Step Sequential Extraction Procedure Research Articles

The study of mercury bioavailability in sediments of petrochemical and Jafari, Bandar Imam Creeks

Background and Objective: Due to high mobility and toxicity of mercury in environment and also high accumulation of mercury in food chain, it is important to understand and predict human exposure and ecological risk assessment of mercury. The purpose of this study was to investigate the total concentration of mercury and it's bioavailabilty in sediment of Petrochemical and Ja'fari creeks. Method: In the present study, 27 sediment samples were collected from the sampling sites. Digestion was employed in sample digestion followed by analysis using MOOPAM. samples were analyzed and determined for mercury concentrations by Mercury Analyzer model VM-3000 MERCURY VAPOR MONITOR. Sediments were further investigated for mercury fractions using a three step sequential extraction procedure of BCR. Findings: The concentrations of THg in sediment samples with a minimum of 2.19 and maximum of 45.71 and average of 23.9 milligram per liter show that area is contaminated with mercury according to the National Oceanographic and Atmospheric Administration standard. Discussion and Conclusion: The sequential extraction procedure showed that most Hg in the sediments was largely bound un exchanable phases. Therefore it can not be exchanged between water and sediment under the physicochemical conditions with alkaline pH. The mercury which bound to exchanagble phase can easily desorb and adsorb by sediments. High content of mercury was in station close to chloralkaline factory and with distance, Hg concentration was decreased.

Bioavailability, Average Daily Dose and Risk of Heavy Metals in Soils from Children Playgrounds Within Owerri, Imo State, Nigeria

Nine public school playgrounds across Owerri metropolis were investigated for metal fractions for three years (2012, 2013 and 2014) in order to assess bioavailability, average daily dose (ADD) and risk assessment code (RAC) of five heavy metals. A six steps sequential extraction procedure was used to quantify metal fractions with A ANALYST 400 Perkin Elmer AAS. Data of metal concentration was subjected to models and results revealed interesting information that could aid in decision making concerning children playground safety. Significant (p > 0.05) amounts of Zn, Co and Cu were found in the bioavailable fractions in all playgrounds for both seasons. Mean Percent bioavailability in 2012 ranged from Co (9.4) to Zn (28.11) though maximum bioavailability was observed for Mn (55) and minimum for Cu (3). In 2013 bioavailability ranged from Zn (36) to Ni (40.2) while maximum bioavailability was observed for Cu (69) and minimum for Mn (20). In 2014 it ranged from Co (58.6) to Mn (61.1) with maximum bioavailability for Cu (80) and minimum for Cu (21). Bioavailability of these metals in dry and rainy seasons followed the order; Zn > Ni > Cu > Mn > Co. Categorizing bioavailability the order was Residual > Non-bioavailable > Bioavailable. Average daily dose (ADD) showed that exposure to metal-contaminated soil by ingestion were most prominent for Zn and Mn but high ADD values were recorded in 2014 with Zn (1583.7 mg/Kg/day) as the highest. In 2012, values of RAC showed that only Zn (50) at CSO was high whereas almost all playgrounds showed RAC above 50. There was a general increase in RAC from 2012 to 2014. Thus, these metals may be readily bioavailable to children and in the long run constitute health problems for children who use these playgrounds regularly.

Effects of natural zeolites on ryegrass growth and bioavailability of Cd, Ni, Pb, and Zn in an Albanian contaminated soil

The use of eco-friendly and cost-effective adsorbent materials in the remediation of soils contaminated by potentially toxic elements (PTE) is a sustainable way of reducing the transfer of these elements into the food chain. However, an evaluation of the potential of natural zeolites to immobilize toxic elements in contaminated soils was required to enable their efficient use. The effect of natural zeolite (Stilbite-Stellerite) from the Munella area (Northern Albania), added at rates ranging from 1.25 to 10 % w/w on a contaminated soil was investigated in a greenhouse pot experiment with ryegrass (Lolium multiflorum L.) and by selective extractions. PTE availability for plants was assessed either as their accumulation in plant tissue or by DTPA-extraction. Oral bio-accessibility was estimated by the in vitro PBET method and the mobility and consequent potential risk of leaching by the USEPA TLCP method. The effect of zeolites on soil properties (pH, electrical conductivity-EC, organic C, and total N) was also investigated. A five steps sequential extraction procedure (SEP) was applied to investigate the immobilization mechanism. The addition of 2.5% w/w of natural zeolites caused a significant decrease of PTE mobility, but to observe a significant reduction of DTPA-extractable metals, it was necessary to reach 10% addition rate. In contrast, plant growth showed a gradual increase with addition rate and a corresponding decrease of concentration of PTE in plant tissue. Correlation between DTPA-extractable PTE and their concentration in both root and shoot plant tissue was rather poor. Human hazard due to soil ingestion (PBET method) changed only for Cu and Zn in the gastric phase with 1.25 and 5% addition rate respectively, whereas decreased for Cu and Zn at 5% rate in the Intestinal phase. The results of SEP support the hypothesis that the main mechanism involved in metals fixation are as follows: (1) insolubilization by pH rise, (2) adsorption on Fe/Mn oxides (3) increase of cation exchange retention, (4) organic complexation. The results of this work suggest that the addition of natural zeolites from the Munella area (AL) is a sustainable practice to reduce the environmental impact of PTE contaminated soils, but an assessment on the longevity of their immobilization need to be evaluated in the long-term perspectives.

Trace metals distribution in different geochemical phases of soils around automobile junk markets in southern Nigeria

Chemical forms of some trace metals in soils around some selected automobile junk markets were studied using five step sequential extraction procedure. The results revealed that nickel, chromium and iron were of lithogenic origin while copper, lead, manganese and cadmium were from anthropogenic sources. The residual fraction was the most important phase for nickel, chromium and iron with the average amounts of 20.38%, 29.93% and 31.09% respectively. Copper and lead were mainly associated with the organic fraction having the average amounts of 24.06% and 22.89% respectively. Manganese predominated in Iron-Manganese oxide phase with an average amount of 23.76% while cadmium existed mainly in the exchangeable phase with an average amount of 30.36%. These results suggest that nickel, chromium and iron cannot be mobilized while cadmium is the most mobile and is easily available for plant uptake. Lead, manganese and copper are relatively stable but may become mobile if there are changes in soil pH or redox potential. The amounts of the metals in the non exchangeable phases were generally high but with relative high mobility factor values obtained for all the metals, changes in the soils physicochemical conditions may lead to remobilization of the metals and they may become bioavailable to plants and may enter food chain which implies a contamination risk for the metals.Keywords: Automobile junks, geochemical phases, sequential extraction, soil pollution, trace metals

Improvement of the sequential extraction procedure based on supercritical CO2 and subcritical H2O solvents for the estimation of the environmentally mobile potentially toxic element fractions of sediments and soils

The estimation of environmental risk caused by pollution with potentially toxic elements (PTE) is usually carried out using the (3+1) step sequential extraction procedure suggested in 1993 by the Community Bureau of Reference (BCR). In the 1st step the water-soluble, exchangeable and carbonate-bound element content is extracted with acetic acid. In 2002 a fractionation procedure based on the application of supercritical CO2, subcritical H2O and of a mixture of subcritical H2O/CO2 was proposed, which allowed the water-soluble and carbonatebound element contents to be extracted separately from sediment or soil samples weighed into the preparative column of a supercritical fluid extractor and diluted with quartz sand in a mass ratio of 1:20. The aim of the present study was to develop a new reduced-size column construction with which this dilution rate could be decreased to 1:2. A kinetic study was performed to determine the extraction time necessary for samples with different carbonate contents and the extracted element contents were compared to the results of the BCR sequential procedure on the same samples. It was established that fractionation using the reduced-size column may be a rapid way to obtain more reliable information on the easily mobilizable (watersoluble and carbonate-bound) PTE content of soils and sediments than was previously available to supplement BCR fractionation.

Changes and Distribution of Modes of Occurrence of Seventeen Potentially-Hazardous Trace Elements during Entrained Flow Gasification of Coals from Ningdong, China

In order to reveal the migration of trace elements from coal to gasification residues, the modes of occurrence of potentially-hazardous trace elements (Be, V, Cr, Co, Ni, Cu, Zn, As, Se, Mo, Cd, Sb, Ba, Hg, Tl, Pb, and U) were determined by a five steps sequential chemical extraction procedure. Samples were collected from a coal-to-methanol plant (GE water-slurry coal gasification, formerly Texaco) and a coal-to-olefins plant (Gaskombimat Schwarze Pumpe pulverized coal gasification, GSP) in the Ningdong Energy and Chemical Industry Base, China. Concentrations of As and Se were determined using atomic fluorescence spectrometry (AFS). The content of Hg was determined using a DMA-80 mercury analyzer. Other trace elements (Be, Cr, Co, Ni, Cu, Zn, Mo, Cd, Sb, Ba, Tl, Pb, and U) were analyzed using inductively-coupled plasma mass spectrometry (ICP-MS). XRD and SEM-EDX were employed to determine the minerals or other inorganic phases in samples. The modes of occurrence of trace elements in feed coals can influence their behavior, including their volatility during coal gasification and, ultimately, the element’s mode of occurrence in the gasification residues. Knowing an element’s mode of occurrence in the feed coal may aid in anticipating which components the elements are likely to combine with during liquid slag cooling. Based on the relative enrichment of trace elements in the residues, elements Be, V, Cu, Mo, Ba, and Hg showed volatility during the GE and GSP gasification processes; As and Se showed volatilization-condensation behavior during the GE and GSP gasification processes; Cr, Ni, Zn, Cd, Sb, Tl, Pb, and U showed volatility during the GE gasification process; Zn, Cd, Sb, Pb, and Tl in the GSP samples, as well as Co in the GE samples, showed volatilization-condensation behavior; and Cr, Co, Ni, and U showed less volatility during the GSP gasification process. In the gasification residues, quartz, calcite, and Al–Si glass were the main inorganic phases, carbonates and iron and manganese oxides (likely recrystallized calcite) were the main hosts of most trace elements in the residues, including Be, V, Cr, Co, Ni, Zn, As, Cd, Ba, Hg, Tl, Pb, and U. Copper, Zn, Se, Cd, and Sb tended to stay in the Al–Si glass. Molybdenum is likely precipitated with the sulfides in the residues.

Molybdenum-phosphate retention and transport in soils

Transport and retention experiments were carried out to quantify the mobility and sorption of molybdenum (Mo) and phosphate (P) in two different soils. Batch experiment was used to determine sorption isotherms over a wide range of concentrations for Mo and P. For both soils, sorption isotherms were nonlinear with higher affinity of P than Mo. Sorption of Mo was significantly reduced as the amount added P in solution increased. This was observed for both soils and is indicative of competitive sorption for available site. Miscible-displacement experiments were carried out using soil column where a pulse of Mo solution was introduced in each soil. Breakthrough curves (BTCs) indicated extensive sorption of Mo where as much as 50% of that applied was retained by a predominant kaolinatic soil. Subsequently, a pulse of mixed solution (of Mo and P) was introduced in each column. Results of BTCs for Mo indicated enhanced mobility of Mo in the presence of P for both soils. A five step sequential extraction procedure provided evidence that majority of applied Mo was strongly and/or irreversibly retained. A competitive transport model (CMRTM) based on the Sheindorf-Rebhun-Sheintuch (SRS) equation was capable of describing BTCs of Mo and to a lesser extent for P. Future research should focus on improvement of models that accounts for chemical mechanisms of competitive sorption.

Heavy metals Fractionation in Bagmati River Sediments, Nepal

The aim of this work was speciation of heavy metals on the level of the geochemical background; in bottom sediments of the Bagmati River in Kathmandu valley. The distribution and accumulation of heavy metals in the sediments of the Bagmati River were investigated. Sediment samples from six locations were collected and characterized for metals content (cadmium, lead, copper and zinc). The determination of extractable heavy metals such as, Cd, Pb, Cu and Zn, in the sediment samples was carried out by atomic absorption spectrometry. The study has been conducted using five steps sequential extraction procedure described by tessier. Apart from total concentration, the distribution of the above metals into five fractions: exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter, and residual, was studied by means of an analytical procedure involving sequential chemical extraction. The result obtained showed total metal concentration to be in the range of Cd 0.89-2.29 mg/kg; Pb 57.58-221mg/kg; Cu 52.2 -198.17 mg/kg and 78.23-362.90 mg/kg in all the areas studied. The fractionated toxic metals like Cd, and Pb were observed to be in the range of 15-36%, and 11- 29%, respectively, in mobile or bio-available fractions of sediments. This potentially mobile fraction could pose a serious threat, with respect to contamination of waterways and aquatic environment.Journal of Hydrology and Meteorology, Vol. 9(1) 2015, p.119-128

Determination of mercury and its fractionation products in samples from legacy use of mercury amalgam in gold processing in Randfontein, South Africa

Abstract This study aimed at determining the levels of total mercury (THg) in tailings dams, soil, sediments and water samples collected in the vicinity of legacy mercury amalgam gold mines. Acid digestion was employed in sample digestion followed by analysis using CVAAS. Tailings dams, community and garden soil, and stream sediments were further investigated for mercury fractions using a five step sequential extraction procedure. The concentrations of THg in tailings dams, community and gardens soil were 0.890–6.755 μg/g, 0.431–0.968 μg/g and 0.471–1.019 μg/g, respectively and the concentrations of THg in the sediments obtained from tailings dams, streams and wetlands were 0.649–1.998 μg/g, 0.604–1.356 μg/g and 0.681–1.356 μg/g, respectively. The concentrations of THg, in aqueous samples obtained from tailings, streams and wetlands were 0.032–0.070 μg/l, 0.004–0.068 μg/l and 0.007–0.012 μg/l, respectively. The sequential extraction procedure showed that most Hg in the tailings dams was largely elemental Hg and Hg bound to sulphur. Soil and sediments were largely dominated by organic bound Hg. Moderate seasonal correlation was observed in tailings dams soil, but weak seasonal correlation in soils collected in the vicinity of tailings. However, a strong seasonal correlation was observed in sediments and water samples. The concentrations of Hg obtained largely existed in organic and sulphate bound Hg and there is elevated potential to methylate Hg.

Sequential extraction procedure as a tool to investigate PTHE geochemistry and potential geoavailability of dam sediments (Almadén mining district, Spain)

Sediments from Castilseras reservoir (Almadén) were collected to assess the potential environmental hazards associated with the availability of Potentially Toxic or Harmful Elements (PTHE) in this freshwater environment. PTHE concentrations in sediments were investigated using a four step (F1–F4) Sequential Extraction Procedure (SEP) and the results were evaluated using Principal Component Analysis (PCA) and different risk indexes and criteria. Considering the fractions results and the PCA treatment, two groups of elements can be differentiated in the easily leached by weak acids fraction F1 and these indicate the presence of sulfate and secondary precipitates of carbonates as the main sink for easily accessible metallic elements. In reducible fraction F2, chemical analysis revealed a significant relationship between the majority of the analyzed elements and the Fe oxy-hydroxides, with the exception of Co, Hg and Ni, which are preferentially associated with Mn oxy-hydroxides. In the oxidizable fraction (F3), a significant relationship between Cu, Fe, Hg and Zn (representative metals of the existing ore deposits) and sulfides/organic matter was observed. The environmental assessment based on the aforementioned criteria provides risk levels varying from moderate to high. The risk appears to be higher near the dam, where the higher PTHE levels in sediment are due to a selective accumulation of fine-grained particles.

Redistribution of cadmium and lead fractions in contaminated soil samples due to experimental leaching

The sequential extraction procedure (SEP) is often applied to soils for identification of binding phases but rarely is it used to monitor binding dynamics temporally. In this study, contaminated soils were subjected to two different leaching scenarios, one analogous to a hydrostatic or stagnant water exposure, and one that represents a hydrodynamic event such as heavy precipitation. A four step SEP was applied before and after each stage of leaching and the adsorption dynamics of cadmium and lead were studied. In the hydrostatic experiment, removal of Cd and Pb occurred largely from the residual fraction (from initially >30%–zero Cd after the 720h experiment, 40%–<20% Pb, and from 50%–20% Cd, >50%–40% Pb, from organic and mineral soil horizons respectively). There was a significant redistribution onto the Fe/Mn oxides (from initially 30%–60% Cd after 720h, 40%–65% Pb, and from 15%–30% Cd, 45%–60% Pb for organic and mineral soils respectively). A significant redistribution of Cd onto the organic matter was observed (from initially zero, to 20% after 720h in organic soil, and from 1%–15% in mineral soil). After the experiment, fraction distribution of the organic soil sample closely matched the distribution pattern of a slightly contaminated fluvisol sample that was taken in a river valley adjacent to the studied soils. When a CaCO3 amendment was applied, dissolution of both elements decreased, >50% less Cd and Pb released from organic soil, and ~80% less Cd released from mineral soil with amendment. However, the fraction distributions remained similar to that of a non-amended sample. In the hydrodynamic leaching experiment, important binding phases of Cd were identified as organic matter (from initially 0%–15% after leaching and from ~2%–~10% in organic and mineral soils respectively) and metal oxides (from initially 40%–50% after leaching in organic soil). Residual Pb increased after leaching, and losses occurred from the Fe/Mn oxides (>50% decrease in organic soil). The CaCO3 amendment had little influence on both element distribution and concentrations in hydrodynamic column leaching. It is anticipated that this study could be a precursor for modelling heavy metal fractionation of contaminated soils based on water regime in the environment.

Automated Determination of Cu(II), Pb(II), Cd(II) and Zn(II) in Environmental Samples by Square Wave Voltammetry Exploiting Sequential Injection Analysis and Screen Printed Electrodes

AbstractThis paper describes the development of a methodology for quantification of Cu(II), Pb(II), Cd(II) and Zn(II) in waters and sediments by anodic stripping voltammetry (ASV) automated by Sequential Injection Analysis (SIA) using a graphite screen printed sensor modified with mercury. Determinations were made by standard addition automated by the SIA system. The limits of detection and quantification were, respectively, 1.3 and 4.3 µg L−1 for Cu(II), 1.4 and 4.6 µg L−1 for Pb(II), 0.6 and 1.8 µg L−1 for Cd(II) and 4.2 and 14 µg L−1 for Zn(II). These limits were obtained for a sample volume of 1000 µL, flow rate of 10 µL s−1 (during the deposition step), and utilizing 3 flow reversals (volume of reversion=950 µL), totalizing a deposition time of 315 s. The potentiostat worked synchronically with the SIA system applying the conditioning potential of −0.1 V vs. pseudo reference of Ag (100 s), deposition potential of −1.0 V for Cu(II), Pb(II) and Cd(II) or −1,3 V for Zn(II), square wave frequency of 100 Hz, potential step of 6 mV and pulse height of 40 mV. For quantification of Zn(II) in sediment extracts, deposition of Ga0 on the working electrode was necessary to avoid the formation of intermetallic between Zn0 and Cu0. The accuracy of the method was assessed by spike and recovery experiments in water samples which resulted recovery rates near 100 % of the spiked concentrations. Recoveries of concentrations in the certified sediment sample CRM‐701 undergoing the three steps sequential extraction procedure of BCR varied from 71.7 % for Zn(II) in the acetic acid extract to 112.4 % for Cu(II) in the oxidisable fraction, confirming that the standard addition approach corrected the matrix effects in the complex samples of sediment extracts.

Leachability and heavy metal speciation of 17-year old stabilised/solidified contaminated site soils

The long-term leachability, heavy metal speciation transformation and binding mechanisms in a field stabilised/solidified contaminated soil (made ground) from West Drayton site were recently investigated following in situ auger mixing treatment with a number of cement-based binders back in 1996. Two batch leaching tests (TCLP and BS EN 12457) and a modified five step sequential extraction procedure along with X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were employed for the testing of the 17-year-old field soil. The results of batch leaching tests show that the treatment employed remained effective at 17 years of service time, with all BS EN 12457 test samples and most of TCLP test samples satisfied drinking water standards. Sequential extraction results illustrate that the leaching of Cu, Ni, Zn, Pb and Cd in all mixes mainly occurred at the Fe/Mn phase, ranging from 43% to 83%. Amongst the five metals tested, Ni was the most stable with around 40% remained in the residual phase for all the different cement-based binder stabilised/solidified samples. XRD and SEM analyses show that the hydration process has been fully completed and further carbonation took place. In summary, this study confirms that such cement-based stabilisation/solidification (S/S) treatment can achieve satisfactory durability and thus is a reliable technique for long-term remediation of heavy metal contaminated soil.

Kinetic modeling of antimony(V) adsorption–desorption and transport in soils

Antimonate [Sb(V)] adsorption–desorption and transport in an acidic red soil (Yingtan) and a calcareous soil (Huanjiang) was investigated using kinetic batch and miscible displacement experiments. Different formulations of a multi-reaction model (MRM) were evaluated for their capabilities of describing the retention and transport mechanisms of Sb(V) in soils. The experimental results showed that adsorption of Sb(V) by two soils was kinetically controlled and largely irreversible. The Sb(V) adsorption capacity and kinetic rate of the acidic red soil was much higher than that of the calcareous soil. The asymmetrical breakthrough curves indicated the strong dominance of non-equilibrium retention of Sb(V). A four step sequential extraction procedure provided evidence that majority of applied Sb(V) was irreversibly retained. A formulation of MRM with two kinetic sorption sites (reversible and irreversible) successfully described Sb(V) adsorption–desorption data. The use of kinetic batch rate coefficients for predictions of breakthrough curves (BTCs) underestimated Sb(V) retention and overestimated its mobility. In an inverse mode with optimized rate coefficients, the MRM formulation was capable of simulating Sb(V) transport in soil columns.

Metal Pollution in Huayuan River in Hunan Province in China by Manganese Sulphate Waste Residue

The Huayuan River in Hunan Province in China is subject to ongoing mining activity with Mn extraction. In this study, the level and environmental significance of metals (including Mn, Cd, Pb, Cu, Zn, Ni and Fe) concentrations in the surface water and river sediments have been investigated along a 187 km reach of the Huayuan River. Using the X-ray fluorescence (XRF) analysis, we analyzed the characterization of metals in manganese sulphate waste residue (MSWR) deposited along the bank of Huayuan River. The speciation of metals in both sediment and MSWR was established using the BCR-three step sequential extraction procedure. In the water samples, the average concentrations of Mn, Cd and Pb exceeded the acceptable concentrations for drinking water in the WHO Guidelines for drinking water quality, Vol. 1, Recommendations, Geneva (2004) and Chinese (GB 5749-2006) guidelines, respectively. The average concentrations of Mn, Cd, Pb and Zn in the river sediments were found to be considerably higher than the corresponding world average shale values. The percentages of Cd (31.4%), Mn (31.1%), Zn (12.8%) and Pb (8.1%) associated with exchangeable and weak acid fraction in the sediments were higher than other metals. Mn (5.81%), Zn (0.208%), Pb (0.0292%) and Cd (0.0113%) were identified in MSWR by XRF analysis. The percentages of Mn, Cd, Zn and Pb associated with the exchangeable and weak acid soluble fraction in MSWR were 41.9%, 31.1%, 23.8% and 9.8%, respectively. The peak solute and sediment-bound metal concentrations were found at the sites of MSWR deposited along the bank of Huayuan River. The results suggested that MSWR deposited along the bank may have a closely relation with the metal pollution of Huayuan River. The results obtained may be useful to assess both short and long-term environmental impact of the MSWR deposited activities and support decisions for a future remediation of this river.

Application of the BCR sequential extraction scheme to dredged pond sediments contaminated by Pb–Zn mining: A combined geochemical and mineralogical approach

The modified BCR sequential extraction procedure [Rauret, G., López-Sanchez, J., Sauquillo, A., Rubio, R., Davidson, C., Ure, A., Quevauviller, Ph., 1999. Improvement of the BCR three step sequential extraction procedure prior to certification of new soil and sediment reference materials. J. Environ. Monit. 1, 57–60.] was applied to 4 sediments from a mine tailing pond in La Calamine (East-Belgium). The results showed a very different behaviour of different samples towards the same extraction scheme. In samples with an elevated acid neutralizing capacity, a significant increase in the pH of the extracts was measured after the first two extraction steps. Other artefacts, such as readsorption of metals and precipitation could be deduced by comparing X-ray diffraction patterns after different extraction steps. For example, anglesite was effectively dissolved during the acid extraction step (step 1) but relatively low Pb concentrations were measured in the CH 3COOH extract because of the readsorption of Pb. Mineralogical analysis of the sediments after each extraction step also indicated the incomplete oxidation of sulphides by H 2O 2. Besides a mineralogical analysis, the monitoring of the pH of the extracts and the analysis of major elements (Fe, Ca, Al, Mn) can be helpful for the interpretation of the results of the sequential extraction. The combination of sequential extractions with mineralogical sample investigation provided information on the reactivity and solubility of minerals in the samples. This improved the interpretation, at least within the detection limits of the mineralogical analysis applied. Besides the improved interpretation of the results of the sequential extractions for sediments in which minerals are identified, the information concerning the reactivity of minerals is an important tool to evaluate the risk associated with contaminated sediments.

The utilization of modified BCR three-step sequential extraction procedure for the fractionation of Cd, Cr, Cu, Ni, Pb and Zn in soil reference materials of different origins

A modified three-step sequential extraction procedure for the fractionation of heavy metals, proposed by the Commission of the European Communities Bureau of Reference (BCR) has been applied to the Slovak reference materials of soils (soil orthic luvisols, soil rendzina and soil eutric cambisol), which represent pedologically different types of soils in Slovakia. Analyses were carried out by flame or electrothermal atomic absorption spectrometry (FAAS or ETAAS). The fractions extracted were: exchangeable (extraction step 1), reducible-iron/manganese oxides (extraction step 2), oxidizable-organic matter and sulfides (extraction step 3). The sum of the element contents in the three fractions plus aqua-regia extractable content of the residue was compared to the aqua-regia extractable content of the elements in the origin soils. The accuracy obtained by comparing the determined contents of the elements with certified values, using BCR CRM 701, certified for the extractable contents (mass fractions) of Cd, Cr, Cu, Ni, Pb and Zn in sediment following a modified BCR-three step sequential extraction procedure, was found to be satisfactory.

Mobility assessment and validation of toxic elements in tunnel dust samples—Subway and road using sequential chemical extraction and ICP-OES/GF AAS measurements

The modified BCR three step sequential extraction procedure has been applied to homogenized urban dust samples collected in sedimentation chambers of two Prague tunnels (road, Letna, subway, and station Museum), and to SRM 1648 urban particulate matter (NIST) to validate the applicability of the procedure. Analyte concentrations in the fourth step were calculated from the total content of analytes determined and verified before, in case of the SRM 1648 certified values have been utilized. Concentrations of chosen elements As, Cd, Cr, Mn, Ni, Pb, Zn (Cu, Fe) in each fraction were measured by ICP-OES and GF AAS (arsenic determination) methods. The work has been focused on (i) levels investigation of toxic elements in dust samples and their distribution following a three-stage sequential extraction procedure, (ii) finding differences between two tunnel samples utilizing the estimation of mobility of trace elements, some macro-component comparisons and main mineralogical phases determinations by XRD analysis, (iii) validation of the proposed procedure using SRM 1648 Urban Particulate Matter (NIST) and comparative data obtained by a capillary electrophoresis (CE) method.

Comparison of three sequential extraction procedures (original and modified 3 steps BCR procedure) applied to sediments of different origin.

The 3 steps sequential extraction procedure proposed by the Standards Measurements and Testing program (SM&T--formerly BCR) of the European Union has been applied for the speciation of metals in sediments. Results obtained by the application of the BCR standardized procedure were compared to those of two four step sequential extraction procedures, which are different from the BCR procedure only for the introduction of an additional step with NaOCl, as 2nd and 3rd step respectively. Five different metals have been taken into consideration: Cd, Cu, Ni, Pb and Zn. The analytical performances of the laboratory have been evaluated using three certified reference materials: the BCR 601 lake sediment for the BCR sequential extraction procedure, PACS-1 and MESS-1 for total metal concentration. Results showed that the efficiency of NaOCl treatment is higher or at least equal to that of H2O2 treatment and that its selectivity is quite satisfying. Moreover the NaOCl treatment doesn't significantly influence the extraction of the easily reducible fraction.

Distribution and origin of major and trace elements (particularly REE, U and Th) into labile and residual phases in an acid soil profile (Vosges Mountains, France)

A 7 step sequential extraction procedure has been conducted on a podzolic soil profile from the Vosges Mountains in order to determine the ability of several elements to be released to the environment. Very little Si, K and Al were extractable (<10% of the total soil concentration) but larger proportions (> 10% of the total soil concentration) of Ca, P, metals (Fe, Pb), REE and actinides (Th, U) could be leached. For each element, preferential binding sites can be recognized. High recovery of P and Ca in the acid soluble fraction (AS) suggests that phosphate minerals are highly involved in this step of the extraction. Organic matter appears to control the adsorption of Ca, Fe, Th, U and REE, even at depths in the soil profile where organic matter content is particularly low (0.5%). Weak acid leaching experiments (with HCl and acetic acid 0.001 N) were also performed in order to characterize the origin of the insoluble material in this soil profile. The leachable REE distributions indicate that a large part of the labile REE in the surface horizon has an atmospheric origin whereas at greater depth phosphate mineral (apatite) alteration is the main factor controlling REE release in the leachate. The study further suggests that adsorbed material holding actinides and REE are not strictly the same. So, caution should be taken when using REE as analogues for actinides in soils systems.