Use of the modified BCR three-step sequential extraction procedure for the study of trace element dynamics in contaminated soils.

The modified BCR three-step sequential extraction procedure was used to examine the temporal dynamics of trace elements in soils contaminated by an accidental spill from an opencast mine in south-west Spain. Soils were mainly contaminated with pyritic sludge and acidic wastewater, whereas some soils were affected only by acidic wastewater. The distributions obtained for both some major (Ca, Fe and Mn) and trace elements (As, Cd, Cu, Pb and Zn) in the sludge and soil samples taken at different times after the accident, 1-3 months and 21 months, were compared. Sequential extractions were useful in identifying different sources of contamination, and in obtaining additional information on the solubility of secondary minerals formed by pyrite oxidation. Thus, the effectiveness of the BCR procedure has proved to be a useful tool for predicting short- and long-term mobility of trace elements, even in complex environmental scenarios.

Radionuclide sorption-desorption pattern in soils from Spain.

The pattern of radiostrontium and radiocesium sorption-desorption was examined in 30 Spanish soils by the quantification of the distribution coefficients (Kd) with batch tests, the evaluation of sorption reversibility with a single extraction, the estimation of sorption dynamics by the application of drying-wetting cycles, and the calculation of Kdadjusted values as an input for risk assessment models. The data obtained overlapped with those found in soils from other climatic areas, suggesting identical interaction mechanisms and allowing the extrapolation of parameterisations and prediction models among different scenarios.

Prediction of radionuclide aging in soils from the Chernobyl and Mediterranean areas.

The aging of soil-pollutant interaction, which may lead to an increase in pollutant fixation, is the main driving force in the natural attenuation of contaminated soils. Here a test was evaluated to predict the aging of radiostrontium and radiocesium in soils from the Chernobyl and Mediterranean areas. After contamination, soils were maintained at various temperatures for up to 12 mo, with or without drying-wetting (DW) cycles. Changes in the quantity of radionuclide reversibly sorbed over time were monitored using an extraction test (1 mol L(-1) NH(4)Cl; 10 mL g(-1); 16 h). The fixed fraction could not be predicted from soil properties controlling the sorption step. Aging was not as relevant for Sr as for Cs. The time elapsed since contamination was the main factor responsible for the slight (up to 1.3-fold) decreases in Sr extraction yields. The additional effect of DW cycles was negligible. Instead, all factors accelerated Cs aging due to the enhancement of Cs trapping by clay interlayer collapse, with up to 20-fold increases in Cs fixation. The DW cycles also caused secondary effects on the Cs-specific sorption pool, which were beneficial or detrimental depending on the soil type. Extraction yields from laboratory aged samples agreed with those from field samples taken a few years after the Chernobyl accident. These results confirm the prediction capacity of the laboratory test and its usefulness in risk assessment exercises and in the design of intervention actions, particularly because neither fixation nor aging were related to the soil properties, such as clay content.

Effect of the cationic composition of sorption solution on the quantification of sorption-desorption parameters of heavy metals in soils.

We obtained the sorption isotherms of Cd, Cu, Pb and Zn in clay, clay saline and organic soils. The distribution coefficients (K(d)) were determined in 0.02 eq l(-1) CaCl(2) and in a solution that simulated the soil solution cationic composition. The K(d) values greatly varied with the composition of the sorption solution and the initial metal concentration. The sorption experiments were complemented with the quantification of the extractable metal, to estimate the reversibility of metal sorption. The extraction yields depended on the metal-soil combination, and the initial metal concentration, showing no correlation with previous K(d) values. The effect of the solution composition in mobility predictions was estimated through a Retention Factor, defined as the ratio of the K(d) versus the extraction yield. Results showed that risk was over- or underestimated using the CaCl(2) medium in soils with a markedly different soil solution composition.

Combination of chemical separation and data treatment for 55 Fe, 63 Ni, 99 Tc, 137 Cs and 90 Sr/90Y activity determination in radioactive waste by liquid scintillation.

Routine operations involving nuclear reactors and decommissioning activities require numerous chemical analyses. Most of the procedures developed for these chemical characterisations involve several separation steps to prepare the sample for measurement. Chemical treatments are time- and manpower-consuming, labour intensive and produce significant quantities of waste. In order to address this problem, we evaluate a data treatment procedure (multivariate calibration--PLS), which we propose as a substitute to some of these separation steps. Mixtures of beta emitter radionuclides of increasing complexity ((90)Sr/(90)Y--(99)Tc, (90)Sr/(90)Y--(99)Tc--(63)Ni--(137)Cs and (90)Sr/(90)Y--(99)Tc--(63)Ni--(137)Cs--(55)Fe) have been measured by liquid scintillation (LS) counting. The influences of quenching and level of activity was evaluated and the activity of unknown samples determined. Despite the spectra overlapping and low resolution of LS, relative errors in the activities quantification of unknown samples inside the range covered by the calibration matrix are lower than 15% whatever the number of radionuclides included in the solution was.

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.

Solvent extraction of lead(II) with N-cyclohexyl-N-nitrosohydroxylamine into methyl isobutyl ketone.

The distribution equilibrium of the lead-cnha complex in the water-methyl isobutyl ketone (MIBK) system has been studied at 25 degrees . From graphical treatment of the equilibrium data, it was deduced that PbL(2) is the complex extracted. By use of the program LETAGROP-DISTR, values for the distribution and the stability constants of PbL(2) have been calculated: log K(DC) = 1.84 +/- 0.11; log beta(1) = 6.68 +/- 0.09 and log beta(2) = 10.28 +/- 0.09. On the basis of these results and those of previous studies, a method for determination of lead(II), copper(II) and cadmium(II) by atomic-absorption spectrometry, after extraction with cnha and 4-methylpyridine into MIBK, is proposed.

Solvent extraction of N-Cyclohexyl-N-Nitrosohydroxylamine (cnha) into some organic solvents and of the Cu(II)-cnha complex into methyl isobutyl ketone.

The distribution equilibria of N-cyclohexyl-N-nitrosohydroxylamine (cnha) in the water-chloroform, water-hexane, water-methyl isobutyl ketone (MIBK) and water-isopentyl alcohol systems, and of the Cu(II)-cnha complex in the water-MIBK system have been studied. From the distribution data the dissociation and distribution constants of the reagent have been calculated; their values are pK(a) = 5.55 +/- 0.10; log K(DR) = 2.46 +/- 0.05 (chloroform), 1.76 +/- 0.11 (MIBK), 1.06 +/- 0.07 (hexane) and 1.48 +/- 0.06 (isopentyl alcohol). In the same way the values of the distribution and stability constants of the Cu(II) complex have been obtained; log K(DC) = 3.51; log beta(1) = 7.23 +/- 0.10 and log beta(2) = 12.00 +/- 0.08. For the determination of cnha in the aqueous phase saturated with MIBK, a spectrophotometric method based on the coloured complex formed by the reagent with Fe(III) has been established. Finally, an analytical method for Cu(II) by atomic-absorption spectrometry after its extraction with cnha into MIBK, is proposed. Its detection limit is 4.6 mug l ., its precision +/- 2.1% and its accuracy 97.5%. This method has been applied to the determination of the copper content in the surface water of the Congest River of Catalonia (Spain).

Speciation of arsenic in mussels by the coupled system liquid chromatography-UV irradiation-hydride generation-inductively coupled plasma mass spectrometry.

A method has been developed for the determination of seven arsenic species in mussel tissues by liquid chromatography-hydride generation-UV photo-oxidation and detection by inductively coupled plasma mass spectrometry. In order to determine the different species, two ion-exchange columns (anionic and cationic) were used with phosphate and nitric acid/ammonium nitrate as mobile phases, respectively. The optimisation of the conditions for separation, photo-oxidation and hydride generation is described. For each of these species, the limits of detection and repeatability are reported with the entire system coupling. This system was applied to the analysis of certified reference material (CRM 278) and mussels collected from Barcelona harbour. Extractions were achieved in methanol/water (1:1) using low-power focused microwaves as leaching process. As expected, arsenobetaine was the main compound extracted from both materials; the typical concentrations found were between 1 and 7 mg kg(-1). Other organoarsenical compounds, probably arsenosugars, were extracted in a concentration range of 0.3-1.5 mg kg(-1) in both cases. Amounts of dimethylarsinate (DMA) were found to be significant in the CRM 278, but very low in mussels from Barcelona harbour. The low limits of detection of the coupled system allow us to quantify low contents of other species (As(V), arsenocholine and monomethylarsonate (MMA)).

Solvent extraction of Cd(II) with N-cyclohexyl-N-nitrosohydroxylamine and 4-methylpyridine into methyl isobutyl ketone.

The distribution equilibria of the complexes cadmium-cnha and cadmium-cnha-4-methylpyridine in the water-methyl isobutyl ketone system have been studied at 25 degrees , by using (109)Cd as a radiotracer to measure the metal distribution ratio. A very sensitive method for detection of (109)Cd, based on the use of a liquid scintillator, has been developed. From the graphical treatment of the equilibrium data, it has been deduced that CdL(2) is the complex extracted in the absence of 4-methylpyridine, and that the adduct CdL(2)B is extracted when the second ligand is present. This model has been checked by treating the data with the program LETAGROP-DISTR and the following equilibrium constants have been obtained: stability constants of CdL(2), log beta(1) = 2.82 +/- 0.14, log beta(2) = 5.981 +/- 0.004; distribution constant of CdL(2), log K(DC) = -0.49 +/- 0.01; adduct formation constant of CdL(2)B, log K(s) = 2.70 +/- 0.07.

Acid volatile sulfide determination in sediments using elemental analyzer with thermal conductivity detector.

A method for the determination of acid volatile sulfides (AVS) in sediments, using a common elemental analyzer with thermal conductivity detector, is proposed. The method uses a mixture of Sn and V(2)O(5) for pyrolysis and combustion to determine total sulfur (TS), and non volatile sulfur (NVS), after an acidic attack. AVS is calculated as the difference between TS and NVS. The method for TS is validated by analyzing a certified reference material. The recovery in the determination of acid volatile sulfide is determined by spiking a river sediment with ZnS. The method is accurate and gives a good reproducibility, recovering 97.7-99.6% of the sulfur in the 0-3% total sulfur content, with SD of approximately 0.015%.

A soil sampling strategy for mapping trace element concentrations in a test area.

A sampling strategy, based on previous knowledge of a test area, was compared with a Reference Sampling in the frame of the EU-funded CEEM project. The aim was a comparison of sampling strategies for the drafting of concentration maps for a set of trace elements (Cd, Pb, Cu and Zn), with three-dimension information that can be used for risk assessment. The main constraint was that only 15 soil samples were to be analysed. The test area (in Dornach, Switzerland) included different soil types and land uses (forest, arable land and permanent grasslands). The sampling strategy proposed defined strata on the basis of land use, then applying a systematic regular sampling within each stratum. A composite sample was formed from each individual sample. In forests, H and Ah horizons were taken separately. In arable lands, a depth within the ploughed layer (0-15 cm) was analysed. In grasslands, samples were taken at two depths (0-10 and 10-20 cm) to provide information on the vertical variability. The comparison of the results obtained with those derived from the Reference Sampling allowed us to estimate if the information obtained from the proposed sampling strategy was sufficiently representative for an assessment of the level of elements considered. It was concluded that recommendations on sampling strategy depend on the interaction pattern of the element. In this case, for mobile trace elements, such as Cd, the information derived from sampling of two soil layers was not as important as that for the rest of metals studied that accumulated in the upper layer. If the H horizons in forests was not considered this led to unreliable predictions of the concentration levels, since the concentrations in H and Ah horizons differed irrespective of whether they were expressed in mg kg(-1) (the H horizon was enriched in those trace elements, except for Cd) and in mg m(-2) (the low bulk density of the H horizon led to a lower trace element level than in Ah horizon). Finally, in undisturbed systems such as grasslands, sampling 0-10 cm instead of 0-20 cm is recommended to prevent dilution of the concentration of trace elements.

Quantitative assessment of the effects of agricultural practices designed to reduce 137Cs and 90Sr soil-plant transfer in meadows.

Agricultural practices (ploughing and reseeding, addition of lime and fertiliser) were tested as a feasible remediation strategy to reduce 137Cs (RCs) and 90Sr (RSr) soil-plant transfer in natural meadows in areas affected by the Chernobyl fallout. Field experiments were carried out for 2 years at six sites, covering dry and wet meadows. Observed results at field scale showed that ploughing plus reseeding provoked the main reduction in RSr transfer, with no further reduction after liming, while ploughing + reseeding + K fertiliser led to the maximum decrease in RCs transfer at most sites. The direct effects of agricultural practices on the exchange complex and soil solution composition were quantified by subsequent soil analyses. At the doses applied, lime did not affect the Ca + Mg concentrations in the exchange complex and soil solution of the ploughed soils, thus suggesting that the decrease in RSr transfer on treated plots was mainly due to the changes in the plant species after reseeding. With respect to RCs, changes in the K+NH4+ concentrations in the exchange complex and soil solution were consistent with changes in soil-plant transfer. Finally, RSr and RCs soil-plant transfer in ploughed plots was well predicted from soil properties, such as the solid-liquid distribution coefficient, the ionic composition of the soil solution and the exchangeable cations, with Pearson correlation coefficients of 0.98 and 0.86, respectively, between calculated and experimental log transfer factors.

Assessment of metal mobility in dredged harbour sediments from Barcelona, Spain.

In order to assess heavy metal mobility in dredged harbour sediments, six superficial sediment samples covering a range of pollution levels and environments were collected in Barcelona Harbour. Samples were characterised in terms of major compounds (Al, Ca, Fe, Mn, Si, Ti, Mg, K and Na); total C, N and S contents; organic matter; and water content. Pseudo-total trace metal contents were assessed after aqua regia digestion (ISO 11466:1995). The modified BCR three-step sequential extraction procedure (BCR-SEP) was applied, and both major compounds (Al, Ca, Fe and Mn) and trace metals (Cd, Cr, Cu, Ni, Pb and Zn) were determined in the different extracts. Both the pseudo-total digestion method and the BCR-SEP were validated using two sediment certified materials from lakes (BCR CRM 701 and BCR CRM 601). The highest metal concentrations were observed in one of the sampling points which receives an urban discharge. The observed mobility order (percentage of metal extracted in the first step) of the six trace metals studied was Cd>Zn>Pb>Cu>Ni>Cr. The good agreement observed with the results obtained as the sum of the four steps (extractable+residue) and the pseudo-total content shows that laboratory working conditions were under control.

Use of sorption and extraction tests to predict the dynamics of the interaction of trace elements in agricultural soils contaminated by a mine tailing accident.

Over 2000 ha of agricultural soils were contaminated by a pyritic sludge and acidic waste waters coming from a spill from a mining exploitation. The affected soils were acidic with sandy-loam texture (SL), loamy with neutral pH (L), and calcareous, saline, with clay texture (Cs). The Cs soils were contaminated only with acidic waste waters. Sorption and extraction tests were applied to examine the medium-term dynamics of the interaction of trace elements (As, Cd, Cu, Pb and Zn) in the soils. The solid-soil solution distribution coefficient (KD) was determined in soil samples taken 3 months (initial stage, 3M samples) and then nearly 2 years (final stage, 21M samples) after the accident. Distribution coefficient values ranged from the lowest values in the SL samples (from 0.2 l kg(-1) for Cd and Zn to 25 l kg(-1) for As) to higher values in the L and Cs soils. Lead and As had the highest KD in all soils (over 10(5) l kg(-1) in the L soils). No clear dynamics pattern could be derived from these data because of the low heavy metal concentrations in the soil solution. As a complementary approach, four single extractions (0.01 and 1 mol l(-1) CaCl2; 0.05 mol l(-1) EDTA; 0.43 mol l(-1) CH3COOH) were applied to soil and sludge samples. Samples derived from submitting field 3M samples to drying-wetting (DW) cycles were included to define a complete laboratory approach to predict field dynamics. Results from extraction tests indicated that changes of the trace element interaction over time depended on the soil pH and on the source of contamination. For those soils affected only by the acidic waste waters, where an increase in fixation occurred, natural processes such as diffusion controlled dynamics. For those soils contaminated by a mixed source, the dynamics of the interaction was the resultant process of the combination of the natural attenuation and the oxidation of the pyritic sludge. This latter process led to an increase in the remobilization for those elements associated with soluble secondary minerals (Cd and Zn) and to an increase in the fixation for those elements coprecipitating with insoluble secondary minerals (Pb and As). Drying-wetting cycles were useful to predict the dynamics in the field at month-year scale. The CH3COOH was recommended as the best test among those studied here to derive conclusions about dynamics pattern because it provided significant desorption yields in most scenarios. Acidic soils with sludge contamination represented the scenarios with the highest risk, while calcareous soils better attenuated contamination. In a longer time scale, the depletion of calcareous components needs to be controlled.

Prediction of the impact of the Aznalcóllar toxic spill on the trace element contamination of agricultural soils.

The interaction of several trace elements (Cd, Zn, Cu, Pb, As, Bi, and Tl) was studied by leaching experiments in agricultural soils affected by the Aznalcóllar toxic spill. The spill led to contamination by acid waste waters and sludge deposition. The levels of contamination recorded after the sludge was removed from soils showed that highly contaminated areas remained. A comparison of soils directly affected by sludge deposition and acid waste waters with soils contaminated only by acid waste waters demonstrated that Zn/As and Cd/As ratios were good indicators of the two contributions to the contamination. Soil samples were characterised and grouped according to their texture and carbonate content. The response of elements to single extractions with CaCl2 0.01 mol l-1, CaCl2 1 mol l-1, CH3COOH 0.43 mol l-1, and EDTA 0.05 mol l-1 enabled us to estimate their mobility in the soils. Cd and Zn were found to be the most mobile elements. Cu showed an intermediate mobility, especially in an acidic medium. Pb, As, Bi and Tl were found to be non-mobile elements. A comparison of referent, low and highly contaminated samples showed that the presence of sludge had an effect on desorption yields, in part due to the short-term after the contamination. Calculations of a relative scale of long-term mobility, between soils and trace elements, provided further conclusions derived from the use of single extractions.

Prediction of trace element mobility in contaminated soils by sequential extraction.

The modified three-step sequential extraction procedure proposed by the Community Bureau of Reference (or Bureau Communautaire de Reference, BCR) was used to predict trace element mobility in soils affected by an accidental spill comprising arsenopyrite- and heavy metal-enriched sludge particles and acid waste waters. The procedure was used to obtain the distribution of both the major (Al, Ca, Fe, Mg, and Mn) and trace elements (As, Bi, Cd, Cu, Pb, Tl, and Zn) in 13 soils of contrasting properties with various levels of contamination and in the sludge itself. The distributions of the major elements enabled us to confirm the main soil fractions solubilized in each of the three steps, and, in turn, to detect the presence of pyritic sludge particles by the high Fe extractability obtained in the third step. Cadmium was identified as being the most mobile of the elements, having the highest extractability in the first step, followed by Zn and Cu, Lead, Tl, Bi, and As were shown to be poorly mobile or nonmobile. In the case of some of the trace elements, the residual fractions decreased at higher levels of contamination, which was attributed to the anthropogenic contributions to the polluted samples. Comparison with soil-plant transfer factors, calculated in plants growing in the affected area, indicated that a relative sequence of trace element mobility was well predicted from data of the first step.

An overview of the effect of organic matter on soil-radiocaesium interaction: implications in root uptake.

This paper aims to give an overview of the effect of organic matter on soil-radiocaesium interaction and its implications on soil-to-plant transfer. Studies carried out after the Chernobyl accident have shown that high 137CS soil-to-plant transfer persists in organic soils over years. In most of these soils, the specific sites in clays control radiocaesium adsorption, organic compounds having an indirect effect. Only in organic soils with more than 95% of organic matter content and negligible clay content does adsorption occur mostly on non-specific sites. After a contamination event, two main factors account for the high transfer: the low solid-liquid distribution coefficient, which is due to the low clay content and high NH4+ concentration in the soil solution, and the low K+ availability, which enhances root uptake. The estimation of the reversibly adsorbed fraction, by means of desorption protocols, agrees with the former conclusions, since it cannot be correlated with the organic matter content and shows the lack of specificity of the adsorption in the organic phase. Moreover, the time-dependent pattern of the exchangeable fraction is related to soil-plant transfer dynamics.

Reusability of plastic scintillators used in beta emitter activity determination.

The use of plastic scintillation in the measurement of beta emitter activity is a suitable alternative to classical detection techniques in spite of the high cost and potential memory effects. Reuse of the plastic scintillator beads after a cleanup procedure would overcome both drawbacks. In the present paper, we tested several cleaning solutions (water, HCl 0.1M, commercial soap, EDTA 0.01 M pH=3, citric acid 0.1 M pH=3). The recommended procedure consists of the immersion of the beads in three consecutive citric acid baths for 24 h. If this protocol is followed, plastic beads contaminated with 90Sr/90Y, 14C, and 3H recover their initial condition, and can be used in successive determinations.

A rapid method for 90Sr determination in the presence of 137Cs in environmental samples.

A rapid method for the determination of 90Sr in the presence of 137Cs using the Cherenkov radiation technique is described. The contribution of 137Cs to gross Cherenkov radiation (90Y + 137Cs) was examined for 137Cs /90Sr ratios ranging from 0.09 to 2.50 for 137Cs activities ranging from 2 to 1,211 Bq. Results from direct Cherenkov radiation measurement and results after radiochemical separation of 90Y from 90Sr for samples containing both 90Sr and 137Cs were compared. Errors below 5% were obtained for 137Cs /90Sr ratios lower than 1, when no separation was performed, independently of the activity level. However, errors between 10% and 35% were obtained for 137Cs/90Sr ratios higher than 1. In order to determine 90Sr activity in the presence of 137Cs using the Cherenkov technique, a multiple linear regression analysis model was established to correct the data for 137Cs content. The mathematical correction proposed was validated using 66 artificially contaminated lettuce samples in a laboratory experiment by taking into account the activity levels of 137Cs and 90Sr and the radionuclide ratios. Comparison of mathematically corrected radionuclide ratios with the results obtained without correction shows that, for radionuclide ratios higher than 1, error values for measuring 90Sr activity using the mathematical model were much smaller than when no radiochemical separation was performed. On the other hand, for ratios lower than 1, error values when measuring 90Sr activity with radiochemical separation were smaller than when mathematical correction was performed. In spite of this, the mathematical correction is an appropriate way of reducing the time needed to determine radiostrontium using the Cherenkov radiation technique. The method proposed could be a powerful tool for environmental research whenever the contents of 90Sr and 137Cs have to be determined.