Arsenite and chromate sequestration onto ferrihydrite, siderite and goethite nanostructured minerals: Isotherms from flow-through reactor experiments and XAS measurements.

Sorption isotherms remain a major tool to describe and predict the mobility of pollutants in natural and anthropogenic environments, but they are typically determined by independent batch experiments. In the present study, the sequestration of As(III), Cr(VI) and competitive As(III)-Cr(VI) on/in 6L-ferrihydrite, siderite and goethite nanostructured minerals was reinvestigated using stirred flow-through reactor experiments. Herein, sorption isotherms were particularly determined from breakthrough curves for inert and reactive tracers monitored simultaneously in a single percolation experiment. In complement, X-ray absorption spectroscopy (XAS) was used to identify As sorption sites on 6L-ferrihydrite and goethite. As expected, the minerals have high potential to remove As and Cr from water (siderite = ferrihydrite (about 60 mg/g) > goethite (20 mg/g)). As and Cr sorption isotherms were modelled with a Langmuir model, and with a sigmoidal Hill model in the case of the competitive sorption. XAS measurements have revealed that As(III) was partially oxidized (up to 22%) in the competitive system with chromate oxyanion Cr(VI). As(III) sorbed on ferrihydrite and goethite adopted edge-sharing and corner sharing complex geometries. Nowadays, a new class of adsorbing phases is being developed for wastewater treatment, including engineered nanostructured materials and nanocomposites. The use of flow through reactor experiments as a high throughput method, combined with XAS, should be considered as efficient screening methods to test their sorbing properties on various contaminants.

Metal and metalloid foliar uptake by various plant species exposed to atmospheric industrial fallout: mechanisms involved for lead.

Fine and ultrafine metallic particulate matters (PMs) are emitted from metallurgic activities in peri-urban zones into the atmosphere and can be deposited in terrestrial ecosystems. The foliar transfer of metals and metalloids and their fate in plant leaves remain unclear, although this way of penetration may be a major contributor to the transfer of metals into plants. This study focused on the foliar uptake of various metals and metalloids from enriched PM (Cu, Zn, Cd, Sn, Sb, As, and especially lead (Pb)) resulting from the emissions of a battery-recycling factory. Metal and metalloid foliar uptake by various vegetable species, exhibiting different morphologies, use (food or fodder) and life-cycle (lettuce, parsley and rye-grass) were studied. The mechanisms involved in foliar metal transfer from atmospheric particulate matter fallout, using lead (Pb) as a model element was also investigated. Several complementary techniques (micro-X-ray fluorescence, scanning electron microscopy coupled with energy dispersive X-ray microanalysis and time-of-flight secondary ion mass spectrometry) were used to investigate the localization and the speciation of lead in their edible parts, i.e. leaves. The results showed lead-enriched PM on the surface of plant leaves. Biogeochemical transformations occurred on the leaf surfaces with the formation of lead secondary species (PbCO(3) and organic Pb). Some compounds were internalized in their primary form (PbSO(4)) underneath an organic layer. Internalization through the cuticle or penetration through stomata openings are proposed as two major mechanisms involved in foliar uptake of particulate matter.

Characterization of lead-recycling facility emissions at various workplaces: major insights for sanitary risks assessment.

Most available studies on lead smelter emissions deal with the environmental impact of outdoor particles, but only a few focus on air quality at workplaces. The objective of this study is to physically and chemically characterize the Pb-rich particles emitted at different workplaces in a lead recycling plant. A multi-scale characterization was conducted from bulk analysis to the level of individual particles, to assess the particles properties in relation with Pb speciation and availability. Process PM from various origins were sampled and then compared; namely Furnace and Refining PM respectively present in the smelter and at refinery workplaces, Emissions PM present in channeled emissions. These particles first differed by their morphology and size distribution, with finer particles found in emissions. Differences observed in chemical composition could be explained by the industrial processes. All PM contained the same major phases (Pb, PbS, PbO, PbSO(4) and PbO·PbSO(4)) but differed on the nature and amount of minor phases. Due to high content in PM, Pb concentrations in the CaCl(2) extractant reached relatively high values (40 mg L(-1)). However, the ratios (soluble/total) of CaCl(2) exchangeable Pb were relatively low (<0.02%) in comparison with Cd (up to 18%). These results highlight the interest to assess the soluble fractions of all metals (minor and major) and discuss both total metal concentrations and ratios for risk evaluations. In most cases metal extractability increased with decreasing size of particles, in particular, lead exchangeability was highest for channeled emissions. Such type of study could help in the choice of targeted sanitary protection procedures and for further toxicological investigations. In the present context, particular attention is given to Emissions and Furnace PM. Moreover, exposure to other metals than Pb should be considered.

Zinc sorption to three gram-negative bacteria: combined titration, modeling, and EXAFS study.

The acid-base and Zn sorption properties of three bacteria, Cupriavidus metallidurans CH34, Pseudomonas putida ATCC12633, and Escherichia coli K12DH5alpha, were investigated through an original combination of extended X-ray absorption fine structure (EXAFS) spectroscopy and equilibrium titration studies. Acid-base titration curves of the three strains were fitted with a model accounting for three conceptual reactive sites: an acidic (carboxyl and/or phosphodiester), a neutral (phosphomonoester), and a basic (amine and/or hydroxyl) group. Calculated proton and Zn equilibrium constants and site densities compare with literature data. The nature of Zn binding sites was studied by EXAFS spectroscopy. Phosphoester, carboxyl, and unexpectedly sulfhydryl ligands were identified. Their proportions depended on Zn loading and bacterial strain and were consistent with the titration results. These findings were compared to the structure and site density of the major cell wall components. It appeared that the cumulated theoretical site density of these structures (<2 Zn nm(-2)) was much lower than the total site density of the investigated strains (16-56 Zn nm(-2)). These results suggest a dominant role of extracellular polymeric substances in Zn retention processes, although Zn binding to inner cell components cannot be excluded.

Accumulation forms of Zn and Pb in Phaseolus vulgaris in the presence and absence of EDTA.

The internalized speciation of Zn and Pb in roots and leaves of Phaseolus vulgaris grown in zinc sulfate, zinc EDTA, lead nitrate, and lead EDTA solutions were studied by electron microscopy (Zn) and extended X-ray absorption fine structure (EXAFS) spectroscopy (Zn and Pb). Zn was predominantly present as Zn phosphate dihydrate in the roots and leaves of the plant regardless of its form in solution. Pb was predominantly found in the leaves as cerussite (lead carbonate) when the plant was grown in Pb nitrate solution and as a mixture of PbEDTA and an undetermined species in contact with PbEDTA solution. Therefore, Phaseolus vulgaris is able to dissociate totally (Zn) or partly (Pb) the two metal-EDTA complexes from the nutrient solution and to bind these metals in other forms.

Mobilization of selenite by Ralstonia metallidurans CH34.

Ralstonia metallidurans CH34 (formerly Alcaligenes eutrophus CH34) is a soil bacterium characteristic of metal-contaminated biotopes, as it is able to grow in the presence of a variety of heavy metals. R. metallidurans CH34 is reported now to resist up to 6 mM selenite and to reduce selenite to elemental red selenium as shown by extended X-ray absorption fine-structure analysis. Growth kinetics analysis suggests an adaptation of the cells to the selenite stress during the lag-phase period. Depending on the culture conditions, the medium can be completely depleted of selenite. Selenium accumulates essentially in the cytoplasm as judged from electron microscopy and energy-dispersive X-ray analysis. Elemental selenium, highly insoluble, represents a nontoxic storage form for the bacterium. The ability of R. metallidurans CH34 to reduce large amounts of selenite may be of interest for bioremediation processes targeting selenite-polluted sites.