J. Cachot 1, C. Clérandeau 1, F. Le Bihanic 1, C. Vignet 1,3, P. Pannetier 1,3, F. Misurale 1, Q. Pedriat 1, B. Morin 1, M. Revel 2, C. Mouneyrac 2, M. Mouloud 2, A. Châtel 2, H. Perrein-Ettajani 2, M. Bruneau 2, M.P. Halm 3, A. Gangnery 3, M.L. Bégout 3, X. Cousin 3, C. Dreanno 3, M. El Rakwe 3, J. Thery 4, C. Bialais 4, S. Souissi 4, M. Kazour 4, R. Amara 4, M.A. Dutertre 5, R. Coulaud 5, T. Monsinjon 5, B. Xuereb 5, L. Boudahmane 6, C. Partibane 6, B. Grassl 7, S. Lecomte 8, J. Gasperi 9. 1. Université de Bordeaux, EPOC, Pessac France ; 2. Université Catholique de l'Ouest, MMS-UCO, Angers France ; 3. Ifremer France 4. Université de Lille-ULCO, LOG, Lille France 5. Université du Havre, Sebio, Le Havre France ; 6. Université de Paris Est, LEESU, Paris, France; 7. Université de Pau, IPREM, Pau, France ; 8. Université de Bordeaux, CBMN, Pessac, France ; 9. Université Gustave Eiffel, GERS-LEE, Nantes, France The Plastic-Seine project (Seine-Aval, 2017-2020) aims to analyse the occurrence, levels of contamination and ecotoxicological effects of microplastics (MPs) in seven species (fishes, worms, copepods and mussels) of the Seine Estuary's ecosystem. MPs were recorded in the digestive tract and/or in the soft tissues of all the species sampled but the level of contamination was very variable depending on the species and the individual. Synthetic (mainly PET) or natural (cellulose) fibres constitute the vast majority of MPs found in biota. The kinetic of MPs ingestion and digestive transit were studied in the worm Hediste diversicolor and in sole, Solea solea. MPs ingestion is rapid (