H. Muntau

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 believ...

Certification of trace metal extractable contents in a sediment reference material (CRM 601) following a three-step sequential extraction procedure

Abstract Sequential extraction schemes have been developed in the past 20 years for the determination of binding forms of trace metals in sediment. The lack of uniformity of these schemes, however, did not allow the results so far to be compared worldwide nor the procedures to be validated. Indeed, the results obtained by sequential extraction are operationally defined, i.e. the ‘forms’ of metals are defined by the determination of extractable elements using a given procedure. Therefore the significance of the analytical results is related to the extraction scheme used. Another problem which hampered a good comparability of data was the lack of suitable reference materials which did not enable the quality of measurements to be controlled. Owing to this lack of comparability and quality control, the Community Bureau of Reference (BCR, now Standards, Measurements and Testing Programme) has launched a programme of which one of the aims was to harmonize sequential extraction schemes for the determination of extractable trace metals in sediment. This programme involved the comparison of existing procedures tested in two interlaboratory exercises, and it developed into a certification campaign of extractable trace element contents in a sediment reference material, following a three-step sequential extraction procedure duly tested and adopted by a group of 18 EU laboratories. This paper briefly describes the results of the interlaboratory studies and gives all details on the preparation of the sediment reference material, CRM 601, the homogeneity and stability studies and the analytical work performed for the certification of the extractable contents of some trace elements, following a standardized sequential (three-step) extraction procedure.

Evaluation of a sequential extraction procedure for the determination of extractable trace metal contents in sediments

The determination of extractable trace metals in sediments using sequential extraction procedures has been performed in many laboratories within the last ten years in order to study environmental pathways (e.g. mobility of metals, bounding states). However, the results obtained by different laboratories could hardly be compared due to lack of harmonized schemes. Owing to the need for standardization and subsequent validation of extraction schemes for sediment analysis, the Measurements and Testing Programme (formerly BCR Programme) of the European Commission has organized a project to adopt a sequential extraction procedure that could be used as a mean of comparison of data of extractable trace metals in sediments. A scheme was designed after a series of investigations on existing schemes and tested in interlaboratory studies. This paper presents the results of two round-robin exercises on extractable trace metals using this sequential extraction protocol and describes the final version of the extraction procedure amended according to the most recent improvements.

Selection and evaluation of sequential extraction procedures for the determination of phosphorus forms in lake sediment

In order to achieve comparable measurements in the determination of phosphate forms in freshwater sediments, the Standards, Measurements and Testing Programme (formerly BCR) of the European Commission has launched a project the first step of which was to select and evaluate collaboratively existing extraction procedures. This was carried out through expert consultations and a literature survey, and was followed by the organisation of a first interlaboratory study for the evaluation of four sequential extraction schemes, one of which was selected as the most promising method for achieving comparability. This scheme, a modified version of the Williams protocol, was further tested in a second interlaboratory study. The so-called SMT extraction scheme seems promising and will provide, in the near future, a valuable tool for water managers in the field of lake restoration. It will be particularly helpful in estimating the stock of P potentially available, hence the risk of eutrophication due to internal P release.

CERTIFICATION OF THE EXTRACTABLE CONTENTS OF CD, CR, CU, NI, PB AND ZN IN A FRESHWATER SEDIMENT FOLLOWING A COLLABORATIVELY TESTED AND OPTIMISED THREE-STEP SEQUENTIAL EXTRACTION PROCEDURE

Sequential extraction procedures have been used during the last decades to study and determine trace element mobility in aquatic sediments. However, the results obtained are operationally defined and, therefore, the significance of the analytical results is related to the extraction scheme used. So, there is a need for suitable reference materials for this type of study to enable the validation of the methodologies and to control the quality of the measurements. This paper describes the preparation of a sediment reference material, BCR-701, the homogeneity and stability studies and the analytical work performed for the certification of the extractable contents of some trace elements, following a collaboratively tested and optimised sequential (three-step) extraction procedure. The paper contains all the results and gives the methods used to certify the extractable contents (mass fractions expressed as mg kg-1 on a dry matter basis) of Cd, Cr, Cu, Ni, Pb and Zn in all steps. Moreover, indicative values are given for the aqua regia extractable contents of the six elements in the sediment and the residue obtained after sequential extraction.

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 dev...

Certified reference materials for the quality control of EDTA- and acetic acid-extractable contents of trace elements in sewage sludge amended soils (CRMs 483 and 484)

Abstract The ecotoxicity and mobility of trace elements in soils are often evaluated through analytical results resulting from operationally-defined determinations (single and sequential extractions), e.g. based on EDTA, acetic acid etc. extractions. The significance and comparability of these results is highly dependent on the procedures used (standardized protocols or standards adopted by international bodies) and their quality control relies on the availability of reference materials certified following these strictly applied procedures. Recognizing the need to harmonize some of the extraction schemes currently used for soil analysis, the Measurements and Testing Programme (formerly BCR) has organized a series of interlaboratory studies, the first aim of which was to evaluate EDTA- and acetic acid-extraction procedures and the second objective was to certify reference materials for their extractable trace element contents. Two sewage amended soils have been prepared for this purpose, originating respectively from Scotland and Catalonia. This paper describes the preparation, homogeneity and stability studies, and gives an overview of the certification campaign.

Interlaboratory comparison of EDTA and DTPA procedures prior to certification of extractable trace elements in calcareous soil

The use of single extraction schemes for soil studies is widely recognized. These procedures are currently performed in many laboratories to assess the bioavailable metal fraction (and related phyto-toxic and nutritional deficiency 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 determinations of extractable trace metal contents in two soils (sewage sludge-amended and terra rossa soils), the first step of which was an interlaboratory study followed by a certification campaign for EDTA- and acetic acid-extractable trace metal contents. This project was complemented by an interlaboratory study on EDTA and DTPA extraction schemes applied to a calcareous soil reference material. The latter study was actually a feasibility study which allowed the necessary precautions to be set up for the use of these schemes prior to certification of a calcareous soil. This paper presents the results of this intercomparison.

Development of a harmonised phosphorus extraction procedure and certification of a sediment reference material.

A harmonised procedure for the determination of the forms of phosphorus in freshwater sediments, developed in the frame of the European Programme, Standards, Measurements and Testing (SMT) has been used for a certification campaign for a reference material. This operationally defined scheme is a good compromise between method performance and reproducibility. Furthermore, the method is rather simple to implement and could be used by water managers on a routine basis. A homogeneous and stable sediment reference material has been prepared and will be available before mid 2001. The so-called SMT protocol, together with the reference material, are useful tools in the field of water management, especially at a time when quality assurance is of paramount importance in laboratory analyses. Knowledge of the bioavailable forms of phosphorus is important not only for analysis of sediments but also for sludge and soils. Therefore, the SMT protocol could be extended to these materials.

Conclusions of the workshop: harmonization of leaching/extraction tests for environmental risk assessment

Leaching/extraction tests are widely used for the assessment of the release of contaminants from different matrices, e.g., leaching tests for waste materials, single extractions for soil and compost materials and sequential extractions for sediments. Extraction procedures are also undertaken for evaluating plant uptake and the effects of landfill applications. In many instances, such schemes are included in national regulations or are considered in the framework of normalizing bodies such as CEN or ISO. If no efforts are made for harmonizing these procedures a multiplicity of tests will result. It is clear that this variety of schemes will not allow the data to be compared worldwide and will hence, create problems for the interpretation of data by the different regulatory bodies. Different groups of analysts (i.e., waste, compost, soil and sediment scientists) often follow radically different approaches, terminologies and data interpretations. Closer relationships between these groups would certainly encourage joint efforts for harmonizing these procedures which could, in some cases, be adapted for different matrices for a given purpose (e.g., assessment of release or soil fertility). At this stage, it was deemed necessary to discuss critically possible strategies to harmonize leaching and extraction schemes for environmental risk assessment and a workshop was held on 4 June, 1994, with participants covering different fields of expertise. The discussions allowed recommendations to be made regarding possible approaches to improve the present situation through, e.g., the creation of networks, interlaboratory studies prior to the adoption of standardized procedures, field validation of leaching/extraction schemes and production of reference materials certified for specified leaching/extraction conditions. This paper gives a summary of the round-table discussions. An outline of the programme along with the panel of experts participating in this workshop is given in the Appendix.