Laurence Denaix

Structure and affinity towards Cd2+, Cu2+, Pb2+ of synthetic colloidal amorphous aluminosilicates and their precursors

Abstract Amorphous aluminosilicates were synthesised at two different initial reagent concentrations. Depending on the concentration used, the final reaction products were identified as either imogolite or allophane. In millimolar medium (millimolar Al initial concentration and Al/Si=2), imogolite precursors are synthesised during hydrolysis and condensed by heating to build up imogolite tubes. In decimolar medium, precursors with varying local structures are synthesised and condense upon heating to build up allophanes spheroids aggregates. In each medium, silica gel coprecipitated in proportions less than 10% in mass, which seems to have only a weak influence on aluminosilicate synthesis. The zero point of salt effect of suspensions of imogolite, allophane and their respective precursors were determined, and the affinity of these four products towards Cd2+ , Cu2+ and Pb2+ was studied. For imogolite and for both precursors, Cu2+ and Pb2+ adsorption can be described as specific, whereas Cd2+ adsorption is only electrostatic. The three metallic cations display specific adsorption towards allophane suspensions.

Dissolved and colloidal transport of Cd, Pb, and Zn in a silt loam soil affected by atmospheric industrial deposition

As a result of processing of metal ores, trace metals have contaminated large areas of northern France. Metal migration from the soil to groundwater presents an environmental risk that depends on the physico-chemical properties of each contaminated soil. Soil water samples were obtained over the course of 1 year with zero-tension lysimeters from an acidic, loamy, metal contaminated soil. The average trace metal concentrations in the soil water were high (e.g. for Zn 11 mg l-1 under the surface horizon), but they varied during the sampling period. Zn concentrations were not correlated with pH or total organic carbon in the solutions but were correlated with Cd concentrations. On average, 95% of the Zn and Cd but only 50% of Pb was present in a dissolved form. Analytical transmission electron microscopy was used to identify the Zn or Pb carriers. Colloids containing Pb and Zn were biocolloids, whereas colloids containing only Zn were smectites.

Characterization of heavy metals in contaminated volcanic soils of the Solofrana river valley (southern Italy)

A number of volcanic agricultural soils from the Solofrana river valley (southwestern Italy), irrigated for a long time with contaminated river water or subjected to overflowing, were collected and examined for fundamental soil parameters and total content and distribution of Fe, Cr, Cu, Mn, Ni, Pb and Zn. Micromorphological properties, the effect of main soil characteristics on the distribution of heavy metals in the various forms, and metal uptake or effects on vegetables were also investigated. Chromium and Cu were the only metal contaminants, occurring in soils in broad ranges of concentrations (Cr 62–335 and Cu 70–565 mg kg 1 ) and in the surface horizons always above the regulatory levels (Cr 150, Cu 120 mg kg 1 ), as established by the Italian Ministry of the Environment for soils of public, private and residential areas. Chromium and Cu, but also Ni, Pb and Zn, were concentrated in silt (20–2 Am) and clay ( 50%). Mn was uniformly distributed among all the extracted fractions. For all metals the soluble and exchangeable forms made a small contribution to the total. Significant amounts of Cr and Cu were recovered in the acid ammonium oxalate extraction, suggesting association of metals with shortrange-order aluminosilicates and organo–mineral complexes. The amounts of metals extracted by oxalate were found to be approximately equal to two thirds of the sequentially removed non-residual amounts. The results of DTPA extraction confirmed the low bioavailability of heavy metals in soil. The metal concentration in dwarf beans and lettuces growing on one contaminated soil did not exceed the maximum concentration recommended by the European Union. However, the enzyme activities in the bean roots indicated the induction of anti-oxidative defense mechanisms due to metallic stress. Optical microscopy (OM) showed occurrence of clay and silt coatings along elongated pores in the surface and subsurface soil horizons, suggesting a risk of metal-rich sediment transfer along the soil pore network during water movement. D 2003 Elsevier Science B.V. All rights reserved.

Physical speciation of trace metals in Fe–Mn concretions from a rendzic lithosol developed on Sinemurian limestones (France)

Abstract Because of their high content in heavy metals, Fe–Mn concretions present in soils can be a source of release of trace metals in the environment. Metal-rich concretions were isolated from a top horizon of a Rendzic Lithosol developed on limestones in France. The distribution of metallic elements (Cr, Co, Ni, Cu, Zn, Pb) was studied at different scales: field sampling, isolated concretions, and individual particles. Methods of investigation combined bulk chemical analysis, optical microscopy, X-ray diffraction (XRD) and microanalysis using scanning and transmission electron microscopes. The concretions are constituted by concentric rings and contain quartz, feldspars, kaolinite, mica, goethite, and Ti oxide as crystalline phases. A strong heterogeneity in the chemical composition is evidenced at all different scales. The total composition of different populations of Fe–Mn concretions depends on field sampling. Metals are detected at the micrometer and nanometer scales with variable frequencies, occurrences reflecting the abundance of metal-bearing components and the size of metal clusters. Statistical treatments of microanalytical data show marked trends. A strong positive correlation of Mn (and to a lesser extent of Ca) with Ni, Zn, (and to a lesser extent with Co and Cu) indicates trace metals to be associated with poorly crystallized Mn–Ca-rich areas. The correlation of Pb with Fe and P suggests its incorporation in an Fe-rich phosphate component. No correlation of metals with well crystallized silicates, Fe-sesquioxides or sulfate minerals is established. Cr was diffusely distributed.

Analytical advances in butyl-, phenyl- and octyltin speciation analysis in soil by GC-PFPD.

The development and validation of a method for organotin analysis in soils, including butyl-, phenyl- and octyl-tins, are described in this study. The influence of pretreatment step based on sample lyophilization was first studied. Different solid-liquid extraction techniques including mechanical stirring (MSAE), accelerated solvent (ASE), microwave (MAE) and ultrasound (UAE), were compared. MSAE gave the best recoveries and repeatability and was thus chosen for OTC extraction from soils. Then, ethylation/extraction step before GC-PFPD analysis was investigated and the best derivatisation conditions were assessed in order to achieve a simple, non-expensive and reliable routine procedure. Finally, the robustness of the method was tested by the analysis of several soils with different organic matter content allowing the validation of developed protocol. The method appears to be reliable and accurate for the OTC determination in a broad range of soils.

Prediction of Zinc and Cadmium Phytoavailability Within a Contaminated Agricultural Site using DGT

Environmental Context.In some agricultural areas, soils are contaminated by trace elements. This contamination of cultivated soils may constitute a serious problem for human health through the accumulation of metals in the edible parts of crops. In order to assess the risk for human health associated with metal contamination of soil, we need to develop simple tools like Diffusive Gradients in Thin Films (DGT) for predicting crop metal accumulation. The present study focuses on an agricultural site contaminated with fallout from industrial dust and reveals that DGT could be a predictive tool of zinc accumulation in lettuce. Abstract.Risk assessment of metal contamination in cultivated soils needs to address metal phytoavailability. The technique of diffusive gradients in thin films (DGT) has been shown to be a promising tool to assess metal phytoavailability in a wide range of soils. The present study has examined the ability of the DGT method to predict metal phytoavailability within a contaminated agricultural site. Lettuce (Lactuva sativa cv Appia) was grown in nine metal-contaminated soils differing mainly by their pH. Metal concentrations (Zn, Cd) in plant shoots were compared with total soil metal concentrations and free ion metal concentrations in soil pore waters, and effective concentrations, CE, measured by DGT. Plant Zn concentrations were highly related to CE, suggesting DGT can be a sensitive tool able to assess Zn phytoavailability within mildly contaminated agricultural soils. Plant Cd concentrations were less closely related to CE, signifying that processes other than Cd re-supply from the solid phase may occur during soil–plant transfer of Cd.

Kinetic degradation processes of butyl- and phenyltins in soils.

The degradation of organotin compounds (OTC) in agricultural and forest soils is studied in sandy soil samples. Individual experiments involving the three butyl- and the three phenyltins were carried out during 90 d in controlled conditions (darkness, 28 degrees C, aerobic conditions, 13% moisture) and with spiking concentration representative of environmental levels (20-50 micrg(Sn) kg(-1)). After the validation of first-order degradation kinetic model, mechanisms involved throughout the study were considered. Degradation pathways are proposed for butyl- and phenyltins and discussed according to literature data. The degradation of mono- (MBT, MPhT), di-organotins (DBT, DPhT) and TBT is clearly identified as a single successive loss of an organic group whereas TPhT is directly degraded to MPhT. The half-life times were dependent on their substitution degree, ranging from 24 (TPhT) to 220 (MBT) d. The less substituted the OTC is, the more persistent it is. In the range 4.3-5.7, pH does not seem to influence OTC degradation under the present operating conditions. Finally this study shows the significant persistence in soil samples in our experimental conditions for most of studied organotins and highlights the potential impact on soil quality.

Tributyltin and triphenyltin uptake by lettuce.

This paper provides quantitative information on the transfer of TBT (tributyltin) and TPhT (triphenyltin) from sludged soil to cultivated lettuce. The effect of their initial concentrations in the soil (varying from 20 to 50 microg(Sn)kg(-1) for each triorganotin), sludge amount (between 1% and 9%), and cultivation duration (32-54 days) was evaluated by means of experimental designs. The impact of the cultivation temperature at 13 degrees C and 19 degrees C on organotin fate in the soil/plant system was also considered. The final concentration of a given organotin in the plant roots was found to depend directly on its initial concentration in the soil. A total of (85+/-15)% of initial TBT in the soil was still present at the end of the experiments, regardless of the cultivation duration. Consequently, TBT appeared to be taken up by lettuce continually. A total of (75+/-5)% of TPhT was found to be degraded in the soil at 54 days. So, this compound could have been taken up by the plant at the beginning of the cultivation. Sludge amount seemed to have a negative effect on TPhT concentration in a plant at 32 days. This could be due to the quantitative TPhT sorption onto the sludge, observed just after spiking. Organotin plant uptake appeared to be more important at 19 degrees C than at 13 degrees C. TBT and TPhT were mainly accumulated in the roots, and up to 2% and 10% of TPhT and TBT, respectively, were translocated to the shoots. Despite TPhT degradation, products in large amounts were present in the soil and were not significantly taken up by the plant. They possibly remained immobilized on solid phases of the sludged soil.

Multimetallic contamination from Zn-ore smelter: solid speciation and potential mobility in riverine floodbank soils of the upper Lot River (SW France)

The former Zn-ore smelting activity in Viviez (Aveyron, France) resulted in multimetallic contamination of the upper Lot River system (SW France). This study addresses for the first time the metals/metalloids mobility in impacted riverside fluvial soils due to reducing conditions during long-term flooding events. Six impacted riverside fluvio-soils were sampled along the Riou Mort and Lot rivers. Their levels of contamination decrease with the distance from the contamination source. Higher enrichment factors (EF) relative to French average soil metallic content occur 1 km far from the contamination source and vary from 3 for Sn, to 5 for As, 9 for Sb, 27 for Pb, 40 for Zn and 63 for Cd. At 20 km downstream from the contamination source, EF still reach a value of 3 for Cd and Zn. A micro-physical mineralogical characterisation of contaminated soils revealed a variety of metal-bearing phases: metallic compounds, oxides and sulphides, Fe oxides, glass and silicates as well as coke. Sequential chemical extraction experiments were conducted on the most contaminated soil in order to identify which mineral phases were the best candidates to release metals/metalloids. At the end of experiments more than 70 % of total Cd and As, 55 % of Zn and Sb, and 40 % of Pb and Sn were extracted from the soil. Only Cd appeared as readily mobilised, with 33 % of its total amount being extracted in the first steps of experiments. Under reducing conditions, iron oxyhydroxides, franklinite and multimetallic oxides are the best candidates, in decreasing order of importance, for metals/metalloids release from the soil.

Cadmium speciation assessed by voltammetry, ion exchange and geochemical calculation in soil solutions collected after soil rewetting

Analytical techniques and speciation models have been developed to characterize the speciation of Cd in soil solution. They provide an estimate of operationally defined species of Cd that need to be compared, especially for soil solutions highly concentrated in organic matter as are the solutions collected after soil rewetting. This work deals with the comparison between the speciation of Cd measured by anodic stripping voltammetry (ASV) and ion exchange and the speciation of Cd calculated using Visual MINTEQ. The aim of this study was to quantify and explain the differences in Cd speciation observed between the three approaches. Cd speciation was assessed in soil solutions collected 4, 8, 24, 48, 96 and 144h after the rewetting of an air-dried contaminated soil. To optimize the computed speciation of Cd, other physico-chemical parameters were followed (e.g. pH, ionic strength and the concentrations of major anions, major cations and dissolved organic carbon) and a brief characterisation of dissolved organic matter (DOM) was performed. The discrepancy between model predictions and analytical measurements highlighted the need for caution in the interpretation of geochemical speciated data for Cd. The major result of this study was that a characterization of DOM based on its specific UV-absorbance at 254 nm improved the accuracy of model predictions. Another finding is that labile Cd complexes, even organic, may have been included in the electrochemically labile fraction of Cd measured by ASV.