A. Boughriet

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

The 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.

Chemistry of metal sulfides in anoxic sediments

Using sequential extraction of solid sulfides, the determination of acid volatile sulfides (AVS) and chromium reducible sulfurs (CRS) in anoxic sediments from the Authie Bay (in northern France) has been undertaken because of the importance of the sediments as sinks for iron, sulfur and trace metals and as possible sources of pollution when reduced sediments are mixed with oxic waters (as a result of a sediment remobilization induced by physical disturbances such as tidal currents and dredgings), and subsequently oxidized. Chemical analysis of solutions recovered after sequential leaching of sediments with 1 M HCl, 1 M HF and concentrated HNO3 has enabled us to obtain profiles, s. sediment depth, of trace metals associated with pyrite. Porewater concentration profiles s. depth have been determined for several cations (Ca2+, Cd2+, Cu2+, Fe2+, Mg2+, Mn2+, Na+, Pb2+, Sr2+ and Zn2+) and anions (CO32−, PO43−, SO42− and S2−). Using the chemical equilibrium modeling program MINEQL+ with these analytical data, thermodynamic calculations have given information about the possibility of precipitation of discrete metal sulfide phases (FeS as greigite and amorphous FeS; ZnS, PbS, CuS and CdS), and coprecipitation with adsorption on solid FeS to produce solid solutions with iron sulfides. The degree of trace metal pyritization, DTMP, has been determined for these metals and compared to the degree of pyritization, DOP. The findings suggest that in Authie-bay sediments Mn is well pyritized; whereas Zn, Cu, Ni and above all Cd are weakly pyritized (MnZn≃Cu>NiCd). These observations seem to be intimately related to the existence of the discrete/separate solid phases CuS, CdS and ZnS, as predicted by thermodynamic calculations. Finally, analysis of crude sediments, heavy minerals and pyrite extracted by a heavy liquid density separation method, has been performed with a Raman microprobe to gain information about the geochemical and mineralogical characteristics of these sediments. The efficiency of sequential leachings of sediments (which were used for sedimentary pyrite recovery/attack and analysis of pyritic Fe and trace metal) has also been evaluated by these techniques.

Artefacts in the speciation of sulfides in anoxic sediments

The determination of sulfides and trace metals in sediment is handicapped by preparation techniques which can alter the chemical speciation of the different elements before the analysis. In this work, sulfide species such as AVS (acid volatile sulfides) and CRS (chromium reducible sulfides) were determined in anoxic sediment and their transformation, their loss and their effect on metal speciation were evaluated. The experiments were concentrated on the determinands which are most commonly used or dedicated to the determination of sulfides and metals, with emphasis on artefacts potentially introduced during sediment preparation such as sample storage, drying or oxygen contamination.

Fractionation of anthropogenic lead and zinc in Deûle River sediments

Environmental context. Metal contamination from smelting plants can have significant environmental and geochemical impacts on surrounding river systems, where large amounts of ores, dusts and slag are often discharged. Pollution levels in a river in northern France in the vicinity of a plant that had been producing zinc and lead have been measured. The authors assessed and identified the forms and phases of these metals in the polluted sediments, in order to assess the ability of these metals to pass into water when physicochemical changes (pH, redox potential) occur in the medium, for instance, as a result of dredging and barge traffic. Abstract. The degradation of a fluvial environment, the Deule River in northern France, with metals has been examined. Sites of environmentally significant sediment metal contamination were identified near a former smelting plant (Metaleurop) that produced lead and zinc. The chemical fractionation of sedimentary lead and zinc was carried out by using a four-stage sequential procedure in the polluted sediments. Chemical treatments were performed on these sediments with increasingly strong phase-specific reagents and under controlled thermal conditions; the recovered solutions were subsequently analysed using inductively coupled plasma–atomic emission spectroscopy (ICP-AES). The partitioning of lead and zinc in Deule River sediment samples was further compared with those found in less contaminated sites upstream and downstream from the former Metaleurop factory. Analytical data showed the extent of industrial pollution in this sediment, particularly, the implication of: (i) anthropogenic lead and zinc on the easily extractable fraction; (ii) smelter inputs containing of sulfidic ores on the sulfide/organic fraction; and (iii) smelter dust, slags and possibly ores derived from oxides in the reducible fraction. Overall, in polluted water, sediment-bound lead and zinc were found to be associated with all the sedimentary phases (the average mass percentages of lead and zinc in the exchangeable ions/carbonate fraction were respectively: 12% and 23%; in Fe and Mn oxides and hydroxides: 48% and 35%; in sulfides and organics: 33% and 29%; and in clays and aluminosilicates: 7% and 14%). Using X-ray diffraction, heavy minerals that were previously separated from sediments by decantation with gravity were shown to consist mostly of galena (PbS), wurtzite (ZnS), and pyrite (FeS2), showing the importance of sulfides in this sedimentary material. Using environmental scanning electron microscopy with energy dispersive X-ray spectroscopy (ESEM/EDS), sediments were found to be highly heterogeneous assemblages or aggregates, but with some isolated crystals that were identified. Detailed ESEM/EDS analyses (with imaging) have enabled us to demonstrate the existence of numerous lead and zinc phases that agree well with X-ray diffraction results and sequential extraction data.

On the chemical properties of sedimentary sulfur in estuarine environments

The composition of iron, sulfur and organic matter and their distributions with depth have been used as sensitive indicators of diagenetic processes occurring in anoxic sediments derived from the Authie and Seine bays in northern France. The contents of acid volatile sulfurs (AVS), chromium reduced sulfurs (CRS), total organic carbon and reactive Fe present in the sedimentary solid phase have been reported. These investigations have revealed that degree of pyritization (DOP) values remain nearly constant in the two sites, suggesting that pyrite formation is limited by the reactivity/availability of iron in the bulk sediment; whereas neither AVS or organic matter are important determinants of the degree of pyritization. The elemental composition of humic acids extracted from these anoxic sediments has also been examined with X-ray photoelectron spectroscopy (XPS). Diagenetic enrichment of sedimentary organic matter with sulfur occurs with depth in Authie Bay sediments, as evidenced by the XPS ratios S/C, whereas a depletion takes place with depth in Seine Bay sediments. Such a phenomenon results mainly from the availability of inorganic reduced sulfurs generated through bacterial sulfate reduction along the sedimentary column and, to a lesser extent, from the absence or weak re-supply of “active organic matter”.

Benthic exchange of sedimentary metals (Cd, Cu, Fe, Mn, Ni and Zn) in the Deûle River (Northern France)

Environmental context Exchange processes at the water–sediment interface can release metals to riverine waters, having negative effects on organisms in the water column. We investigate the geochemical processes and metal exchange between the surface sediment and the overlying water under metal contamination conditions. Results suggest that the sediment can be a significant source of metal pollution in aquatic systems, particularly during anoxic events. Abstract Experiments were performed on the Deule River (Northern France), which is strongly polluted by smelting plants, in the aim to investigate the influence of diagenetic processes and benthic macro-faunal activity on trace metal (Cd, Cu, Ni and Zn) and major metal (Fe, Mn) exchanges occurring at the water–sediment interface. Diffusive metal fluxes were determined from pore water metal concentration gradients measured in sediment cores. Benthic metal fluxes were evaluated using incubation chambers under dark conditions, and by further examining key variables (O2, CO2, redox potential and pH) affecting metal release and sequestration processes. As a whole, it was demonstrated that benthic fluxes were strongly dependent upon medium oxygenation and generation of colloidal iron oxides and hydroxides at the overlying water–sediment interface, raising the possibility of trace-metal adsorption and (co)precipitation.

Spectroscopic studies of vanadyl–calcite–water–oxygen systems and characterization of oxo-vanadium species deposited on CaCO3

The reactivity of vanadyl ions towards calcite has been studied in deoxygenated and oxygenated ultra-pure water at room temperature using several techniques: electron paramagnetic resonance (EPR), infrared (IR), laser Raman spectroscopy (LRS), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and liquid-phase and solid-state 51V NMR. Our investigations reveal that the surface chemistry of calcite depends strongly on the concentrations of VO2+ solutions applied in the process. Indeed, for low VO2+ concentrations (⩽5×10-5 mol dm-3) in interaction with calcite (4×10-2 mol dm-3), it was found that vanadium(IV) is well dispersed on CaCO3 surface in the form of solid solutions, (VO)xCa1-xCO3, and the kinetics of its oxygenation on a monolayer type structure is relatively rapid (half-life time: 9–10 min). However , for higher VO2+ concentrations (10-4 mol dm-3), metallic multilayers (and/or clusters) grow in the medium, and a three or four components solid solution of CaCO3–VOCO3–VO(OH)2–(H2O) appears as a new phase. Such VO(II) complexes (that can be written as follows: (OH)z(H2O)y(VO)xCa1+(z/2)-xCO3) in contact with oxygen lead slowly to the generation of polyoxovanadate species at the calcite surface that contain both V(IV) and V(V) atoms. The combined use of EPR, LRS, IR, XPS and 51V NMR techniques has allowed the successful monitoring of these calcite surface phenomena, proving the existence of these layers, and even identifying the chemical composition of such coatings.

Distribution coefficient and redox behaviour of uranium in Authie Bay (northern France)

Some mechanistic aspects associated with uranium release/immobilization and sedimentation in Authie Bay are presented in the present work. For this purpose, U contents in estuarine oxic waters, porewaters and sediment solids are determined. These analytical data allow us to appraise the partitioning of this metal between the liquid phase and the particulate matter/sedimentary material by calculating its distribution coefficient. Our findings further reveal that the distribution coefficient varies significantly with depth probably in response to the microbial activities in these sediments. This is confirmed by our studies on the geochemical behaviour of Fe and Mn in Authie Bay sediments. Finally, studies on the thermodynamic characteristics of sedimentary U in Authie Bay are undertaken in order to select possible U water–mineral equilibria that could involve in this environment, and to help define conditions of sedimentary U bioreduction.

The chemical behavior of sedimentary uranium in Authie Bay (France)

A general study on uranium present at trace levels in anoxic sediments derived from Authie Bay (in northern France) has been undertaken. For that purpose, concentrations of various uranium species in pore waters and recovered solutions (after mineralization of sediments) were determined by ICP-AES and ICP-MS. To access the extent of early diagenesis occurring in these sediments, reduced solid sulfur species were determined after their conversion into H2S gas following sequential extraction procedures. Our preliminary findings reveal that dissolved U(VI) precipitates rapidly with depth in pore waters certainly in the form of insoluble U(IV). Under stronger reducing conditions, new aqueous species [mostly and ] in which uranium is in oxidation state IV are formed in the pore water. Valuable interpretation of these particular properties of sedimentary U has necessitated a global examination of sediment biochemistry because of the influence of bacterial activities on the chemistry of Fe, Mn, S and more particularly U by metal-reducing bacteria.

Electrochemical and thermodynamic properties of oxygenated nitrogen compounds and aromatics in nitromethane. Application to the energetic aspects of the nitration process via inner-sphere and/or outer-sphere electron-transfer mechanisms

The electrochemical and thermodynamic behaviour of oxygenated nitrogen compounds and aromatics has been studied in nitromethane (under weak solvation conditions) in order to provide energetic and mechanistic information concerning aromatic nitration comparable to that from gas-phase studies.