A new method based on selective fluorescent polymers (PSresin) for the analysis of 90Sr in presence of 210Pb in environmental samples.

90Sr is of major concern in emergency and environmental control plans. It is one of the main fission products in nuclear facilities and is a high-energy beta emitter that presents chemical properties similar to those of calcium. 90Sr is commonly detected using methods based on liquid scintillation counting (LSC) following a chemical separation to remove potential interferences. However, these methods generate mixed wastes (hazardous and radioactive). In recent years, an alternative strategy using PSresins has been developed. For 90Sr analysis with PSresins, 210Pb is the main interferent that should be considered, as it is also strongly retained in the PSresin. In this study, a procedure was developed involving a precipitation with iodates to separate lead from strontium before the PSresin separation. Moreover, the method developed was compared with well-established and routinely used methods based on LSC, revealing that the new method produced equivalent results in less time and with less waste generation.

Effect of ageing on the availability of heavy metals in soils amended with compost and biochar: evaluation of changes in soil and amendment properties.

Remediation strategies using soil amendments should consider the time dependence of metal availability to identify amendments that can sustainably reduce available pollutant concentrations over time. Drying-wetting cycles were applied on amendments, soils and soil + amendment mixtures, to mimic ageing at field level and investigate its effect on extractable Cd, Cu, Ni, Pb and Zn concentrations from three contaminated soils. The amendments investigated were municipal waste organic compost and biochars. The amendments, soils and mixtures were characterised by their physicochemical properties at different ageing times. The amendments were also characterised in terms of sorption capacity for Cd and Cu. The sorption capacity and the physicochemical properties of the amendments remained constant over the period examined. When mixed with the soils, amendments, especially the compost, immediately reduced the extractable metals in the soils with low pH and acid neutralisation capacity, due to the increase in pH and buffering capacity of the mixtures. The amendments had a relatively minor impact on the metal availability concentrations for the soil with substantially high acid neutralisation capacity. The most important changes in extractable metal concentrations were observed at the beginning of the experiments, ageing having a minor effect on metal concentrations when compared with the initial effect of amendments.

Removal of Cd, Cu, Pb, and Zn from aqueous solutions by biochars.

Sorption and desorption of heavy metals (Cd, Cu, Pb, and Zn) was evaluated in biochars derived from sugarcane bagasse (SB), eucalyptus forest residues (CE), castor meal (CM), green coconut pericarp (PC), and water hyacinth (WH) as candidate materials for the treatment of contaminated waters and soils. Solid-liquid distribution coefficients depended strongly on the initial metal concentration, with K d,max values mostly within the range 10(3)-10(4) L kg(-1). For all biochars, up to 95 % removal of all the target metals from water was achieved. The WH biochar showed the highest K d,max values for all the metals, especially Cd and Zn, followed by CE (for Cd and Pb) and PC (for Cd, Pb, and Zn). Sorption data were fitted satisfactorily with Freundlich and linear models (in the latter case, for the low concentration range). The sorption appeared to be controlled by cationic exchange, together with specific surface complexation at low metal concentrations. The low desorption yields, generally less than 5 %, confirmed that the sorption process was largely irreversible and that the biochars could potentially be used in decontamination applications.

Sorption behaviour of nonylphenol and nonylphenol monoethoxylate in soils.

Sorption behaviour of two alkylphenolic compounds (APCs), nonylphenol (NP) and nonylphenol monoethoxylate (NP1EO), was studied in five soils with contrasting characteristics. Sorption isotherms were obtained by equilibrating the soil samples with 0.01 mol L(-1) CaCl2 solutions containing different initial concentrations of NP or NP1EO. Linear fitting was generally appropriate for describing the sorption behaviour of NP and NP1EO in the soils, with the exception of two cases, for which the Freundlich model was more suitable for describing the sorption pattern of NP1EO. Solid-liquid distribution coefficients derived from sorption isotherms (Kd) varied from 24 to 1059 mL g(-1) for NP and from 51 to 740 mL g(-1) for NP1EO. For most soils, sorption Kd values were higher for NP than for NP1EO due to the higher hydrophobicity of NP. Sorption reversibility of NP and NP1EO was also tested from desorption isotherms. Desorption solid-liquid distribution coefficients (Kd,des), obtained from linear fitting, were between 130 and 1467 mL g(-1) for NP and between 24 and 1285 mL g(-1) for NP1EO. Kd,des values were higher than Kd values, which demonstrated that target compounds were irreversibly sorbed into soils, with the exception of the high desorption yield (45%) of NP1EO in the soil with the lowest content of organic matter. The fraction of soil organic carbon (FOC) was a key parameter that influenced the sorption of NP and NP1EO in soils, with logKOC values of 4.0 and 3.8, respectively.

Viability of organic wastes and biochars as amendments for the remediation of heavy metal-contaminated soils.

Composts derived from municipal (MOW and MSW) and domestic wastes (DOM), wastes from the olive oil industry (OWH and OP), green waste (GW), and biochars (BF and BS) were investigated to test their viability for remediating metal-contaminated soils. In addition to common analyses, the characterisation included structural analyses (FTIR and (13)C NMR), determination of the acid neutralisation capacity (ANC) and the construction of sorption isotherms for target metals (Pb, Zn, Cd, Ni and Cu). MOW and GW had the highest ANC values (4280 and 7100 meq kg(-1), respectively), and MOW, GW, DOM, BF and BS exhibited the highest solid-liquid distribution coefficients (Kd) with maximum values in the 10(4) L kg(-1) range. Sorption isotherms were fitted using linear and Freundlich models for better comparison of the sorption capacities of the materials. Based on their basic pH, high ANC and high sorption capacity, MOW, GW and biochars are the most promising materials.

Remediation of metal-contaminated soils with the addition of materials - part II: leaching tests to evaluate the efficiency of materials in the remediation of contaminated soils.

The effect of the addition of materials on the leaching pattern of As and metals (Cu, Zn, Ni, Pb, and Cd) in two contaminated soils was investigated. The examined materials included bentonites, silicates and industrial wastes, such as sugar foam, fly ashes and a material originated from the zeolitization of fly ash. Soil + material mixtures were prepared at 10% doses. Changes in the acid neutralization capacity, crystalline phases and contaminant leaching over a wide range of pHs were examined by using pH(stat) leaching tests. Sugar foam, the zeolitic material and MX-80 bentonite produced the greatest decrease in the leaching of pollutants due to an increase in the pH and/or the sorption capacity in the resulting mixture. This finding suggests that soil remediation may be a feasible option for the reuse of non-hazardous wastes.

Remediation of metal-contaminated soils with the addition of materials--part I: characterization and viability studies for the selection of non-hazardous waste materials and silicates.

Contamination episodes in soils require interventions to attenuate their impact. These actions are often based on the addition of materials to increase contaminant retention in the soil and to dilute the contaminant concentration. Here, non-hazardous wastes (such as sugar foam, fly ash and a material produced by the zeolitization of fly ash) and silicates (including bentonites) were tested and fully characterized in the laboratory to select suitable materials for remediating metal-contaminated soils. Data from X-ray fluorescence (XRF), N(2) adsorption/desorption isotherms, X-ray diffraction (XRD) and scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM-EDX) analyses revealed the chemical composition, specific surface area and the phases appearing in the materials. A pH titration test allowed the calculation of their acid neutralization capacity (ANC). The metal sorption and desorption capacities of the waste materials and silicates were also estimated. Sugar foam, fly ash and the zeolitic material were the best candidate materials. Sugar foam was selected because of its high ANC (17000 meq kg(-1)), and the others were selected because of their larger distribution coefficients and lower sorption reversibilities than those predicted in the contaminated soils.

Comparison of mechanistic and PLS-based regression models to predict radiocaesium distribution coefficients in soils.

Radiocaesium sorption interaction descriptors were examined in 30 soil samples from Spain. Mechanistic and regression models were used to predict the solid-liquid distribution coefficients of radiocaesium (K(d)(Cs)) based on soil properties, and the obtained values were compared with the experimental ones, which were derived from batch experiments. The batch experiments used two contact solutions: one simulated the composition of the soil solution, and the other was the wash-off from the soil. Several mechanistic models of different complexity were tested based on the Radiocaesium Interception Potential (RIP), with satisfactory agreement between experimental and predicted values. A simplified model based on either the RIP, or the clay content and K status of the soil was proposed. Various multivariant regression models, which were constructed using the Partial Least Square Regression (PLS), were also evaluated. The RIP, clay content, and the K and NH(4)(+) contents were also identified by the regression models as the most relevant soil parameters to predict the K(d). As seen for the mechanistic models, the goodness of fit of the regression models was demonstrated by an excellent agreement between experimental and predicted values.

The use of hard- and soft-modelling to predict radiostrontium solid-liquid distribution coefficients in soils.

The solid-liquid distribution coefficient (K(d)) is the parameter that governs the incorporation of contaminants in soils. Its estimation allows the prediction of the fate of contaminants in the short- and long-term after a contamination event. Here, the K(d) of radiostrontium (K(d)(Sr)), a radionuclide of significant environmental interest, was predicted by hard models, which are based on knowledge of the mechanisms governing its sorption, and by soft models based on Partial Least Squares (PLS), using a large data set with the main soil parameters. The two approaches were tested and compared for 30 soils in Spain. Correlations between the predicted and experimental values of K(d)(Sr) obtained using hard- and soft-modelling showed slopes close to 1 and regression coefficients higher than 0.95, which confirms that both approaches are able to obtain satisfactory estimates for K(d)(Sr) from soil parameters.

Comparison of laboratory methodologies for evaluating radiostrontium diffusion in soils: planar-source versus half-cell methods.

A planar-source method, initially designed to obtain diffusion coefficients in compacted clay, is adapted here to determine the apparent diffusion coefficient (D(a)) of radiostrontium in soils representative of the Spanish territory. Experiments were carried out by varying the moisture content (F(moist)), and bulk dry density (ρ(bulk)) of the soil samples, in order to study the influence of these soil packing parameters on D(a) values. The moisture in the soil samples was established as the percentage of occupancy of each soil's field capacity (OFC). For a similar OFC, D(a) values in the examined soils ranged by approximately one order of magnitude (e.g. from 6.2 × 10(-)(11) to 6.5 × 10(-)(12)m(2)s(-)(1), at 100% of OFC; from 3.0 × 10(-)(11) to 3.8 × 10(-)(12)m(2)s(-)(1), at 60% of OFC). For a given soil, D(a) values increased when water content was increased. F(moist), and tortuosity (τ) explained D(a) variability, with R(2) values usually over 0.9. However, no good simple or multiple regressions between the soil packing parameters and D(a) were obtained with the whole dataset of all soils, which indicated that soil sorption capacity affects the diffusion of reactive radionuclides in soils. The inclusion of calculated K(d) values in the multiple regressions improved the correlations in all cases. Finally, D(a) values were compared with those obtained by the application of a half-cell method. The values of D(a) obtained by the planar-source methods were systematically lower than the half-cell ones, with a good correlation between the D(a) derived from both methods (R(2)=0.98).

Diffusion experiments for estimating radiocesium and radiostrontium sorption in unsaturated soils from Spain: comparison with batch sorption data.

As sorption data obtained from batch tests are often used to estimate pollutant transport in unsaturated soils, comparison between sorption data obtained in the two conditions is required to ensure a correct risk assessment. With this aim, radiostrontium and radiocesium apparent diffusion coefficients (D(a)) were quantified in nine unsaturated soils, and the derived distribution coefficients (K(d)) were compared with K(d) data from batch experiments. The D(a)(Sr) and the D(a)(Cs) ranged from 1.8x10(-11) to 1.5x10(-10) m(2) s(-1), and from 1.0x10(-13) to 5.9x10(-11) m(2) s(-1), respectively. The D(a)(Sr) varied according to both soil packing parameters and properties governing Sr interaction. For Cs, the soil sorption properties explained the variation on D(a)(Cs). The K(d) values derived from D(a) (from 0.014 to 1.8 L kg(-1) for Sr; from 0.55 to 942 L kg(-1) for Cs) were lower than from batch tests (from 1 to 97 L kg(-1) for Sr; from 10 to 14,600 L kg(-1) for Cs), thus indicating that batch data may not accurately describe radionuclide transport in unsaturated soils. However, the two sets of data correlated well, thus suggesting that radionuclide transport can be estimated from batch tests, which are faster than diffusion experiments.

Laboratory experiments to characterize radiochloride diffusion in unsaturated soils.

Diffusion transport of (36)Cl was examined in seven soils under unsaturated conditions in tubes packed with two portions of each soil having different (36)Cl activity concentrations. Apparent diffusion coefficients (D(a)) derived from diffusion profiles varied within a narrow range (from 3x10(-10) to 7x10(-10) m(2) s(-1)) confirming the minor effect of soil properties on the diffusion of a non-reactive radionuclide like (36)Cl. Instead, packing conditions had a major effect. Solid-liquid distribution coefficients (K(d)) derived from D(a) (0.02-0.2 L kg(-1)) were systematically lower than those obtained from batch experiments (0.6-1.0 L kg(-1)), but with a similar variation pattern among soils. The low values of K(d) (Cl) confirmed an almost negligible radiochloride-soil interaction.

New best estimates for radionuclide solid-liquid distribution coefficients in soils. Part 2: naturally occurring radionuclides.

Predicting the transfer of radionuclides in the environment for normal release, accidental, disposal or remediation scenarios in order to assess exposure requires the availability of an important number of generic parameter values. One of the key parameters in environmental assessment is the solid liquid distribution coefficient, K(d), which is used to predict radionuclide-soil interaction and subsequent radionuclide transport in the soil column. This article presents a review of K(d) values for uranium, radium, lead, polonium and thorium based on an extensive literature survey, including recent publications. The K(d) estimates were presented per soil groups defined by their texture and organic matter content (Sand, Loam, Clay and Organic), although the texture class seemed not to significantly affect K(d). Where relevant, other K(d) classification systems are proposed and correlations with soil parameters are highlighted. The K(d) values obtained in this compilation are compared with earlier review data.

New best estimates for radionuclide solid-liquid distribution coefficients in soils. Part 3: miscellany of radionuclides (Cd, Co, Ni, Zn, I, Se, Sb, Pu, Am, and others).

New best estimates for the solid-liquid distribution coefficient (K(d)) for a set of radionuclides are proposed, based on a selective data search and subsequent calculation of geometric means. The K(d) best estimates are calculated for soils grouped according to the texture and organic matter content. For a limited number of radionuclides this is extended to consider soil cofactors affecting soil-radionuclide interaction, such as pH, organic matter content, and radionuclide chemical speciation. Correlations between main soil properties and radionuclide K(d) are examined to complete the information derived from the best estimates with a rough prediction of K(d) based on soil parameters. Although there are still gaps for many radionuclides, new data from recent studies improve the calculation of K(d) best estimates for a number of radionuclides, such as selenium, antimony, and iodine.

New best estimates for radionuclide solid-liquid distribution coefficients in soils. Part 1: radiostrontium and radiocaesium.

Best estimates for the solid-liquid distribution coefficients (K(d)) of radiostrontium and radiocaesium for various soil types, were derived from geometric means (GM) calculated from grouping soils by texture and organic matter content, and also using soil cofactors governing soil-radionuclide interaction. The K(d) (Sr) GM for Sand, Loam, Clay and Organic groups were similar, although the value for the Sand group was significantly lower. The Sr cofactor approach, based on the ratios of cation exchange capacity (CEC) to Ca and Mg concentrations in the soil solution, leads to K(d) (Sr) GM with a lower variability, from which best estimates could be proposed. The K(d) (Cs) GM for Sand and Organic groups differed, although similar values were obtained for Loam and Clay groups. Grouping the K(d) (Cs) according to the Radiocaesium Interception Potential (RIP) and the RIP divided by the K concentration in the soil solution also allows to suggest K(d) (Cs) best estimates with a lower variability.

pH(stat) vs. single extraction tests to evaluate heavy metals and arsenic leachability in environmental samples.

Here we compared the pH(stat) test, which examines the leachability of major elements (Ca, Mg, Al, Fe, and Mn), dissolved organic carbon, and trace elements (Cd, Zn, Cu, Pb, and As) in a wide pH range, with single extraction tests based on the use of mild extractants (calcium chloride, acetic acid or EDTA). For this purpose, we examined samples from a variety of environmental conditions (sludges, mineral soils, organic soils, and soils with particulate and/or soluble contamination). Extraction yields obtained with CaCl(2) (0.01 mol L(-1)) and CH(3)COOH (0.43 mol L(-1)) correlated well with those from the pH(stat) at the same pH (r=0.98 and 0.95, respectively), while the use of EDTA (0.05 mol L(-1)) led to systematically higher extraction yields than those quantified with the pH(stat) at the same pH. However, the pH(stat) test had three distinct advantages: (1) it revealed the relationship between the solubility of the main soil phases and pH; (2) it showed the variation in pollutant leachability due to changes in pH; and (3) it better predicted the maximum contaminant availability. Thus we propose that the pH(stat) is the best laboratory tests to evaluate the contaminant leachability over a wide range of sample types (soil, sludge, and sediment).

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.

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.

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.

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.