Relationship between vegetable metal and soil-extractable metal contents by the BCR sequential extraction procedure: chemometrical interpretation of the data

The contents of heavy metals in soil and vegetable samples collected from an urban garden in Kayseri, Turkey, were investigated. Both wet- and dry-ashing methods were used for dissolving vegetable samples. A sequential extraction procedure proposed by the Commission of the European Communities, Community Bureau of Reference (now superseded by the Standards, Measurement and Testing Programme, SM&T) was applied to the soil samples to extract the metals which are present in exchangeable and acid soluble (i.e. bound to carbonates), reducible (bound to Fe/Mn oxides), and oxidisable forms (bound to organic matter and sulphides) in the soil samples. Trace metals in the soil and vegetable samples were determined using flame atomic absorption spectrometry (FAAS). The total metal contents acquired by summing of metal levels in all the sequential extraction steps were compared with pseudo-total metal levels obtained with aqua regia for all the soil samples. The recovery values obtained by proportioning the results obtained by the BCR procedure to those of the pseudo-total digestion were found to be satisfactory. The limits of detection for the elements investigated were in the range of 0.04 to 0.59?µg?mL^?1 for all the extraction stages of the BCR procedure. Similarities among the variables were identified by correlation analysis, principal component analysis and hierarchical cluster analysis. The relationship between the vegetable metal and soil-extractable metal concentrations was examined in order to evaluate the bioavailability of metals.     

Determination of Al, Cu, Fe, Mn, Pb and Zn in certified reference materials using the optimized BCR sequential extraction procedure

Sequential extraction procedures are widely used to characterize the fractionation of metal species in solid media. With the variety of different sequential procedures used in environmental and geochemical exploration studies, it is difficult to compare results between studies. Thus, harmonization and standardization are required to provide greater inter-study comparability for fraction-specific metals. In this study, the optimized BCR three-step sequential extraction procedure is applied to five certified reference materials (SRM 2710, SRM 2711, CRM 483, CRM 601 and CW 7). Four fractions are reported, acid extractable, reducible, oxidizable, and residual for Al, Cu, Fe, Mn, Pb and Zn. The objectives of this study were to characterize experimental precision and/or accuracy and to establish baseline data of fraction-specific element concentrations for future studies applying the optimized BCR three-step extraction procedure. The optimized procedure was found to be precise (typically <5%) for all metals in all fractions. Accuracy was acceptable (typically ±15% relative to published indicative values for Cu, Pb and Zn for CRM 483 and CRM 601) for all individual fractions. Detailed fraction-specific concentration data are presented, based on five replicates, for the first time using the optimized procedure for Al, Fe and Mn in CRM 483 and CRM 601, and for Al, Cu, Fe, Mn, Pb and Zn in SRM 2710, SRM 2711 and CW 7.     

Determination of trace metals in the River Ye?il?rmak sediments in Tokat, Turkey using sequential extraction procedure

Sequential extraction procedure (acid extractable, reducible, oxidizable, and residual) proposed by BCR was applied for the determination of trace metals in the River Yesilirmak sediments, Tokat, Turkey. The determination of trace metals in sediment samples was performed by flame atomic absorption spectrometry. The proposed method showed satisfactory recovery, detection limits and standard deviation for trace metals determination in sediment samples. Generally, most of the elements were found in the oxidizable and residual fractions. The total concentrations of trace metals analyzed were found to be (mg/kg) Cu: 37.9, Mn: 392.2, Zn: 126.2, Fe: 3726, and Pb: 29.6, respectively. Results obtained are in agreement with data reported in the literature.     

Utilization of optimized BCR three-step sequential and dilute HCl single extraction procedures for soil-plant metal transfer predictions in contaminated lands

The prediction of soil metal phytoavailability using the chemical extractions is a conventional approach routinely used in soil testing. The adequacy of such soil tests for this purpose is commonly assessed through a comparison of extraction results with metal contents in relevant plants. In this work, the fractions of selected risk metals (Al, As, Cd, Cu, Fe, Mn, Ni, Pb, Zn) that can be taken up by various plants were obtained by optimized BCR (Community Bureau of Reference) three-step sequential extraction procedure (SEP) and by single 0.5 mol L(-1) HCl extraction. These procedures were validated using five soil and sediment reference materials (SRM 2710, SRM 2711, CRM 483, CRM 701, SRM RTH 912) and applied to significantly different acidified soils for the fractionation of studied metals. The new indicative values of Al, Cd, Cu, Fe, Mn, P, Pb and Zn fractional concentrations for these reference materials were obtained by the dilute HCl single extraction. The influence of various soil genesis, content of essential elements (Ca, Mg, K, P) and different anthropogenic sources of acidification on extraction yields of individual risk metal fractions was investigated. The concentrations of studied elements were determined by atomic spectrometry methods (flame, graphite furnace and hydride generation atomic absorption spectrometry and inductively coupled plasma optical emission spectrometry). It can be concluded that the data of extraction yields from first BCR SEP acid extractable step and soil-plant transfer coefficients can be applied to the prediction of qualitative mobility of selected risk metals in different soil systems.     

A comparison of an optimised sequential extraction procedure and dilute acid leaching of elements in anoxic sediments, including the effects of oxidation on sediment metal partitioning

The effect of oxidation of anoxic sediment upon the extraction of 13 elements (Cd, Sn, Sb, Pb, Al, Cr, Mn, Fe, Co, Ni, Cu, Zn, As) using the optimised Community Bureau of Reference of the European Commission (BCR) sequential extraction procedure and a dilute acid partial extraction procedure (4 h, 1 mol L⁻¹ HCl) was investigated. Elements commonly associated with the sulfidic phase, Cd, Cu, Pb, Zn and Fe exhibited the most significant changes under the BCR sequential extraction procedure. Cd, Cu, Zn, and to a lesser extent Pb, were redistributed into the weak acid extractable fraction upon oxidation of the anoxic sediment and Fe was redistributed into the reducible fraction as expected, but an increase was also observed in the residual Fe. For the HCl partial extraction, sediments with moderate acid volatile sulfide (AVS) levels (1-100 μmol g⁻¹) showed no significant difference in element partitioning following oxidation, whilst sediments containing high AVS levels (>100 μmol g⁻¹) were significantly different with elevated concentrations of Cu and Sn noted in the partial extract following oxidation of the sediment. Comparison of the labile metals released using the BCR sequential extraction procedure (ΣSteps 1-3) to labile metals extracted using the dilute HCl partial extraction showed that no method was consistently more aggressive than the other, with the HCl partial extraction extracting more Sn and Sb from the anoxic sediment than the BCR procedure, whilst the BCR procedure extracted more Cr, Co, Cu and As than the HCl extraction.     

Distribution of heavy metals of agricultural soils of central Greece using the modified BCR sequential extraction method

The state of heavy metal (Cd, Cu, Ni, Zn, Pb, and Cr) pollution was studied, in 440 texturally different soil profiles in Thessaly, an intensely cultivated region in Central Greece. The study was carried out in 2004 and 2005 on 220 soil samples for each year. Soil samples were classified in three soil orders: Endisols, Alfisols, and Vertisols according to the Soil Taxonomy System. The pseudo-total concentrations of heavy metals were determined by the aqua regia procedure. Heavy metals were also determined after division into four fractions by sequential extraction with (a) acetic acid (exchangeable and specifically adsorbed metals), (b) a reducing agent (bound to Fe/Mn hydroxides), (c) an oxidizing agent (bound to soil organic matter), and (d) aqua regia (bound to mineral structures, residual). The concentrations of all the metals studied were higher in the topsoil (0–30?cm) and lower in the second soil layer (30–60?cm). Concentrations of 70–82% of Cd, 39–64% of Cu, 41–69% of Ni, 29–51% of Zn, 75–89% of Pb, and 52–87% of Cr were found in the first two fractions. Cd appeared to be the most mobile of the metals studied, while Cu and Zn were found in forms associated with soil organic matter. The chemical partitioning patterns of Pb and Cr indicated that these metals are largely associated with the Fe–Mn hydroxides, while Cr was also found in the residual fractions. Significant correlations between heavy metals fractions and soil physicochemical parameters were obtained and discussed.     

Comparison of three sequential extraction procedures used to study trace metal distribution in an acidic sandy soil

On an acid sandy soil contaminated with trace metals (Fe, Mn, Cu, Pb and Zn), three sequential extraction procedures were compared to determine the efficiency of the reagents used and the effects of the step order on the fractionation of metal species. In all cases, a magnesium nitrate solution (MgNIT) was previously used to extract exchangeable forms. In the first procedure (I), the next extraction step was performed with sodium acetate buffer (NaOAc), as used on calcareous soils, to dissolve active calcium carbonate. Then trace metals bound to different forms of oxi-hydroxides (NH(2)OH, TAMOx and TAMAs fractions) were extracted before organic matter/sulfide oxidation with hydrogen peroxide at pH 2.0 in nitric acid medium (OMHyd). Finally, residual bound metals (RESID) in each procedure were extracted with a nitric-hydrofluoric-perchloric acid mixture. The second procedure (II) was the same as I, but without the NaOAc step, because of the absence of carbonate in the study soil. In procedure III, the NaOAc step was omitted and the oxidizable organic/sulfide fraction was extracted with sodium hypochlorite at pH 8.5 (OMOCl) before the reducible fractions. This study first showed that NaOAc may remove considerable amounts of metals (especially Mn and Zn) in other forms than exchangeable ones. Procedures II and III give similar results for Fe, Mn and Zn forms, which were mainly found in fractions of inorganic soil components, but not for Cu and Pb. Copper distribution was affected by the position of the oxidation step in the sequence. In procedure II, where the oxidation step (OMHyd) ended the sequence, Cu was mainly recovered in the TAMOx fraction. However, in procedure III, where the oxidation step (OMOCl) preceded the NH(2)OH, TAMOx and TAMAs steps, Cu was found in both OMOCl and TAMOx fractions. Lead distribution varied with oxidation reagent: it was partly removed in the OMHyd fraction of procedures I and II, and to a much lower extent in the OMOCl fraction of procedure III, probably due to the alkaline pH of the reagent in the latter case.     

Heavy metals contamination in roadside soil near different traffic signals in Dubai,United Arab Emirates

The present research was conducted to study heavy metal contamination in roadside soil viz. (i) at sites having more than two traffic signals (ii) roads having only one traffic signal and (iii) roads having no traffic signals. The samples were collected and analyzed for seven heavy metals i.e. cadmium (Cd), lead (Pb), copper (Cu), nickel (Ni), iron (Fe), manganese (Mn) and zinc (Zn) by Atomic Absorption Spectroscopy (AAS) following the acid digestion of the respective soil samples. The range of the metals observed in soil having more than two traffic signals were Cd (0.17–1.01), Pb (259.66–2784.45), Cu (15.51–65.90), Ni (13.31–98.13), Fe (325.64–5136.37), Mn (57.95–166.43), and Zn (91.34–166.43) mg kg^?1 respectively. Similarly, the range of metals analyzed in samples collected from the roadside having only one traffic signal were Cd (nd–0.80), Pb (145.95–308.09), Cu (0.82–18.04), Ni (18.29–59.36), Fe (88.51–3649.42), Mn (25.88–147.34) and Zn (8.97–106.11 mg kg ^?1) respectively. However, the range of metals at roads having no traffic signals were Cd (0.0–0.57), Pb (8.34–58.20), Cu (2.88–5.81), Ni (3.34–73.80), Fe (55.34–332.81), Mn (2.98–98.73) and Zn (1.23–46.6 mg kg^?1) respectively. Cd, Cu, Ni, Fe, Mn and Zn in soil were present within the normal range of background levels, whereas lead was reported in high concentration. The level of lead had a correlation with the traffic density attributing its origin to vehicular exhaust. The values from three different sites of monitoring suggest that automobiles are a major source of the studied metals for the roadside environment.     

One hundred and forty years “Fresenius’ Journal of Analytical Chemistry”

The distribution of rare earth elements (REE) in a pooled soil sample collected from Zhangzhou, Fujian Province, China, was screened by a five-step sequential extraction procedure coupled with ICP–MS determination after preconcentration of REE and removal of the matrix by extraction with 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (HPMBP). The results showed that the distribution of REE in the different fractions of the pooled soil sample studied followed the order soluble species (46.76%) > species bound to organic matter (22.08%) > species in the residue (16.77%) > species bound to Fe–Mn oxides (2.02%). An effective method for speciation of REE, which utilized weak cation-exchange HPLC separation hyphenated with post-column derivatization and visible or on line ICP–MS detection, was, moreover, developed and successfully applied to the speciation of REE in the soluble extract of the pooled soil sample. The stability of known complexes of lanthanum during the HPLC separation was investigated with fluoride, citrate, and ethylenediamine tetraacetic acid (EDTA) chosen as ligands modeling those in the soil. REE in the soluble extract of the pooled soil sample were subsequently classified into three types of species –≤ + 1 charged complexes (negatively charged, neutral, and +1 charged), + 2 charged complexes, and “free” REE species. This method is expected to be useful for identification of bioavailable (or toxic) species of REE in environmental samples.     

Evaluating the mobility of toxic metals in untreated industrial wastewater sludge using a BCR sequential extraction procedure and a leaching test

The distribution and speciation of toxic metals in industrial wastewater sludge (IWS) was investigated. In this work, the modified BCR three-stage sequential extraction procedure was applied to the fractionation of Cr Pb Ni, and Cd in untreated industrial wastewater sludge from industrial sites in Hyderabad (Pakistan). The extracts were analyzed using electrothermal atomic absorption spectrometry. The procedure was evaluated using a certified reference material for soil mixed with sewage sludge BCR 483. The results from the partitioning study indicate that more easily mobilized forms (acid exchangeable) of Cd were dominant. The oxidizable fraction was dominant for all four toxic metals. Metal recovery was good, with <4% difference between the total metal recovered through the extractant steps and the total metal determined after microwave digestion. Lixiviation tests (DIN 38414-S4) were used to evaluate the leaching of toxic species from IWS, and it was observed that levels of leachable toxic metals were low compared to the amount of metal extracted in the exchangeable fraction of the BCR protocol.     

Analytical fractionation of labile metals in selected groundwater humic substances by means of chelating ion-exchanger

Summary Trace metals remaining in humic substances (HUS) after their acidic isolation (XAD 2) from aquatic sources may preferably be bound in inert form. In the present study, the reactivity (lability) of such a trace metal fraction (e.g. Cu, Fe, Mn, Zn) in selected groundwater HUS (BOC 1 and 3 from the DFG Versuchsfeld Bocholt, FRG) is characterized by its different separation behaviour towards a chelating ion-exchanger (e.g. Hyphan) using a time-controlled sequential batch procedure (96 h). Under standardized conditions, the kinetics and the degree of the ion-exchange reaction serve as parameters for the operational evaluation of metal lability in the above mentioned HUS. Surprisingly, according to the above ion-exchange procedure, about 50% of the total Fe, 81 (95)% Cu, 65 (97)% Mn, 69 (97)% Ni and 82 (95)% Zn in BOC 1 (BOC 3) proved to be bound in labile form. However, 20 to 30% of the labile metal fraction only react following very slow first order kinetics (half-time 24 h). In contrast, trace metals freshly bound to BOC 1 are quantitatively recovered by the collector Hyphan within 1 to 2 h, with the exception of Fe. Moreover, in this way HUS samples can be purified for molecular spectroscopy investigations (e.g. NMR, ESR, fluorescence) which are highly sensitive to metal interferences.     

Investigation of heavy metals mobility in shrimp aquaculture sludge—Comparison of two sequential extraction procedures

Influence of heavy metals was investigated by conducting various tests on the samples collected from aquaculture shrimp in Selangor, Malaysia. The concentration of heavy metals in the sludge and potential of mobility based on its association forms was studied. Two sequential extraction methods (five stages Tessier method and three steps BCR method) were used to determine the binding forms of the metals.From the analysis, Ca, Fe and Mn were found to be highest concentrated metals compared to Zn, Cu, Cr, Cd and Pb in aquaculture shrimp sludge. From the sequential extraction, Cd, Mn and Pb were mostly found in exchangeable/carbonate form, showed its susceptibility to be leached easily. Also Cu and Zn were extracted predominantly in oxidizable form. All metal concentrations (except Cd, Zn and Cu) were extracted to be higher in residual fraction in this method. The results of BCR method are totally similar to the five stages Tessier method. By comparing the percent of recovery, the BCR method was better than Tessier method. Nevertheless for both methods the percent of their recoveries were acceptable. For Pseudototal metal digestion, although the concentration of Cd is less than other heavy metals, it is very harmful as a fertilizer because Cd is one of the heavy metals that might be in the leaf or fruit of plants. Also for investigation of Ca in the sludge, this element was measured and high amounts of that show sludge is useful for growing of plant. The results of direct digestion of heavy metals show that with the control of Cd in this sludge we can use this sludge as fertilizer in soils for agriculture but it is better if it is used for fruitless plants.     

Fractionation of lead in soils affected by smelter activities using a continuous-flow sequential extraction system

A continuous-flow sequential extraction system was used to study the distribution of Pb, and its association with other elements (Fe, Al and Ca), in soils around a Pb smelter. Soil samples were analysed by a four-step continuous-flow sequential extraction procedure employing a modified Tessier/BCR scheme. Recoveries of Pb using the flow system (88–111%) were higher than those obtained using a conventional batch extraction system. There were also some differences in Pb distribution between fractions as determined using the two extraction systems. The most abundant fraction of Pb was extracted during the dissolution of soil oxides (Fe/Al). Extractograms (plots of concentration of elements vs. extractant volume/time) indicated that anthropogenic Pb was predominantly adsorbed onto Fe oxide surfaces in contaminated soils. In soil profiles, the highest amounts of Pb were found in the topsoil surface layers (0–5?cm) of the contaminated soils with only limited movement into subsurface layers.     

Preparation of candidate certified reference materials for the quality control of EDTA-and acetic acid-extractable trace metal determinations in sewage sludge-amended soil and terra rossa soil

The determination of extractable trace metal contents in soil using single extraction procedures is currently performed in many laboratories to assess the bioavailable metal fraction (and related phytotoxic effects) and the accessability to the environment (e.g. contamination of ground waters). Owing to the need for validation of the extraction schemes used and of the analytical techniques, the EC Measurements and Testing Programme (formerly BCR) has organized a project for improving the quality of determination of extractable trace metal contents in soil, the first step being an interlaboratory study to adopt common extraction procedures and the second being a certification campaign to certify two soils for their extractable trace element contents following these procedures. This paper gives a brief overview of the project organisation and describes the preparation, homogeneity and stability studies of two soil candidate reference materials (sewage sludge-amended and terra rossa soils).     

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.     

Determination of water soluble trace metals in airborne particulate matter using a dynamic extraction procedure with on-line inductively coupled plasma optical emission spectrometric detection

A novel continuous-flow system for the dynamic extraction of water soluble metal fractions in airborne particulate matter (APM) with subsequent inductively coupled plasma optical emission spectrometric (ICP-OES) analysis of derived extracts is presented. The fully automated extraction system with on-line multi-element detection offers enhanced sensitivity when compared to batch-wise counterparts; additionally it provides information about the extraction process. With the developed procedure detection limits in the order of 1.5 (Ba) to 8.0 (Ni) ng extractable mass per investigated sample could be achieved, which translates to method detection limits for soluble metal concentrations in APM ranging from 0.2 ng m⁻³ (Ba) to 0.9 ng m⁻³ (Fe). Reproducibility of analysis was determined by replicate measurement (n = 6) of an APM sample with an aerodynamic diameter ≤10 μm (PM10), derived results varied between 3.5% (Mn) and 12.1% (Ni) relative standard deviation. Method validation was accomplished by comparison of extracted soluble and remaining non-soluble fractions with the total metal contents of the investigated PM10 samples, showing an excellent mass balance for all elements. Application of the developed procedure for the analysis of water soluble metal fractions in PM10 samples (n = 16) from Linz (Austria) indicated a high variability of extractable fractions ranging from 11.7 ± 7.2% (Fe) to 48.8 ± 15.4% (Mn) of the total metal contents.     

Improvement of Analytical Measurements within the BCR-Programme: Single and Sequential Extraction Procedures Applied to Soil and Sediment Analysis

Abstract

The determination of extractable trace metal contents in soil and sediment, using respectively single and sequential extraction procedures, is currently performed in many laboratories to assess the bioavailable metal fraction (and related phyto-toxic effects) and the accessability to the environment (e.g. contamination of ground waters).

Owing to the need for validation of the extraction schemes used and of the analytical techniques, the Community Bureau of Reference (BCR) decided to organize a project for the improvement of the quality of determinations of extractable trace metal contents in soil and sediment. The implementation of this project follows a stepwise approach involving feasibility studies, intercomparisons to detect and remove sources of errors in the application of the analytical methods, and the certification of the extractable compounds. This paper describes the organization of the work completed so far (feasibility studies and first intercomparison) and discusses its further development.     

Microanalytical flow-through method for assessment of the bioavailability of toxic metals in environmental samples

The application of a recently proposed microanalytical flow-through system for on-line sequential extraction of heavy metals from solid samples of environmental interest is described. Using various extraction schemes (a nitric acid scheme, a two-stage extraction scheme using two reagents applied in the BCR procedure) and comparison with the common batch sequential BCR procedure, the suitability of the system for fast screening of solid environmental samples is demonstrated. By pumping leaching agents sequentially through the sample held in a micro cartridge, the different metal fractions present can be assessed in less than an hour. Method evaluation was performed using SRM 1648 urban particulate matter and BCR 701 lake sediment reference material certified for extractable metals. The need for and design of laboratory internal reference material suitable for simulating the natural (dynamic) processes of metal release into the environment is also discussed. For the first time correlation is sought between fractionation techniques and physiologically based methods for assessment of the bioaccessibility of metals in biomatrices.     

Metal distribution and binding in balneological peats and their aqueous extracts

Binding of metals in typical bath peat samples (“Großes Gifhorner Moor”, Sassenburg/North Germany) and their aqueous extracts was characterized by means of a multi-method approach. For that purpose a sequential extraction procedure based on peat-filled chromatography columns was developed. Water-soluble metal and DOM (dissolved organic matter) fractions were subdivided by use of a stepwise increased pH gradient (pH 3.8–5), finally by the chelator EDTA and 0.1 mol L^–1 hydrochloric acid. Metal fractions very strongly bound to peat were assessed by an aqua regia extraction. Metal determinations required were performed by atomic spectrometry methods (AAS, ICP–OES, and TXRF). The metal and DOM concentrations in the peat extracts varied significantly, depending on the natural variety of the peat matter under study (e.g., Al: 25–674, Cd: 0.05–0.2, Cu: 5– 15.4, Fe: 77–1785, Mn: 21–505, Ni: 2–33, Pb: < 1, Zn: 9– 715 (μg L^–1); Na: 8–45, K: 1.3–14.9, Ca: 2–51, Mg: 1.1– 7.9 (mg L^–1); 26–73 mg L^–1 DOC). An increase of the pH increased the DOC (dissolved organic carbon) of the peat extracts, but hardly the concentration of heavy metals. The latter could only be re-mobilized by EDTA and dilute hydrochloric acid. Additional investigations of the peat extracts using tangential-flow ultrafiltration revealed that the heavy metals extracted at pH < 4 were predominantly dissociated. At higher pH (pH > 4.5) they were preferentially bound to macromolecular DOM. Moreover, using multistage ultrafiltration the size distribution of the DOM and their metal species was assessed.