Background: Plastic pollution is of growing concern in marine ecosystems worldwide. Specifically, microplastics (<5 mm) may interact with a variety of biota with the potential to cause harm to organism health. Studies investigating microplastics are increasing, yet their occurrence within free-ranging and living marine mammals remains largely unexplored. Methods: By using a protocol involving enzymatic digestion, filtration and microscopic identification, faecal samples collected from a grey seal (Halichoerus grypus) haul-out site in the North Sea were investigated for microplastic presence. Results: Altogether, 71 suspected microplastic particles, consisting of both fibres and fragments in a variety of colours and sizes, were identified across 66 analysed faecal subsamples. Conclusion:The present study indicates that marine mammals are ingesting microplastics and that faecal material can be used to indirectly and noninvasively record microplastic uptake data in pinnipeds. Since the current paper is the first to document potential microplastic exposure among wild, living and free-ranging grey seals of the western North Sea, further research is needed to begin to understand the biological significance of these findings.

Plastic pollution is of increasing concern to marine ecosystems worldwide. Specifically, microplastics (<5mm) may interact with a variety of biota with potential to cause harm to organism health. Studies concerning microplastics are increasing, yet their occurrence within live marine mammals remains largely unexplored. Here, faecal samples collected from a haul-out site in the North Sea, were used to investigate microplastic pollution within grey seals (Halichoerus grypus). 71 microplastic particles, consisting of both fibres and fragments in a variety of colours and sizes, were identified across 66 scat subsamples analysed. This indicates that marine mammals are ingesting microplastics and that faecal material can be used to indirectly and humanely record microplastic uptake data in pinnipeds. Since the current paper is the first to document microplastic exposure amongst wild, living and free-ranging grey seals in the North Sea, further research is needed to begin to understand the biological significance of these findings.