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

Fine and ultrafine metallic particulatematters (PMs) are emitted frommetallurgic activities in peri-urban zones into the atmosphere and can be deposited in terrestrial ecosystems. The foliar transfer ofmetals andmetalloids 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 fromthe 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 (PbCO3 and organic Pb). Some compounds were internalized in their primary form (PbSO4) 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

Bacterial number and genetic diversity in a permafrost peatland (Western Siberia): Testing a link with organic matter quality and elementary composition of a peat soil profile

Permafrost peatlands, containing a sizable amount of soil organic carbon (OC), play a pivotal role in soil (peat) OC transformation into soluble and volatile forms and greatly contribute to overall natural CO2 and CH4 emissions to the atmosphere under ongoing permafrost thaw and soil OC degradation. Peat microorganisms are largely responsible for the processing of this OC, yet coupled studies of chemical and bacterial parameters in permafrost peatlands are rather limited and geographically biased. Towards testing the possible impact of peat and peat pore water chemical composition on microbial population and diversity, here we present results of a preliminary study of the western Siberia permafrost peatland discontinuous permafrost zone. The quantitative evaluation of microorganisms and determination of microbial diversity along a 100 cm thick peat soil column, which included thawed and frozen peat and bottom mineral horizon, was performed by RT-PCR and 16S rRNA gene-based metagenomic analysis, respectively. Bacteria (mainly Proteobac-teria, Acidobacteria, Actinobacteria) strongly dominated the microbial diversity (99% sequences), with a negligible proportion of archaea (0.3–0.5%). There was a systematic evolution of main taxa according to depth, with a maximum of 65% (Acidobacteria) encountered in the active layer, or permafrost boundary (50–60 cm). We also measured C, N, nutrients and ~50 major and trace elements in peat (19 samples) as well as its pore water and dispersed ice (10 samples), sampled over the same core, and we analyzed organic matter quality in six organic and one mineral horizon of this core. Using multiparametric statistics (PCA), we tested the links between the total microbial number and 16S rRNA diversity and chemical composition of both the solid and fluid phase harboring the microor-ganisms. Under climate warming and permafrost thaw, one can expect a downward movement of the layer of maximal genetic diversity following the active layer thickening. Given a one to two orders of magnitude higher microbial number in the upper (thawed) layers compared to bottom (frozen) layers, an additional 50 cm of peat thawing in western Siberia may sizably increase the total microbial population and biodiversity of active cells

Bioaccessibility of selenium after human ingestion in relation to its chemical species and compartmentalization in maize

International audienceSelenium is a micronutrient needed by all living organisms including humans, but often present in low concentration in food with possible deficiency. From another side, at higher concentrations in soils as observed in seleniferous regions of the world, and in function of its chemical species, Se can also induce (eco)toxicity. Root Se uptake was therefore studied in function of its initial form for maize (Zea mays L.), a plant widely cultivated for human and animal food over the world. Se phytotoxicity and compartmentalization were studied in different aerial plant tissues. For the first time, Se oral human bioaccessibility after ingestion was assessed for the main Se species (SeIV and SeVI) with the BARGE ex vivo test in maize seeds (consumed by humans), and in stems and leaves consumed by animals. Corn seedlings were cultivated in hydroponic conditions supplemented with 1 mg L−1 of selenium (SeIV, SeVI, Control) for 4 months. Biomass, Se concentration, and bioaccessibility were measured on harvested plants. A reduction in plant biomass was observed under Se treatments compared to control, suggesting its phytotoxicity. This plant biomass reduction was higher for selenite species than selenate, and seed was the main affected compartment compared to control. Selenium compartmentalization study showed that for selenate species, a preferential accumulation was observed in leaves, whereas selenite translocation was very limited toward maize aerial parts, except in the seeds where selenite concentrations are generally high. Selenium oral bioaccessibility after ingestion fluctuated from 49 to 89 % according to the considered plant tissue and Se species. Whatever the tissue, selenate appeared as the most human bioaccessible form. A potential Se toxicity was highlighted for people living in seleniferous regions, this risk being enhanced by the high Se bioaccessibility

Variations in the accumulation, localization and rate of metabolization of selenium in mature Zea mays 2 plants supplied with selenite or selenate

International audienceQuantification of selenium bioavailability from foods is a key challenge following the discovery of the antioxidant role of this micronutrient in human health. This study presents the uptake, accumulation and rate of metabolization in mature Zea mays plants grown in hydroponic solution supplemented with selenate or selenite.Selenium content was lower in plants supplemented with selenate and accumulated mainly in the leaves compared with selenite-treated plants where the selenium was retained in the roots. Selenite-treated grains accumulated more selenium. Selenate was metabolized less than selenite in whole plants, but in grains selenium was present exclusively as organic selenium compounds.For humans, the bioavailability of organic selenium was evaluated at 90% compared with only 50% for inorganic forms. Our results show that the potential for selenium bioavailability is increased with selenite treatment

Major and trace element and Sr isotope constraints on fluid circulations in the Barbados accretionary complex. Part 1: Fluid origin

International audienceWe measured the chemical and Sr isotope compositions of vent and pore fluids and associated sediments from a diapiric field located near 13.5°N, east of the deformation front of the Barbados accretionary complex. The two diapiric structures with the largest thermal anomalies and characterized by active fluid conduits exhibit the strongest chemical and 87Sr/86Sr variations. These two diatremes (Atalante and Cyclope) also have low chloride contents and non-radiogenic 87Sr/86Sr, which may be explained by interaction between seawater and volcanic ash or with underlying oceanic crust. In the central zone of the two structures, 87Sr/86Sr varies little with depth, which implies that fluid expulsion is at such a high rate that it is not affected by seawater 87Sr/86Sr.The expelled fluids probably circulate along the decollement zone and ascend along faults which act as channels. A deep component is probably located in the decollement zone whereas another component may be recirculated seawater. The ascending fluid interacted with numerous materials, causing dehydration of clay minerals and alteration of volcanic ash and/or underlying oceanic crust. To explain the low chloride contents of the Atalante fluids, gas hydrate decomposition, yielding dilution of the fluid without modifying its Sr isotope ratio, needs to be superimposed on the mixing between seawater and the deep component. The occurrence of gypsum in these two diatremes implies higher fluid temperatures and more intense activity, at least temporarily, to allow the deposition of such a mineral

Trinidad mud volcanoes: Where do the expelled fluids come from?

International audienceIn order to establish the origin of fluids expelled from mud volcanoes in Trinidad, we analyzed their major-element, trace-element, and isotopic (H, O, Sr) compositions. The mineralogical, chemical, and Sr isotope compositions of associated expelled muds were also determined.On the basis of their chemical and Sr isotope compositions, the fluids were divided into two groups—those southwest and northeast of a major right lateral wrench fault (the Los Bajos fault) that both controls the chemical quality of the fluids and acts as a drain. Strontium isotopes were derived via mixing between a radiogenic source (0.71135) and a nonradiogenic source (≤0.70671) for both southwest and northeast groups. However, the nonradiogenic source possibly feeding the northeast group showed a lower Sr concentration than that of the southwest group. H and O isotope data show that the fluids became enriched in δ18O through interaction with wall rocks. The fluids were originally oceanic, but their properties were subsequently modified by diagenesis as evidenced by chemical data, and mixing between fluids issued from two deep-seated reservoirs and surface aquifer end-members.The gas phase expelled with the mud and the fluid through the mud volcanoes is composed mainly of methane with minor carbon dioxide. The amount of expelled gas seems the same in samples from both sides of the Los Bajos fault. The almost unique methane content of the gas phase and the large positive δ18O shifts of the reservoir end-member, as well as B, Li, and Ba contents, reveal that the fluids from the deep-seated reservoirs inherited their chemical compositions at high-temperature fluid–rock interactions. Estimates of equilibrium temperatures of the two deep-seated reservoirs suggest that, to acquire the estimated higher temperature (150°C), the mud volcanoes must have been fed partly by a reservoir located at a depth of more than 3 km. This depth corresponds to previous geologic information, which located the deep-seated reservoir in Miocene sediments at such a comparable depth. The mixing of the original fluids with a less deep-seated reservoir and meteoric waters on the ascending path suggests the presence of a recharge mechanism and contributes to the dynamics of the expulsion itself

Distribution spatiale des éléments traces dans les sols des écosystèmes subarctiques : quelle est l’influence de la végétation ?

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