Microplastics in marine bivalves from the Nordic environment: MP were analysed in mussels at 100 sites from Grenland to the Baltic. MP were found in 4 out of 5 species. The coastal waters of the North Sea, Kattegat, Skagerrak, and the western Baltic appear to be areas of MP accumulation. Mussels from urbanized areas and harbours contained the most MP. The abundance of MP was especially high in the Oslofjord. A total of 11 different polymer types were detected through 3 chemical characterisation methodes. Black rubbery particles, possibly derived from tyre wear, were the dominant particle type. The presence of rubber compounds was confirmed for Blue mussels (Mytilus) in analysis using pyrolysis GC-MS. This is the first study to document these polymer types in mussels. Mussels, especially Mytilus spp., Limecola balthica and Abra nitida are suitable for monitoring of MP in Nordic waters.