential extraction procedure (SEP), recommended by the Institute for Reference Materials and Measurements (IRMM), was applied and used as a reference extraction method. A single-step extraction with 0.05 mol dm⁻³ ethylenediaminetetraacetic acid (EDTA) was adapted for sediments when extraction conditions were optimised. The extraction efficiency of the single-step procedure was compared with that of SEP. The contents of elements extracted by Na2EDTA were in good agreement with the sum of the first three steps of the SEP for Fe, Mn, and Co. Na₂EDTA can therefore be considered capable to extract the majority of elements associated with the reducible sedimentary phase — bound to Fe and Mn oxides in the regional geological conditions of the monitored region. Thus, Na₂EDTA extraction of Fe and Mn can serve as an economical, time-saving supplementary test for the IRMM procedure. This paper is dedicated to the memory of Erika Krakovská Presented at the XVIIIth Slovak Spectroscopic Conference, Spišská Nová Ves, 15–18 October 2006.     

Comparison of three sequential extraction procedures (original and modified 3 steps BCR procedure) applied to sediments of different origin

The 3 steps sequential extraction procedure proposed by the Standards Measurements and Testing program (SM&T--formerly BCR) of the European Union has been applied for the speciation of metals in sediments. Results obtained by the application of the BCR standardized procedure were compared to those of two four step sequential extraction procedures, which are different from the BCR procedure only for the introduction of an additional step with NaOCl, as 2nd and 3rd step respectively. Five different metals have been taken into consideration: Cd, Cu, Ni, Pb and Zn. The analytical performances of the laboratory have been evaluated using three certified reference materials: the BCR 601 lake sediment for the BCR sequential extraction procedure, PACS-1 and MESS-1 for total metal concentration. Results showed that the efficiency of NaOCl treatment is higher or at least equal to that of H2O2 treatment and that its selectivity is quite satisfying. Moreover the NaOCl treatment doesn't significantly influence the extraction of the easily reducible fraction.     

The utilization of modified BCR three-step sequential extraction procedure for the fractionation of Cd, Cr, Cu, Ni, Pb and Zn in soil reference materials of different origins

A modified three-step sequential extraction procedure for the fractionation of heavy metals, proposed by the Commission of the European Communities Bureau of Reference (BCR) has been applied to the Slovak reference materials of soils (soil orthic luvisols, soil rendzina and soil eutric cambisol), which represent pedologically different types of soils in Slovakia. Analyses were carried out by flame or electrothermal atomic absorption spectrometry (FAAS or ETAAS). The fractions extracted were: exchangeable (extraction step 1), reducible-iron/manganese oxides (extraction step 2), oxidizable-organic matter and sulfides (extraction step 3). The sum of the element contents in the three fractions plus aqua-regia extractable content of the residue was compared to the aqua-regia extractable content of the elements in the origin soils. The accuracy obtained by comparing the determined contents of the elements with certified values, using BCR CRM 701, certified for the extractable contents (mass fractions) of Cd, Cr, Cu, Ni, Pb and Zn in sediment following a modified BCR-three step sequential extraction procedure, was found to be satisfactory.     

Evaluation of As and Sb Mobility in Contaminated Stream Sediments

Single and sequential extraction procedures were applied to four sediment samples collected from an industrially polluted region of Eastern Slovakia. A sequential extraction procedure (SEP) for sediments recommended by the IRMM (Institute for Reference Materials and Measurements) – was applied and used as a reference extraction method. Single-step extraction (for soils) with 0.05 mol L⁻¹ ethylenediaminetetraacetic acid (EDTA) was slightly modified for this study of sediments. The removal ability of “Na₂EDTA extraction” was compared with the SEP recommended by the IRMM. After optimisation, the elements’ contents extracted into Na₂EDTA were in good agreement with the sum of the 1^st, 2^nd, 3^rd and 4^th step of SEP for As and Sb. Therefore Na₂EDTA extraction can serve as a supplementary test to the SEP recommended by the IRMM (under locally tested conditions). Alternatively, optimised extraction of sediments in chelating agents could be applied as an economically interesting and time-saving supplementary test to routinely used SEPs. This paper describes the sample preparation and the analytical results for each extraction step and compares the results with those of total element analyses (performed by an independent method) for As and Sb.     

Fractionation of heavy metals in sediment by using microwave assisted sequential extraction procedure and determination by inductively coupled plasma mass spectrometry

In this work, a fast microwave assisted extraction procedure was developed and optimized for the heavy metals (Cu, Ni, Cr, Pb and Cd) partitioning in the three-stage sequential extraction procedure proposed by the European Standards, Measurements and Testing (SM&;T) Program, formerly the Community Bureau of Reference (BCR). The microwave oven procedure was optimized to obtain extraction efficiencies similar to the conventional BCR procedure, in less time, while using smaller volumes of reagents. In the optimization process, three variables (extraction time, ramping time and microwave power) were considered as factors and as a response the concentration of different metal ions in each individual BCR fraction. Interactions between analytical factors and their optimized levels were investigated using a central composite design. Extractable metals obtained by both comparable methodologies were measured by inductively coupled plasma mass spectrometry. With the use of optimal microwave conditions, steps 1–3 of the sequential extraction (including the hydrogen peroxide digestion in step 3) could be completed between 21 and 22 min. Detection limits were between 1 and 18 ng l^{− 1}. The accuracy of the proposed method was checked with a certified reference material (CRM) of Lake Sediment BCR 701. Values obtained were in accordance with those reported for the certified material with only a few exceptions. Different origin sediments (river and marine) were analyzed by both BCR and MW procedures, and the results obtained were comparable according to the t-paired-test for a 95% confidence level.     

Speciation of Heavy Metals in Soils and Sediments. An Account of the Improvement and Harmonization of Extraction Techniques Undertaken Under the Auspices of the BCR of the Commission of the European Communities

Abstract

An account is presented of a series of investigations and collaborative studies, initiated by BCR, on current methods of metal speciation by extraction of soils and sediments with chemical reagents. It was established by extensive consultation with European experts that the diverse procedures used could be harmonized into agreed methods. These methods, including both single extractant and sequential extraction procedures were subjected to collaborative, interlaboratory trials and the results, presented briefly here, showed that it was both possible and desirable that reference soils and sediments, characterised by certified values for extractable contents, be prepared. As a consequence of these studies two soils have been prepared and will shortly be the subject of interlaboratory analysis with a view to certification of their EDTA and acetic acid extractable contents of some heavy metals. Following this workshop a feasibility study of the agreed sequential extraction procedure will, it is believed, shortly lead to certification of sediments for contents extractable by a defined sequential extraction procedure.     

Kinetic speciation of BCR reference materials

The accurate study of heavy metal speciation is important in environmental monitoring. There has been much work developing various operationally defined speciation methods for soil and sediment, but there is a need to compare the different approaches by evaluating them for the same sample. In this article, a kinetic method was applied for the heavy metal speciation of the two BCR reference materials, CRM601 and BCR701, which have been specifically developed as materials to evaluate the validated BCR three-step sequential extraction method. When EDTA was used as an extractant, 81.0% of Cd, 68.0% of Cu, 21.5% of Ni, 80.3% of Pb and 71.9% of Zn was extracted from CRM601. For BCR701, the removal ratios were 92.0, 52.3, 18.7, 50.6 and 67.5% with EDTA and 95.7, 25.2, 20.0, 52.4 and 68.5% with hydroxylamine hydrochloride as an extractant, for Cd, Cu, Ni, Pb and Zn respectively. A two-component kinetic model was applied to the extraction curve and the extractable metals were readily classified into two categories, namely, labile fraction and non-labile fractions. The rate constants obtained from the regression model were found to be useful in quantifying the lability of an element. The rate constants obtained from the labile fractions in BCR701 were higher than that of obtained from CRM601, which indicated the high lability of metals in BCR701. When compared with the sequential extraction data, it seemed that the lability of an element was positively correlated to the first step extraction fraction.     

Chromium available fractions in arousa sediments using a modified microwave BCR protocol based on microwave assisted extraction

In a research of chromium availability, the three-stage sequential extraction procedure, proposed by European Community Bureau of Reference (BCR), has been applied for the metal fractionation in marine sediment samples. The procedure has been modified, evaluating the effect of microwave energy to perform the sequential method. Results achieved a substantial reduction in time in comparison to the traditional shaking technique. The time of the first and the second extractions were reduced to 30 s in both steps using microwave heating and working at 66 W of power. To the third extraction, higher power was necessary so it was chosen to work at 198 W. In the last step investigated, time was reduced to 1 min, being a great improvement respect to the conventional BCR sequential extraction protocol.Chromium determinations in these extracts were carried out by Electrothermal Atomic Absorption Spectrometry (ETAAS). The developed method was applied for chromium determination in marine sediment samples from Ria de Arousa (Galicia, NW of Spain). The values obtained by our laboratory ranged from 0.10 to 1.02 μg g⁻¹ for soluble and reducible fractions, and from 5.5 to 60.0 μg g⁻¹ for the oxidisable fraction. The higher concentrations obtained were the chromium associated with the organic fraction of the marine sediments.     

Comparison of Two Sequential Extraction Procedures for Trace Metal Partitioning in Sediments

Abstract

Two sequential extraction schemes (a modified Tessier procedure with five steps and a three steps protocol designed by BCR) are applied to four sediment samples with different heavy metal contents. The results obtained for Cd, Cr, Cu, Ni, Pb and Zn partitioning show that the metal distribution obtained with both procedures are significantly different. With the second procedure amounts of all the heavy metals are extracted with the oxidizing reagent (third fraction) whereas with the first one the non residual metals are distributed among the second, third and fourth fractions (acetic acid-acetate buffer (pH=5), reducing and oxidizing reagents respectively). The residual fraction obtained applying the three steps procedure is in general higher than that obtained using the five steps procedure, except for cadmium.     

Mercury determination in solid phases from application of the modified BCR-sequential extraction procedure: a valuable tool for assessing its mobility in sediments

The present paper presents a feasibility study for the evaluation of mercury mobility in sediments by application of the modified BCR three-step sequential extraction procedure (BCR-SEP). The aim of the study was to evaluate the effect of acidification, reduction and oxidation processes on mercury mobility from sediments, once the SEP was validated with other trace metals.As extractable mercury amounts were mostly found below detection limits of the advanced mercury analyser (AMA-254) used for measuring the extracts (L.D.<0.5 ng), the use of a solid sampling atomic absorption spectrometer with a specially designed furnace for Hg atomisation was found to be an optimal technique to quantify Hg in the solid residues coming from the SEP.With this approach, mercury was found to be hardly mobile and only for one of the moderately polluted sediments (BCR CRM 320), extractable mercury (exchangeable fraction, BCR procedure step 1) has been found. An oxidation step with H(2)O(2) was required to obtain extractability up to 64% of the total content in a highly polluted lagoon sediment.     

Sequential extraction of U, Th, Ce, La and some heavy metals in sediments from Ortigas river, Spain

The extractable contents of U, Th, Ce, La, Cu, Cr, Ni and Zn in two sediment samples collected from the Ortigas river have been analysed using the three step sequential extraction procedure (SEP) described by BCR, Community Bureau of Reference (now Standards Measurements and Testing Programme) of the European Union. In order to perform a mass balance, a fourth step has been included, i.e. digestion of the residue from the third extraction step. ICP-AES was used for the determination of Cu, Cr, Ni, Zn, Th, Ce and La. Because of the inadequate sensitivity of ICP-AES for the analysis of uranium, ICP-MS was used for the determination of this element. Standard addition method was required, because of the matrix effects. Finally, SEP was applied to the Ortigas river sediments, showing that most of the elements were found mainly associated with the residual sediment fraction, except for uranium, which was found as an exchangeable species in approximately 60% of its total content. Recoveries of 86-108% have been obtained.     

Comparison of original and modified BCR sequential extraction procedures for the fractionation of copper, iron, lead, manganese and zinc in soils and sediments

This article describes a detailed comparison between the original BCR sequential extraction procedure, step 2 of which involves treatment with 0.1 mol l⁻¹ hydroxylammonium chloride at pH 2, and the revised BCR procedure (step 2: 0.5 mol l⁻¹ hydroxylammonium chloride at pH 1.5). An intermediate protocol was also evaluated in which 0.5 mol l⁻¹ hydroxylammonium chloride at pH 2 was used. The procedures were applied to five soil and sediment substrates: a sewage sludge-amended soil, two different industrially contaminated soils, a river sediment and an inter-tidal sediment. Extractable iron and manganese concentrations were measured to assess the effects of the procedural modifications on dissolution of the reducible matrix components. Trace elements copper, lead and zinc were also determined. Statistical analysis (two-tailed t-tests at 95% confidence interval) indicated that recovery of iron in step 2 was not markedly enhanced when the intermediate protocol was used. However, significantly greater amounts were isolated with the revised BCR scheme than with the original procedure. Copper behaved similarly to iron. Lead recoveries were increased by use of both modified protocols, with the greatest effect occurring for the revised BCR extraction. In contrast, manganese and zinc extraction did not vary markedly between procedures. The work indicates that the revised BCR sequential extraction provides better attack on the iron-based components of the reducible matrix for a wide range of soils and sediments.     

A rapid fractionation method for heavy metals in soil by continuous-flow sequential extraction assisted by focused microwaves

A microwave-assisted continuous-flow sequential extraction system was developed for rapid fractionation analysis of heavy metals in soil. Insertion of pressure-adjusted air between the extractants provided stable flows of the extractants without mutual mixing and back-pressure influence of a column packed with soil, thereby facilitating reliable continuous-flow extractions. In addition, use of pure water as a pumping solvent removed metal contamination because of direct contact between corrosive extractants and the pump containing metallic materials. Focused microwave irradiation to the soil accelerated the selective extractions of the acid-soluble and reducible fractions of heavy metals in soil in the first and second steps of the sequential extraction conditions, as defined by the Commission of the European Bureau of Reference (BCR). The microwave-assisted continuous-flow extraction provided high correlations in amounts of six heavy metals except Zn in the first step and Cu in the second step extracted from a reference sludge soil, BCR CRM 483, with a conventional batchwise extraction proposed by BCR; continuous-flow extraction assisted by conductive heating provided lower correlations for all the six metals. The proposed method drastically reduced the time required for the sequence extraction to ca. 65 min without losing accuracy and precision of the fractionation analysis of heavy metals in soil, whereas the BCR batchwise method requires ca. 33 h. An erratum to this article can be found at     

Kinetic approach to heavy metal mobilization assessment in sediments: choose of kinetic equations and models to achieve maximum information

Studies of trace metal mobilization in sediments are generally performed using sequential extraction schemes at equilibrium. In the present work, a kinetic fractionation of trace metals in sediments has been developed to assess that information. The extraction rate data have been obtained using a single extraction scheme with EDTA and following a protocol previously optimized. Two kinetic equations and two kinetic models were used to fit the experimental data. The two constants equation fits well the extraction rate data used in this work but does not present any physico-chemical meaning. The diffusion model and the two first-order reactions model allow determining which parameter (the reaction between the metal M and the EDTA or the diffusion of the complex M/EDTA) is rate limiting in the trace metal extraction by EDTA. It appears that the two first-order reactions model is more efficient than the diffusion model to fit the present extraction rate data so it can be deduced that the diffusion of the complex M/EDTA is not the limiting step of the trace metal extraction by EDTA in estuarine sediments. In a second part, relationships between the fraction of metals determined with the two first-order reactions model and the sediments composition were established.     

Speciation of waste water sediments

A sequential extraction procedure for waste water sediments was elaborated based on CO₂ and water extractants using supercritical fluid extraction instrumentation. The procedure gives information on water-soluble, carbonate-bound and mobile organic-bound trace metal fractions. The chemical interpretation of this procedure is comparable with the BCR recommended three-stage sequential extraction. The validation of the proposed procedure requires more detailed investigations.     

Ultrasound and microwave-assisted extraction of metals from sediment: a comparison with the BCR procedure

In this paper we investigate alternatives to mechanical stirring for the extraction of the mobile fraction of metals from sediment, and analyze whether these techniques can reduce extraction time and improve reproducibility. We compare the quantities of metal extracted from BCR601 and BCR701 certified sediments using ultrasound bath, microwave-assisted extraction and the first step in the certified BCR sequential extraction procedure. Some environmentally important not-certified metals such as As, Mn, Co, Fe and Al have been included in this study. In the case of microwave-assisted extraction, we compare tests in which samples are exposed to constant, low power irradiation with tests using pulsed high power.

In the tests using the ultrasound bath, less metal was extracted than with the other extractive techniques and standard deviations were comparable to those obtained with the BCR procedure; in assays using microwaves at constant power, extraction efficiencies were different for different metals and for different reference materials and, in some cases, standard deviations were higher than those for the reference method. In contrast, tests with microwaves and constant temperature produced encouraging results: R.S.D.s lay in the 2–4% range, both for certified and not-certified metals; these values are very low compared to those for the reference method. Extraction efficiencies for certified metals were close to 100% for Cd, Zn, Cu and Ni and around 80% for Pb and Cr.     

Voltammetric behaviour at gold electrodes immersed in the BCR sequential extraction scheme media: Application of underpotential deposition-stripping voltammetry to determination of copper in soil extracts

The development of mercury-free electroanalytical systems for in-field analysis of pollutants requires a foundation on the electrochemical behaviour of the chosen electrode material in the target sample matrices. In this work, the behaviour of gold working electrodes in the media employed in the BCR sequential extraction protocol, for the fractionation of metals in solid environmental matrices, is reported. All three of the BCR sequential extraction media are redox active, on the basis of acidity and oxygen content as well as the inherent reducing or oxidising nature of some of the reagents employed: 0.11 M acetic acid, 0.1 M hydroxylammonium chloride (adjusted to pH 2) and 1 M ammonium acetate (adjusted to pH 2) with added trace hydrogen peroxide. The available potential ranges together with the demonstrated detection of target metals in these media are presented. Stripping voltammetry of copper or lead in the BCR extract media solutions reveal a multi-peak behaviour due to the stripping of both bulk metal and underpotential metal deposits. A procedure based on underpotential deposition-stripping voltammetry (UPD-SV) was evaluated for application to determination of copper in 0.11 M acetic acid soil extracts. A preliminary screening step in which different deposition times are applied to the sample enables a deposition time commensurate with UPD-SV to be selected so that no bulk deposition or stripping occurs thus simplifying the shape and features of the resulting voltammograms. Choice of the suitable deposition time is then followed by standards addition calibration. The method was validated by the analysis of a number of BCR 0.11 M acetic acid soil extracts. Good agreement was obtained been the UPD-SV method and atomic spectroscopic results.     

Oxidative extraction versus total decomposition of soil in the determination of thallium

An aqua regia extraction and a total decomposition of soil were compared in terms of thallium determination. A sequential extraction of soil, according to the BCR protocol, was also performed for additional information on thallium distribution in soil fractions. Certified reference material—soil GBW 07401 of Chinese origin, containing 1 ± 0.2 ppm of thallium was used in these experiments. Thallium was determined by flow injection-differential pulse-anodic stripping voltammetry (FI-DP-ASV). Only 35% of total thallium was extracted in the aqua regia extraction, while the total decomposition led to satisfactory recovery. The sequential extraction showed that only 5% of thallium in GBW 07401 is dissolvable in the four BCR procedure fractions, and that 95% of the element is entrapped in the residual parent matter. These results show that the aqua regia extraction does not ensure complete thallium extraction from soil. Surprisingly, the total decomposition is significantly less time consuming than the aqua regia extraction.     

Spatial and vertical distributions of natural and anthropogenic radionuclides and cesium fractionation in sediments of the Var river and its tributaries (southeast France)

This paper reports results on the natural and anthropogenic radionuclides activity concentrations in sediments of the Var river and its tributaries. Natural (²³⁸U, ²³²Th and ⁴⁰K) and artificial (¹³⁷Cs) radionuclides activities were measured using high purity germanium detector. Measured activity concentrations differ widely; they depend on the pertinent environmental situation such as the presence of dams, and sediments type. Other factors controlling the distribution of the studied radioisotopes have been discussed. A sequential extraction method consisting of six operationally-defined fractions has been used for determining the geochemical partitioning of anthropogenic radionuclide ¹³⁷Cs in a 405–410 cm deep sediments collected in the lower valley of the Var river. This method corresponds to a modification of the three-stage sequential extraction procedure proposed by the Commission of the European Communities Bureau of Reference (BCR, now Standards, Measurements and Testing Program). Two steps with weak reagents, (fraction A: water; fraction B: nitric acid 0.001 M), were added before the first step of BCR (carbonate fraction) in order to better detect anthropogenic components. A total acid digestion of solid residues by microwave assisted was also added. The 6-steps extraction method was tested and validated by certified reference materials. ¹³⁷Cs was found mostly in the hydrosoluble fraction (20–24 %), oxide and hydroxide fraction (22–25 %) and in the residue (51–58 %), while ¹³³Cs was mostly found in the residual fraction (>97 %).     

Effects of freeze-drying on partitioning patterns of major elements and trace metals in lake sediments

The effect of freeze-drying on elemental partitioning pattern in four lake sediments was evaluated using the sequential extraction method developed under the auspices of Community Bureau of Reference (BCR) of the Commission of European Communities. Redox-sensitive elements like iron, manganese, phosphorus, and sulfur were analyzed simultaneously with several trace metals. This allows a qualitative determination of which trace metal-scavenging phases commonly found in freshwater sediments that are most susceptible to freeze-drying.The comparison of a surface layer and a deeper more reduced layer collected from four sediment cores ranging from sub-oxic to anoxic condition indicate the changes in partitioning pattern due to freeze-drying. Two of the lakes exhibiting clearly reduced environments are most affected by freeze-drying in terms of change in partitioning patterns. However, this effect is element specific and varies with sediment depth along the redox gradient. Elements commonly associated with a sulfide phase (S, Fe, Cu, Zn, and Pb) and extracted in BCR step 3 are the most affected elements, but at the same time also dependent on the organic matter content in the sediment. Si and Al that are often considered as conservative elements show a shift from step 3 to step 2, and it is interpreted as a release of Si and Al from organic matter and the subsequent formation of oxides during freeze-drying. Calcium and manganese, elements that are often associated with a carbonate phase, do not seem to be severely affected by this kind of treatment. Carbonate-associated iron (operationally defined), however does show a clear tendency to oxidize during the freeze-drying process. In fact, the shift in iron (carbonate to oxide fraction) corresponds to 3-4% (w/w) of the total sediment in some cases. Surprisingly, a significant fraction of iron originally extracted in step 1 (as “carbonate”) seems to be immobilized during freeze-drying.These results clearly show that freeze-drying does not preserve the speciation pattern of major elements, trace metals, phosphorus, and sulfur in anoxic lake sediment core sections during storage prior to BCR sequential extraction procedures.