| Summary: | The contamination by microplastics (particle inferior of 5 mm) was evaluated in all environmental compartments around the world with widely varying concentrations. This variability is due to spatial and temporal differences in contamination but also results from the lack of standardization of sampling, sample preparation and analysis methods. In this context, this thesis aimed to develop and validate fast analytical procedures of characterization and quantification of microplastics for sedimentary and biological matrices. The application of the validated protocols allowed to characterize the microplastic contamination of two bivalve species (the blue mussel Mytilus edulis and the pacific oyster Crassostrea gigas), wild and cultivated, and the sediments from three mudflats of the Atlantic coast (Pen-Bé, Coupelasse and Aiguillon Bay), at two seasons. The mean contamination was evaluated at 0.61 ± 0.56 and 2.1 ± 1.7 microplastic per mussel (N=120) and per oyster (N=60) respectively. In sediments, a mean of 67 ± 76 microplastic per kg dry weight (N=60) was measured. A large proportion of polyethylene and polypropylene fragments were observed in both matrices with a notable difference in the size range of detected microplastic: <100 μm for bivalves and between 100 and 250 μm for sediments. No significant effect of site, season or lifestyle for bivalves has been highlighted on microplastic contamination. In parallel, the sorption of six organic contaminants of marine waters has been studied on model microplastics made of polyethylene and polypropylene. A l’échelle mondiale, la contamination en microplastiques (particule plastique inférieure à 5 mm) a été évaluée dans tous les compartiments environnementaux avec des concentrations très variables, traduisant des pressions de contamination différentes mais résultant aussi d’un manque de standardisation des méthodes d’échantillonnage, de préparation d’échantillons et d’analyse. Dans ce contexte, cette thèse a visé à développer et valider des protocoles rapides ...
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