Biogeochemical factors affecting the distribution, speciation, and transport of Hg species in the Deûle and Lys Rivers (Northern France)

The Deûle River is a highly polluted River by heavy metals caused by the historical discharges of ore minerals from the former ore smelter “Metaleurop.” The potential mercury (Hg) pollution in the Deûle River implicates the importance of Hg distribution study in the river. As well as to configure the different biogeochemical factors that control the distribution and the potential transport of Hg to distant places. Four different sites were studied as follows: D-A (Deûle River, a site located upstream the river), D-B (Deûle River, a site located near a Zn, Pb, Cu, and Ni smelter that closed in 2003), L-C (Lys River, a site located upstream the confluence of the Deûle River with Lys River), and L-D (downstream the rivers confluence). Different Hg analyses were performed including total mercury in sediment (HgTS), methylmercury (MeHg) in sediment, total mercury in pore water (HgTPW), total mercury in surface water (HgTD), and total suspended particulate Hg in water (HgTP). HgTS decreases downstream from the Deûle River sites with a mean value of 11 ± 0.34 mg/kg to Lys River site (L-D) with a mean value of 0.53 ± 0.02 mg/kg at the confluence. The unaffected side of the Lys River, localized before the confluence (L-C), is characterized by low HgTS of an average value of 0.042 ± 0.003 mg/kg and high % MeHg reaching 4.2 %. Whereas, the highly contaminated Deûle sites are designated by low % MeHg with an average value of 0.053 %. Low pristine environments like that found in L-C site with more favorable biogeochemical conditions of lower concentrations of HgTS, sulfides, and Corg host more active biotic methylation than that of the highly polluted Deûle sites with high concentrations of HgTS and sulfides concentrations. Methylation in D-B (the closet site to Metaleurop smelter) is an old and recent methylation activity that has contributed to MeHg accumulation in the sediments as opposed to the exclusive recent events of methylation in Lys sites. MeHg in all sites is produced in situ rather than exported from other potential sources confirmed by significant relations of % MeHg with %Corg and AVS. Hg pollution is transported from the Deûle River to the Lys River (L-C and L-D) through suspended particles leached or remobilized from the River catchment. The dominance of reducing conditions in the Deûle River attributed to higher sulfide concentration has contributed to higher HgTPW than the Lys sites. Diffusive fluxes of HgT from sediment to water column for the Deûle and Lys River sites (L-C and L-D) were estimated to be 224, 53, and 2 ng/cm2 year, respectively

Determination of metal partitioning in porewater extracted from the Seine River Estuary sediment (France).

International audienc

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 (MnZnCu>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

Analytical and thermodynamic approach to the mineralogical and compositional studies on anoxic sediments

BACKGROUND, AIM AND SCOPE. The identification of certain minerals directly in the raw sediment has proved to be difficult, if not impossible, because of their instability and/or low contents. This explains why the characterization/composition/crystalline nature of multiple (co)precipitates and solid solutions often necessitate the combined use of density separation methods and macro and microanalytical techniques, and in some cases the possible existence of certain mineral solids is only sustained from thermodynamic considerations. In this context, the comparison of porewater concentration profiles with thermodynamic calculations recently proved to be a convenient way of obtaining clues relative to the potential occurrence of natural minerals. METHODS. Porewaters and sedimentary-solid phases were extracted from sliced sediment samples collected in the Seine estuary (northern France), and studied as a function of sediment depth. Porewater concentration profiles were determined for Ca, Fe, Mg, Mn, Na, P and Sr using inductively coupled plasma atomic emission spectroscopy, and for dissolved sulfur using square wave, cathodic stripping voltammetry. To obtain information about sediment mineralogy, sedimentary solid phases were analysed directly and after density separation with a heavy liquid (CHBr3) by means of several techniques: X-ray diffraction; electron spin resonance and micro-Raman spectroscopies. Furthermore, using sequential extraction procedures, the chemical speciation versus depth of several elements (Al, Ca, Fe, Mg, Mn, P, Pb, Sr, Ti, and Zn) and particularly sulfur [i.e. acid volatile sulfides (AVS) and chromium reducible sulfurs (CRS)] were undertaken. RESULTS AND DISCUSSION. From these analytical data, some thermodynamic calculations [using ion activity products (IAP)] were attempted for the anoxic porewaters where most of the ionic complexing species were measured to support the involvement of relevant geochemical equilibria between these ions and some metals and the existence of any discrete solid phases (calcite, dolomite, greigite and probably vivianite, apatite and siderite), as well as coprecipitates and solid solutions in calcium carbonate. CONCLUSIONS. Thermodynamic equilibria in sedimentary media are rarely achieved because many chemical processes in these systems are established in long periods. Nevertheless, these calculations remain useful to increase our insight into the considered system. They help to support our view about the possible existence of certain minerals (iron sulfides, calcite, dolomite...). They also help account for the real power of ESR for indicating the presence of hypothesised solid solutions, MnxCa1-xCO3. The critical investigations of the authors, however, reveal some weaknesses of XRD and Raman microscopy for identifying minor minerals/precipitates, which result from combinations between the inorganic anions PO43–, CO32– and S2– and the metallic cations Fe2+, Mn2+, Mg2+, and Sr2+

Caractéristiques de ressources en eau des plateaux de Akkar au Nord du Liban

L'analyse chimique de 20 ressources en eau des plateaux de Akkar au Nord du Liban a été effectuée avec une recherche des éléments à l'état de trace par ICP-AES. Les résultats obtenus révèlent l'absence d'une pollution chimique, le caractère doux des eaux et la diversité chimique des sources étudiées. Confrontées avec les connaissances sur les aquifères de la région, les sources se regroupent en fonction de la formation géologique des plateaux. Néanmoins certaines sont uniques ; c'est le cas de la source de Ain Al-Jaouzé à Hrar que se caractérise par son aspect très faiblement minéralisé (conductivité 63 µ/cm), par la quasi absence des ions majeurs (Na, Ca, K, Mg) et la présence à l'état de trace des oligo-éléments (Fe, Mn, Si, Al) ; la source de Ain Al-Aarbit à Barqayel qui se distingue par son pH légèrement acide (5.6), par la faible teneur en Mg et par la présence du Ba et du Cr à l'État de trace, alors que la source de Ain El-Helzane à Jebrayel est la plus fortement minéralisée (conductivité 310 µ/cm), c'est elle qui contient le plus de Ca, K, Na, Mg, Ni, B, quant à la source de Ain El-Delbet à El-Qamouaa, elle se caractérise par sa pureté exceptionnelle et son pH légèrement basique (8.13). Cette première étude sur la caractérisation des sources en eau à Akkar pourrait servir de base à l'exploitation de certaines de ces sources

Multi-component adsorption of copper, nickel and zinc from aqueous solutions onto activated carbon prepared from date stones

The removal of Cu2+, Ni2+, and Zn2+ ions from their multi-component aqueous mixture by sorption on activated carbon prepared from date stones was investigated. In the batch tests, experimental parameters were studied, including solution pH, contact time, initial metal ions concentration, and temperature. Adsorption efficiency of the heavy metals was pH-dependent and the maximum adsorption was found to occur at around 5.5 for Cu, Zn, and Ni. The maximum sorption capacities calculated by applying the Langmuir isotherm were 18.68 mg/g for Cu, 16.12 mg/g for Ni, and 12.19 mg/g for Zn. The competitive adsorption studies showed that the adsorption affinity order of the three heavy metals was Cu2+ > Ni2+ > Zn2+. The test results using real wastewater indicated that the prepared activated carbon could be used as a cheap adsorbent for the removal of heavy metals in aqueous solutions

Abundance, Diversity and Activity of Sulfate-Reducing Prokaryotes in Heavy Metal-Contaminated Sediment from a Salt Marsh in the Medway Estuary (UK)

International audienceWe investigated the diversity and activity of sulfate-reducing prokaryotes (SRP) in a 3.5-m sediment core taken from a heavy metal-contaminated site in the Medway Estuary, UK. The abundance of SRPs was quantified by qPCR of the dissimilatory sulfite reductase gene β-subunit (dsrB) and taking into account DNA extraction efficiency. This showed that SRPs were abundant throughout the core with maximum values in the top 50 cm of the sediment core making up 22.4% of the total bacterial community and were 13.6% at 250 cm deep. Gene libraries for dsrA (dissimilatory sulfite reductase α-subunit) were constructed from the heavily contaminated (heavy metals) surface sediment (top 20 cm) and from the less contaminated and sulfate-depleted, deeper zone (250 cm). Certain cloned sequences were similar to dsrA found in members of the Syntrophobacteraceae, Desulfobacteraceae and Desulfovibrionaceae as well as a large fraction (60%) of novel sequences that formed a deep branching dsrA lineage. Phylogenetic analysis of metabolically active SRPs was performed by reverse transcription PCR and single strand conformational polymorphism analysis (RT-PCR-SSCP) of dsrA genes derived from extracted sediment RNA. Subsequent comparative sequence analysis of excised SSCP bands revealed a high transcriptional activity of dsrA belonging to Desulfovibrio species in the surface sediment. These results may suggest that members of the Desulfovibrionaceae are more active than other SRP groups in heavy metal-contaminated surface sediments

Metals sediment toxicity: Chemical approach by SEM/AVS ratio. Application on Seine estuary sediments

Within the framework of environmental quality criteria for certain heavy metals in sediment, Acid Volatile Sulphides (AVS) has been proposed as the primary standardisation parameter in combination with the amount of simultaneously extracted metals (SEM) [1]. AVS, comprising essentially iron monosulphides in sediments, are available for binding divalent cationic metals through the formation of insoluble metal-sulphide complexes, thereby controlling the metal bioavailability and subsequent toxicity for benthic biocommunities. AVS is operationally defined as the amount of sulphides that can be volatilised during a cold acid extraction. The AVS-bound metals, with environmental concern (usually Cd, Cu, Ni, Pb and Zn), are extracted at the same time and are called simultaneously extracted metals (SEM). The ratio or the difference between AVS and SEM gives an indication of the potential sediment toxicity. Such problems on extraction procedure appears: for AVS hydrochloric acid 6 mol.dm$^{-3}$ is current1y used [2-3] even so for SEM use of hydrochloric acid 1 mol.dm$^{-3}$ is advised [4-5]. To investigate the influence of acid strength, sulphides and metals extractions are realized on anoxic sediments from seine estuary. SEM/AVS ratio for different acid was calculated and toxicity associated is discussed