Contamination of surface waters by mining wastes in the Milluni Valley (Cordillera Real, Bolivia): Mineralogical and hydrological influences

This study is one of very few dealing with mining waste contamination in high altitude, tropical-latitude areas exploited during the last century. Geochemical, mineralogical and hydrological characterizations of potentially harmful elements (PHEs) in surface waters and sediments were performed in the Milluni Valley (main reservoir of water supply of La Paz, Bolivia, 4000 m a.s.l.), throughout different seasons during 2002-2004 to identify contamination sources and sinks, and contamination control parameters. PHE concentrations greatly exceeded the World Health Organization water guidelines for human consumption. The very acidic conditions, which resulted from the oxidation of sulfide minerals in mining waste, favoured the enrichment of dissolved PHEs (Cd > Zn » As >> Cu ∼ Ni > Pb > Sn) in surface waters downstream from the mine. Stream and lake sediments, mining waste and bedrock showed the highest PHE content in the mining area. With the exception of Fe, the PHEs were derived from specific minerals (Fe, pyrite; Zn, Cd, sphalerite, As, Fe, arsenopyrite, Cu, Fe, chalcopyrite, Pb, galena, Sn, cassiterite), but the mining was responsible for PHEs availability. Most of the PHEs were extremely mobile (As > Fe > Pb > Cd > Zn ∼ Cu > Sn) in the mining wastes and the sediments downstream from the mine. pH and oxyhydroxides mainly explained the contrasted availability of Zn (mostly in labile fractions) and As (associated with Fe-oxyhydroxides). Unexpectedly, Pb, Zn, As, and Fe were significantly attenuated by organic matter in acidic lake sediments. Hydrological conditions highly influenced the behaviours of major elements and PHEs. During wet seasons, major elements were diluted by meteoric waters, whereas PHEs increased due to the dissolution of sulfides and unstable tertiary minerals that formed during dry seasons. This is particularly obvious at the beginning of the wet season and contributes to flushes of element transport downstream. The high altitude of the study area compensates for the tropical latitude, rendering the geochemical behaviour of contaminants similar to that of temperate and cold regions. These results might be representative of geochemical processes in ore deposits located in the high Andes plateau, and of their influence on PHE concentrations within the upper Amazon basin. Although mining activities in this region stopped 10 years ago, the impact of mining waste on water quality remains a serious environmental problem

Spéciation et transfert du zinc dans un dépôt de sédiment de curage contaminé : évolution le long du profil pédologique

Pour assurer l'entretien des voies navigables, les sédiments de canaux sont régulièrement curés et généralement mis en dépôt. Cette pratique peut s'avérer dangereuse pour l'environnement lorsque ces sédiments sont contaminés. Le but de ce travail était d'identifier la spéciation du zinc dans un sédiment pollué et dans le sol sous-jacent après dépôt. Le transfert du zinc du sédiment vers le sol au cours du temps a été suivi par analyse des eaux, du sédiment et du sol. Les formes chimiques du zinc dans les phases solides ont été déterminées en combinant des techniques de micro-analyse (MEB-EDS, u-PIXE, u-RBS, u-SXRF) et la spectroscopie EXAFS, après fractionnement physique et chimique des échantillons. Les spectres EXAFS ont été exploités par analyse en composantes principales. Les principaux résultats de ce travail sont les suivants: * Dans le sédiment initial, le zinc est majoritairement présent sous forme de sphalérite (ZnS) et associé aux oxyhydroxydes de fer mal cristallisés. Trois espèces minoritaires, la willémite (Zn2SiO4), la zincite (ZnO) et un phyllosilicate zincifère ont été également identifiées. La présence de willémite, de zincite, et d'au moins une partie de la sphalérite, est attribuée aux activités anthropiques de grillage du minerai de zinc. La fixation d'une partie du zinc par les oxyhydroxydes de fer et les phyllosilicates résulte de l'altération des minéraux primaires. * L'oxydation des sulfures est le processus majeur contribuant à la mise en solution du zinc au cours du temps. La réduction des oxyhydroxydes de fer survenant lors des périodes d'hydromorphie concourt, dans une moindre mesure, à la mise en solution du zinc associé. * Au cours du temps, la proportion de ZnS diminue dans le sédiment au profit des formes secondaires. Un enrichissement en zinc a été mesuré après 16 mois de dépôt dans les premiers centimètres du sol sous-jacent. La majorité du zinc est alors sous forme de ZnS du fait d'une importante migration particulaire per descensum. Une autre partie du métal présent dans le sol est associée aux phyllosilicates et oxyhydroxydes de fer. Les conditions physico-chimiques du milieu (pH, Eh, concentrations en zinc, silice et fer dissous) sont favorables à la précipitation du zinc et de la silice libre sous forme de phyllosilicate zincifère, et à celle du fer dissous sous forme d'oxyhydroxydes de fer amorphes susceptibles de fixer le zinc. * Les bilans géochimiques montrent que la quantité de zinc exportée en solution, pendant la période de suivi du dépôt (16 mois), est faible en regard du stock contenu dans le sédiment, mais que cette quantité augmente de façon significative au cours du temps. Cependant, la majorité du zinc exporté en solution est vraisemblablement refixée par les phases d'altération. * Les phases d'altération comme les oxyhydroxydes de fer et les phyllosilicates pourraient être exploitées à des fins de rémédiation.pas de résum

Use of the synchrotron radiation to characterize metals in plants: the case of Cd in the hyperaccumulator Arabidopsis halleri

info:eu-repo/semantics/publishe

LUCIA To Decipher Metal Homeostasis And Toxicity In Plants

Some metals such as iron (Fe) are essential to plants whilst others such as cadmium (Cd) are toxic even at low concentration. The identification of the chemical forms of these metals (speciation) and their localization at the tissue and cell level are crucial to understand theirtrafficking and storage and finally the ability for the plant to cope with their potential toxicity or requirement. LUCIA beamline offers the possibility to access the metal distribution thanks to micro X-ray fluorescence with a micrometer sized lateral resolution and to investigate the metal speciation using micro X-ray Absorption Near Edge Structure. Importantly, the beamline is designed for measurements in cryogenic conditions, which is necessary to limit metal redistribution and speciation change in biologic samples. Here, we present twoexamples of our work performed on Lucia during the last years. The first one deals with Fe homeostasis and the discovery of an important pool of iron in plant cell nucleus (1) as well as the Fe species in plant embryos (2). The second example is dedicated to the study of Cd sequestration in Anthyllis vulneraria used as a pioneer plant in the phytostabilization of mining sites (3).REFERENCES1. H. Roschzttardtz, L. Grillet, M.P. Isaure, G. Conejero, R. Ortega, C. Curie, and S. Mari, J. Biol. Chem. 286, 27863-27866 (2011).2. L. Grillet, L. Ouerdane, P. Flis, M. Thi Thanh Hoang, M. P. Isaure, R. Lobinski, C. Curie, and S. Mari, J. Biol. Chem. 289, 2515-2525(2014).3. S. Huguet, S. Soussou, J. C. Cleyet-Marel, N. Trcera, M. P. Isaure, ‘Rhizostabilization of a mine tailing highly contaminated:preliminary study of Cd localization and speciation in Anthyllis vulneraria in ‘Proceedings of the 16th International Conference onHeavy Metals in the Environment’, edited by N. Pirrone, Roma, Italy, 2013, n°19008

Coupling fluorescent probes to characterize S-containing compounds in a sulfate reducing bacteria involved in Hg methylation

The microbial methylation of inorganic mercury Hg(II) is governed by S-containing compounds such as thiols (RSH) and sulfides (S2−). Various S-containing molecules in an environmental or culture medium can be difficult to assess because of the complexity of the medium, poor stability, and low concentration ranges of sulfide and thiol compounds. Here, we applied two fluorescence spectroscopy-based methods using α, β-unsaturated ethanoylcoumarin fluorophore (DHC) for the quantification of sulfides, and monobromo (trimethylammonio) bimane (qBBr) to quantify total thiol concentrations (in extracellular and bacterial cell fractions). The potential interferences of both organic and inorganic compounds from the matrix were evaluated. In the presence of Hg species, both methods allowed the quantification of free sulfides or thiols (not forming complexes with Hg). The two methods were highly sensitive, with detection limits of 100 nM and 20 nM for thiols and sulfides, respectively. They also exhibited high selectivity for the detection of thiols or sulfides against other tested matrix compounds. Finally, both methods were applied to characterize S-containing compounds in a culture of Pseudodesulfovibrio hydrargyri strain BerOc1, a methylating sulfate-reducing bacterium (SRB) exposed to 0.1 mM of cysteine. During bacterial growth, we used (i) DHC probe to quantify sulfide concentration in the bulk fraction, (ii) qBBr for total extracellular thiols and total thiols adsorbed on the cells, and (iii) liquid chromatography-tandem mass spectrometry to track cysteine degradation and characterize other thiols. The time series until the end of BerOc1 growth showed biodegradation of cysteine, and biosynthesis of sulfides and other thiol compounds

Ascorbate efflux as a new strategy for iron reduction and transport in plants

Iron (Fe) is essential for virtually all living organisms. The identification of the chemical forms of iron (the speciation) circulating in and between cells is crucial to further understand the mechanisms of iron delivery to its final targets. Here we analyzed how iron is transported to the seeds by the chemical identification of iron complexes that are delivered to embryos, followed by the biochemical characterization of the transport of these complexes by the embryo, using the pea (Pisum sativum) as a model species. We have found that iron circulates as ferric complexes with citrate and malate (Fe(III)3Cit2Mal2, Fe(III)3Cit3Mal1, Fe(III)Cit2). Because dicotyledonous plants only transport ferrous iron, we checked whether embryos were capable of reducing iron of these complexes. Indeed, embryos did express a constitutively high ferric reduction activity. Surprisingly, iron(III) reduction is not catalyzed by the expected membrane-bound ferric reductase. Instead, embryos efflux high amounts of ascorbate that chemically reduce iron(III) from citrate-malate complexes. In vitro transport experiments on isolated embryos using radiolabeled (55)Fe demonstrated that this ascorbate-mediated reduction is an obligatory step for the uptake of iron(II). Moreover, the ascorbate efflux activity was also measured in Arabidopsis embryos, suggesting that this new iron transport system may be generic to dicotyledonous plants. Finally, in embryos of the ascorbate-deficient mutants vtc2-4, vtc5-1, and vtc5-2, the reducing activity and the iron concentration were reduced significantly. Taken together, our results identified a new iron transport mechanism in plants that could play a major role to control iron loading in seeds

Pinus nigra bark from a mercury mining district studied with high resolution XANES spectroscopy

International audienceTree bark near former mercury (Hg) mines and roasting plants is known to have exceptionally high (up to several mg kg−1) Hg concentrations. This study explores the change of Hg speciation with depth (down to 25–30 mm from the outermost surface) in black pine (Pinus nigra) bark by means of high-resolution X-ray absorption near edge structure (HR-XANES) spectroscopy at the Hg LIII-edge. Principal component analysis and linear combination fitting applied to the HR-XANES spectra suggested that in the outermost layer (∼0–2 mm from the surface), roughly 50% of Hg is in the form of nanoparticulate metacinnabar (nano-β-HgS). A progressive increase in Hg-organic species (Hg bound to thiol groups) is found in deeper bark layers, while nano-β-HgS may decrease below the detection limit in the deepest layers. Notably, bark layers did not contain cinnabar (α-HgS), which was found in the nearby soils along with β-HgS (bulk), nor Hg0, which is the main Hg species in the atmosphere surrounding the sampled trees. These observations suggested that nano-β-HgS, at least in part, does not originate from mechanically trapped wind-blown particulates from the surrounding soil, but may be the product of biochemical reactions between gaseous elemental Hg and the bark tissue