Christine M. Davidson

Improvement of the BCR three step sequential extraction procedure prior to the certification of new sediment and soil reference materials

The Standards, Measurements and Testing Programme (formerly BCR) of the European Commission proposed a three-step sequential extraction procedure for sediment analysis, following extensive expert consultations and two interlaboratory studies. This scheme was recently used to certify the extractable trace element contents of a sediment reference material (CRM 601). Although this procedure offers a means to ensure the comparability of data in this field, some difficulties concerning the interlaboratory reproducibility still remain, and a new project is currently being conducted to determine the causes of poor reproducibility in the extraction scheme. The final objective of the project is the certification of new sediment and soil reference materials for their extractable contents of Cd, Cr, Cu, Ni, Pb and Zn. This paper presents the results of a small-scale interlaboratory study, which aimed to test a revised version of the extraction schemes by comparing the original and the modified protocols using the CRM 601 sample. This work offers an improvement to the BCR sequential extraction procedure through intercomparison exercises. This improved procedure will allow the obtaining of CRMs to validate analytical data in the analysis of soils and sediments, and it will also facilitate comparability of data in the European Union.

Is there a future for sequential chemical extraction

Since their introduction in the late 1970s, sequential extraction procedures have experienced a rapid increase in use. They are now applied for a large number of potentially toxic elements in a wide range of sample types. This review uses evidence from the literature to consider the usefulness and limitations of sequential extraction and thereby to assess its future role in environmental chemical analysis. It is not the intention to provide a comprehensive survey of all applications of sequential extractions or to consider the merits and disadvantages of individual schemes. These aspects have been covered adequately in other, recent reviews. This review focuses in particular on various key issues surrounding sequential extractions such as nomenclature, methodologies, presentation of data and interpretation of data, and discusses typical applications from the recent literature for which sequential extraction can provide useful and meaningful information. Also covered are emerging developments such as accelerated procedures using ultrasound- or microwave energy-assisted extractions, dynamic extractions, the use of chemometrics, the combination of sequential extraction with isotope analysis, and the extension of the approach to non-traditional analytes such as arsenic, mercury, selenium and radionuclides.

Use of a certified reference material for extractable trace metals to assess sources of uncertainty in the BCR three-stage sequential extraction procedure

Various potential sources of irreproducibility in the BCR three-stage sequential extraction procedure have been investigated using the lake sediment CRM 601. Of the variables considered, the pH of the hydroxylamine hydrochloride in Step 2 proved most important. Factors such as the type of acid used in pH adjustment, the temperature and duration of extraction, and working under nitrogen did not affect precision, although they did alter the amounts of metals extracted. Improved precision was obtained when the hydroxylamine hydrochloride concentration was increased from 0.1 to 0.5 mol l(-1) and when the speed of the centrifugation was increased from 1500 to 3000 x g. The addition of a MgCl2 wash between the steps of the extraction procedure gave rise to increased uncertainty. Although it did not adversely affect reproducibility, the use of filtration to separate solid and liquid phases was not recommended since it promoted dissolution of non-target phases. Neither ammonium hydrogen oxalate nor oxalic acid proved suitable alternatives in Step 2 owing to precipitation of insoluble lead salts, particularly in the presence of calcium

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 CRITICAL EVALUATION OF THE THREE-STAGE BCR SEQUENTIAL EXTRACTION PROCEDURE TO ASSESS THE POTENTIAL MOBILITY AND TOXICITY OF HEAVY METALS IN INDUSTRIALLY-CONTAMINATED LAND

Cadmium, chromium, copper, lead, manganese, nickel, vanadium and zinc have been determined in samples of made-up ground from layers of a trial pit excavated on a recently derelict, industrially contaminated site. The pseudototal metal content of the layers was determined following a microwave-assisted digestion with aqua regia. Operational speciation was performed using the BCR three-step sequential extraction procedure. Analyses were carried out by flame or electrothermal atomic absorption spectrometry (FAAS or ETAAS). A suppressive interference (30%) was observed in the determination of cadmium in aqua regia digests by ETAAS, but not in 0.11 mol l ˇ1 acetic acid, 0.1 mol l ˇ1 hydroxylammonium chloride or 1.0 mol l ˇ1 ammonium acetate extracts. Agreement between duplicate samples was acceptable (i.e. within 10%) for most elements in most layers, but some large discrepancies were apparent, especially for lead. The amount of metal extracted in the sequential procedure (i.e. Step 1aStep 2aStep 3aresidual) did not generally agree well with pseudototal digestion. Various layers of the trail pit contained significant levels of contaminant metals, but these were not always in easily mobilized forms. For example, less than 0.2% of the lead (4000 m gg ˇ 1 ) at 65‐85 cm depth was present as exchangeable or acid-soluble species. The study illustrates the importance of considering metal speciation when assessing the mobility of potentially toxic elements in industrially-contaminated land. # 1998 Elsevier Science B.V.

Evaluation of a sequential extraction procedure for the speciation of heavy metals in sediments

The three-stage sequential extraction procedure for speciation of heavy metals, proposed by the Commission of the European Communities Bureau of Reference (BCR), has been applied to a freshwater sediment collected from the River Clyde, Lanarkshire, UK. Initial studies were carried out using flame atomic absorption spectrometry (FAAS). Iron, manganese and zinc could be determined in the sediment extracts by FAAS, but the technique proved insufficiently sensitive for the determination of chromium, copper, nickel and lead. Detection methods based on electrothermal AAS were therefore developed and applied. Furnace conditions were optimised for the determination of the four analytes mentioned, plus molybdenum and vanadium, in acetic acid, hydroxylammonium chloride and ammonium acetate matrices. Interferences by components in the sediment extracts necessitated analysis by the method of standard additions in most cases. The sequential extraction procedure was found to be both repeatable and reproducible. The amounts of analytes released by the sequential extraction procedure plus aqua regia digestion of the residue remaining after extraction were similar to those released by pseudo-total digestion of the sediment (using aqua regia).

Three-stage sequential extraction procedure for the determination of metals in river sediments

A three-stage sequential extraction procedure, following a protocol proposed by a European working group coordinated and supported by the Community Bureau of Reference (BCR), has been applied to two river sediments from an industrial region of East Catalonia, Spain. The extractant solutions were: Step One, acetic acid (0.11 mol l(-1)); Step Two, hydroxylammonium chloride (0.1 mol l(-1), pH 2); Step Three, hydrogen peroxide (8.8 mol l(-1)) oxidation followed by extraction with ammonium acetate (1 mol l(-1), pH 2). The six elements determined in the extracts were Cd, Cr, Cu, Ni, Pb and Zn. Analysis of the extracts was carried out by flame atomic absorption spectrometry (FAAS). There were slight differences in analyte sensitivity between calibrants prepared in the extractant matrices and acidified aqueous calibrants. No significant matrix interferences were found except for Cr in the acetic acid and hydroxylammonium chloride extracts, which required determination by the standard additions method. The other elements (plus all the elements in the ammonium acetate extracts) were determined by direct calibration against calibrant solutions prepared in the same matrices as the samples.

Soil pollution by PAHs in urban soils: a comparison of three European cities

The purpose of this study was to determine the degree of contamination with polycyclic aromatic hydrocarbons (PAHs) in samples of urban soil from three European cities: Glasgow (UK), Torino (Italy) and Ljubljana (Slovenia). Fifteen PAHs (naphthalene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenzo[a,h]anthracene, benzo[g,h,i]perylene, indeno[1,2,3-c,d]pyrene) were measured in urban soil samples, using harmonised sampling, sample extraction and analyte quantification methods. Although the mean concentration of each PAH in urban soils of each city showed a wide range of values, high levels of contamination were only evident in Glasgow, where the sum of concentrations of 15 PAHs was in the range 1487-51,822 microg kg(-1), cf. ranges in the other two cities were about ten-fold lower (89.5-4488 microg kg(-1)). The three predominant PAHs were phenanthrene, fluoranthene and pyrene, with the sum of these compounds about 40% of the total PAH content. These data, together with some special molecular indices based on ratios of selected PAHs, suggest pyrogenic origins, especially motor vehicle exhausts, to be the major sources of PAHs in urban soils of the three cities. The largest concentrations for PAHs were often found in sites close to the historic quarters of the cities. Overall, the different climatic conditions, the organic carbon contents of soil, and the source apportionment were the dominant factors affecting accumulation of PAHs in soil.

Novel SERS-active optical fibers prepared by the immobilization of silver colloidal particles

A novel sensor based upon surface-enhanced Raman scattering (SERS) has been constructed by immobilizing colloidal silver particles onto the distal end of an optical fiber. This same single fiber was then used to both transport the exciting laser radiation and collect the Raman scattering from analytes sorbed onto the colloidal particles. The colloidal particles were immobilized by functionalization of the end of the optical fiber with (3-aminopropyl)trimethoxysilane prior to immersion of the fiber in silver colloid. Spectra were obtained from both 4-(5′-azobenzotriazol)3,5-dimethoxyphenylamine and crystal violet. The within-batch variation of a set of five fibers has been measured as approximately 10%. Raman imaging experiments demonstrated that the effects due to spatial variations in the intensity of the SERS recorded over the distal end of the fiber are removed by the use of a multimode fiber.

20. Single and sequential extraction schemes for trace metal speciation in soil and sediment

Abstract The need for trace metal speciation in soils was recognised and its practice well established in agricultural laboratories long before the term “speciation” entered the literature of analytical or agricultural chemistry. The “species” concerned, and determined, in these early and continuing studies are the plant-available “species” involved in plant and animal nutritional deficiency disease and in plant and animal toxicity. The common perception of speciation as the study of the actual compounds in which elements occur in a material is a practicable one for materials that are solutions, as, for example, natural waters. This conception is too restrictive for general application. In most solid samples, including soils and sediments, the determination of chemical species is in most cases a difficult challenge and suitable means to characterize the actual chemical combination in soils and sediments in a broader view is necessary. In practice, for trace metals a more general definition of speciation is required to encompass the requirements of soil and sediment science, among others. Such a definition has been given [1] and is summarised as: Speciation is the identification and determination (or the description) of the defined species of an element that occur in a material. The species can be defined: 1- by their function , e.g. as “plant-available” or “exchangeable” forms, 2- by the operation designed to isolate and determine them e.g. as the species isolated in the soil solution obtained by centrifugation or displacement or the moderately reducible species isolated by a particular reagent and, 3- as a particular compound or oxidation state of an element e.g. as tributyltin or Cr 3+ . This chapter will focus on the speciation in soils and sediments using single and sequential extraction schemes. Although the defined “species” should preferably be referred to as “extractable forms”, the term speciation will be used throughout the text for facility.