Chemical extractions and predicted free ion activities fail to estimate metal transfer from soil to field land snails.

International audienceThis study investigates the relevance of several soil chemical extractions (calcium chloride, acetic acid, citric acid and a four-step sequential procedure) and predicted free metal ion activities in the soil solution to characterise the transfer of trace metals (Cd, Pb, and Zn) from soil to snail soft tissues over a large smelter-impacted area (Metaleurop Nord, Nord-Pas-de-Calais, France). The study was first performed on six snail species together and then specifically on Cepaea sp. and Oxychilus draparnaudi. When the six species were considered together, the accumulation of metals depended mostly on the species. When significant, total or extractable metal concentrations, or the predicted free ion activities, accounted for less than 7% of the variation of the metal concentrations in the snail tissues. Species-specific analyses showed that extractable concentrations explained approximately 25% of the variation of the metal concentrations in O. draparnaudi, and up to 8% in Cepaea snails. When using total soil concentrations and soil properties as explanatory variables, the models were generally slightly better, explaining up to 42% of the variance. The soil extraction procedures and predicted free ion activities used in this study did not accurately estimate the metal transfer from soil to snails and could not be used in risk assessment

Spectrocolorimetric interpretation of sedimentary dynamics: The new "Q7/4 diagram"

International audienceColour is a fundamental property of sediment and is often used for lithographic description to determine sedimentological structures, facies etc. However, the sedimentary information contained in this parameter is difficult to extract because it is difficult to quantify. Colour can be quantified by spectrocolorimetry which provides very high resolution data quickly and non-destructively. When adapted to sedimentology, spectrocolorimeters prove to be powerful tools due to their low purchase and maintenance costs, and some are portable and easily used in-the-field. Several methods have been used to extract sedimentological data from colorimetric spectra (first derivatives, factorial analysis, etc.). In the present study, we first provide a review of the sedimentological application of spectrophotometers and, after having described these methods, their advantages and disadvantages, we then describe a new tool called the Q7/4 diagram (abscissa L*; Ordinates 700/400 ratio). This new technique permits sedimentological units to be defined, allows the identification of different sediment components and provides 5 distinct poles: Clayey deposits, organic rich deposits (chlorophyll a and by products), altered organic matter deposits, iron rich deposits, carbonated deposits. Coupled with the analysis of first derivative spectra, it is possible to distinguish different pigments linked to the degradation and/or nature of the organic material (Chlorophyll a, melanoidin, etc.), the state of iron oxidation (for example, hematite and goethite-like signatures) and the nature of clays. The Q7/4 diagram permits rapid acquisition of high resolution data on changes of sediment dynamics in geosystems that have been subjected to highly varied climatic/environmental conditions. The instrument is non destructive, easy to use and maintain, portable for use in the field, fast to implement, is capable of high resolution, and has a vast range of possible applications. Spectrocolorimetry appears to provide many advantages and could become an essential and robust tool for preliminary sedimentological studies

PLoS Biol

Microorganisms must make the right choice for nutrient consumption to adapt to their changing environment. As a consequence, bacteria and yeasts have developed regulatory mechanisms involving nutrient sensing and signaling, known as "catabolite repression," allowing redirection of cell metabolism to maximize the consumption of an energy-efficient carbon source. Here, we report a new mechanism named "metabolic contest" for regulating the use of carbon sources without nutrient sensing and signaling. Trypanosoma brucei is a unicellular eukaryote transmitted by tsetse flies and causing human African trypanosomiasis, or sleeping sickness. We showed that, in contrast to most microorganisms, the insect stages of this parasite developed a preference for glycerol over glucose, with glucose consumption beginning after the depletion of glycerol present in the medium. This "metabolic contest" depends on the combination of 3 conditions: (i) the sequestration of both metabolic pathways in the same subcellular compartment, here in the peroxisomal-related organelles named glycosomes; (ii) the competition for the same substrate, here ATP, with the first enzymatic step of the glycerol and glucose metabolic pathways both being ATP-dependent (glycerol kinase and hexokinase, respectively); and (iii) an unbalanced activity between the competing enzymes, here the glycerol kinase activity being approximately 80-fold higher than the hexokinase activity. As predicted by our model, an approximately 50-fold down-regulation of the GK expression abolished the preference for glycerol over glucose, with glucose and glycerol being metabolized concomitantly. In theory, a metabolic contest could be found in any organism provided that the 3 conditions listed above are met

Historique, zones contributrices et dynamique des polluants à l’échelle du fleuve - Le cas des PCB

National audienc

Contribution de l'approche sédimentologique à la reconstitution de l'histoire des sols. Définition de traceurs pédologiques et application sur des sédiments lacustres de montagne (Maurienne, Savoie, France).

Soil is a natural body occurring at the interface between the lithosphere, atmosphere and biosphere. As a result, the physical and chemical properties of soils evolve with time, and the reconstruction of their history represents a key to understand past environmental changes. Palaeolimnological techniques such as sediment geochemistry can be used to investigate changes in vegetation history by providing information about catchment soil development. However, due to the lack of conservative pedosignatures, there have been few attempts to reconstruct soil changes from the paleorecord. The main objective of the present work is to reconstruct the soil and environmental history from lake sediments of two small lake basins of the Maurienne Valley in the French Alps. Two main issues arise in using the sedimentary approach: i) the geochemical differentiation of different soil processes and soil types, which controls the identification of tracers; ii) the conservative behaviour of these tracers during sediment mobilisation, transport and accumulation in aquatic systems. In a first step, podzolization and chemical weathering processes were assessed on present day soils using a broad geochemical approach. Normalized REE patterns provide a precise tracer of the degree of weathering of materials whereas the proportions of organic-bound Al and Fe provide a sediment tracer to reconstruct the intensity and degree of podzolisation. Then, the same tracers were assessed on the two investigated lake sediment sequences (Loup and Thyl lakes). Evidence of changes is preserved in both sediment records which render possible the reconstruction of aspects of soil genesis from lake sediments. The resulting proxy records, spanning ca. 4 500 yr at the Thyl lake and ca. 13500 yr at the Loup lake, indicate that progressive and regressive pedogenesis occurred after deglaciation. Loup environment and soil history is characterised by a progressive and stable evolution leading to present day old growing forests and Podzol soil type. On the other hand, Thyl record is much contrasted: the progressive setting of the mixed cembra pine ecosystem associated with podzolisation process is followed by abrupt and rapid secondary processes that could result from drastic transformation of the plant cover with changes in fire regimes.Alors que de nombreuses études paléoenvironnementales traitent de l'évolution du climat et de la végétation au cours de l'Holocene, il n'existe que très peu d'études portant sur l'évolution des sols au cours de cette même période. Cependant, les propriétés physiques et chimiques des sols ayant un rôle clef au sein d'un écosystème, la reconstitution de l'histoire des sols constitue un enjeu important pour comprendre les changements environnementaux passés. Un des facteurs limitant pour reconstituer l'histoire des sols réside dans l'absence d'enregistrement continu des processus pédologiques sur de longues échelles de temps (103 à 104 ans). Notre intérêt s'est donc porté sur l'utilisation d'archives sédimentaires lacustres dans le but de reconstruire l'histoire de la couverture pédologique en lien avec celle de l'écosystème. Cette étude a été menée sur deux petites dépressions lacustres de l'étage subalpin (Vallée de la Maurienne, Savoie) ayant a priori des histoires de l'occupation humaine différentes. Dans un premier temps, une approche géochimique a été appliquée sur des sols actuels afin de caractériser les pédosignatures des processus de podzolisation et d'altération chimique. Il en résulte que les terres rares (numéros atomiques de 57 à 71) constituent un indicateur du degré d'altération chimique tandis que les proportions des complexes organo-métalliques d'Al et Fe permettent de tracer l'intensité de la podzolisation. Dans un deuxième temps, ces mêmes traceurs ont été mesurés sur deux séquences sédimentaires couvrant 4500 ans Cal. BP (lac du Thyl) et 13500 ans (lac du Loup). La comparaison de ces pédosignatures avec des marqueurs indépendants (végétation, climat, feux) révèle des pédogenèses progressives et régressives après la déglaciation de la fin du Tardiglaciaire. Les sols et l'environnement du lac du Loup sont caractérisés par une évolution progressive et stable menant aux forets de résineux et aux podzols actuels. L'enregistrement du lac du Thyl est plus contrasté : le développement progressif d'une forêt de pin cembro associé au processus de podzolisation est suivi par des perturbations secondaires (principalement l'augmentation du régime des feux) qui pourraient expliquer la mise en place d'une végétation semi-ouverte associée à des processus de dépodzolisation. Finalement, ce travail a permit d'ajouter un volet pédologique aux études paléoenvironnementales classiques. Il en résulte que les deux schémas d'évolution des sols sont très cohérents avec les marqueurs indépendants et qu'ils offrent une meilleure résolution temporelle que l'on ne pourrait l'obtenir avec les chronoséquences

Enjeux de connaissances et mobilisations sur les risques liés aux pollutions industrielles (PFAS)

International audienc

Enjeux de connaissances et mobilisations sur les risques liés aux pollutions industrielles (PFAS)

International audienc

Enjeux de connaissances et mobilisations sur les risques liés aux pollutions industrielles (PFAS)

International audienc

Description des carottes du RCC de Pierre-Bénite. OSR4 | Action II.3

Le présent rapport constitue le livrable correspondant à l’action II.3 de l’OSR4 2015-2017 : « Détermination de la dynamique sédimentaire spatiale et temporelle de la plaine alluviale du secteur de Pierre-Bénite (PBN) : Rapport d'exécution, traitement et analyse des carottes (ouverture, description, granulométrie). Il fait suite à une caractérisation électromagnétique de la zone de Pierre-Bénite par radar géologique qui avait permis d’identifier des zones préférentielles de carottage peu profond (anciens chenaux, remplissages postérieurs au XIXème siècle, etc.)

Description des carottes du RCC de Donzère-Mondragon. OSR4 | Action II.3

Le présent rapport constitue le livrable correspondant à l’action II.3 de l’OSR4 2015-2017 : « Détermination de la dynamique sédimentaire spatiale et temporelle de la plaine alluviale du secteur de Donzère-Mondragon (DZM) : rapport d'exécution, traitement et analyse des carottes (ouverture, description, granulométrie). Il fait suite à une caractérisation électromagnétique de la zone de Donzère par radar géologique qui avait permis d’identifier des zones préférentielles de carottage peu profond (anciens chenaux, remplissages postérieurs au XIXème siècle, etc.)