Reagentless and calibrationless silicate measurement in oceanic waters

Determination of silicate concentration in seawater without addition of liquid reagents was the key prerequisite for developing an autonomous in situ electrochemical silicate sensor (Lacombe et al., 2007) [11]. The present challenge is to address the issue of calibrationless determination. To achieve such an objective, we chose chronoamperometry performed successively on planar microelectrode (ME) and ultramicroelectrode (UME) among the various possibilities. This analytical method allows estimating simultaneously the diffusion coefficient and the concentration of the studied species. Results obtained with ferrocyanide are in excellent agreement with values of the imposed concentration and diffusion coefficient found in the literature. For the silicate reagentless method, successive chronoamperometric measurements have been performed using a pair of gold disk electrodes for both UME and ME. Our calibrationless method was tested with different concentrations of silicate in artificial seawater from 55 to 140×10−6 mol L−1. The average value obtained for the diffusion coefficient of the silicomolybdic complex is 2.2±0.4×10−6 cm2 s−1, consistent with diffusion coefficient values of molecules in liquid media. Good results were observed when comparing known concentration of silicate with experimentally derived ones. Further work is underway to explore silicate determination within the lower range of oceanic silicate concentration, down to 0.1×10−6 mol L−1

Potential risks of metal toxicity in contaminated sediments of Deûle river in Northern France

International audienceThe aim of this paper was to evaluate the potential sediment cumulative damage and toxicity due to metal contamination in a polluted zone of Deûle river (in northern France) from nearby two smelters. Metal-enrichment factors and geoaccumulation indices measured with sediment depth revealed that - compared to background levels either in local reference soils or in world rivers sediments/suspended particulate matter - Cd contributed to the highest pollution levels, followed by Zn, Pb and to a much lesser extent Cu and Ni. A comparison of the vertical distribution of AVS (acid volatile sulfides), SEM (simultaneously extracted metals), TMC (total metal concentrations), TOC (total organic carbon) and interstitial water-metal concentrations in the sediment allowed us to highlight the extent of toxicity caused by Cd, Pb, Zn, Ni and Cu and to raise the possibility of their association with certain geochemical phases. To assess the actual environmental impacts of these metals in Deûle river, numerical sediment quality guidelines were further used in the present work. Sedimentary Pb, Zn, and Cd contents largely exceeded PEC (probable effect concentration) values reported as consensus-based sediment quality guidelines for freshwater ecosystems. As for risks of toxicity from pore waters, metal concentrations reached their maxima at the surficial layers of the sediment (1-3. cm) and IWCTU (Interstitial Water Criteria Toxicity Unit) observed for Pb and to a lesser extent Cd, violated the corresponding water quality data recommended by USEPA

Trace metal behaviour in the sediment : a key compartment of aquatic environment

La contamination de l'environnement aquatique par les éléments traces métalliques (ETM) est un des problèmes majeurs auxquels est confrontée la société actuelle. Ces métaux transitent dans la colonne d'eau avant de s'accumuler dans les sédiments où ils sont impliqués dans de nombreuses réactions biogéochimiques susceptibles de modifier plus ou moins fortement leur spéciation et donc leur (bio)disponibilité pour l'ensemble du réseau trophique. C'est au sein de ces problématiques centrées sur le devenir des ETM dans l'environnement aquatique que s'oriente ce travail de recherche. Inscrites dans le programme européen INTERREG-III Stardust, nos recherches ont été menées principalement dans trois sites d'études transfrontaliers franco-belge: l'Escaut, la Lys et !'Espierre. La distribution des ETM dans les sédiments des 3 sites a mis en évidence une forte contamination par le cadmium. Cependant, ces sédiments sont caractèrisés par un bon piégeage des ETM par les sulfures (principalement Cd, Cu, Pb et Zn) et dans une moindre mesure Ni et Co, plus labiles. Différents indices de qualité des sédiments et des eaux interstitielles ont ici été utilisés et ont montré que les sédiments de l'Espierre paraissaient peu toxiques en raison des fortes teneurs en AVS alors que les eaux interstitielles l'étaient davantage à cause d'une dureté relativement faible. D'autre part, la mise au point de DGT-AgI pour la mesure des sulfures a été mise en application et a permis de mettre en évidence l'effet saisonnier sur la production de sulfures dans les sédiments de la Mer du Nord. Parallèlement à ces recherches, le développement de microélectrodes d'or a finalement permis de suivre en continu dans la colonne d'eau, la concentration en Zn et Pb à des concentrations de l'ordre du ppb et des essais ont été réalisés directement dans le sédiment.The pollution of aquatic ecosystems by trace metals (TM) is one of the major problems to which is faced our present society. These metals pass in transit through the water column and are finally trapped in sediments. From then on, they are involved in several biogeochemical reactions that likely modify more or less significantly their speciation and therefore their (bio)availability for the whole trophic chain. My researches are involved in this environmental topic and take part in the European Program INTERREG-III, Stardust. Three cross-border sites between France and Belgium have mainly been considered for this thesis: Scheldt, Lys and Spierre rivers. Trace metal analysis in the three sites sediments have pointed out high contamination by cadmium. However the metals (mainly Cd, Cu, Pb and Zn) are mostly trapped in the reduced sulphur pool in these sediments. Conversely, Co and Ni are less trapped in these sediments due to their higher availability. Several sediment and porewater quality indexes have been used and shown that Spierre sediments seem to have a low toxicity according to the high AVS concentrations whereas interstitial waters are more polluted because of the low water hardness. Furthermore, the DGT -AgI technique used for the determination of dissolved sulphides has been deployed successfully in the North Sea sediment core to emphasize the sëasonal effect on the sulphides production. ln the same way, our work on gold microelectrodes results finally in the monitoring on line of Zn and Pb concentration in Deùle river, and sorne preliminary measurements directly in the Deûle sediments

Submillimetric pH measurement in interstitial water using a DET method based on an anion exchange resin coupled with pH indicators in a binding gel

International audienc

On the use of passive sampling (DGT) to understand the impact of changes in weather conditions on surface water quality

International audienc

Microstructure and corrosion behavior of extruded mg‐sn‐y alloys

10.3390/met11071095Metals117109

Voltammetric procedure for trace metal analysis in polluted natural waters using homemade bare gold-disk microelectrodes

International audienceVoltammetric procedures for trace metals analysis in polluted natural waters using homemade bare gold-disk microelectrodes of 25- and 125-μm diameters have been determined. In filtered seawater samples, square wave anodic stripping voltammetry (SWASV) with a frequency of 25 Hz is applied for analysis, whereas in unfiltered contaminated river samples, differential pulse anodic stripping voltammetry (DPASV) gave more reliable results. The peak potentials of the determined trace metals are shifted to more positive values compared to mercury drop or mercury-coated electrodes, with Zn always displaying 2 peaks, and Pb and Cd inversing their positions. For a deposition step of 120 s at −1.1 V, without stirring, the 25-μm gold-disk microelectrode has a linear response for Cd, Cu, Mn, Pb and Zn from 0.2 μg L−1 (1 μg L−1 for Mn) to 20 μg L−1 (30 μg L−1 for Zn, Pb and 80 μg L−1 for Mn). Under the same analytical conditions, the 125-μm gold-disk microelectrode shows linear behaviour for Cd, Cu, Pb and Zn from 1 μg L−1 (5 μg L−1 for Cd) to 100 μg L−1 (200 μg L−1 for Pb). The sensitivity of the 25-μm electrode varied for different analytes from 0.23 (±0.5%, Mn) to 4.83 (±0.9%, Pb) nA L μmol−1, and sensitivity of the 125-μm electrode varied from 1.48 (±0.7%, Zn) to 58.53 (±1.1%, Pb nA L μmol−1. These microelectrodes have been validated for natural sample analysis by use in an on-site system to monitor Cu, Pb and Zn labile concentrations in the Deûle River (France), polluted by industrial activities. First results obtained on sediment core issued from the same location have shown the ability of this type of microelectrode for in situ measurements of Pb and Mn concentrations in anoxic sediments

ADSORPTION OF IRON (II) ON SODIC ZEOLITES─BEARING BRICK (IN BATCH): INSIGHTS INTO INTERFACIAL CHEMICAL PROCESSES AND THERMODYNAMIC EQUILIBRIA

International audienc

Understanding the impact of the changes in weather conditions on surface water quality

International audienc

Adsorption des métaux sur brique transformée en zéolite : application au traitement de l’eau

International audienc