Laura Sigg: Investigating the Speciation, Bioavailability and Ecotoxicology of Trace Metals in Natural Waters

Laura Sigg is an internationally renowned expert in the aquatic geochemistry and ecotoxicology of trace metals. During her outstanding career as a researcher at Eawag, the Swiss Federal Institute of Aquatic Science and Technology, and adjunct professor at the Department of Environmental Systems Science of ETH Zurich, she pioneered the development of new theoretical concepts as well as practical methods for the assessment of the speciation, fate and effect of trace metals in the hydrosphere (Fig. 1). During his stay in Toulouse as invited professor some years ago, George Luther III proposed us to edit a special issue of Aquatic Geochemistry to honor our colleague Laura Sigg, who serves as a long-term associate editor of this journal. We were very happy to take up this challenge and invited people to submit original manuscripts to a special issue focusing on the fields of speciation, bioavailability and ecotoxicology of trace metals in natural waters. After being educated in chemistry with Paul W. Schindler at the University of Bern, where she learned the precision and rigor of experimental work and how to assess and synthetize ideas, Laura Sigg moved to Zurich and worked for her PhD with Werner Stumm. She started the first part of her career with ground-breaking research on thermodynamic models for adsorption processes at the solid–water interface and published two highly influential papers which became classics in this field (Stumm et al. 1980; Sigg and Stumm 1981)

Hg(II) trace electrochemical detection on gold electrode: Evidence for chloride adsorption as the responsible for the broad baseline

Investigations were performed in order to clarify the origin of the broad baseline observed during Hg(II) trace electrochemical detection on gold electrode in the presence of Cl- anions. The influence of Cl- concentration on the shape of the voltammograms was studied in the presence and in the absence of Bovine Serum Albumin (BSA) in order to bring out adsorption/desorption processes. On the basis of these experiments, and contrary to what has been proposed by several authors in the literature, it was proved that the broad baseline does not result from calomel (Hg2Cl2) formation but is rather related to an interaction between Cl- and polycrystalline Au electrode surface. The evolution of the shape of the baseline was also studied in the presence of other halide anions, namely F-, Br-, and I-. The latter two were found to induce a broad baseline similar to that recorded in the presence of Cl-. Finally, it was shown that BSA addition is not suitable for Hg(II) detection since it prevents Hg(0) deposition onto the electrode surface

Sources et cheminements des polluants

Dans l’environnement, un ensemble complexe de processus chimiques, physiques, biologiques et géologiques régule le cycle des éléments et des composés chimiques. La composition des eaux, qui résulte de ces processus, est naturellement contrôlée par l’altération des minéraux qui consomme du CO2 atmosphérique et l’activité des organismes vivants. Les activités anthropiques génèrent des contaminants véhiculés dans les différents compartiments interdépendants: eaux, biosphère, atmosphère, sol et roches). Pour comprendre le cheminement des composés dans les eaux, il faut tenir compte du trajet des eaux dans chaque compartiment et des relations entre les compartiments. Les processus physico-chimiques sont associés aux échanges entre les phases dissoutes et solides particulaires , aux interactions avec les organismes, ainsi qu’aux processus physiques. Ceux-ci sont plus ou moins fortement perturbés par les activités humaines, dont l’expansion et l’intensification accroissent la dispersion des polluants dans les milieux naturels. Il en est ainsi des flux de certains polluants qui peuvent être très largement supérieurs aux flux d’éléments naturels libérés par l’érosion chimique et les interactions avec les organismes

Influence of the gold nanoparticles electrodeposition method on Hg(II) trace electrochemical detection

Gold nanoparticles (AuNPs) were deposited on Glassy Carbon (GC) substrate by using three electrochemical techniques: Cyclic Voltammetry (CV), Chronoamperometry (CA) and Potentiostatic Double-Pulse (PDP). For each electrodeposition method, the resulting AuNPs-modified electrodes were characterized by CV in H2SO4 and Field Emission Gun Scanning Electron Microscopy (FEG-SEM). CA was found to be the best electrodeposition mode for controlling the morphology and the density of AuNPs. The modified electrodes were used for low Hg(II) concentration detection using Square Wave Anodic Stripping Voltammetry (SWASV). AuNPs obtained by CA afforded the best amperometric response while involving the lowest amount of charge during the electrodeposition step (QAu(III)). This analytical response is correlated to both the smallest particle size (ca. 17 nm in diameter) and the highest particle density (332 particles μm−2), thus displaying high electrode effective surface area. In these optimal conditions, using a Hg(II) preconcentration time of 300 s, the nanosensor array exhibited a linearity range from 0.80 to 9.9 nM with a sensitivity of 1.16 μA nM−1. A detection limit of 0.40 nM (s/n = 3) was reached

Adsorption of Copper, Nickel, and Cadmium on Goethite in the Presence of Organic Ligands

Adsorption of copper, cadmium and nickel at low concentrations on goethite was studied in the presence of the simple organic ligands oxalate, salicylate, and pyromellitate. The experimental metal adsorption behavior was compared to calculations with a surface complexation model to evaluate the most important interactions. Oxalate mostly decreased Cu and Ni adsorption at high pH-values by competition between solution and surface complexation but had no effect on Cd adsorption. Cu adsorption in the presence of oxalate below pH 6 could best be described by defining a ternary complex of type A (surface-metal-ligand). Salicylate had only minor effects on metal adsorption. The adsorption of Cu in the presence of salicylate above pH 5 could be explained by a ternary complex of type A. Pyromellitate increased the adsorption of Cu and Cd in the acidic pH-range, likely by formation of ternary surface complexes of type B (surface-ligand-metal

Effect of the presence of pyrite traces on silver behavior in natural porous media

In order to better understand the fate of the toxic element Ag(I), sorption of Ag(I) was studied from batch experiments, at different pHs (2–8) and at 298K. A pure quartz sand (99.999% SiO2) and “natural” quartz sand (99% SiO2, and traces of Fe, Al, Mn (hydr)oxides, of clays and of pyrite) were used as sorbents. The Ag(I) sorption behavior depends strongly on pH with isotherm shapes characteristic of Langmuir-type relationship for initial Ag concentration [Ag(I)], range between 5.0×10−7 and 1.0×10−3M. Even if the Ag (I) sorption capacity on pure quartz sand is very low compared to the natural quartz sands, its affinity is rather high. From speciation calculations, several sites were proposed: at pHi 4, 6 and 8, the first surface site is assumed to be due to iron (hydr)oxides while the second surface site is attributed to silanols. At pHi 2, sorption of Ag(I) was assumed to be on two surface sites of iron (hydr)oxides and a third surface site on silanol groups. Even if the sand is mainly composed of silica, the trace minerals play an important role in sorption capacity compared to silica. The conditional surface complexation constants of Ag(I) depend on pH. On the other hand, it is shown that the Ag speciation depends strongly on the history of “natural” quartz sand due to initial applied treatment, little rinsing or longer washing. In the presence of low amount of pyrite, strong complexes between Ag(I) and sulfur compounds such as thiosulfates due to oxidative dissolution of pyrite are formed what decreases Ag sorption capability. SEM–EDS analyses highlighted the surface complexation–precipitation of Ag2S and Ag(0) colloids which confirmed the important role of pyrite on Ag(I) speciation

Chromatographic Methods and Transport of Chemicals in Soils

Transport of chemicals in soils and groundwater aquifers has become an increasingly important field in hydrology and soil science. Much progress in this field originates from the picture of the soil as a giant chromatography column. Therefore, one uses successfully concepts borrowed from chromatography theory. The applicability of such ideas for the description of the transport of chemicals in the field is reviewed

Fluvial trasnports of mercury pollution in the Ill river basin (Northeastern France): pertitioning into aqueous phases, suspended matter and bottom sediments.

The increase and dispersion in aquatic systems of mercury, which is not very abundant in the global environment, are mainly due to the industrial development and intensification of human activities (halogen chemicals, dental and pharmaceutic industries, agriculture, gold mining, etc.). In the Alsace region (northeastern France), the Ill river and one of its tributaries, the Thur, are the most polluted because of industrial wastewaters from the chlorine and soda industry which uses mercury as a cathode in electrolysis

Interactions between Kluyveromyces marxianus from cheese origin and the intestinal symbiont Bacteroides thetaiotaomicron: Impressive antioxidative effects

The effects of yeast Kluyveromyces marxianus S-2-05, of cheese origin, were assessed on the intestine anaerobe symbiont Bacteroides thetaiotaomicron ATCC 29741 to unveil any changes in its antioxidant properties. To this end, these microorganisms were grown and incubated either separately, or co-incubated, under anaerobic atmosphere. Afterwards, the microbial cells were recovered and washed, and extracts were prepared using a sterile detergent solution to mimic the intestine detergent content. The extracts prepared from K. marxianus S-2-05 and reference strain K. marxianus MUCL 29917, grown under different conditions, were assessed for their antioxidant properties against superoxide anion and hydrogen peroxide. Extracts from both yeasts showed antioxidative effects, which were particularly important for K. marxianus S-02-5 after anaerobic incubation. Moreover, K. marxianus S-02-5 displayed a high level of activity against the aforementioned reactive oxygen species, enhancing that of B. thetaiotaomicron ATCC 29741, after the co-incubation process. Two-dimensional polyacrylamide gel electrophoresis was used to separate the proteins extracted. Superoxide dismutase, thiol peroxidase, rubrerythrin -intensively produced by B. thetaiotaomicron induced by the yeast-were identified by mass spectrometry. The antioxidative potential evidenced for K. marxianus S-02-5 is another advantage which could justify the utilization of this strain as a probiotic for countering intestinal inflammatory processes. © 2017 Elsevier Lt