Determination of the distribution of rare earth elements La and Gd in <i>Daphnia magna</i> via micro and nano-SXRF imaging

While our awareness of the toxicity of rare earth elements to aquatic organisms increases, our understanding of their direct interaction and accumulation remains limited. This study describes the acute toxicity of lanthanum (La) and gadolinium (Gd) in Daphnia magna neonates and discusses potential modes of action on the basis of the respective patterns of biodistribution. Ecotoxicological bioassays for acute toxicity were conducted and dissolved metal concentrations at the end of the tests were determined. The results showed a significant difference in nominal EC50 (immobility) between La (>30 mg L−1) and Gd (13.93 (10.92 to 17.38) mg L−1). Daphnids that were then exposed to a concentration close to the determined EC50 of Gd (15 mg L−1, nominal concentration) for 48 h and 72 h were studied by synchrotron micro and nano-X-ray fluorescence to evaluate the biodistribution of potentially accumulated metals. X-ray fluorescence analyses showed that La was mainly found in the intestinal track and appeared to accumulate in the hindgut. This accumulation might be explained by the ingestion of solid La precipitates formed in the media. In contrast, Gd could only be detected in a small amount, if at all, in the intestinal tract, but was present at a much higher concentration in the tissues and became more pronounced with longer exposure time. The solubility of Gd is higher in the media used, leading to higher dissolved concentrations and uptake into tissue in ionic form via common metal transporting proteins. By studying La and Gd biodistribution in D. magna after an acute exposure, the present study has demonstrated that different uptake pathways of solid and dissolved metal species may lead to different accumulation patterns and toxicity.PeerReviewe

Fate of cadmium in the rhizosphere of Arabidopsis halleri grown in a contaminated dredged sediment

International audienceIn regions impacted by mining and smelting activities, dredged sediments are often contaminated with metals. Phytotechnologies could be used for their management, but more knowledge on the speciation of metals in the sediment and on their fate after colonization by plant roots is needed. This work was focused on a Zn, Cd-contaminated contaminated dredged sediment from the Scarpe river (North of France). Zn, Cd hyperaccumulating plants Arabidopsis halleri from metallicolous and non metallicolous origin were grown on the sediment for five months in a pot experiment. The nature and extent of the modifications in Cd speciation with or without plant were determined by electron microscopy, micro X-ray fluorescence and bulk and micro X-ray absorption spectroscopy. In addition, changes in Cd exchangeable and bioavailable pools were evaluated, and Cd content in leachates was measured. Finally, Cd plant uptake and plant growth parameters were monitored. In the original sediment, Cd was present as a mixed Zn, Cd, Fe sulfide. After five months, although pots still contained reduced sulfur, Cd-bearing sulfides were totally oxidized in vegetated pots, whereas a minor fraction (8%) was still present in non vegetated ones. Secondary species included Cd bound to O-containing groups of organic matter and Cd phosphates. Cd exchangeability and bioavailability were relatively low and did not increase during changes in Cd speciation, suggesting that Cd released by sulfide oxidation was readily taken up with strong interactions with organic matter and phosphate ligands. Thus, the composition of the sediment, the oxic conditions and the rhizospheric activity (regardless of the plant origin) created favourable conditions for Cd stabilization. However, it should be kept in mind that returning to anoxic conditions may change Cd speciation, so the species formed cannot be considered as stable on the long term

XANES spectroscopy for the clinician

XANES spectroscopy, which uses synchrotron radiation as a probe, offers substantial information about the local structure of biological samples, encompassing those without long range order such as Pt anticancer molecules, and nanometre scale or amorphous particles of calcium phosphate. Its subcellular spatial resolution, as well as its capacity to operate at room temperatures and pressures represent major advantages for medical research. Moreover, paraffin embedded biopsy samples can be analysed without any further preparation, Key publications which illustrate these capacities are presented

XANES spectroscopy for the clinician

XANES spectroscopy, which uses synchrotron radiation as a probe, offers substantial information about the local structure of biological samples, encompassing those without long range order such as Pt anticancer molecules, and nanometre scale or amorphous particles of calcium phosphate. Its subcellular spatial resolution, as well as its capacity to operate at room temperatures and pressures represent major advantages for medical research. Moreover, paraffin embedded biopsy samples can be analysed without any further preparation, Key publications which illustrate these capacities are presented

REPARTITION DES CATIONS DANS LA COUCHE OCTAEDRIQUE DES MONTMORILLONITES (REPERCUSSIONS SUR LES PROPRIETES COLLOIDALES)

L'INFLUENCE DES PARAMETRES CRISTALLOCHIMIQUES SUR LE COMPORTEMENT COLLOIDAL DE HUIT MONTMORILLONITES DE CHARGE STRUCTURALE 0.76 A 1.04 ET DE TENEUR EN FER 0.1 A 2.7 (PAR MAILLE) A ETE ETUDIEE. LES PARAMETRES RHEOLOGIQUES (SEUIL D'ELASTICITE ET VISCOSITE) DE SUSPENSIONS A 5% DE CES MONTMORILLONITES S'ETAGENT SUR DEUX ORDRES DE GRANDEUR, SANS LIEN APPARENT AVEC LES VALEURS DE POTENTIEL ELECTROCINETIQUE ET L'ORGANISATION DES FEUILLETS OBSERVEE PAR DIFFUSION DES RAYONS X. IL N'APPARAIT PAS, NON PLUS, DE CORRELATION DIRECTE AVEC LA CHARGE STRUCTURALE OU LA TENEUR EN FER. L'ORIGINE DE CES DISPARITES A ETE RECHERCHEE A PARTIR D'UNE ANALYSE FINE DE LA CRISTALLOCHIMIE DES ECHANTILLONS ET, PLUS PARTICULIEREMENT, DE LA REPARTITION DES CATIONS OCTAEDRIQUES, A L'AIDE DE TROIS METHODES SPECTROMETRIQUES COMPLEMENTAIRES : IR, RPE ET EXAFS. IL A ETE MONTRE QUE LA DISTRIBUTION DES CATIONS OCTAEDRIQUES PEUT, SOIT ETRE ALEATOIRE, SOIT OBEIR A UNE LOI D'EXCLUSION OU DE REGROUPEMENT. IL A AINSI ETE MIS EN EVIDENCE QUE LA REPARTITION DES CATIONS OCTAEDRIQUES ALLIEE A LA CHARGE STRUCTURALE EST UN INDICATEUR PERTINENT DES GRANDEURS RHEOLOGIQUES MESUREES, ET CECI TRES PROBABLEMENT PAR LE BIAIS DE LA MORPHOLOGIE DES FEUILLETS. CE LIEN ENTRE CRISTALLOCHIMIE ET PROPRIETES MACROSCOPIQUES EST PARTICULIEREMENT BIEN ILLUSTRE PAR LES MONTMORILLONITES DU WYOMING DONT LES PARAMETRES RHEOLOGIQUES EXCEPTIONNELLEMENT ELEVES SONT RELIES A UNE REPARTITION ORDONNEE DES CATIONS OCTAEDRIQUES.NANCY/VANDOEUVRE-INPL (545472102) / SudocSudocFranceF

Ferric deposit at riverbank surface: redox filter between wetland and river

International audienceRiverbank is the exchange zone between the soil and the river alongside the bed of a river between which theflow is confined. The redox conditions roughly change at this interface due to the seasonal changes and thestrong presence of O2 in surface. Riverbank thus plays the role of the redox barrier/filter between soil and river,controlling the chemical speciation, bioavailability, toxicity and mobility of major and trace elements (nutrients,metals and metalloids) as well as organic compounds. Iron speciation between solid and aqueous phases is largelycontrolled by redox conditions, which govern the Fe oxidation states and the thermodynamic stability of solidphases. At such redox interface, soluble Fe(II) precipitates as solid Fe(III) at the surface due to oxidation processdriven by O2 entering anoxic systems.The present study aims at determining the Fe speciation in riverbank containing ferric deposits at the redoxsurface between wetland and river and the environmental impact on the ability of iron oxide to trap chemicalelements. Riverbanks samples were collected from the Mercy riparian wetland of Kervidy-Naizin located inBrittany (France). Their chemical and mineralogical compositions have been determined. XANES analyses havebeen performed at LUCIA beamline in SOLEIL to determine Fe speciation.XANES results on total bulk fraction (<2mm) show that Fe is mainly hosted by goethite (23-36%) and muscovite(up to 35%) at the riverbank subsurface, when Fe is progressively hosted by ferrihydrite, goethite and Fe-clustersbound to organic matter (OM) at the riverbank surface (16-31%, 23-36% and 29-41%, respectively). XANESanalysis on clay fraction (<4m) has additionally permitted to detect the presence of Fe hosted by lepidocrocite(up to 34%). Modification of Fe speciation is accompanied by change of Fe and trace metals concentrations. Ironconcentration gradient is observed between the subsurface (from 2.9 to 4.3 wt%) and surface (up to 11.1 wt%).Trace metals concentrations demonstrated that As, Co, Cu, Mn, Ni, Pb, Sb, Zn and REE (especially Ce, La andNd) are also systematically enriched in riverbank surface. In contrast, Cr contents do not show any differencebetween surface and subsurface.Enrichment of some trace metals are correlated with the increase of Fe hosted by ferrihydrite and Fe-OM and theCorg content. Goethite, lepidocrocite and clay mineral do not appear as reactive phases to act on the chemicalelement mobility. Therefore, the formation of amorphous structures (ferrihydrite and Fe clusters bound to OM) onriverbank surface and their strong surface-sorption capacity appear to control chemical elements speciation (As,Co, Cu, Mn, Ni, Pb, Sb, Zn and REE) and their transport/mobility at this redox interface between wetland and rive

Novel interface for cultural heritage at SOLEIL

International audienc

Probing the local environment of substitutional Al3+ in goethite using X-ray absorption spectroscopy and first-principles calculations

International audienceWe present experimental and calculated Al K-edge X-ray absorption near-edge structure (XANES) spectra of aluminous goethite with 10 to 33 mol % of AlOOH and diaspore. Significant changes are observed experimentally in the near and pre-edge regions with increasing Al concentration in goethite. First-principles calculations based on density-functional theory (DFT) reproduce successfully the experimental trends. This permit to identify the electronic and structural parameters controlling the spectral features and to improve our knowledge of the local environment of Al3+ in the goethite-diaspore partial solid solution. In the near-edge region, the larger peak spacing in diaspore compared to Al-bearing goethite is related to the nature (Fe or Al) of the first cation neighbours around the absorbing Al atom (Al*). The intensity ratio of the two near-edge peaks, which decreases with Al concentration, is correlated with the average distance of the first cations around Al* and the distortion of the AlO6 octahedron. Finally, the decrease in intensity of the pre-edge features with increasing Al concentration is due to the smaller number of Fe atoms in the local environment of Al since Al atoms tend to cluster. In addition, it is found that the pre-edge features of the Al K-edge XANES spectra enable to probe indirectly empty 3d states of Fe. Energetic, structural and spectroscopic results suggest that for Al concentrations around 10 mol %, Al atoms can be considered as isolated whereas above 25 mol %, Al clusters are more likely to occur

Al and Si oxyanions impact on the structural organization of Fe-OM nanoaggregates

International audienceNatural colloids composed of iron (Fe) and organic matter (OM) are a key factor controlling the mobility of metallic pollutants due to their high adsorption capacity, a consequence of their high density of binding sites. The physico-chemical conditions under which Fe-OM nano-aggregates are formed influence their structural organization, and more particularly the speciation of Fe. In this study, we probe the influence of two major elements of natural systems: aluminum (Al) and silicon (Si). Al is known to have a high affinity with OM but also easily enters the structure of Fe hydroxides. Si, on the other hand, is known to inhibit the growth and crystallinity of Fe hydroxides, although the mechanisms remain unknown. Al and Si are therefore expected to influence the Fe-OM nano-aggregates organization and to have an impact on the Fe speciation.Fe-OM-Al/Si nano-aggregates, mimicking environmental ones, have been synthesized with different Fe/OM and oxyanion/Fe ratios. In these systems, the Fe speciation is complex and variable, depending on the Fe and oxyanion content relative to OM. The Fe phases appear to be composed of oligomers and ferrihydrite-like nanoparticles (Fh-Np), both integrated in the OM matrix. The Fh-Np form a fractal network whose organization is controlled by the OM. As Fe/OM increases, the oligomer content decreases in favor of the Fh-Np, which increases in size. By adding Al or Si, this phenomenon may strongly differ. Al, forming oligomers and bound to both Fe and OM, clearly allows the growth of the Fh-Np/oligomer ratio, the Fh-Np size and the whole nano-aggregates structure. On the contrary, Si, bound to Fe, has the exact opposite effect. These differences result from the different interactions between Al and Si and the components of the Fe-OM nano-aggregates.These results clearly highlight the antagonist effect of the major elements, Al and Si, on the structural organization of Fe-OM colloids. They impact all the levels of organization: the Fe speciation and the OM and Fh-Np arrangement. This structural variability has a direct consequence on the ability of Fe-OM nano-aggregates to trap and transport pollutants in the hydrographic network