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

Mechanisms and modalities of the spatial and temporal distribution of metals in Loire basin sediments

Cette étude correspond à une approche multiscalaire de la variabilité spatiale des contaminations métalliques enregistrées dans les sédiments du bassin de la Loire. Ce manuscrit est organisé en trois parties exposant la démarche et les résultats de ces travaux. La première partie permet de formuler les problématiques de l’étude en proposant une synthèse des connaissances concernant l’archivage des contaminations sédimentaires dans les environnements fluviatiles. La seconde partie s’intéresse à l’influence des environnements de dépôts sur l’archivage des sédiments et contaminants associés. Les objectifs de ces recherches sont d’étudier la représentativité des signaux géochimiques enregistrés dans les compartiments de stockage sédimentaire. La troisième partie permet de mettre en évidence la variabilité spatiale et l’origine des contaminations sédimentaires à l’échelle du bassin versant de la Loire.This multi-scale focuses on the spatial and temporal variability of the metallic contamination in sediments of the Loire basin. This manuscript presents methods and results in three sections. The first section deals with scientific issues concerning the recording of sedimentary contaminations in fluvial environments. The second section shows the influence of depositional environments on sediments and associated contaminants archiving. The aim of this study is to analyse the representation of geochemical signals recorded in sedimentary infills. The third section highlights spatial variabilities of recorded sedimentary contaminations at the entire Loire basin-scale. Historical sources are here characterized

Influence of fluvial environments on sediment archiving processes and temporal pollutant dynamics (Upper Loire River, France)

International audienceFloodplains are often cored to build long-term pollutant trends at the basin scale. To highlight the influences of depositional environments on archiving processes, aggradation rates, archived trace element signals and vertical redistribution processes, two floodplain cores were sampled near in two different environments of the Upper Loire River (France): (i) a river bank ridge and (ii) a paleochannel connected by its downstream end. The base of the river bank core is composed of sandy sediments from the end of the Little Ice Age (late 18th century). This composition corresponds to a proximal floodplain aggradation (< 50 m from the river channel) and delimits successive depositional steps related to progressive disconnection degree dynamism. This temporal evolution of depositional environments is associated with mineralogical sorting and variable natural trace element signals, even in the < 63-μm fraction. The paleochannel core and upper part of the river bank core are composed of fine-grained sediments that settled in the distal floodplain. In this distal floodplain environment, the aggradation rate depends on the topography and connection degree to the river channel. The temporal dynamics of anthropogenic trace element enrichments recorded in the distal floodplain are initially synchronous and present similar levels. Although the river bank core shows general temporal trends, the paleochannel core has a better resolution for short-time variations of trace element signals. After local water depth regulation began in the early 1930s, differences of connection degree were enhanced between the two cores. Therefore, large trace element signal divergences are recorded across the floodplain. The paleochannel core shows important temporal variations of enrichment levels from the 1930s to the coring date. However, the river bank core has no significant temporal variations of trace element enrichments and lower contamination levels because of a lower deposition of contaminated sediments and a pedogenetic trace elements redistribution

Évolution longitudinale de la contamination en microplastiques dans les sédiments de la retenue de Villerest (Loire, France)

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Influences of major flood sediment inputs on sedimentary and geochemical signals archived in a reservoir core (Upper Loire Basin, France)

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Archivage et variabilité spatiale des microplastiques dans les sédiments fluviatiles

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Archivage et variabilité spatiale des microplastiques dans les sédiments fluviatiles

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Hydro-sedimentary dysfunctions as a key factor for the storage of contaminants in mountain rivers (Bienne River, Jura Mountains, France)

International audienceAs within many European rivers in mountainous areas, the Bienne River (Jura Mountains, France) has been severely impacted by the implementation of obstacles to river flow. The aim of this study is to better understand how hydro-sedimentary dysfunctions (complex alterations of sediment transport in response to river engineering) can influence contaminants storage along the river. The sediment pollution trajectory was reconstructed based (1) on a well-dated sediment core, and (2) on several sediment samples taken at different depths on six riverbank profiles. Age control was established with a well-defined 137Cs profile and time-related grain size transitions in the sediment core, and only relatively for riverbank profiles using a plasticizer and PCB contents as chemical markers of the Anthropocene. Riverbanks and the core are composed of fine-grained legacy sediments deposited during the 20th century. They covered the former active channel mostly composed of pebbles and cobbles. Historical contaminants were the highest in the most upstream station and declined in the downstream direction to reach relatively low values in the lower river section. This historical upstream signal poorly influences the geochemical composition of sediments in the lower reaches, due its attenuation by numerous human-made obstacles to river flow and to the limited sediment transport capacity of the river. According to an unmixing model, the contribution of the upper sediments only weights a small percentage of the sedimentary mixture at the river outlet. These results highlight the sedimentary storage capacity of historical contaminants in mountain coarse-bedded river. This phenomenon has been led by a riverbed narrowing and stabilization caused by deep alterations of hydro-sedimentary processes. It finally emphasizes storage of sedimentary contaminants and leads to limited source influences. Hence, this study shows the key role of sedimentary transport, which triggers spatial and temporal variability of contaminants stored in sediments

Évolution longitudinale de la contamination en microplastiques dans les sédiments de la retenue de Villerest (Loire, France)

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Archivage et variabilité spatiale des microplastiques dans les sédiments fluviatiles

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