Solid-solution partitioning of Rare Earth Elements in mine-tailings and soils in China: experimental results and multi-surface modelling. Interfaces Against Pollution

La problématique air-climat-société est caractérisée à l’heure actuelle par une double propriété de transversalité (les polluants altérant la qualité de l’air et responsables des gaz à effet de serre sont souvent les mêmes) et de multiscalarité (de l’échelle du bâti à celle de la planète). À partir de ce point de départ et sous l’angle des sciences sociales, l’article interroge la place dévolue à ces enjeux au sein du répertoire de la « ville durable », qui marque de plus en plus les façons de faire et vivre la ville. Nous déplaçons le regard à partir de ce qui est souvent lu d’abord comme des questions techniques (mesure de la pollution atmosphérique, etc.), pour les restituer dans leur épaisseur sociale, celle de l’action publique autant que des modes de vie en ville. Méthodologiquement, nous procédons par une approche bibliométrique comparée, à partir d’un corpus de 18 revues scientifiques, francophones et anglophones. Une analyse statistique et textuelle a été conduite avec le logiciel libre IRaMuTeQ, spécifiant des univers de co-occurrence lexicale. Elle établit la portée de trois déclinaisons structurantes dans les lectures à la fois notionnelles, critiques et plus appliquées de la durabilité urbaine : le changement climatique et ses modèles, les déplacements et transports urbains, et le métabolisme urbain rapporté aux consommations d’énergie et aux flux de matières. Au final, c’est une double dimension théorique et pratique qui fait sens, et qu’atteste la démonstration à travers la force des liens entre les termes récurrents, les classes lexicales et les segments significatifs dégagés.

Understanding how essential and toxic elements are distributed in cereal grains is a key to improving the nutritional quality of cereal-based products. The main objective of this work was to characterize the distribution of Cd and of nutrients (notably Cu, Fe, Mn, P, S and Zn) in the durum wheat grain. Laser ablation inductively coupled mass spectrometry and synchrotron micro X-ray fluorescence were used for micro-scale mapping of Cd and nutrients. A dissection approach was used to quantitatively assess the distribution of Cd and nutrients among grain tissues. Micro X-ray absorption near-edge spectroscopy was used to identify the Cd chemical environment in the crease. Cadmium distribution was characterized by strong accumulation in the crease and by non-negligible dissemination in the endosperm. Inside the crease, Cd accumulated most in the pigment strand where it was mainly associated with sulfur ligands. High-resolution maps highlighted very specific accumulation areas of some nutrients in the germ, for instance Mo in the root cortex primordia and Cu in the scutellum. Cadmium loading into the grain appears to be highly restricted. In the grain, Cd co-localized with several nutrients, notably Mn and Zn, which challenges the idea of selectively removing Cd-enriched fractions by dedicated milling process.

Development of a flux DMT with integrated adsorptive stripping voltammetry for free metal ions detection in solution. Interfaces Against Pollution

Microbes play a major role on the behavior of metals and metalloids in soils. Arsenic speciation, in particular, is related to the activity of bacteria able to oxidize, reduce or methylate this element, and determines mobility, bioavailability and toxicity of As. Arsenate (AsV) is less toxic and less mobile than arsenite (AsIII). Bacterial As(III)-oxidation tends therefore to reduce the toxicity of arsenic in soils and its risk of transfer toward underlying aquifers. It is well known that organic matter influences abiotically the speciation of arsenic and thus its mobility in soils. Previous results suggest an effect of organic matter on the kinetics or efficiency of bacterial As(III)-oxidation in presence of oxygen, thus in conventional physico-chemical conditions of a surface soil. The objective of the present project is to quantify the influence of organic matters on the bacterial speciation of arsenic in polluted soils. Moreover, the biogeochemical consequences of this phenomenon on the mobility and ecotoxicity of this metalloid will be studied. The first task of this program is the systematic investigation of the influence of different types and concentrations of organic matters on the activity of As(III)-oxidizing pure strains. Influence of simple substrates (aspartate, succinate) and complex substrate (yeast extract) on As(III)-oxidation kinetics has been studied. For each experiment, the bacterial growth and the expression of genes involved in the speciation of arsenic, i.e. aio and ars genes, has been monitored. A direct perspective of this work will be to perform experiments with humic and fulvic acids (complex organic matter commonly found in soils), and with water-extracted organic matter from polluted soils. Then the As(III)-oxidation activity of bacterial communities extracted from contaminated soils will be followed. These assays should allow the screening of conditions which will be applied in subsequent experiments with several real contaminated soils, including a former mining site, impacted industrial sites, and a forest soil heavily contaminated after arsenical ammunitions storage. This work is co-funded by BRGM and ADEME (convention TEZ 11-16).

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The SOLEPUR process for the treatment of pig slurry, using soil as a treatment medium, was developed in France. This process decreased the COD of pig slurry by 99,9% bound 99,9% of the phosphorus and removed approximately 80% of the nitrogen. The remaining nitrogen was oxidized in the soil into nitrate and leached out in drainage water. The process of denitrification was selected to remove nitrate from the leachate and raw pig slurry was used as an external carbon source. The field and laboratory experiments demonstrated efficient denitrification of nitrate-rich leachate at an appropriate carbon/nitrogen ratio. Although nitrite appeared during denitrification as a transient product, it was effectively removed by the en of denitrification. Depending on the C/N ratio, the process of denitrification was accomplished after between 7 and 60 days and the denitrification rate varied between 0,5 and 1 kg N/d. Although a COD/NO3--N ration of 7 : 1 was essential for efficient denitrification, a higher ration of 8,75 : 1 preferable in order to obtain a complete and rapid denitrification. Further improvements are proposed are proposed in order to optimize the denitrification process. | Le procédé SOLEPUR pour le traitement du lisier de porc utilisant le sol comme support principal d'épuration a été développé en France. Ce procédé élimine 99,9% de la DCO du lisier, piège 99,9% du phosphore et élimine environ 80% de l'azote. Le procédé de dénitrification a été choisi pour éliminer les nitrates issus des percolats et le lisier de porc a été utilisé comme source de carbone. Les essais au champ et en laboratoire démontrent l'efficacité de la dénitrification dès lors que le rapport Carbone-sur-Azote était approprié. Selon ce ratio C/N, le processus de dénitrification se déroule au cours de séquences allant de 7 à 60 jours et le taux de dénitrification varie de 0,5 à 1 kgN/jour. Un ration DCO/N-NO3 de 7:1 est indispensable au bon déroulement de la dénitrification.