This study investigated the adsorption of Cu2+ and Pb2+ onto a histosol (peat soil) as a function of pH and compared it to their adsorption onto its humin fraction. The use of the NICA-Donnan model, considering humic acid and humin as soil reactive solid phases and fulvic acid as reactive dissolved organic matter, satisfactorily described the adsorption behaviour of Cu2+ and Pb2+ onto histosol. Both metals were adsorbed mainly via carboxylic sites of both solid phases with a higher contribution of humic acid. Nevertheless, this study highlighted the significant role of humin, accounting for up to 37

Humin, which is the insoluble part of humic substances, plays an important role in regulating the behavior and fate of metallic trace elements at the soil/water interface. However, compared to the two other fractions of humic substances, humic and fulvic acids, humin has been the least studied due to its insolubility and difficulties in purification. In this study, humin was extracted from a peat soil following the International Humic Substances Society (IHSS) protocol. The adsorption behavior of copper(II) and lead(II) onto humin as a function of pH was studied at different solid charges and metallic cation concentrations and was described by the NICA–Donnan model. The proportion of the two types of functional groups considered in this model, carboxylic and phenolic groups, was determined by cross polarization/magic angle spinning solid-state 13C nuclear magnetic resonance spectroscopy (13C CP/MAS NMR). The NICA–Donnan model was applied to describe the adsorption of copper(II) and lead(II) onto humin using generic parameters previously defined for humic acids with only few parameter adjustments. This approach allowed a good description of experimental adsorption data at the different tested conditions with the main involvement of carboxylic moieties in the metallic cation adsorption. This study highlights the reactivity of humin, an important fraction of soil organic matter little studied until now, toward copper(II) and lead(II) and proposes, for the first time, a simple and pertinent approach using the NICA–Donnan model to successfully describe and predict the binding of these two metallic cations onto humin.

La prise en compte des connaissances locales de la variabilite de surface du sol constitue un levier pour optimiser la production vegetale et elaborer des strategies de gestion durable des agrosystemes saheliens. L'objectif de cette etude est d'evaluer les connaissances locales sur la variabilite de surface du sol et la gestion des contraintes pedologiques pour la production du niebe au Niger. Pour y parvenir, des enquetes semi-directives ont ete conduites au sud de la region de Tillaberi et a l'extreme nord de la region de Maradi. Ces deux regions offrent des conditions agro-ecologiques, pedoclimatiques (climat, sols, pratiques culturales) et socio-economiques (utilisation et commercialisation) differentes vis-a-vis de la culture du niebe. Au total, 600 producteurs de niebe ont ete soumis a un questionnaire semi-structure visant (1) a determiner leurs connaissances de la variabilite de surface du sol et (2) a hierarchiser les entites homogenes de la surface de leurs champs selon leurs potentiels productifs et leurs niveaux de fertilite. Les resultats obtenus ont revele que 96 % des producteurs enquetes sur l'ensemble des sites sont conscients de la variabilite de surface du sol. Ils reconnaissent que la variabilite de la surface du sol est liee a la nature du sol, le travail du sol, l'erosion, la topographie ou le type de vegetation. L'erosion des sols apparait comme une cause de la variabilite de surface pour 57 a 61 % des producteurs de la region de Tillaberi, tandis que dans la region de Maradi, les producteurs identifient la nature du sol (61 %), la topographie (39 %) et le couvert vegetal (36 %) comme principales causes de la variabilite de surface du sol. Les entites de surface a croutes structurales sous houppier de Faidherbia albida sont considerees comme les plus productives pour 41 a 67 % des paysans interroges. Les entites de surface a croutes structurales et a croutes d'erosion sont considerees comme etant les moins productives. Les resultats presentes dans cette etude permettront de faciliter le dialogue entre les producteurs, les conseillers agronomiques et les chercheurs en vue de proposer des solutions pour ameliorer la production du niebe dans des parcelles avec une grande heterogeneite de surface en zone sahelienne.

Les sols viticoles contiennent des traces metalliques, notamment de cuivre, du fait de decennies d'application de produits phytosanitaires. Etude de l'impact que cela peut avoir sur la biomasse microbienne des sols, ainsi que sur les invertebres.

Anthropogenic inputs of trace elements (TE) into soils constitute a major public and environmental health problem. Bioavailability of TE is strongly related to the soil physicochemical parameters and thus to the ecosystem type. In order to test whether soil parameters influence the response of the bacterial community to TE pollution, we collected soil samples across contrasting ecosystems (hardwood, coniferous and hydromorphic soils), which have been contaminated in TE and especially lead (Pb) over several decades due to nearby industrial smelting activities. Bacterial community composition was analysed using high throughput amplicon sequencing and compared to the soil physicochemical parameters. Multivariate analyses of the pedological and biological data revealed that the bacterial community composition was affected by ecosystem type in the first place. An influence of the contamination level was also evidenced within each ecosystem. Despite the important variability in bacterial community structure, we found that specific bacterial groups such as γ-Proteobacteria, Verrucomicrobia and Chlamydiae showed a consistent response to Pb content across contrasting ecosystems. Verrucomicrobia were less abundant at high contamination level whereas Chlamydiae and γ-Proteobacteria were more abundant. We conclude that such groups and ratio's thereof can be considered as relevant bioindicators of Pb contamination.

Trace element (TE) speciation modelling in soil solution is controlled by the assumptions made about the soil solution composition. To evaluate this influence, different assumptions using Visual MINTEQ were tested and compared to measurements of free TE concentrations. The soil column Donnan membrane technique (SC-DMT) was used to estimate the free TE (Cd, Cu, Ni, Pb and Zn) concentrations in six acidic soil solutions. A batch technique using DAX-8 resin was used to fractionate the dissolved organic matter (DOM) into four fractions: humic acids (HA), fulvic acids (FA), hydrophilic acids (Hy) and hydrophobic neutral organic matter (HON). To model TE speciation, particular attention was focused on the hydrous manganese oxides (HMO) and the Hy fraction, ligands not considered in most of the TE speciation modelling studies in soil solution. In this work, the model predictions of free ion activities agree with the experimental results. The knowledge of the FA fraction seems to be very useful, especially in the case of high DOM content, for more accurately representing experimental data. Finally, the role of the manganese oxides and of the Hy fraction on TE speciation was identified and, depending on the physicochemical conditions of the soil solution, should be considered in future studies.

Major and trace elements in soils originate from natural processes and different anthropogenic activities which are difficult to discriminate. On a 17-ha impacted site in northern France, two industrial sources of soil contamination were xidentified: a former iron foundry and a current secondary lead smelter. To discriminate and map natural and anthropogenic sources of major and trace elements on this site, the rarely applied MULTISPATI-principal component analysis (PCA) method was used. Using a 20-m × 20-m grid, 247 topsoil horizons were sampled and analysed with a field-portable X-ray fluorescence analyser for screening soil contamination. The study site was heavily contaminated with Pb and, to a lesser degree, with Sn. Summary statistics and enrichment factors allowed the differentiation of the main lithogenic or anthropogenic origin of the elements. The MULTISPATI-PCA method, which explained 73.9 % of the variability with the three first factors, evidenced strong spatial structures. Those spatial structures were attributed to different natural and artificial processes in the study area. The first axis can be interpreted as a lithogenic effect. Axes 2 and 3 reflect the two different contamination sources. Pb, Sn and S originated from the secondary lead smelter while Fe and Ca were mainly derived from the old iron foundry activity and the old railway built with foundry sand. This study demonstrated that the MULTISPATI-PCA method can be successfully used to investigate multicontaminated sites to discriminate the various sources of contamination.

Smelting activities are one of the most common sources of trace elements in the environment. The aim of this study was to determine the lead distribution in upper horizons (0–5 and 5–10cm) of acidic soils in the vicinity of a lead-acid battery recycling plant in northern France. The combination of chemical methods (sequential extractions), physical methods (Raman microspectroscopy and scanning electron microscopy with an energy dispersive spectrometer) and multi-surface complexation modelling enabled an assessment of the behaviour of Pb. Regardless of the studied soil, none of the Pb-bearing phases commonly identified in similarly polluted environments (e.g., anglesite) were observed. Lead was mainly associated with organic matter and manganese oxides. The association of Pb with these soil constituents can be interpreted as evidence of Pb redistribution in the studied soils following smelter particle deposition.

To assess the influence of the composition of dissolved organic matter (DOM) on metal speciation, two models have been used: Model VI and NICA-Donnan. The speciation of Cu, Ni, Pb and Zn in the soil solution of 36 samples characterized by alkaline pH and different contamination levels has been determined. Four assumptions about DOM composition have been tested: (i) 100% of humic substances (HS) are fulvic acids (FA), (ii) 100% are humic acids (HA), (iii) 35% are HA and 65% FA and (iv) 84% are HA and 16% FA. The results obtained with the two distinct models are of the same order of magnitude; however, few differences have been highlighted regarding the description of the non-specific interactions, the Zn–FA interactions and the lowest free ion concentrations. The main result of this study is that the free ion concentrations calculated with the two models may differ by one order of magnitude depending on whether HA and/or FA are used to represent DOM. This work demonstrates the impact of the assumptions made about the DOM nature for metal speciation modelling.

Field portable X-ray fluorescence (FPXRF) technology can offer a rapid and cost-effective determination of the total elemental concentrations in soils. The aims of this study were (i) to test the capability of FPXRF to predict the element concentrations of a very large soil sample set and (ii) to assess the influence of soil moisture, known to strongly affect the quality of FPXRF analyses.

A method for the simultaneous determination of methylated, ethylated and butylated tin compounds in landfill leachates has been developed in this work. The assessment of the organotin compound composition has been achieved by the development of a specific GC-ICP-MS protocol adapted to these complex matrices. The analytical procedure consists in three major steps which have been carefully optimized, taking into account the variety of alkyltin compounds and the high organic content of the leachate matrix: nitric acid digestion under microwave, derivatization using sodium tetrapropylborate and chromatographic separation. Different quantification approaches are proposed for the determination of the alkyltin species in the leachates. In this way, isotope dilution analyses in the species-specific and species-unspecific spiking modes have been found to provide results in agreement with external and internal calibration approaches. A single analysis with an addition of three isotopically enriched butyltin species is found to be suitable for the routine quantitative and semi-quantitative determination of all occurring alkyltin species in landfill leachates. The different qualitative and quantitative GC-ICP-MS complementary approaches developed in this work allow the full organotin composition assessment of landfill leachates.

Due to the complex nature of landfill leachates, metal and metalloid analyses prove to be tricky and suffer from a lack of standard protocols. A complete approach has been adopted to investigate the influence of the different steps during the sample processing of French landfill leachates. The validation of the entire protocol has been achieved using a laboratory reference material. This material, which is a real landfill leachate, is representative of real samples. Its evaluation has allowed a quality control for metal and metalloid analyses in landfill leachates. Precautions concerning storage temperature, aeration and filtration are proposed to perform accurate metal analyses in these complex matrices. The sample processing has been applied to the seasonal monitoring of a French landfill. The assessment of major leachate metallic contaminants such as As, Cr, Sb, Sn, has been performed by evaluating the relative enrichment of metals and metalloids in comparison with rain water and groundwater. In addition, hydrological data are useful and complementary information for pointing out the main factors affecting metal concentrations and thus their potential remobilisation pathways.