| Summary: | The Rare Earths Elements (REEs) are a group of 17 metallic elements used in many industrial and medical applications. For several years, their use has been expanding rapidly, leading to numerous enrichments in aquatic ecosystems. This thesis focused on studying these emerging contaminants in the Loire estuary, which represent an area marked by a strong anthropogenic pressure which can be a source of REEs. For the first time, the REE concentration of the abiotic compartment was characterized as a whole : sediment and water column (dissolved and particulate phases). The study of bioaccumulation in muscle of two benthic fish species, the European eel (Anguilla anguilla) and the common flounder (Platlchthys flesus), highlighted intraspecific and interspecific variations.In addition, REE quantification in different organs and tissues allowed their organotropism determination in eels. A particularly marked bioaccumulation of gadolinium in the gonads of female silver eels has thus been demonstrated. Finally, the spatiotemporal study of the bioaccumulation of REEs in eel muscles showed a slight spatial variation but a significant temporal increase between 2011/2012 and 2018/2019. This temporal variation was not observed in sediments collected at the same time periods. The sentinel species status of the eel is thus underlined, since it seems to be particularly suitable for monitoring the evolution of REE contamination in dynamic environments, such as estuaries, influenced by current and tides. Les Terres Rares (TR) regroupent 17 éléments métalliques utilisés dans diverses applications industrielles et médicales. Depuis plusieurs années, leur utilisation est en pleine expansion, conduisant à de nombreuses observations d'enrichissement dans les écosystèmes aquatiques. Cette thèse s'est attachée à étudier ces contaminants émergents au niveau de l'estuaire de la Loire, milieu marqué par une forte pression anthropique pouvant être source de TR. Pour la première fois, la concentration en TR du compartiment abiotique a été ...
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