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This study compared effects of pH, ionic strength and complexation with Mg2+ on the chromophores and fluorophores of aquatic and terrestrial NOM exemplified by the standard isolates Suwannee River fulvic and humic acid (SRFA and SRHA) and Pahokee Peat fulvic and humic acids (PPFA and PPHA) provided by the International Humic Substance Society (IHSS). The intensity of the differential spectra of the NOM isolates increased monotonically with pH. These spectra comprised contributions of similar chromophore systems associated with the carboxylic and phenolic moieties. The intensity of SRFA and PPFA fluorescence changed non-monotonically vs. pH indicating that the deprotonation of the phenolic fluorophores decreased their emission yields. Examination of the effects of pH on the slopes of the log-transformed absorbance of NOM showed that the influence of deprotonation on the conformations of PPFA and PPHA molecules was less prominent than those for SRFA but not dissimilar to those of SRHA. Changes of the differential spectra and spectral slopes showed that Mg2+/PPFA and Mg2+/PPHA complexation was more effected by electrostatic interactions while the involvement of phenolic groups was notable for SRFA. The observed trends highlight similarities and differences in the properties of the chromophores and fluorophores in the standard isolates of soil and aquatic NOM. These results necessitate further systematic comparison of the properties of NOM isolates and those of unaltered NOM.

The difficulties when studying the behavior of engineered nanoparticles (ENPs), and the subsequent metal speciation in aquatic ecosystems, at environmentally relevant concentrations (i.e., ppt level) are often related to the occurrence of ENP constitutive elements at high concentrations as a background in aquatic media. In this study, the physicochemical behavior of CdSe/ZnS quantum dots (QDs) when spread at very low concentrations in surface waters was investigated. The above-mentioned issues were overcome with the use of isotopically labeled QDs, separated by centrifugal ultrafiltration (CU) and measured by high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS), combined with the detection of free and labile metal ions by scanned stripping chronopotentiometry (SSCP). They firmly provided a thorough comprehension regarding the transformation of QDs in surface waters. The physicochemical conditions of the medium including the presence of an analog of natural organic matter and a mineral (i.e., fulvic acid and goethite), the manufactured coating of the QDs [here thioglycolic acid (TGA)], and the occurrence of added Zn in the medium were considered in the study. The overall results show that, in the absence of mineral/organic matter, the TGA ligands in solution that detached from the QD surface after dissolution control the metal speciation, especially for Cd. Conversely, in a more representative aquatic ecosystem condition (i.e., with Zn in the background media together with fulvic acid and goethite), almost no Zn or Cd dissolution from the QDs is detected. SSCP measurements reveal that the Zn complexes formed with the organic/mineral material in the system are inert, whereas the speciation model calculations indicated that Cd2+ is bound to TGA ligands in solution and organic/inorganic matter—therefore suggesting that, under the studied conditions, aquatic organisms will be exposed to a very low concentration of free and labile metal ions issued from the QDs.

Natural organic matter (NOM) is known to play an important role in the transport and binding of trace metal elements in aquatic and soil systems. Thallium is a pollutant for which the extent of the role played by NOM is poorly known. Consequently, this study investigates thallium(I) and its complexation to a purified humic substance as proxy for NOM. Experiments were performed with the Donnan Membrane Technique to separate, for the first time, the free Tl+ ion from its complexed form in the bulk solution. Various pH and concentrations were investigated at constant ionic strength and constant NOM proxy concentrations in solution. Experimental results were described with NICA-Donnan model. Thallium complexation was compared to silver complexation using literature data and using the same NICA-Donnan formalism. Parameters for these two cations (Tl+ and Ag+) are reported in this article, for the first time. Results display low thallium complexation to the NOM proxy while silver competes with divalent cations for the NOM binding sites. Calculated speciation for dissolved thallium highlights the dominance of free thallium (Tl+) in solution whereas Tl-NOM complexes contribute roughly 15% to total Tl(I) species in river and lake type waters. Similar results are obtained for soil solutions, Tl-bound to NOM

International audience; The increasing application of Quantum Dots (QDs) is cause of concern for the potential negative effects for the ecosystem, especially in soils that may act as a sink. In this study, soil leaching experiments were performed in quartz sand packed columns to investigate the behavior of core-shell CdSe/ZnS QDs coated with either small ligands (TGA-QDs) or more complex polymers (POAMA-QDs). Fluorescence emission was compared to mass spectrometric measurements to assess the nanoparticles (NPs) state in both the leachate (transported species) and porous media (deposited amounts). Although both QDs were strongly retained in the column, large differences were observed depending on their capping ligand stability. Specifically, for TGA-QDs elution was negligible and the retained fraction accumulated in the top-columns. Furthermore, 74% of the NPs were degraded and 38% of the Se was found in the leachate in non-NPs state. Conversely, POAMA-QDs were recovered to a larger extent (78.1%), and displayed a higher transport along the soil profile. Further experiments with altered NPs showed that homo-aggregation of the QDs prior injection determined a reduced mobility but no significant changes in their stability. Eventually, ageing of the NPs in the column (15 days) caused the disruption of up to 92% of the original QDs and the immobilization of NPs and metals. These results indicate that QDs will accumulate in top-soils, where transformations phenomena will determine the overall transport, persistency and degradation of these chemicals. Once accumulated, they may act as a source for potentially toxic Cd and Se metal species displaying enhanced mobility.

Fluorescence of the hydrophobic acid fraction (HPOA) of Suwannee River natural organic matter and Tb3+ excitation spectra were measured in tandem using the instantaneous and time-resolved emission modes. The intensity of HPOA fluorescence decreased in the presence of Tb3+, while the intensity of the emission from Tb3+ cations bound by HPOA increased by up to several orders of magnitude due to energy transfer (ET) from HPOA to Tb3+ ions. To determine intrinsic ET and fluorescence quenching (FQ) coefficients, NICA–Donnan modeling was carried. It showed that phenolic groups in HPOA dominated both the ET and FQ processes and that the binding of Tb3+ by HPOA could be described using the non-ideality parameter nTb, median binding constant log $$\tilde{K}_{\text{Tb}}$$ for the phenolic sites and intrinsic ET and FQ coefficients (denoted as ηTbΦ and αTbΦ), and were 0.48, 8.5, 1385 and 0.12, respectively. The high value of the energy transfer coefficient of Tb3+ ions bound by the phenolic groups in HPOA is indicative of both the match between the electronic levels of the donor and acceptor, and the short distance between them. The deviation of the data of Nica–Donnan modeling of the ET and FQ dependence of versus [Tb]total for a 1.0 M ionic strength highlights the need to quantify the distribution of donor–acceptor distances in HPOA molecules in more detail.

The behaviour and fate of copper (Cu) and zinc (Zn) at river confluences is poorly understood, although chemical and physical processes during mixing of compositionally different tributaries might condition metal availability and fluxes to the ocean. To identify and quantify the effect of such processes in river mixing zones, particulate Cu and Zn isotope signatures (delta(65) Cu-SPM and delta Zn-66(SPM)) were measured along cross sections and vertical profiles at the largest river confluence in the world, the "Encontro das Aguas" mixing zone of the Amazon River, where the organic-rich Negro River meets the sediment-rich Solimoes River. The Negro River suspended sediments, with highly variable Cu and Zn concentrations as well as delta Cu-65(SPM) and delta(66) Zn-SPM, are mostly influenced by organic matter and by the lateritic cover of the watershed. The Solimoes River suspended sediments, more homogeneous in Cu and Zn concentration and isotope composition across the river section, reflect the signature of weathered silicate-rich sediments derived from the Andes. The Solimoes River supplies the majority of the suspended Cu and Zn to the Amazon River, and despite important flux losses across the confluence (-35% for Cu and -27% for Zn), delta(65) Cu-SPM and delta(66) Zn-SPM show a conservative behaviour during the mixing. In the dissolved load, Cu concentrations and delta(65) Cu-diss, mostly supplied by the Solimoes River, behave conservatively whereas Zn, derived mainly from the Negro River, suffers an important loss ( -58%) that can be attributed to Zn adsorption onto the suspended sediments from the Solimoes River. This transfer does not induce a significant delta(66) Zn-SPM shift in the Amazon River suspended sediments. Therefore, Cu and Zn isotope ratios in the suspended sediments behave conservatively through this confluence, which mixes two very chemically-contrasted rivers. Our findings thus suggest that the riverine isotopic information on the sources of particulate Cu and Zn is preserved during tributary mixing.

Because of their mechanical, thermal, and chemical resistance, ceramic materials are suitable for challenging water treatments, where different metal oxides (MeO) have been tested as active layers. However, organic fouling is a major drawback impacting its performance. Organics adsorb onto the membrane surface and into their pores during long-term operation, resulting in irreversible fouling. This investigation focussed on the interfacial interactions between model organic acids and MeO to obtain a fundamental understanding of the adsorption phenomena. Batch adsorption experiments of a series of small molecular weight, oxygenated, aromatic organic acids were performed with Al2O3, TiO2, and ZrO2 particles, at pH 4.2 and 7.6. The adsorption of simple acids was described by the Langmuir model and exhibited a strong dependence on the relative abundance of carboxyl groups, aliphaticity/aromaticity, alkyl chain length, and presence of hydroxyl groups. The adsorption of model compounds was higher at low pH and decreased with increasing pH. The difference in Al2O3, TiO2, and ZrO2 surface characteristics, as evidenced by TEM, XRD, and BET, led to differences in the adsorption density. The results obtained with these well-defined organic structures will assist in better understanding the interfacial interactions between complex natural organic matter molecules and MeO of different characteristics.

International audience; The complex behaviour of Zn and Cu at the soil-river interface was investigated in soil and riverine water samples from the Rio Negro basin, a secondary tributary of the Rio Amazonas, using their stable isotope compositions. This acidic and organic river drains two types of intensely weathered terrains: podzols in its upstream part, and lateritic soils downstream. Bulk soil particles, suspended particulate matter (SPM) as well as colloidal fractions were sampled across the whole basin during low and high water stages.In the basin, Zn and Cu are mostly exported from lateritic soils and transported by organic colloids where significant losses are observed in the downstream part of the river. The use of delta Zn-66 and delta Cu-66 measurements reveals distinct stories for these two metals in suspended sediments and colloids. In the colloids, the constant delta Zn-66(coll) across the basin is induced by the same weak association mode between Zn and organic ligands, regardless of the origin of the water. By contrast, in SPM, the speciation of Zn and thus delta Zn-66(SPM) differ according to the type of drained soils. Zn is associated with organic complexes in particles exported with water draining podzol whereas Zn2+ is incorporated in the structure of the remaining kaolinite clays in lateritic output.The stronger reactivity of Cu than Zn with organic ligands induces its complete complexation. Copper is controlled by refractory particulate organic matter (POM) and by reactive colloidal organic matter; the latter being enriched in delta Cu-65 due to stronger binding interactions than in POM. While the Cu content remains constant in the upstream part of the Rio Negro, downstream, the decrease of SPM and colloidal Cu fluxes is associated with a constant delta Cu-65(SPM) and with an increase of delta Cu-65(coll) at the Rio Negro outlet. Geochemical mass balance modelling, based on SPM, Cu and Zn fluxes in SPM and their associated isotopic signatures, confirms distinct host phases for Zn and Cu, and identifies the most probable places where losses of these two metals occur. In colloids, the observed Cu isotope fractionation (from 0.24 to 0.45%) superimposed on the significant Cu-coll loss is assumed to result from a new isotopic equilibrium in a low velocity and high productivity zone: Cu-rich colloids enriched in Cu-63 aggregate and settle down, whereas the remaining heavy Cu is partially complexed on strong organic ligands secreted by phytoplankton, forming new Cu-colloids

This research has been conducted over the last 10 years to characterise the spatio-temporal variability of aquatic organic matter (OM) composition in the Seine River watershed upstream and downstream of Paris Megacity and its effect on micro-pollutants. For this purpose, a large number of samples were collected under different hydrological conditions, and, over 1 year, three representative sites were monitored monthly. Furthermore, the evolution of the OM composition along an urbanisation gradient, from upstream to downstream of the Paris agglomeration, was characterised, highlighting the very strong impact of urban discharges, especially during low-water periods. Substantial differences in the chemical composition are emphasised relative to the urban or natural origin of the organic matter. Dissolved organic matter (DOM) interactions with metallic and organic micro-pollutants were studied, allowing us to (1) identify the key role of DOM on their speciation and bioavailability in aquatic systems and (2) demonstrate that these interactions depend on DOM composition and origin. The essential role of urban DOM on the speciation of trace metals in the Seine River downstream of the Paris agglomeration is also shown.

Summary Chemical extraction, multi-element stable isotopic dilution (ID) and multi-surface modelling were used to investigate the lability of cadmium (Cd) and copper (Cu) in nine types of soil with different properties and contaminated or not with Cd and Cu. The chemical extraction and ID analyses both showed that Cd was more labile than Cu in all the soil types studied. From the ID results, 32.8–93.3% of total Cd and 14.7–71.8% of total Cu were isotopically exchangeable after 3 days of equilibration. A single extraction in 0.43 m HNO3 gave similar results to the 3-day ID assay for Cu in most of the soils and for Cd in the non-calcareous soils. However, an eight-step selective sequential extraction (SSE) procedure gave different results from the ID assay for both metals. Predictions of the multi-surface model for the amounts of Cd and Cu adsorbed, based on measured metal ion activities in the soil solution and the concentrations of reactive surfaces in the soil, agreed with the ID results. The model predicted that soil organic matter was the predominant sorbent for Cd and Cu in the soils and that manganese oxide was the least important sorbent. The contributions of iron oxides to sorption were predicted to be small except in soil with a high pH and little organic matter. The predicted sorption on different soil components did not match SSE measurements.

International audience; The concentration and size fractionation of major and trace elements (TEs) linked to organo-mineral colloids along the landscape gradient soil water–peat mire–humic lakes–river–large oligotrophic lake have been investigated within two watersheds located in the subarctic region (Karelia, Russia) in the summer base-flow period. A large volume of natural waters was filtered in the field using cascade filtration and ultrafiltration (UF) with a progressively decreasing pore size [100, 20, 10, 5, 0.8, 0.4, 0.22, 0.1, 0.046, 0.0066 (100 kDa), 0.0031 (10 kDa) and 0.0014 µm (1 kDa)] followed by multi-elemental ICP-MS and dissolved organic carbon (DOC) analysis. In situ dialysis with 10 and 1 kDa molecular weight cutoff membranes was also conducted. According to the TE distribution among different size fractions in the continuum soil (mire)–humic lake–river–large lake, the following groups of elements could be distinguished: (1) elements significantly bound to the colloidal (1 kDa—0.22 µm) fraction and decreasing the proportion of this fraction from the feeding lake and stream to the terminal oligotrophic lake (Fe, Ti and U); (2) colloidally dominated (>80 %) elements exhibiting similar size fractionation in all studied settings (Y, REEs, Zr, Hf and Th); (3) elements appreciably bound to colloids (20–40 %) in organic-rich soil and bog waters and decreasing their colloidal fraction to approximately 10 % in the oligotrophic lake (Mg, Ca, Sr, Rb and Mo); and (4) elements linked to the colloidal fraction (40–80 %) and not demonstrating any systematic variation between different landscape units (Ni, Co, Cu, Cd, Cr, Mn, Zn and Pb). The in situ dialysis technique produced a similar picture of the colloidal size fractionation with generally lower proportions of elements in the colloidal fraction compared to the UF. Thermodynamic modeling of trace element speciation using available codes demonstrated that complexation with dissolved organic matter and adsorption at the surface of ferric colloids can adequately model the observed colloidal speciation of divalent metals. However, the modeling could not describe the distribution of trivalent and tetravalent hydrolysates (TE3+,4+) among different size fractions and cannot reproduce the experimentally observed proportion of their colloidal forms. Therefore, coprecipitation with organo-ferric colloids should be considered to account for the partitioning of TE3+,4+ between truly dissolved (

International audience; This study utilized the methods of fluorescence quenching and differential absorbance to probe in situ the extent and the nature of the interactions between rare earth ions (REIs) and humic substances. Experiments were conducted with the standard Suwannee river humic acid (SRHA) in the presence of varying amount of lanthanum, europium and terbium. The data of differential absorbance showed that the mechanism of SRHA-metal complexation was largely the same for all the examined REIs. In all cases several discrete bands whose properties were discerned via numerical decomposition of the differential spectra absorbance were observed. Their nature was examined based on the comparison of the experimental data and those of NICA-Donnan modeling carried out for Eu3+. The observed effects suggested that the changes of SAHA absorbance induced by REIs binding are likely to be caused by a bathochromic shift of the absorbance bands associated with such chromophores. The intensity of the Gaussian band with a maximum at 387 nm was observed to be proportional to the total concentration of SRHA-bound REIs. The data obtained in this study demonstrate the existence of complex yet quantifiable changes of the spectroscopic properties of humic species in the presence of REIs and their utility to quantify modes of interactions in such systems.

Environmental contextStudying the mechanism of binding between metals and natural organic matter is fundamental to understanding the transport and availability of these contaminants in the environment. The influence of sample treatment on the purification of organic matter showed significant differences in the interaction with metals. The results will contribute to improved modelling of metal binding to organic matter in soils, thereby providing a basis for a more realistic risk assessment. AbstractWe studied the changes in metal binding characteristics of extracted humic acids induced by HF/HCl treatment followed by dialysis, i.e. the last step of the International Humic Substances Society (IHSS) extraction protocol. We performed metal binding experiments with both the alkaline-extracted material (AE) and the fully purified (FP) humic acid using the electrochemical stripping technique (AGNES) and modelled the results using the NICA-Donnan model. The results showed an increase of free Zn, Cd and Pb concentrations of similar to 1 order of magnitude for the AE compared with the FP. These differences may be mostly explained by the different carbon content (51.3% FP and 36.5% AE) associated with an AE/FP carboxyl ratio of 0.5. Simulations using the NICA-Donnan model showed that halving the amount of carboxylic groups (Q(max,1)) for the FP reduced this difference to 0.25 log units for Cd and Zn and to 0.15 log unit for Pb. There is a clear need for further research on the differences between purified v. less-disturbed natural organic material, which will contribute to improved modelling of metal binding to organic matter in soils, hence providing a basis for a more realistic risk assessment. Coordenadoria de Aperfeicoamento do Pessoal de Nivel Superior (CAPES CSF) [981313-6] Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq PVE) [400572/2013-3] French national research agency (ANR) [ANR-10-LABX-21-01/LABEX RESSOURCES 21] Portuguese national funding agency for science, research and technology [FCT-ANR/AAG-MAA/0065/2012] Region Lorraine

In this work, modelling of Eu(III) speciation in a ternary system, i.e., in presence of purified Aldrich humic acid (PAHA) and α-Al2O3, is presented. First, the mineral surface charge is measured by potentiometric titrations and then described using the CD–MUSIC model. This model is also used to describe Eu(III) binding to the α-Al2O3 surface at different pH values, ionic strength and mineral concentrations. Time-resolved luminescence spectroscopy (TRLS) is then used to study the binding of Eu(III) to PAHA at pH 4 with different humic acid concentrations. The spectra are used to calculate a spectroscopic “titration curve”, used to determine Eu(III)/PAHA binding parameters in the NICA-Donnan model. Following a previous study (Janot et al., Water Res. 46, 731–740), modelling of the ternary system is based upon the definition of two PAHA pools where one fraction remains in solution and the other is adsorbed onto the mineral surface, with each possessing different proton and metal binding parameters. The modification of protonation behaviour for both fractions is examined using spectrophotometric titrations of the non-adsorbed PAHA fraction at different organic/mineral ratios. These data are then used to describe Eu(III) interactions in the ternary system: Eu(III) repartitioning in the ternary system is calculated for different pH, ionic strength and PAHA concentrations, and results are compared to experimental observations. The model is in good agreement with experimental data, except at high PAHA fractionation rates. Results show that organic complexation dominates over a large pH range, with the predominant species existing as the surface-bound fraction. Above pH 8, Eu(III) seems to be mostly complexed to the mineral surface, which is in agreement with previous spectroscopic observations (Janot et al., Environ. Sci. Technol. 45, 3224–3230).

The central Amazon floodplains are particularly productive ecosystems, where a large diversity of organic carbon sources are available for aquatic organisms. Despite the fact that C-4 macrophytes generally produce larger biomasses than C-3 macrophytes, food webs in the central Amazon floodplains appear dominantly based on a C-3 carbon source. In order to investigate the respective fate and degradation patterns of C-4 and C-3 aquatic plant-derived material in central Amazon floodplains, we developed a 23-days batch experiment. Fatty acid and carbon concentrations as well as stable isotope compositions were monitored over time in 60 L tanks. These tanks contained Amazon water, with different biomasses of C-3 and C-4 macrophyte, representative of in situ densities occurring in central Amazon floodplains. In the C-4 Paspalum repens treatments, organic (POC, DOC) and inorganic carbon (DIC) got rapidly enriched in C-13, whereas in the C-3 Salvinia auriculata treatments, POC and DOC showed little change in concentration and isotopic composition, and DIC got depleted in C-13. The contribution of P. repens to POC and DOC was estimated to reach up to 94.2 and 70.7%, respectively. In contrast, no differences were reported between the C-3 S. auriculata and control treatments, an observation attributed to the lower C-3 biomass encountered in the field, to a slower degradation rate of C-3 compared to C-4 compounds, and to similar isotopic compositions for river POC and DOC, and C-3 compounds. The C-13 enrichments of POC, DOC, and DIC from P. repens treatments were attributed to an enhanced bacterially-mediated hydrolysis and mineralization of C-4 material. Evolutions of bacterial abundance and branched fatty acid concentrations confirmed the role of heterotrophic microbial communities in the high P. repens decomposition rate. Our experiment highlights the predominant role of C-4 aquatic plants, as a large source of almost entirely biodegradable organic matter available for heterotrophic activity and CO2 outgassing to the atmosphere.

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.

International audience; Soils and ore samples influenced by mining and metallurgical activity were collected in ultramafic soils (UM) complexes of Barro Alto and Niquelândia, in order to determine the contribution of each Ni bearing phases to the total exchangeable pool of Ni, and to point out if this pool was affected by anthropic activities. For this purpose, the IEK-model previously developed by the group (Zelano et al., submitted) was applied, on the basis of IEK experiments performed on pure typical Ni scavengers (serpentines, chlorite, smectite and iron oxydes) from ultramafic systems. For each typical scavenger, this model describes the percentage of Ni associated to exchangeable pool(s) as well as their corresponding kinetic constant(s) of exchange. The mineralogical composition of soil and ore samples and Ni solid speciation were first determined, and the IEK-model was applied on these bases. In almost all samples, an important contribution of serpentine to Ni exchangeable pool was highlighted, ranging between 10% and 45%. The important amount of organic matter (OM) in one of the studied soil samples, allowed to extrapolate generic OM ENi and k parameters, which were introduced in the IEK-model to improve its predictive capability. Obtained results provided evidences of how even a small content (3 wt%) of organic carbon (OC), can represent an important contribution of OM to the total ENi pool (60%). In the investigated ore samples, up to the 60% of ENi was attribute to smectite, responsible for fast ENi pool kinetic evolution. In addition, the model highlighted the role of the Fine Black Ash (FBA), by-products of the pyrometallurgical activity, detected into a soil sample, that is responsible for the 15% of ENi. This approach allowed to determine, for the first time, the relative contribution of each Ni bearing phase to the total exchangeable pool, in terms of concentration and kinetics.

International audience; Zinc isotopes have been studied along two smelter-impacted soil profiles sampled near one of the largest Pb and Zn processing plants in Europe located in northern France, about 50 km south of Lille. Mean delta(66)Zn values along these two soil profiles range from +0.22 +/- 0.17 parts per thousand (2 sigma) to +0.34 +/- 0.17 parts per thousand (2 sigma) at the lowest horizons and from +0.38 +/- 0.45 parts per thousand (2 sigma) to +0.76 +/- 0.14 parts per thousand (2 sigma) near the surface. The delta(66)Zn values in the lowest horizons of the soils are interpreted as being representative of the local geochemical background (mean value +0.31 +/- 0.38 parts per thousand), whereas heavier delta(66)Zn values near the surface of the two soils are related to anthropogenic Zn. This anthropogenic Zn occurs in the form of franklinite (ZnFe(2)O(4))-bearing slag grains originating from processing wastes at the smelter site and exhibiting delta(66)Zn values of +0.81 +/- 0.20 parts per thousand (2 sigma). The presence of franklinite is indicated by EXAFS analysis of the topsoil samples from both soil profiles as well as by micro-XANES analysis of the surface horizon of a third smelter-impacted soil from a distant site. These results indicate that naturally occurring Zn and smelter-derived Zn exhibit significantly different delta(66)Zn values, which suggests that zinc isotopes can be used to distinguish between geogenic and anthropogenic sources of Zn in smelter-impacted soils. In addition to a possible influence of additional past sources of light Zn (likely Zn-sulfides and Zn-sulfates directly emitted by the smelter), the light delta(66)Zn values in the surface horizons compared to smelter-derived slag materials are interpreted as resulting mainly from fractionation processes associated with biotic and/or abiotic pedological processes (Zn-bearing mineral precipitation, Zn complexation by organic matter, and plant uptake of Zn). This conclusion emphasizes the need for additional Zn isotopic studies before being able to use Zn isotopes to trace sources and pathways of this element in surface environments

International audience; Eu(III) sorption onto $\alpha$-Al$_2$O$_3$ in the presence of purified Aldrich humic acid (PAHA) is studied by batch experiments and time-resolved laser-induced luminescence spectroscopy of Eu(III). Experiments are conducted at varying pH, at 0.1 mol/L NaClO$_4$, 10$^{-6}$ mol/L Eu(III), 1 g/L $\alpha$-Al$_2$O$_3$ and 28 mg/L PAHA, which assured a complete Eu(III)-PAHA complexation. Adsorption of Eu(III) presents the expected pH-edge at 7, which is modified by addition of PAHA. Presence of Eu(III) slightly increases PAHA sorption throughout the pH range. The evolutions of luminescence spectra and decay times of the binary systems, that is, Eu(III)/$\alpha$-Al$_2$O$_3$ and Eu(III)/PAHA, indicate a progressive surface- and humic-complexation with increasing pH. The typical biexponential luminescence decay in Eu(III)/PAHA system is also recorded; the fastest deactivation depending barely on pH. In ternary Eu(III)/PAHA/$\alpha$-Al$_2$O$_3$ system, the existence of a luminescence biexponential decay for all pH means that Eu(III) is always in the direct neighborhood of the humic substance. Below pH 7, the spectra of the ternary system (Eu(III)/PAHA/$\alpha$-Al$_2$O$_3$) are not different from the ones of Eu(III)/PAHA system, implying the same complex symmetry. Nevertheless, the increase of luminescence decay time points to a change in PAHA conformation onto the surface

We evaluated in situ rates of bacterial carbon processing in Amazonian floodplain lakes and mainstems, during both high water (HW) and low water (LW) phases (p < 0.05). Our results showed that bacterial production (BP) was lower and more variable than bacterial respiration, determined as total respiration. Bacterial carbon demand was mostly accounted by BR and presented the same pattern that BR in both water phases. Bacterial growth efficiency (BGE) showed a wide range (0.2–23%) and low mean value of 3 and 6%, (in HW and LW, respectively) suggesting that dissolved organic carbon was mostly allocated to catabolic metabolism. However, BGE was regulated by BP in LW phase. Consequently, changes in BGE showed the same pattern that BP. In addition, the hydrological pulse effects on mainstems and floodplains lakes connectivity were found for BP and BGE in LW. Multiple correlation analyses revealed that indexes of organic matter (OM) quality (chlorophyll-a, N stable isotopes and C/N ratios) were the strongest seasonal drivers of bacterial carbon metabolism. Our work indicated that: (i) the bacterial metabolism was mostly driven by respiration in Amazonian aquatic ecosystems resulting in low BGE in either high or LW phase; (ii) the hydrological pulse regulated the bacterial heterotrophic metabolism between Amazonian mainstems and floodplain lakes mostly driven by OM quality.

International audience; Knowledge of the speciation of heavy metals and the role of dissolved organic matter (DOM) in soil solution is a key to understand metal mobility and ecotoxicity. In this study, soil column-Donnan membrane technique (SC-DMT) was used to measure metal speciation of Cd, Cu, Ni, Pb, and Zn in eighteen soil solutions, covering a wide range of metal sources and concentrations. DOM in these soil solutions was also fractionated into humic acid (HA), fulvic acid (FA), hydrophilic acid (Hy), and hydrophobic neutral organic matter (HON) by a rapid batch technique using DAX-8 resin. Our results show that in soil solution Pb and Cu are dominant in complex form, whereas Cd, Ni and Zn mainly exist as free ions; for the whole range of soil solutions, only 26.2% of DOM is humic substances and consists mainly of fulvic acid (FA). The metal speciation measured by SC-DMT was compared to the predicted ones obtained via the NICA-Donnan model using the measured FA concentrations. The free ion concentrations predicted by speciation modeling were in good agreement with the SC-DMT measurement. Moreover, we show that to make accurate modeling of metal speciation in soil solutions, the knowledge of DOM composition, especially FA fraction, is the crucial information, especially for Cu and Cd; like in previous studies the modeling of Pb speciation is not optimal and an update of Pb generic binding parameters is required to reduce model prediction uncertainties. (C) 2015 Elsevier B.V. All rights reserved.

The proton and Cd binding capacities of microbially produced exopolysaccharides, EPS, were quantified by the determination of stability constants and the concentration of complexing sites using H(+) or Cd(2+) selective electrodes in dynamic titrations. The influence of ionic strength, pH and the Cd to EPS ratio was evaluated over large concentration ranges. The applicability of the non-ideal competitive adsorption isotherm combined with a Donnan electrostatics approach was tested with respect to the EPS. Proton and cadmium binding data were compared with literature data examining other ubiquitous environmental ligands including humic substances, alginate, bacteria, etc. Subsequent modelling of Cd speciation in aquatic (fresh and marine waters) and soil systems suggested that the exopolysaccharides would play non-negligible role, under most conditions. The quantitative information provided in this paper thus represents an important advance in our understanding of Cd transport, bioavailability and impact in aquatic and terrestrial systems. (c) 2006 Elsevier Ltd. All rights reserved.

Nowadays, environmental problems related to soil pollution with heavy metals are numerous, therefore, it is important to understand metals behaviour in aquatic sediments and soils and to estimate their transfer. The fate of metals in the environment is closely related to their interactions with the major reactive compartments (organic matter, iron and manganese oxides, clays). The objective of this work is to develop an approach based on the combination of several models to study metal ion speciation in different environmental systems. Models used to describe the interactions of metals with the main reactive phases in the soil are CD-MUSIC (amorphous and crystallized iron oxides), NICA-Donnan (organic matter and manganese oxides) and cationic ion exchange model (clays). First, this work implies the definition of generic parameters to describe the interactions of the studied metals with iron and manganese oxides and part of this information is missing in the literature. Then, after a validation of the approach by comparison with analytical results, this multi-surface model is applied to test sites corresponding to one soil and two riverine environments. These new models give good predictions of the behaviour of major and trace metal ions even in heterogeneous systems characteristic of natural environment. The measured free metal concentrations in the solution are in agreement with those obtained from model calculations. In the case of the soil test site, the soil solution composition and speciation are predicted using the soil major constituents characteristics. D 2005 Elsevier B.V. All rights reserved.

The present study deals with the direct determination of colloidal forms of iron in river-borne solids from main rivers of the Amazon Basin. The contribution of different forms of colloidal iron have been assessed using ultrafiltration associated with various techniques including electron paramagnetic resonance spectroscopy (EPR), high resolution transmission electron microscopy (HRTEM), and micro proton-induced X ray emission analysis (μPIXE). EPR shows the presence of Fe3+ bound to organic matter (Fe3+-OM) and colloidal iron oxides. Quantitative estimate of Fe3+-OM content in colloidal matter ranges from 0.1 to 1.6 weight % of dried solids and decreases as the pH of the river increases in the range 4 to 6.8. The modeling of the field data with the Equilibrium Calculation of Speciation and Transport (ECOSAT) code demonstrates that this trend is indicative of a geochemical control resulting from the solubility equilibrium of Fe oxyhydroxide phase and Fe binding to organic matter. Combining EPR and μPIXE data quantitatively confirms the presence of colloidal iron phase (min. 35 to 65% of iron content), assuming no divalent Fe is present. In the Rio Negro, HRTEM specifies the nature of colloidal iron phase mainly as ferrihydrite particles of circa 20 to 50 Å associated with organic matter. The geochemical forms of colloidal iron differentiate the pedoclimatic regions drained by the different rivers, corresponding to different major weathering/erosion processes. Modeling allows the calculation of the speciation of iron as mineral, organic and dissolved phases in the studied rivers.

We studied the changes in major elements and organic carbon concentrations during the initial stage of the mixing of the black (Rio Negro) and the White (Rio Solimoes) waters in the Amazon River basin to understand the geochemical processes that could control the redistribution between particulate and dissolved fractions. Water samples were collected at six stations including the Rio Negro and the Rio Solimoes and four stations downstream from the confluence. The relative contributions of the two tributaries were determined using a triple tracer approach (d 18 O, dD, Cl � ). Particulate (>0.2 Am) and dissolved (

The bioavailability and the potential toxicity of heavy metals in the environment depend on their speciation in the soil and the soil solution. The analytical task is rendered difficult because the individual chemical species are often present at nano- and picomolar concentration in natural systems. To determine the free metal ion (FMI) concentration, both analytical and computational approaches were used. The recently developed Donnan Membrane Technique (DMT) succeeded in measuring the free metal ion concentration. In a first analytical step, some Zn smelter impacted topsoil (0–5 cm) columns were linked to the DMT cell and metal concentrations were measured at different pHs. The measured free metal concentrations in the soil solution were compared to those obtained from model calculations. In the second part, metal concentrations in the soil solution are predicted with the soil major constituents characteristics. These combined approaches allow a good description of the soil solution chemistry. Cd and Zn are mainly in solution as free aquo-ion that will migrate easily. The speciation of Pb and Cu is regulated by the dissolved organic matter. Their transport will be controlled by organic matter mobility. Cd, Zn and Pb speciation in the soil is controlled by organic matter, metallic oxides (Fe, Mn) and newly formed Zn-bearing minerals. All these calculated speciation and distribution are in reasonable agreement with EXAFS data previously published for the same soil sample.

Colloidal and particulate natural organic matter was size-fractionated and concentrated from the Rio Negro river using tangential-flow filtration (TFF). Flow field-flow fractionation (F-FFF), with UV absorbance detection (UVA), was used to investigate the molecular weight distributions of the organic colloids. To further characterize the nature of the Rio Negro colloids, the size distributions of the iron concentrations were determined by direct on-line coupling of the F-FFF to an inductively coupled plasma emission spectrometer (ICP-AES). The size distributions obtained by both F-FFF-UVA and F-FFF-ICP-AES were considerably smaller than expected from the stated pore size of the TFF membranes. These results demonstrate that care must be taken in using TFF to classify the size distribution of organic colloids and associated elements present in rivers. The iron distribution is more closely correlated to the organic matter distribution in the colloidal fraction than in the particulate fraction, but it is shifted towards heavier molecular weights for both fractions. The combination of electron paramagnetic resonance spectroscopy (EPR) and transmission electron microscopy (TEM) reveals the presence of iron occurring as: specific complexes with organic functional groups, as Fe-oxide/oxihydroxide phases, or as structurally incorporated component in kaolinite. Particulate and colloidal fractions are differentiated from each other with respect to the iron forms, which is in qualitative agreement with the F-FFF-ICP-AES results.

I Zinc speciation was studied by EXAFS spectroscopy, μ-SXRF elemental mapping, XRD, and chemical extraction methods in two smelter-impacted soils sampled near one of the largest Pb and Zn processing plants in Europe, which is located in northern France about 50 km south of Lille. The tilled and wooded soils chosen for study differ in Zn concentration (=600 and 1400 mg/kg, respectively), soil pH (7.5 and 5.5, respectively), and organic matter content (1.5 and 6.4 wt% TOC, respectively). In both soils, the occurrence of Fe- and Zn-rich (up to 10 wt% Zn) slag particles ranging in size from a few micrometers to a few millimeters, was shown by μ-SXRF elemental mapping of soil thin sections as well as by SEM and chemical analysis of different soil size fractions. For both soils, XRD analysis of the dense coarse fraction, which contains up to 10 wt% Zn, revealed the presence of a minor amount (1-1.5 wt%) of crystalline ZnS (sphalerite and wurtzite). In this fraction, EXAFS data show that Zn is mainly incorporated in the tetrahedral sites of a magnetite-franklinite solid solution. The clay fraction (

Humic substances typically constitute 40-60% of the dissolved organic matter (DOM) in surface waters. However, little information is available regarding the metal binding properties of the nonhumic hydrophilic portion of the DOM. In this study, humic and nonhumic DOM samples were isolated from the South Platte River (Colorado, DOC = 2.6 mg x L(-1), SUVA254 = 2.4 L/mg x m) using a two-column array of XAD-8 and XAD-4 resins. The three major isolated fractions of DOM, which accounted for 57% of the bulk DOM,were characterized using a variety of analytical tools. Proton and copper binding properties were studied for each fraction. The main objective of this work was to compare the structural and chemical characteristics of the isolated fractions and test models describing DOM reactivity toward metal ions. The characterization work showed significant structural differences between the three isolated fractions of DOM. The hydrophobic acid fraction (i.e., humic substances isolated from the XAD-8 resin) gave the largest C/H, C/O, and C/N ratios and aromatic carbon content among the three isolated fractions. The transphilic acid (TPHA) fraction ("transphilic" meaning fraction of intermediate polarity isolated from the XAD-4 resin) was found to incorporate the highest proportion of polysaccharides, whereas the transphilic neutral (TPHN) fraction was almost entirely proteinaceous. The gradual increase of the charge with pH for the three DOM fractions is most likely caused by a large distribution of proton affinity constants for the carboxylic groups, as well as a second type of group more generally considered to be phenolic. In the case of the DOM fraction enriched in proteinaceous material (i.e., TPHN fraction), the results showed that the amino groups are responsible for the charge reversal. For low copper concentrations, nitrogen-containing functional groups similar to those of amino acids are likely to be involved in complexation, in agreement with previously published data.

Complexation of Al3+ by NOM will change the speciation of Al and influence its toxicity. Competitive binding data between Al and metal ions to humic acids are needed to understand changes in specia...

– The analysis of organic matter in the rio Negro, rio Solimoes and rio Amazonas focused on total organic car-bon (TOC), as determined at two main sizes, the particulate form (> 0.2 µm) and the colloidal form (0.2 µm to 5000 dal-ton). These fractions were obtained by tangential ultrafiltration carried out on 50 l water samples. The total polysaccha-ride contents were determined by a colorimetric method, the main classes of organic compounds by pyrolysis and gaschromatography coupled with mass spectrometry (Py-GC-MS), and the lignin or non-lignin phenols by cupric oxidealkaline oxidation and high performance liquid chromatography (HPLC) with photodiode array spectrophotometer detec-tion. Upstream of the confluence of the rio Negro and rio Solimoes, the rivers show characteristic differences. The rioNegro has low discharge, high levels of TOC% for the two fractions, high levels of polysaccharides, low levels of ligninphenols and high levels of hydroxybenzyl non-lignin phenols. The main classes of organic compounds also give a dis-tribution different for the particulate (phenols associated to aromatic compounds) and the colloidal (aromatic compoundsand sugars). For the rio Solimoes, the compositional features are generally reversed. Downstream of the confluence, thecolloidal fraction showed noteworthy levels of lignin-derived compounds associated with increasing levels of polysac-charides correlated to the distance from the confluence.biogeochemistry / organic matter / Py-GC-MS / HPLC / phenols / lignin / particulate / colloidalResume – Caracteres biogeochimiques de la matiere organique particulaire et colloidale en aval de la confluencedes rios Negro et Solimoes. L’analyse de la matiere organique dans les eaux du rio Negro, du rio Solimoes et du rioAmazonas a porte sur la charge totale en suspension (TSM) ainsi que sur les fractions particulaire (> 0.2 µm) et colloi-dale (0.2 µm a 5000 dalton). Ces fractions ont ete obtenues par ultrafiltration tangentielle executee sur des echantillonsAgronomie 20 (2000) 477–490

Knowledge of the speciation of Pb in natural aquatic systems is important if we want to understand the bioavailability and mobility of Pb in polluted and natural environments. The results given in this paper were obtained under conditions as close as possible to natural conditions. These new data show that Pb strongly binds to fulvic acids. We also show that the competitive effect of Pb on Ca binding to the same fulvic acid is smaller than the salt effect on Ca binding to fulvic acids as pH varies from 4 to 8. All the data were analyzed with the NICCA−Donnan model developed to describe metal ion binding to natural organic matter. The model predictions of competitive and salt effects are excellent. Comparison of our results with previously published data suggests that metal ion binding strength is similar for fulvics acids from different origins. Thus, all data sets could be interpreted within the framework of a unified modeling approach.

International audience; We have studied the effect of TiO2 nanoparticles (NPs) on the model cyanobacteria Synechocystis PCC6803. We used well-characterized NPs suspensions in artificial and natural (Seine River, France) waters. We report that NPs trigger direct (cell killing) and indirect (cell sedimentation precluding the capture of light, which is crucial to photosynthesis) deleterious effects. Both toxic effects increase with NPs concentration and are exacerbated by the presence of UVAs that increase the production of Reactive Oxygen Species (hydroxyl and superoxide radicals) by TiO2 NPs. Furthermore, we compared the responses of the wild-type strain of Synechocystis, which possesses abundant exopolysaccharides surrounding the cells, to that of an EPS-depleted mutant. We show, for the first time, that the exopolysaccharides play a crucial role in Synechocystis protection against cell killing caused by TiO2 NPs

International audience; In this study, the optical properties of dissolved organic matter (DOM) were investigated using UV/visible photometry and excitation emission matrix (EEM) fluorescence spectroscopy. Differences in quality and quantity of organic carbon were observed and highlighted discrimination of organic matter typologies between the four studied areas in the catchment of the Seine river. \textcopyright 2013 Zhejiang University Press and Springer Science+Business Media Dordrecht. All rights are reserved.

A Donnan-type model for nonspecific binding of electrolyte ions has been combined with the non-ideal competitive adsorption (NICA) model for specific binding to produce a model for ion binding to humic substances. The model considers site heterogeneity, non-ideality, multicomponent competition, and electrostatic interactions. The NICA-Donnan model was fitted to data for H, Ca, Cd, Cu, and Pb binding by a purified peat humic acid. The model fits were good and covered a wide range of pH and free metal concentrations. The parameters from these single metal data sets were then used to predict the competitive effect of Ca on Cd and Cu binding at various pHs. These predictions agreed well with the experimental data although there were some small but systematic differences. The new NICA-Donnan model also predicted reasonably well the increase in Cd and Cu binding on changing from a 0.1 M KNO3 background electrolyte to 0.01 M KNO3. A shortcoming of the model is that in some cases it significantly underestimated t...

With the newly developed NICCA-Donnan model, we estimate the activity of toxic metal ions from simple measurements like total metal concentration and organic matter content. The model evaluates Cu and Cd binding from three field systems, a mountain lake and two sandy soils, using model parameters calibrated for natural organic matter analogues with laboratory measurements. This is possible because the model includes site binding heterogeneity, electrostatic effects, competitive binding, and ion specific nonideality. The predictions derived closely matched the field observations when site binding densities are adjusted. The partition coefficients between soil and soil solution were also predicted for Cd and Cu under conditions where the organic matter controls the metal binding in both soil and soil solution. The model calculations show that in soil solutions 50% of the Cd and 99.99% of the Cu is bound to the dissolved organic matter. The model can be used to evaluate the effects of variations in the chemical conditions (e.g., acidification or total metal loading) on the free metal ion concentration in solution.

Adsorption of purified Aldrich humic acid (PAHA) onto α-Al(2)O(3) is studied by batch experiments at different pH, ionic strength and coverage ratios R (mg of PAHA by m(2) of mineral surface). After equilibration, samples are centrifuged and the concentration of PAHA in the supernatants is measured. The amount of adsorbed PAHA per m(2) of mineral surface is decreasing with increasing pH. At constant pH value, the amount of adsorbed PAHA increases with initial PAHA concentration until a pH-dependent constant value is reached. UV/Visible specific parameters such as specific absorbance SUVA(254), ratio of absorbance values E(2)/E(3) and width of the electron-transfer absorbance band Δ(ET) are calculated for supernatant PAHA fractions of adsorption experiments at pH 6.8, to have an insight on the evolution of PAHA characteristics with varying coverage ratio. No modification is observed compared to original compound for R ≥ 20 mg(PAHA)/g(α)(-)(A)1₂(O)₃. Below this ratio, aromaticity decreases with initial PAHA concentration. Size-exclusion chromatography - organic carbon detection measurements on these supernatants also show a preferential adsorption of more aromatic and higher-sized fractions. Spectrophotometric titrations were done to estimate changes of reactivity of supernatants from adsorption experiments made at pH ≈6.8 and different PAHA concentrations. Evolutions of UV/Visible spectra with varying pH were treated to obtain titration curves that are interpreted within the NICA-Donnan framework. Protonation parameters of non-sorbed PAHA fractions are compared to those obtained for the PAHA before contact with the oxide. The amount of low proton-affinity type of sites and the value of their median affinity constant decrease after adsorption. From PAHA concentration in the supernatant and mass balance calculations, "titration curves" are experimentally proposed for the adsorbed fractions for the first time. These changes in reactivity to our opinion could explain the difficulty to model the behavior of ternary systems composed of pollutants/HS/mineral since additivity is not respected.

International audience; In the Rio Negro basin, podzols develop at the expense of clay-depleted laterites through localized and spectacular weathering fronts. This natural process leads to the remobilization of previously accumulated organic matter (OM) which is redistributed within soil profiles and exported towards rivers, hence their typical black coloration. We investigate the fate of OM in the soil-water continuum in the Rio Negro basin through description of the composition of OM potentially mobile at different stages of podzol development and exploration of evidence for contributions from different soil horizons to the exportation of OM into waters. OM was water-extracted from seven key soil samples from a sequence representative of the transition between latosol and podzol on the low elevation plateaux of the Rio Negro basin, thus enabling following both vertical and lateral differentiations. The chemical structure of freeze-dried samples, investigated using (13)C nuclear magnetic resonance and thermally assisted hydrolysis and methylation (THM), shows contrasting features depending on the horizon considered. The bulk features of water extracts were first compared with samples collected in the water-tables and rivers draining the soil sequence. A molecular level comparison was then performed with groundwater draining the well-developed podzol. This approach evidenced a contribution from deep horizons of well-developed podzols. It highlights that OM is certainly remobilised after being accumulated in Bh horizons during the development of podzols through accumulation of OM redistributed from surface horizons. The identification of specific compounds opens new perspective to trace a "podzolic origin" of OM in drainage networks.

International audience; Organic matter is an important factor that cannot be neglected when considering global carbon cycle. New data including organic matter geochemistry at the small watershed scale are needed to elaborate more constrained carbon cycle and climatic models. The objectives are to estimate the DOC and DIC fluxes exported from small tropical watersheds and to give strong constraints on the carbon hydrodynamic of these systems. To answer these questions, we have studied the geochemistry of eleven small watersheds around Basse-Terre volcanic Island in the French West Indies during different hydrological regimes from 2006 to 2008 (i.e. low water level versus floods). We propose a complete set of carbon measurements, including DOC and DIC concentrations, δ13C data, and less commonly, some spectroscopic indicators of the nature of the organic matter. The DOC/DIC ratio varies between 0.07 and 0.30 in low water level and between 0.25 and 1.97 during floods, indicating that organic matter is mainly exported during flood events. On the light of the isotopic composition of DOC, ranging from -32.8 to -26.2 ‰ during low water level and from -30.1 to -27.2 ‰ during floods, we demonstrate that export of organic carbon is mainly controlled by perennial saprolite groundwaters, except for flood events during which rivers are also strongly influenced by soil erosion. The mean annual yields ranged from 2.5 to 5.7 t km-2 yr-1 for the DOC and from 4.8 to 19.6 t km-2 yr-1 for the DIC and exhibit a non-linear relationship with slopes of watersheds. The flash floods explain around 60% of the annual DOC flux and between 25 and 45% of the DIC flux, highlighting the important role of these extreme meteorological events on global carbon export in small tropical volcanic islands. From a carbon mass balance point of view the exports of dissolved carbon from small volcanic islands are important and should be included in global organic carbon budgets.

International audience; In aquatic systems, soprtion of organic matter (OM) on environmental surfaces or its preference to remain dissolved is highly important for determining its potential transport and/or susceptibility to degradation. In the Amazon and other major rivers of the world, transported OM is either adsorbed to fine minerals or remains dissolved. The fate of autochthonous OM in Amazon floodplains and allochthonous OM from the river can be addressed by characterizing the nature of OM interactions with the sediment material. This goal was pursued in this study using Rio Negro and Amazon River samples as well as those collected from floodplain lakes during phytoplanktonic blooms, small black rivers, soil solution issued from podzolic areas in the Rio Negro watershed and "terra firme" stream flowing into the floodplain. The amount of carbon surface loading expressed as the adsorbed organic carbon per unit of surface area of the substrate was obtained by batch experiments with mineral phases representative of soils, suspended matter found in the Amazon basin and extracted OM fractions (the hydrophobic, HPO and the transphilic, TPH fractions of OM). The bulk dissolved organic matter samples were characterized by carbon and nitrogen isotopic measurements as well as elementary composition, specific UV absorbance (SUVA), molecular weight (Mw) and FTIR spectroscopy. To our knowledge, these are the first C and N isotopic composition data reported for extracted OM fractions in the Amazon basin. The Rio Negro basin water samples had high [DOC] correlated with conductivity. The SUVA values ranged from 4.0 to 7.3 m(-1)l mg(-1)C and were within the range of measurements reported for the Amazon River. The delta C-13 values of all HPO fractions varied from -27.7 to -30.2%.. The delta C-13 values for the TPH fractions were systematically 1%. higher than their respective HPO fraction. An increasing trend between the weight average Mw of the DOC as function of the C/N ratio (the higher C/N the higher Mw) is reported. This trend is inferred to result from both mixing between 2 end-members and OM fractionation. Carbon surface loadings calculated for HPO and TPH fractions ranged between 23 to 309 mu gC m(-2) and 38 to 145 mu gC m(-2), respectively. Carbon surface loadings with goethite and the Rio Negro organic matter fractions cluster around the average value of 24.5 +/- 4 mu gC m(-2). With the help of the pH dependant dissociation measurements and NICA-Donnan model parameters, it was possible to estimate the amount of deprotonated sites on the OM interacting with the sediment material. The amount of carbon surface loading was correlated with the calculated residual negative charge of the OM fractions (i.e. HPO or TPH). These analyses showed that higher residual negative charges were associated with lower carbon surface loadings on the treated sediment. The decrease of the negative charge was suggested to reduce the net electrostatic repulsion between the OM fractions and the clay surfaces and promote ligand exchange reactions governing sorption to clays. The preferential uptake of the high molecular weight fraction demonstrates that the chemical nature of the organic matter remaining in solution differs from that of the adsorbed fraction.

International audience; Potentiometric titration is a common method to characterize dissolved organic matter (DOM) reactivity. Because of the sensitivity of pH electrodes, it is necessary to work with very high DOM (>1 g/L) concentrations that are unrealistic compared to those found in natural waters (0.1 to 100 mg/L). To obtain proton binding data for concentrations closer to environmental values, spectroscopic titration methodology is a viable alternative to traditional potentiometric titrations. Spectrophotometric titrations and UV−visible spectra of a diluted solution of purified Aldrich humic acid (5 mg$_{DOC}$/L) are used to estimate changes in proton binding moieties as function of pH and ionic strength after calculation of differential absorbance spectra variations. After electrostatic correction of spectrophotometric data, there is a linear operational correlation between spectrophotometric and potentiometric data which can be used as a transfer function between the two properties. Spectrophotometric titrations are then used to determine the changes of humic acid protonation after adsorption onto $\alpha$-alumina.

International audience; Zinc isotopic fractionation during adsorption onto a purified humic acid (PHA), an analogue of organic matter (OM), has been investigated experimentally as a function of pH. The Donnan Membrane device (DM) was used to separate Zn bound to the PHA from free Zn2+ ions in solution and allowed us to measure the isotopic ratios of free Zn2+. Below pH 6, adsorption of Zn on the PHA resulted in no measurable isotopic fractionation, while at higher pH, Zn bound to PHA was heavier than free Zn2+ (Delta Zn-66(PHA-FreeZn2+) = +0.24 parts per thousand +/- 0.06 2 sigma, n = 4). This can be explained by changes in Zn speciation with pH, with higher complexation constants and shorter bond lengths for Zn-PHA complex compared to the free Zn2+. Complexation of Zn with PHA occurred mostly through binding to high affinity sites (HAS) and low affinity sites (LAS). Fractionation factors for Zn-66/Zn-64 ratios determined by mass balance calculations were equal to 1.0004 for HAS (alpha(HAS-solution)) and 1.0000 for LAS (alpha(LAS-solution)). Delta 66Zn(OM-FreeZn2+) should then vary according to the heterogeneous nature of the OM, because of the variable relative proportions of these two types of sites. The NICA-Donnan model, along with these fractionation factors and measured delta Zn-66(TotalDissolved), was used to simulate the corresponding isotopic composition of free Zn 21 in the Seine River, France: Delta Zn-66(TotaIDissolved-FreeZn2+) varied from +0.02 parts per thousand to +0.18 parts per thousand, depending on the HAS/LAS ratio assumed for the OM. This study allows a better understanding of Zn isotope fractionation mechanisms associated with organic matter binding.

International audience; The competition between REE, alkaline earth and d-transition metals for organic matter binding sites is still an open field of research; particularly, the mechanisms governing these phenomena need to be characterized in more detail. In this study, we examine spectroscopically the mechanisms of competitive binding of Eu(III)/Cu(II) and Eu(III)/Ca(II) pair to Gorleben humic acid (HA), as previously proposed in the framework of the NICA-Donnan model. The evolution of time-resolved laser induced luminescence spectra of humic-complexed Eu(III) showed two strikingly different environments for a comparable bound proportion for Cu(II) and Ca(II). Cu(II) seems to compete more effectively with Eu(III) inducing its release into the Donnan phase, and into the bulk solution as free Eu3+. This is evidenced both by the shapes of the spectra and by the decrease in the luminescence decay times. In contrast with that, Ca(II) induces a modification of the HA structure, which enhances the luminescence of humic-bound Eu(III), and causes a minor modification of the chemical environment of the complexed rare earth ion.

International audience; Colloidal organic matter (COM) collected in small and large watercourse tributaries of the Negro River (Brazil) were fractionated and characterized by an asymmetrical flow field-flow fractionation (AFIFFF) coupled to UV and seven angle laser light scattering (LS) detectors, and by size exclusion chromatography (SEC) coupled with a UV detection. Number and weight average molar masses, weight average gyration radiuses R-Gw and polydispersity indexes were obtained for each sample in two separate runs under conditions optimized for lower and larger size fractions. The results demonstrate the existence of a decrease of size of the colloidal matter when passing from first order streams to higher order rivers. No significant changes were found in size distributions of samples collected during the low and high flow stages at the same site. The influence of selected pre-treatments such as filtration and reverse osmosis pre-concentration on the size and molar mass distributions was also studied

The oxidative dissolution of mine wastes gives rise to acidic, metal-enriched mine drainage (AMD) and has typically posed an additional risk to the environment. The poly-metallic mine Dabaoshan in South China is an excellent test site to understand the processes affecting the surrounding polluted agricultural fields. Our objectives were firstly to investigate metal ion activity in soil solution, distribution in solid constituents, and spatial distribution in samples, secondly to determine dominant environment factors controlling metal activity in the long-term AMD-polluted subtropical soils. Soil Column Donnan Membrane Technology (SC-DMT) combined with sequential extraction shows that unusually large proportion of the metal ions are present as free ion in the soil solutions. The narrow range of low pH values prevents any pH effects during the binding onto oxides or organic matter. The differences in speciation of the soil solutions may explain the different soil degradation observed between paddy and non-paddy soils.

International audience; In an area that contains high concentrations of natural organic matter, it is expected that it plays an important role on the behavior of rare earth elements (REE), like europium, and of trivalent actinides. Competitive interactions with H+, inorganic species, major cations, e.g. Ca(II) or Mg(II), could influence these metals transport and bioavailability. Competitive experiments between cations, which can bind differently to humic substances and Eu3+, will bring an improved understanding of the competitive mechanisms. The aim of this study is to acquire data for Eu(III)/Cu(II) and Eu(III)/Ca(II) competitive binding to a sedimentary originated humic acid (Gorleben, Germany). The NICA-Donnan parameters for Ca2+, Cu2+, and Eu3+ obtained from competitive binding experiments using Ca2+ or Cu2+ ion selective electrodes were used to model time-resolved laser fluorescence spectroscopy (TRLFS) measurements. Eu3+ and Cu2+ are in direct competition for the same type of sites, whereas Ca2+ has an indirect influence through electrostatic binding.

Gold has been measured in water and suspended particulate matter samples coming from the Oubangui-Congo system. Gold anomalies up to 800 pico M /l were measured at two different locations. These are interpreted as the result of gold transport by dissolved organic complexes. Everywhere else the gold content is in the range of 10 −11 M /l and gold is present as an aurous hydroxichloride complex. The knowledge of both discharge rates and gold content allows a quantification of the gold input into the Atlantic ocean. Respective values for dissolved and particulate gold input are equal to 2.86 t/a and 2.95 t/a. Both chemical denudation and physical weathering rates were computed from this new set of data.

International audience; The role of metals in the behaviour of soil organic matter (SOM) is not well documented. Therefore, we investigated the influence of metals (Pb, Zn, Cu and Cd) on the dynamic of SOM in contaminated soils where maize (C4 plant) replaced C3 cultures. Three pseudogley brown leached soil profiles under maize with a decreasing gradient in metals concentrations were sampled. On size fractions, stable carbon isotopic ratio (d13C), metals, organic carbon and nitrogen concentrations were measured in function of depth. The determined sequence for the amount of C4 organic matter in the bulk fractions: M3 (0.9) > M2 (0.4) > M1 (0.3) is in agreement with a significant influence of metals on the SOM turnover. New C4 SOM, mainly present in the labile coarser fractions and less contaminated by metals than the stabilised C3 SOM of the clay fraction, is more easily degraded by microorganisms

International audience; Metal ion toxicity is not simply related to the total concentration but to the free or labile metal ion concentration. One of the techniques that can measure the free metal ion concentration is the Donnan Membrane Technique (DMT). However, this method has limitations in terms of a relatively high detection limit (in relation to typical environmental concentrations) and a long equilibration time. We have therefore developed the Flux Donnan Membrane (FDM) Technique, which is a dynamic modification of the standard DMT with improved detection limits and a more rapid response. We show that experimental calibrations of metal ion transport in the FDM can be used to measure [M]free under conditions of either solution-controlled or membrane-controlled diffusive transport. The FDM was used to measure cobalt binding isotherms by a humic substance over a large range of free Co concentrations and pH.