Extraction procedures for the determination of heavy metals in contaminated soil and sediment

Extraction tests are commonly used to study the mobility of metals in soils and sediments by mimicking different environmental conditions or dramatic changes on them. The results obtained by determining the extractable elements are dependent on the extraction procedure applied. The paper summarises state of the art extraction procedures used for heavy metal determination in contaminated soil and sediments. Two types of extraction are considered: single and sequential. Special attention is paid to the Standard, Measurement and Testing projects from the European Commission which focused on the harmonisation of the extraction procedures and on preparing soil and sediment certified reference materials for extractable heavy metal contents.     

Different strategies to assess Cu and Pb mobilization in polluted river sediments

Summary For studying the mechanisms of trace metal mobilization in sediments several strategies have been employed, such as single extraction, sequential extractions, ion exchange, or progressive acidification. Several authors assert that sequential extraction is the best option. In this study two procedures are used in order to assess the mobility of copper and lead in heavily polluted river sediments: sequential extraction using a modified Tessier procedure, and progressive acidification, using an automated method. Six heavily polluted sediment samples are studied by applying the two procedures. The amount of metal released at different pH-values (pH 5 and pH 2) is compared with the resulting distribution when the sequential extraction procedure is applied. The information obtained from the two different approaches is discussed. For both metals a different behaviour is observed when applying each of the two procedures. Thus, copper is more easily released than lead when progressive acidification is followed, whereas an inverse situation is observed when sequential extraction is applied.     

Effect of chloride on heavy metal mobility of harbour sediments

To evaluate the environmental impact of polluted sediments, several operationally defined sequential extraction procedures (SEPs) have been described. Salinity has long been recognised as an important variable determining the physicochemical behaviour of heavy metals in marine sediments. Thus, in the present paper, the modified BCR-SEP has been applied to harbour sediments in order to assess to what extent trace metal mobility (Cd, Cr, Cu, Ni, Pb and Zn) could be influenced by chloride content in sediments. For this, washed (W) and non-washed (NW) sediments were compared. The relative mobility order observed for the six trace metals studied was not seen to be influenced by the presence of chloride in the sediments, but an increase of mobility was observed for Cd and Zn (the most mobile metals) when chloride was present in the sediments. Characterisation of the sediments and of the pseudo-total metal contents by means of an aqua regia extraction was also assessed.     

Comparison of metal analysis in sediments using EDXRF and ICP-OES with the HCl and Tessie extraction methods

The work presents an investigation on metal availability in sediments during 13 months using the dispersive-energy X-ray fluorescence (EDXRF) and atomic emission spectrometry with induced argon plasma (ICP-OES) techniques and single extraction (0.1 mol l⁻¹ HCl) and Tessie’s sequential speciation methods. The EDXRF technique could yield essentially the same profile as ICP-OES for the seasonal variation of metals in sediments, but in a more practical way. The sequential extraction procedure (SEP) was more efficient in metal dissolution than single extraction. The Pb, Ni, Al, Cr, and Fe elements were less efficiently extracted with single extraction in relation to sequential extraction. For Co both methodologies were equivalent, but for Cu and Mn the extraction was higher with single extraction. Single extraction does not mobilize Pb, Ni, Al, Cr, and Fe adsorbed on oxides and bound to organic matter. However for Cu and Mn, not only extracted these metals from the four fractions, but it also dissolved part of the fifth fraction (residual). Principal Component Analysis discriminated seasonal variations in the content of several metals, mainly Fe, Co, Ni, and Zn. The mobility of metallic ions in the sediments is conditioned to the seasonal flow of organic and inorganic material coming from the river or by the erosion of adjacent soils.     

The use of sequential extraction procedures for the characterization and management of contaminated soils

Metal mobility and availability in solid samples, such as soils, sediments and sludges, is frequently studied with sequential extraction procedures, which allow to partition the total metal content into classes of different reactivity. From the experimental point of view, each extraction step requires many practical operations, which can represent sources of error if they are not properly executed. The first part of the paper gives indication on how to perform sequential extractions, from sample pretreatment to extract analysis, in order to reduce experimental errors. The second part describes the main applications of sequential extraction schemes for the characterization and management of contaminated soils: the assessment of the risks associated to metal pollution, the evaluation of the feasibility and efficiency of remediation techniques, the study of soil properties and of metal behaviour and plant availability.     

Evalution of sequential extractions on dry and wet sediments

A five-step sequential extraction procedure was applied on dried and wet Ballastplaat Scheldt estuary sediments. When wet (fresh) sediments were used, all sample handling up to the 3rd extraction step, inclusive, was carried out under inert atmosphere. The repeatability of the procedure was very good on dry samples. For Fe as for Mn, RSD values are lower than 4%, except for Mn in the fifth extraction step where a spread of 10% is observed. The observed RSDs for Pb are of the same order of magnitude as those for Mn. On wet samples the spread of the results is higher than on dried ones. The highest RSDs observed for Fe amount to 20%, for Mn to 15% but for Pb an RSD of up to 44% was found. Better homogenization of the solid sediment part of lyophilized sediments and different porosities of wet sediment sub-samples may be the explanation. These results also indicated that drying/oxidizing of the sediment sample causes a shift from less available/mobile metal fractions to more available/mobile fractions. The Mn and Fe oxyhydroxide spikes added to a wet sediment sample were recovered between 100±10%. The results obtained after changing the sequence of the extraction steps (multiple rotations and inversions were tested) corroborated the progressive increase in the aggressive nature of the extraction solutions in our standard scheme. Although there is also no need to change the ratio volume of extractant to amount of sediment, increasing the number of extraction repetitions in steps 1 to 3 resulted, for some of those extraction steps, in a partially modified analyte distribution. Finally the method was applied to sandy and muddy sediment cores of the Scheldt estuary and revealed clear differences between metal distributions in both types of sediment.     

Application of Rotating Coiled Columns to the Fractionation of Soil Particles and to the Sequential Extraction of Heavy-Metal Species from Silty,Dusty, and Sandy Fractions

A complex procedure has been developed for evaluating the degree of soil contamination. Rotating coiled columns (RCCs) were used for both the fractionation of soil samples by their grain-size composition and the sequential extraction of heavy-metal species from silty, dusty, and sandy fractions. During the extraction of heavy-metal species, the soil fraction to be analyzed was retained in the column as a stationary phase, while aqueous solutions of extracting agents (mineral salts, acids, and complexing compounds) were sequentially pumped through the heterogeneous sample. The sequential extraction of element species from various soil fractions was carried out in the dynamic mode favorable to more complete extraction of metals. The use of RCCs allows the extraction of various heavy-metal species from soils to be performed in accordance with their grain-size composition. The process of the extraction of metal species can be automated, and in this case the losses of sample components are reduced to a minimum.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 7, 2005, pp. 765–772.Original Russian Text Copyright © 2005 by Katasonova, Fedotov, Karandashev, Spivakov.     

海湾河口表层沉积物中重金属形态连续萃取方法的优化研究

采用单一萃取程序对建立的重金属形态连续萃取方法的萃取条件进行优化.分别以Ca和Mg、Fe、有机质(OM)和酸可挥发性硫(AVS)作为萃取剂释放酸溶态、还原态、有机质结合态和硫化物结合态等重金属目标形态的表征参量,考察萃取剂对相应目标形态的萃取能力和选择性.分别根据表征参量和重金属在萃取溶液中的含量变化确定最优萃取时间和萃取样液比.结果表明,优化萃取条件后,萃取剂对目标形态重金属均有很强的释放能力.酸溶态萃取剂对其它非残留态影响很小;还原态萃取剂除对酸溶态有少量提取外,对其它形态影响较小;有机质结合态萃取剂对硫化物结合态有少量萃取,对其它形态影响较小.硫化物结合态在酸溶态、还原态和有机质结合态之后萃取,避免了对这三种形态的影响.优化后的连续萃取方法对重金属形态有较好的选择性,可对海湾和河口表层沉积物中重金属的目标形态进行较为合理地分离和评价.     

Influence of land development on heavy metal forms in the Bobrza River ecosystem (Świętokrzyskie Province,Poland)

Metals are perceived as pollutants but they are also natural substances found in the environment. The surface water environment is under the influence of continuing industrial pollution/effluents. Therefore it is necessary to determine various metal forms present in each component of the water ecosystem. The study presents analysis for Cd, Cu, Cr, Fe, Mn, Ni, Zn and Pb content in the Bobrza River bottom deposits and water. The analysis of water and sediment samples from the Bobrza River taken from the littoral zone at three sampling points: the riverhead, i.e. the natural environment; Białogon — the acidic environment; and Sitkówka-Nowiny — the alkaline environment, were analyzed. Sample quality indicators were defined with pH value, conductivity, heavy metal content for water and suspended matter samples. The metal forms in river sediment were also analyzed. The sediment samples were subjected to Tessier’s five-stage sequential extraction procedure assisted by microwave radiation. Analyte concentration in water samples and in the extracts was determined with the use of F-AAS and GF-AAS techniques. The results obtained reveal a relationship between land development, the degree of metal bonding with suspended matter and metal forms found in river sediments.     

Fractionation studies of trace elements in Polish uranium-bearing geological materials: potential environmental impact

The samples of U deposits from Podlasie Depression (East Poland) and Peribaltic Syneclise (Northeast Poland) were studied to state the U and accompanied metal content and to estimate a potential environmental impact caused by the studied area. Sequential extraction is an effective method for assessing the heavy metal behaviour in environment in such environmental materials as soils, sediments, different wastes and ores.

The modified Bureau of Reference of the European Commission sequential extraction procedure has been used for fractionation study of nine elements (U, V, Mn, Co, Ni, Cu, Zn, Cd and Pb) in two kinds of U ores: dictyonema shale and sandstone. The total content and the content in each fraction of metals of interest were determined by the inductively coupled plasma mass spectrometry method.

The obtained results show the high mobility of such elements as Co, Zn and Ni in shale and U, Co and Mn in sandstone. These results make it possible to assess the environmental risk associated with heavy metals occurring in tested U-bearing ores.     

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.     

Assessment of heavy metals pollution in Sudanese harbours along the Red Sea Coast

The levels of some heavy metals in sediments of two harbours along the Sudanese Coast of the Red Sea were examined and reported for the first time. A total of thirty-six surface sediment samples were collected from Port-Sudan and Sawakin harbours. Part of each sample was partitioned into five fractions with grain-size ranges of 1000–500, 500–250, 250–125, 125–63 and less than 63 μm. The Mn, Fe, Ni, Cu, Zn and Pb concentration in bulk samples and sub-samples were determined by atomic absorption spectrophotometry. The spatial distribution pattern of heavy metal content of crustal origin in the sediments is more uniform in Port-Sudan harbour than in Sawakin harbour. The granulometric normalization revealed that some sites in Port-Sudan harbour and one site in Sawakin harbour have been exposed to different levels of heavy metal contamination, which probably originated from ships, industrial and domestic activities.     

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.     

Determination of heavy metals in macrozoobenthos from the rivers Tisza and Szamos by total reflection X-ray fluorescence spectrometry

In 2000, accidents in the Romanian mining industry in key catchment areas led to heavy metal contamination of the Hungarian rivers Tisza and Szamos resulting in substantial heavy metal loads in several sediments of the upper river basins. This enhanced metal content might have been bioaccumulated in benthic organisms during the following years. Therefore, the aim of this study was to test, whether the zoobenthic fauna showed an enhanced metal content 3 years after the industrial accident. Macrozoobenthic insect larvae (chironomids) were sampled 100 m below and above the confluent site of the rivers Tisza and Szamos during summer 2003 and for comparison purpose also in the river Maros, a tributary of the Tisza river, during 2005. In order to determine their heavy metal content, single specimens were prepared and analysed by Total Reflection X-ray Fluorescence Spectrometry (TRXF) according to the modified dry method. Fe was much lower and Mn and Zn much higher concentrated in benthos from the more contaminated Szamos river compared to the Tisza and Maros rivers. In this sense, the benthic organisms reflected very well the enhanced metal concentrations in the contaminated rivers being suitable as bioindicators of metal contamination. However, the sediment bioaccumulation factor was low at all sampling sites indicating a low bioavailability of trace metals for benthic organisms.     

Estimation of ecotoxicological potential of contaminated sediments based on a sequential extraction procedure with supercritical CO2 and subcritical H2O solvents

Sediment samples were taken from the Tisza–Szamos area and Gödöll lake system. A new sequential extraction scheme in a supercritical extractor using supercritical CO₂, subcritical H₂O, and a subcritical mixture of 90% H₂O and 10% CO₂ as solvents was employed. This procedure provides relevant information about environmentally mobile heavy metal fractions (water-soluble, bicarbonate-forming) of sediments during a reasonably short time (5 h). The environmental mobility of Zn and Cd was found to be the highest among the sediments involved in these investigations. This mobility represents detectable ecotoxicity, which can be tested with the subcritical water extracts. Performance of pollen tube growth (PTG) test and the ecotoxicological stable isotope metabolic assay (ESIMA) was compared. Potential ecotoxicity of aqueous extracts was reliably detectable by PTG test during a relatively short time (1 day).     

Investigation of acidic pharmaceuticals in river water and sediment by microwave-assisted extraction and gas chromatography–mass spectrometry

Investigations were performed along the Danube river at Budapest (Hungary) by collecting water and sediment samples simultaneously for 1 year in order to clarify the possible hazard of selected acidic pharmaceuticals (ibuprofen, naproxen, ketoprofen, and diclofenac) on the water supply used for the production of drinking water by bank filtration. In the case of water samples, the sample preparation procedure included solid phase extraction (SPE), meanwhile, in the case of sediment samples, microwave-assisted extraction (MAE) followed by dispersive matrix extraction (DME) for pre-cleaning as well as SPE for enrichment. The quantification was carried out using gas chromatography–mass spectrometry (GC–MS). The calculated recoveries were 97–99% (± 7%) for the water and 95–103% (± 12%) for the sediment samples. In the river water, ketoprofen concentration was always below the limit of quantification (LOQ) level; ibuprofen, naproxen and diclofenac could be quantified in the range of 8–50, 2–30, 7–90 ng/L. In sediments, only naproxen and diclofenac were found in the range of 2–20 and 5–38 ng/g, respectively. According to the obtained results, the concentration ratios of the two phases linearly depended on the total organic carbon content (TOC) of the sediments at each sampling date. The linear regressions were 0.925 and 0.946 for naproxen and diclofenac, respectively.     

Recent applications of atomic spectroscopy coupled with magnetic solid-phase extraction techniques for heavy metal determination in environmental samples: A review

Atomic spectroscopy is the most popular approach to determine the presence of heavy metals in the environment. Heavy metals are potentially toxic and have various negative effects on many living organisms, including humans. With the rapid increase in the variety of industries and human activities, large amounts of heavy metals are released into the atmosphere, water, and soil. Heavy metal analysis of environmental samples is very important for determining the exposure limits. Environmental samples are highly complex matrices, and various sample preparation techniques have been developed for the extraction of heavy metals from them, including magnetic solid-phase extraction (MSPE). The use of MSPE in heavy metal analysis has recently gained significant attention owing to a number of advantages. MSPE technique overcomes main issues such as phase separation, handling, and column packing. The use of magnetic adsorbents in sample preparation has grown over the past few years, making MSPE a promising technique for sample preparation. The objective of this review article is to provide the latest applications of MSPE coupled with atomic spectroscopy for heavy metal determination in environmental samples. In addition, new magnetic adsorbents and their analytical merits are emphasized.     

Optimizing standard sequential extraction protocol with lake and ocean sediments

The environmental mobility/availability behavior of radionuclides in soils and sediments depends on their speciation. Experiments have been carried out to develop a simple but robust radionuclide sequential extraction method for identification of radionuclide partitioning in sediments and soils. The sequential extraction protocol was optimized for temperature, concentration of reagents and reaction time. Optimum extraction conditions were chosen based on the release of ^239,240Pu, ²³⁸U and stable elements. Results from the experiments with lake sediment (SRM 4354) are compared to the previous trials where the sequential extraction protocol was optimized with the ocean sediment (SRM 4357). Based on these two trials the NIST standard sequential extraction protocol is established for defined extraction settings for temperature, reagent concentration and time.     

Vacuum fusion determination of oxygen in gadolinium,terbium metal and iron-terbium alloy

The extraction conditions for the accurate determination of oxygen in gadolinium, terbium and iron-terbium alloy using vacuum fusion analysis were studied. The influence of the gettering effect, the analyzing temperature and the weight ratio of the bath metal to the sample were investigated. Oxygen values of gadolinium and terbium were measured by the graphite crucible, the graphite capsule, the tin bath, the iron-tin bath and the platinum-tin bath techniques in the temperature range of 1500–2100 °C using vacuum fusion analysis. These oxygen values were compared with those obtained by inert gas fusion analysis. In inert gas fusion analysis, the samples were analyzed with iron and tin in a tin capsule, and the samples with platinum in a tin capsule were analyzed in a graphite capsule enclosing with carbon powder. Oxygen values of both metal samples in the graphite capsule at 2000 °C, with an iron-tin bath at 1850 °C and a platinum-tin bath at 2000 °C in vacuum fusion analysis, were respectively in good agreement within their errors; the oxygen values of gadolinium were also in good agreement with that from inert gas fusion analysis in the iron-tin bath, but those of terbium were not in agreement. This agreement for gadolinium guarantees the reliability of the conditions for the accurate determination, and the difference of oxygen values for terbium suggests a need for further consideration on the conditions of the inert gas fusion analysis.     

Trace Metal Speciation and Research in Marine Geochemistry

Abstract

In order to precise the origin and behaviour of trace metals associated with coastal marine sediments, marine geochemists frequently utilize various methods of sequential extraction. The main objective is to test the potential mobility / stability of particulate metals in the natural environments. Several examples are presented in the article, namely: i/ Exchangeable Pb from podzolic soils of the drainage basin of a lagoon which sediments and phreatic waters are for a large part inherited from the surrounding soils; ii/ Evolution of particulate metals in an estuary; iii/ Mobility of metals at the sea bottom interface; iv/ Role of amorphous components of estuarine sediments and suspended matter; v/ Effects of dredging activities on solubility of metals in an estuary; vi/ Behaviour of heavy metals in lagoons.

Main results obtained from the extraction procedures are described, as well as particular difficulties encountered when applying some classical methods.