Adoption of Common Schemes for Single and Sequential Extractions of Trace Metal in Soils and Sediments

Abstract

The various methods for determining the mode of occurrence of trace metals in sediments and soils have a long history which dates back to the determinations of the availability of metals for plant nutrition performed earlier. Various methods have been developed in the 70′s and 80′s dealing with both single and sequential extraction schemes. Although some schemes received wide acceptance, none of them developed into a commonly accepted procedure. As a result, the information obtained was site-specific and the interpretation of the results scientist-specific. The workshop on single and sequential extraction in sediments and soils held at Sitges     

Trace Element Speciation in Soils and Sediments Using Sequential Chemical Extraction Methods

Abstract

Several commonly used sequential chemical extraction procedures of heavy metals in soils and sediments are compared, and their advantages and disadvantages are discussed focusing on selected case studies. In particular, problems caused by handling of anoxic samples, and of specific phases (e.g. organic fractions and sulfides) are addressed.

Eventually, recommendations for the improvement of extraction selectivity as well as the reduction of readsorption effects are given.     

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.     

Chemical Speciation and Fractionation in Soil and Sediment Heavy Metal Analysis: A Review

Abstract

Today it is generally recognized that the particular behaviour of trace metals in the environment is determined by their specific physicochemical forms rather than by their total concentration. Several chemical speciation and fractionation methods for heavy metal analysis in soils and sediments have been and are still being developed and applied. They primarily are intended to understand the particular environmental behaviour of metals, present in a variety of forms and in a variety of matrices.

Analytical developments, modifications of existing methods, and recent new approaches are reviewed and discussed. Techniques used include chemical extractions, ion-exchange/gel chromatography, filtration, centrifugation and sieving, selective solvent extraction.

Moreover, the application of these various techniques in different research fields over the last years is explored. The value and the limitations of speciation and fractionation techniques applied in specific experimental work is outlined. It is discussed to what extent these methods have, up to now, filled in the expectations or have been satisfactory in particular applications.     

Evaluation of some Isolation Methods for Organomercury Determination in Soil and Fish Samples by Capillary Gas Chromatography—Atomic Fluorescence Spectrometry

Abstract

Three extraction methods, acidic KBr/CuSO₄ isolation-methylene chloride extraction. acidic KBr/CuSo₄ isolation-methylene chloride extraction with an alkaline digestion pretreatment, and an extration method at a milder condition with citrate buffer and dithizone in chloroform, were studied for methylmercury and ethylmercury determination in soils, sediments and fish samples by the recently developed capillary gas chromatography—atomic fluorescence spectrometry system (GC-AFS). The acidic KBr/CuSO₄-methylene chloride extraction and the acidic KBr/CuSO₄-methylene chloride extraction with an alkaline digestion pretreatment were shown to be the effective methods for soils/sediments and fish samples analysis, respectively. The presence of ethylmercury species in soils of the Florida Everglades, observed with the acidic KBr/CuSO₄ isolation and methylene chloride extraction procedure, was further confirmed with the dithizone complexation/extraction procedure. The GC-AFS analytical method offers high senstivity and selectivity for the determination of organomercury halides. The GC column maintenance, a critical step for organomercury halides analysis using GC, is also discussed.     

New Sediment and Soil CRMs for Extractable Trace Metal Content

Abstract

The lack of uniformity in leaching procedures used to measure broadly defined forms of heavy metals does not allow the results to be compared world-wide nor the methods to be validated since the results obtained are “operationally defined”. An attempt was made to certify several mineral soils CRMs for single extraction by using acetic acid, EDTA and DTPA for Cd, Cr, Cu, Ni, Pb and Zn. Recently, to complete the series of soil CRMs, an organically enriched soil was prepared SO25. For sediments a CRM 601 was produced and certified for metals extractable by using the BCR three step sequential extraction. Not all the trace elements were certified and only indicative values were given for some of them due to poor reproducibility. We performed a systematic study of the effect of the variables identified as potential sources of uncertainty in the use of this scheme. With this study the sources of uncertainty were revealed and an optimised version of the protocol was proposed. With this new version it was possible to certify all the trace elements studied. New sediment material S33 is now proposed for certification and additional data are given for the sediment CRM 601. This modified procedure was also applied to a soil CRM 483 and good results were obtained. This procedure may thus be applied to polluted soils.     

Sequential Extraction of Copper and Zinc from Sewage Sludges. Use of Organic Solvents

Abstract

Sequential extraction procedures were used to evaluate the bioavailability of metals from two sewage sludges after application in soils. Organic solvents were used prior to sequential extraction to evaluate the influence of oil and waxes on heavy metals extractability.

The preliminary results showed that a extraction of oil and waxes present in the sewage sludges by n-hexane followed by acetone increased the accessibility of Cu and Zn and did not remove substantial metal amounts.     

Single and Sequential Extraction in Sediments and Soils

Abstract

The determination of extractable trace metal contents in soils and sediments is currently performed in many laboratories to assess the bioavailable metal fraction (and related potential phyto-toxic effects) and the importance and possibility of mobilization of trace metals from polluted soil, sludge and sediment upon landfill application. Single and sequential extraction schemes are used for the assessment of the different “forms” of trace metals (e.g. “mobile/bioavailable”, “carbonate-bound” etc.). The lack of uniformity in the different extraction procedures used throughout the world does not allow the results to be compared or the procedures to be validated which has led to many criticisms in the past few years. Moreover, the lack of suitable reference materials for this type of operationally defined determinations did not enable the quality of the measurements to be controlled. Owing to the need for establishing common schemes for single and sequential extractions as well as for the improvement of the quality of extractable trace metal determinations in soil and sediments, the Community Bureau of Reference (BCR) has organised a project which results along with the state of the art of extractable trace metal determinations, use and applicability of extraction schemes and analytical limitations were decided to be thoroughly discussed in a workshop. This paper presents its main conclusions.     

Application of Leaching Tests for the Assessment of Available Heavy Metals from Domestic and Industrial Sludges

Various sludge samples from different domestic and industrial wastewater treatment plants were analyzed by Flame Atomic Absorption Spectrometry to evaluate their total and available contents of heavy metals (Cu, Cr, Ni, Pb, Zn and Fe). The EDTA and acetic acid single extraction procedures were applied to these samples with the aim to study the leaching behaviour of the metals in the different sludges and also to predict their possible mobility when these wastes are disposed on the environment and landfills. In acidic medium, a higher extraction efficiency was observed for the major part of the elements studied in the industrial sludges, except for Ni and Zn, which were also considerably released from domestic sludges. In contrast, in the presence of the EDTA complexing ligand, a more elevated mobility of metals was found in the domestic sludges and little or no metals were released from the industrial sludges. Moreover, the results of the microwave total digestions were compared, for all metals, with those obtained using a more simplified pseudototal digestion procedure (based on the EPA Method 3051, named microwave assisted acid digestion of sediments, sludges, soils and oils) and a good agreement was found between them, except for Cr and Ni in some particular samples. The between-batch precision (expressed as RSD) of both compared digestion methods was very similar and values lower than 7.7% were obtained in both cases. A certified domestic sludge material (SRM 2781) was employed to validate the two digestion procedures and no significant differences were found between the certified and experimental values for all the elements studied.     

The Analysis of Inorganic and Organic Pollutants in Soil with Special Regard to Their Bioavailability

Abstract

The most important inorganic pollutants in soil are the heavy metals. Problems related to the determination of the total and soluble content are discussed. Soluble contents are of interest in connection with studies about bioavailability. Because some of the heavy metals are essential for plant growth, most of the work about bioavailability has been done in the field of plant nutrition. Much less is known about the situation in polluted soils.

It was shown that neutral salt solutions which do not really change the pH of soil during the extraction procedure are best suited to define thresholds of excess. This is in contrast to much stronger extractants like EDTA or DTPA often proposed for the analysis of soils which are deficient in trace elements.

With three sets of experiments the correlation between the contents of cadmium, copper, nickel and zinc extracted by 0.1 M NaNO₃ (as an example of a neutral salt solution) and the plant response (phyto- or zootoxicity) are shown:

—pot experiments using soils which were contaminated by metal salt solutions

—pot experiments using soils from contaminated areas

—field studies in polluted areas. In these studies the aspect of heavy metal leaching was also considered.

The results were converted to indicative values in the Swiss Ordinance of Pollutants in the Soil. These indicative values derived from plant reactions were checked by the carbon mineralisation as an example of a soil microbiological process.

As it was found that organic pollutants are not easily taken up by plant roots the problem of bioavailability is much less important. However, the biodegradation and formation of metabolites has to be considered.     

Optimization of a Sequential Extraction Scheme for the Characterization of Heavy Metal Mobility in Iron Oxide Rich Sediments

Abstract

Several parameters governing the extraction of metals from iron oxide rich sediments, using sequential extraction schemes were optimized. The mode of shaking, soil/extractant ratio and concentrations of MgCl₂ and NH₂OH·HCl, for samples collected in the Odiel Marshes Natural Park (SW Spain), were considered. The concentration of NH₂OH·HCl deserved particular attention due to the nature of the studied sediments. A 0.4 M concentration of this extractant was needed to avoid readsorption of Cu and As in the samples. In addition, readsorption processes were studied using a candidate to reference material with a high organic matter content that was previously analyzed in an interlaboratory study.     

Rotating coiled columns in the speciation analysis of natural samples: Dynamic fractionation of element forms in soils,sludges, and bottom sediments

The potentials of dynamic extraction in rotating coiled columns (RCCs) for the speciation analysis of soils, sludges, and bottom sediments is discussed on an example of the fractionation of element forms. A comparative study of the results of the fractionation of the forms of heavy metals differing in physicochemical mobility and bioavailability (Zn, Cd, Pb, Cu, Ni, Cr), obtained using a number of procedures of sequential extraction, is performed. Particular attention is paid to mercury, which is quite different from other metals in biogeochemical properties. Conditions are described for the dynamic fractionation of arsenic species occurring in natural samples in anionic forms. It is revealed that, in contrast to batch extraction, the continuous renewal of the eluent in a rotating column eliminates the problem of readsorption and overlapping of isolated fractions and enables the correct assessment of the concentration of the most mobile and bioavailable forms of toxic elements. A hyphenated method for the fractionation and determination of certain forms of elements (based on the ICP-AES detection of elements in the column eluate in the on-line mode) is described, ensuring the processing and a real-time control of the dynamic extraction of the forms of elements. The kinetic aspects of selective leaching are considered. It is shown that a comparison of the elution curves of micro- and macrocomponents makes possible a judgment about the selectivity of the leaching reagent, optimization of the conditions for the isolation of each fraction, and the investigation of the features of the binding of heavy metals and matrix elements in soils and bottom sediments. Some recommendations are given for the dynamic fractionation of the forms of elements in soils, sludges, and bottom sediments in RCCs.     

The impact of nitrogen fertilizers on degradation and leaching of chlorotoluron in soil

Abstract

This study presents the developed and applied methods for the determination of carbendazim in environmental samples originating from several field studies.

For water samples sample pretreatment consisted of a solid phase extraction (SPE) on cartridges packed with 200 mg SDB-1. In case of solid samples the performance of microwave assisted solvent extraction (MASE) and classical ultrasonic extraction with acetone-ethyl acetate were studied. The latter technique was selected because of the reduced time of manual operations. Instrumental analysis of extracts of water samples was performed on-line with coupled column reversed phase liquid chromatography (LC/LC) and UV detection (280 nm) allowing to assay carbendazim to a level of at least 0.1 μg/l. Improved column life time was obtained by performing the favorable LC separation of carbendazim at high pH on newly developed 5 μm Extend-pH bidentate C18 material.

The combination of a short column packed with 5 μm Inertsil ODS-5 and a mobile phase at low pH material was most adequate as the regards the robust and fast processing of extracts of solid samples and allowed in most cases the screening of carbendazim in soils and sediments to a level of 10μg/kg.

The developed procedures yield overall recoveries for carbendazim of 101, 80 and 71 % in water (levels, 0.1—1.2 μg/l: n=12), soil (levels, 10 and 100 μg/kg; n=22) and sediments (levels, 10 and 100 μg/kg; n=11), respectively, with a repeatability and reproducibility below 7 % for all method/matrix combinations. Soil samples with aged residues (level, 100 μg/kg; n=10) provided an overall recovery of 71% and no significant decrease of carbendazim was observed during nine weeks of storage in the refrigerator.     

Approaches to Sampling and Sample Pretreatments for Metal Speciation in Soils and Sediments

Abstract

The main aspects of sampling and sample pretreatment in metal speciation studies of soils and sediments are discussed. The risks of sample contamination by the use of inappropriate materials, containers and tools as well as the possibilities of losses of analyte during sample handling are pointed out. Field sampling methods are described and minimum sample weight criteria for representative sampling of dry soils are presented. Sampling by traps and continuous flow centrifugation methods for suspended sediments and of bottom sediments by grabs or corers are compared. To avoid significant changes in some metal species drying and storage temperatures may need to be controlled and preservation in an inert atmosphere or by irradiation is discussed. The difficulties of establishing definitive protocols for sampling and sample pretreatment are emphasized as well as the need for selecting the appropriate technique in each particular case.     

Metal Speciation - General Concepts and Applications

Abstract

Several aspects of metal speciation in sediments are reviewed: (1) Due to the instability of polluted solid materials, sample handling and storage prior to analysis is problematic. In particular, changes from reducing to oxidizing conditions, which involve transformations of sulfides and a shift to more acid conditions, increase the mobility of critical metals. (2) Simple “standard” leaching tests can be used for easily soluble components such as halides or sulfates, but in most cases are not adequate for assessing mobility of trace metals. With sequential extraction procedures rearrangements of specific solid “phases” can be evaluated prior to their actual remobilisation. (3) Estimation of long-term release of metals from solids can be made using a test procedure, which combines data from column experiments applying controlled intensivation of parameters such as pH-value, redox potential and temperature with results from sequential extraction of the contaminated solids before and after exposure. (4) Partitioning studies on materials from core profiles are particularly useful, since they provide information on relative variations of elemental phases irrespective of the method applied, and thereby an insight into diagenetic processes taking place after deposition of the sediment components. (5) The leachable fraction does not necessarily correspond to the amount available to biota. Studies on the prediction of the trace metal levels in benthic organisms have shown, that the prognostic value of sequential extraction data is improved, when the trace metal concentrations are normalized with respect to the iron (hydrous oxide) and/or organic content of the sediments.     

Possibilities for the harmonization of methods of the dynamic fractionation of elements in soils and bottom sediments

The paper presents the first comparative study of the fractionation of heavy metals, arsenic, antimony, and selenium in soils, sludge and bottom sediments using two systems for dynamic extraction, rotating coiled columns (RCC) and cylindrical microcolumns (MC). It has been revealed that the results of the fractionation of the forms of elements are related with the physicochemical properties of soils, sludge, and bottom sediments and the special features of mixing the sample and eluent in RCC and MC. In particular, it has been demonstrated that, as compared to MC, RCC provides more efficient recovery of the most mobile (ecologically relevant) forms of arsenic, antimony, and selenium from samples rich with organic matter. However, in the majority of cases, despite the different efficiency of the recovery of individual fractions, RCC and MC provide comparable diagrams of the distribution of the extracted forms of elements. The influence of the rate of the eluent flow on the processes of the dynamic extraction of heavy metals, arsenic and antimony in RCC and MC has been estimated. The directions of research for the further harmonization of the methods of dynamic fractionation of forms of elements in soils, sludge, and bottom sediments with different physicochemical mobilities and potential biological availabilities are outlined.     

Evaluation of Extraction Procedures of Organochlorine Pesticides from Natural Waters and Sediments

Abstract

This study aims to evaluate different procedures for the extraction of organochlorine pesticides (OCP's) from natural waters and sediments. In the case of extraction from water, a C18 disk solid-phase extraction method was employed. Recovery experiments in the range of 40 to 200 ng/l with selected organochlorine compounds resulted in average recoveries between 80 and 100%. Four different solvents, hexane, ethyl acetate, acetonitrile and methanol, were tested as eluting agents. Best recoveries were obtained with ethyl acetate and hexane. A comparative study of OCP sediment extraction procedures was performed employing sonication, Soxhlet extraction and shake-flask methods. The capacity of these methods to recover OCP's from a sediment sample fortified at 50 ng/g was evaluated using hexane : acetone (1:1 v/v), hexane: acetone (8:2 v/v), acetonitrile and dichlorometane. The three extraction techniques gave similar results and dichloromethane was the most effective solvent. The optimised methods were applied in the analysis of waters and sediments from the “Aiguamolls de l'Empordà” Nature Park, Girona (Spain).     

Determination of Lead,Cadmium and Mercury in Surface Marine Sediments and Mussels

Abstract

Lead, cadmium and mercury were determined in sediments and mussels, and the ability of these indicators to record metal variations in coastal marine environment is described in this work. The results of an extended investigation of the status of three gulfs at Northern Greece are given, regarding the content of these metals in surface sediments and Mytilus galloprovincialis. The samples were collected during a four-year period. The total concentration of the above heavy metals was determined after digestion of the samples by suitable mixtures of acids, including nitric, perchloric and hydrofluoric acid. The digestion was carried out in a steel pressurised bomb with closed teflon vessels. Lead and cadmium were determined by means of electrothermal atomic absorption spectrometry (ETAAS), and mercury by cold vapour atomic absorption spectrometry (CVAAS). The results were statistically evaluated by analysis of variance, and emphasis was given to annual, seasonal and spatial sources of variation. The annual changes during the last four years and the spatial distribution of heavy metals load is also discussed.     

Determination of Trace Metals in Antarctic Sediments from Terra Nova Bay - Ross Sea

Abstract

Trace metals (Cu, Pb, Zn, Cd, Cr, Ni, Co, Mn) and iron concentration were determined in several sediments collected in the Antarctica (Terra Nova Bay—Ross Sea). Samples were analyzed by inductively coupled plasma (ICP-AES) after selective and total extraction. The results are in good agreement with the data previously collected in the same area.     

Ammonium Acetate Extracts and Their Analysis for the Speciation of Metal Ions in Soils and Sediments

Abstract

The use of ammonium acetate (1 mol/l at pH 7) extraction of soils and sediments for the speciation of metal ions is briefly discussed. Because the sensitivity of flame atomic absorption spectrometry (FAAS) is insufficiently sensitive for the determination of many of the heavy metals in ammonium acetate extracts of unpolluted, and even in some polluted soils, the use of electrothermal atomic absorption spectrometry (ETAAS) was studied. A general procedure, using graphite furnace atomisation and the “universal” matrix modifier, palladium, was developed, that was sufficiently sensitive for the determination of Cd, Cr, Cu, Ni, Pb and Zn even in unpolluted soils. The concentration of zinc, however, will almost always be high enough for determination of FAAS and this method is to be preferred to ETAAS for this element.

While, for Cr, Cu, Ni and Pb, direct calibration with external standard solutions is practicable, it is necessary to use the standard additions calibration method for cadmium, to avoid matrix interference effects. The standard additions technique is recommended, however, because it compensates for real differences in the operating parameters of different instruments set to the same nominal values. This is particularly important for interlaboratory comparisons or for certification analyses in the preparation of reference materials.