A. Sahuquillo

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.

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

Overview of the use of leaching/extraction tests for risk assessment of trace metals in contaminated soils and sediments

Abstract Comparison of the information obtained from the application of leaching/extraction procedures to contaminated soils and sediments is required to make the most appropriate choice for studying a given metal. In this article, the information obtained for Cd, Cr, Cu, Ni, Pb and Zn, when applying various single extraction and sequential extraction procedures, is critically assessed for contaminated samples with distinct origins and characteristics. The single-extraction procedures comprised the application of mild (CaCl 2 and NaNO 3 ) and acidic (CH 3 COOH) extractants and complexing agents (EDTA and DTPA). The original and modified BCR three-step sequential extraction procedures are also compared. Finally, useful criteria are proposed for the selection of leaching/extraction tests in certain scenarios.

Determination of Cd, Cu, Pb and Zn in environmental samples: microwave-assisted total digestion versus aqua regia and nitric acid extraction

Abstract We validated the determination of the content of Cd, Cu, Pb and Zn using two digestion protocols: a microwave-assisted total digestion and an aqua regia extraction procedure based on the International Organization for Standardisation (ISO) 11466 method. Our goal in validating these two protocols, along with a nitric acid digestion, is to propose a rapid, cheap and easily automated digestion method for monitoring heavy metal content in environmental samples. We applied the digestion protocols to samples with a wide range of organic matter such as sediments, soils, sludges and plant material. For samples with a low carbonate or organic matter contents, such as sediments and agricultural soils, aqua regia digestion in an aluminium block was revealed to be an optimum estimator for the total metal content. For samples with a high organic matter content, such as organic horizons of forest floor layers, plant material and organic soils, nitric acid digestion could substitute microwave (MW)-hydrofluoric acid (HF) digestion. Except in a few samples with high organic matter or low heavy metal content, the RSD values obtained after the application of the proposed digestion procedures were lower than 5%. Based on the obtained results, a decision flow chart for choosing the fit-for-purpose digestion procedure is suggested.

CRM 601, A stable material for its extractable content of heavy metals

Sequential extraction schemes provide information on the mobility of heavy metals from polluted sediments. The lack of uniformity of these schemes, however, does not allow results to be compared nor the procedures to be validated. In 1987 the Community Bureau of Reference, (BCR, now Standard, Measurements and Testing Programme) of the European Commission launched a programme to harmonise single and sequential extraction schemes for soils and sediments. As a result certified reference material CRM 601 (lake sediment) was prepared and certified for the extractable contents of some trace elements, following a standardised sequential (three-step) extraction procedure. In order to verify the long-term stability of the material an intercomparison exercise was designed with the participation of eight expert laboratories. The results confirm the stability of the extractable contents of Cd, Cr, Ni, Pb and Zn in this type of material, and demonstrate that the preparation of this kind of CRM can be achieved.

Comparison of single and sequential extraction procedures for the study of rare earth elements remobilisation in different types of soils.

With the continual increase in the utilisation of rare earth elements (REE) for industrial and agricultural purposes, research into the environmental and biogeochemical behaviour of REE had attracted much interest in recent times. This study principally describes the distribution of REE in four different types of soils like lateritic soil (S-1), in situ natural soil (S-2), soil contaminated by mining activity (S-3) and accidentally polluted soil (S-4) utilizing the optimised BCR sequential extraction procedure and partial extractions with various types of single extractants such as unbuffered salt solutions 0.1 M NaNO(3), 0.01 M CaCl(2), 1 M NH(4)NO(3); complexing agents 0.005 M DTPA and 0.05 M EDTA; acid solutions 0.43 M CH(3)COOH and 1 M HCl. Comparison of the sum of the four BCR fractions, which included an aqua regia attack on the residue, with the pseudo-total aqua regia digest values to assess the accuracy of the BCR partioning approach has been undertaken. Partial extraction results with several single extractants have also been reported for all the REE elements including yttrium which have been analysed by the optimised BCR procedure. Results obtained after 24 h extraction with each of the single extractant have also been discussed. The extraction with 1 M HCl during 24 h yielded similar quantities of REE as those released under the combined steps of 1, 2 and 3 of the BCR sequential extraction for all the four different type of soil samples indicating that this reagent can be used successfully to estimate the total extractable contents of REE in various types of soil samples.

Comparison of leaching tests for the study of trace metals remobilisation in soils and sediments

Several leaching tests were applied and compared to study metal remobilisation on various unpolluted and contaminated soils and on several contaminated sediments. The trace elements considered were Cd, Cr, Cu, Ni, Pb and Zn, and leaching tests consisted of the application of reagents with contrasting characteristics and strengths in order to assess the information provided. An extraction with aqua regia permitted the estimation of the pseudo-total metal content in the sample. Mild extractants such as H2O, CaCl2 and NaNO3 showed low and similar leaching capacities. Acid (CH3COOH) and complexing (EDTA) agents were more effective in remobilising trace metals from soils and sediments. Cd and Zn showed similar extraction characteristics under both extractant solutions, whereas Cu and Pb were more sensitive to complexation, and Ni and Cr to acidification processes. Sequential chemical extractions provided additional information on the association of the trace elements with the different soil and sediment phases. Cd and Zn showed the highest mobility, Pb was associated to reducible solid phases, Cu and Ni to oxidisable phases, and Cr remained mostly in the residual fraction. The results obtained in this paper provided valuable information for choosing a leaching test, which is an instrument of environmental analysis for the estimation of trace metal mobility.

Migration of antimony from polyethylene terephthalate used in mineral water bottles.

The influence of storage time and temperature on Sb migration from PET bottles into mineral water was studied in short-term tests lasting up to 15 days and long-term studies lasting up to 220 days. Samples purchased were stored in three different coloured bottles: clear (CL), light blue (LB) and dark blue (DB). Sb migration was assayed by HG-AFS for total determination and HPLC-ICP-MS for speciation analysis. Migration studies showed that waters stored at 4 and 20 °C were not subject to Sb migration. At 40 °C there was a significant increase in Sb concentration, although the maximum limit established by the European Union (5.0 μgL(-)(1)) was not exceeded, whereas at 60 °C samples were subject to considerable Sb migration after 30 days of storage. In this case, the maximum limit established by the European Union was exceeded and both Sb (V) and Sb (III) were detected.

Determination of Chromium in Environmental and Biological Samples by Atomic Absorption Spectroscopy: A Review

Abstract The technique most widely used for chromium determination in biological and environmental samples is atomic absorption spectrometry with flame (FAAS) or graphite furnace (GFAAS). In this regard, there are many articles in the literature dealing with the effect of the interferences upon chromium solutions of different oxidation state. These effects are not well established and the results are contradictory. With the aim of joining all this information, we review the state of the art in chromium determination with AAS in environmental and biological samples. The first part of the paper is related with the different sample pretreatment methods proposed for natural and seawaters, sediments, soils, plant materials, biological materials, sewage sludges and urban particulate matter. The second part deals with the instrumental parameters and interference effects which affect chromium measurements by FAAS and GFAAS. The last part presents different certified reference materials available for the quality c...

Assessment of arsenic bioaccessibility in raw and cooked edible mushrooms by a PBET method.

The present study reports arsenic analysis in Lentinula edodes, Agaricus bisporus and Pleurotus ostreatus before and after being cooked. Furthermore, arsenic in raw and cooked mushroom was determined in the gastric and gastrointestinal bioaccessible fractions obtained after simulating human digestion by means of an in vitro physiologically based extraction test (PBET). Several certified reference materials (SRM 1568a, SRM 1570a, CRM 7503-a, BC211 and IPE-120) were analysed to evaluate the proposed methods. Total arsenic content was 1393, 181 and 335μgAskg(-1) for L. edodes, A. bisporus and P. ostreatus, respectively, and decreased by between 53% and 71% in boiled mushroom and less than 11% in griddled mushroom. High bioaccessibility was observed in raw, boiled and griddled mushroom, ranging from 74% to 89% and from 80% to 100% for gastric and gastrointestinal extracts, respectively, suggesting the need to consider the potential health risk of consumption of the mushrooms analysed.