Intérêt de différents réactifs d'extraction chimique pour l'évaluation de la biodisponibilité des métaux en traces du sol

L’évaluation de la biodisponibilité des métaux en traces du sol intéresse deux grands domaines d’application : d’une part, le diagnostic de fertilité chimique basé sur l’établissement de seuils de carence, employé depuis plusieurs décennies dans différents pays ; d’autre part, l’estimation du risque de phytotoxicité ou de contamination de la chaîne alimentaire qu’entraîne la pollution du sol par les éléments en traces. Dans ce cas, très peu de pays sont allés jusqu’à l’élaboration de références de diagnostic. Afin de guider le choix d’une méthode d’extraction chimique pour permettre l’ébauche de telles références en France, une synthèse bibliographique a été entreprise. Elle reprend les principaux résultats obtenus depuis les vingt dernières années concernant l’évaluation de la biodisponibilité de Cd, Cu, Zn, Pb, Cr et Ni. De cette étude, il ressort que les solutions salines non tamponnées semblent les mieux adaptées à l’estimation rapide du transfert des éléments du sol aux végétaux et à la mise au point de valeurs guides permettant de statuer quant aux risques de toxicité susceptibles d’être engendrés par des sites pollués.The prediction of soil trace metal bioavailability using extractions has two direct applications: i) evaluation of soil chemical fertility and nutrient deficiency, as has been used widely in different countries for many years; and ii) risk assessment of phytotoxicity and contamination of the food chain induced by polluted soils. In this latter case, few countries have defined guide values. In order to choose one of the extraction methods proposed in the literature, and then define such references for France, a review of research concerning the chemical estimation of Cd, Cu, Zn, Ni, Cr and Pb plant uptake in the last twenty years was undertaken. In conclusion, the use of unbuffered salt solutions seems to be the most suitable way to i) estimate trace element transfert from polluted soil to plant and ii) define guide values for risk assessment

Environmental impacts of heavy metal discharges from a smelter in Deûle-canal sediments (Northern France): concentration levels and chemical distribution

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On the chemical behavior of sedimentary uranium in Authie Bay (France)

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Fractionation of anthropogenic lead and zinc in Deûle river sediments

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Distribution coefficient and redox behaviour of uranium in Authie Bay (Northern France).

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Impact of a zinc processing factory on surrounding surficial soil contamination

International audienceZn smelting plants located at Auby (Northern France) have strongly polluted the surroundings through dust emissions, storage of ores and slag without strong environmental concerns. Although highly contaminated surficial soils have been removed in the private and public gardens to safeguard health of the inhabitants, one small public area, called the Peru Park, has not been treated because of the presence of peculiar calamine grasslands. Our investigations in the soils of this park clearly evidenced a very strong contamination by several metals with concentrations up to 21,000 mg kg−1 for Zn, 3500 mg kg−1 for Pb and 160 mg kg−1 for Cd. Additionally, the mobility of these metals is important in soils and increases with the pollution level. In the pore waters of strongly polluted zones, our findings are more contrasted with high concentrations of dissolved Zn (3.6–32 mg L−1) and to a lesser extent Cd (0.02–0.25 mg L−1), whereas dissolved Pb remains at low concentrations (0.0001–0.021 mg L−1) and, according to calculations, is quite exclusively bound to humic substances. Finally, this study obviously underlines that this severe pollution and the high mobility of Zn and Cd could strongly impact the surficial aquifer and the trophic chain present in this area

Imagined speech can be decoded from low- and cross-frequency intracranial EEG features

Reconstructing intended speech from neural activity using brain-computer interfaces holds great promises for people with severe speech production deficits. While decoding overt speech has progressed, decoding imagined speech has met limited success, mainly because the associated neural signals are weak and variable compared to overt speech, hence difficult to decode by learning algorithms. We obtained three electrocorticography datasets from 13 patients, with electrodes implanted for epilepsy evaluation, who performed overt and imagined speech production tasks. Based on recent theories of speech neural processing, we extracted consistent and specific neural features usable for future brain computer interfaces, and assessed their performance to discriminate speech items in articulatory, phonetic, and vocalic representation spaces. While high-frequency activity provided the best signal for overt speech, both low- and higher-frequency power and local cross-frequency contributed to imagined speech decoding, in particular in phonetic and vocalic, i.e. perceptual, spaces. These findings show that low-frequency power and cross-frequency dynamics contain key information for imagined speech decoding

Rôle du silicium dans la culture du blé en France : biodisponibilité, bioaccumulation et effet sur les rendements

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Rôle du silicium dans la culture du blé en France : biodisponibilité, bioaccumulation et effet sur les rendements

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