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Marine plastic floating on the sea surface is an extensive environmental problem. The present study investigated the transport patterns of marine litter and areas of its accumulation in the Baltic Sea by using a hydrodynamic model coupled with a particle-tracking model. We also studied the extent of marine litter from the main polluting rivers. Mapping of marine plastic debris distribution in 2017–2018 revealed that the largest plastic accumulation area is between latitude 59° N and 61° N, which includes the Northern Baltic Proper, Archipelago Sea, and the Gulf of Finland. The floating plastic spreads from the largest plastic pollution sites River Vistula, Oder and Neman to the waters of all the countries around the Baltic Sea. • Hydrodynamic and particle-tracking coupled model revealed the transport pattern of plastic • Homogeneous and quasi-realistic simulations showed the same plastic accumulation areas. • The largest plastic accumulation area lies between the latitudes 59° N and 61° N. • Plastic particles migrated over the Baltic Sea from the biggest sources of pollution, the Vistula, Oder, and Neman rivers. [ABSTRACT FROM AUTHOR]

Marine litter and, particularly, plastics are a growing concern at global scale. The Mediterranean Sea is among the zones in the world with the highest concentration of floating plastic debris. However, our knowledge remains limited on the spatial distribution of litter across this basin. Here, a set of different numerical model simulations were conducted to examine the dynamic conditions of the surface layer of the Mediterranean and how this drives the circulation and accumulation of floating litter. Seasonal dynamics of surface water circulation led to contrasting distribution patterns of floating litter along the year. Multiple hot spots of litter zones appeared across the basin in summer, while litter disperses and moves towards the Eastern Mediterranean and nearshore waters in winter. Taking into account such seasonal variability in the spatial patterns of litter in the Mediterranean seems to be key in the design of further sampling surveys and management strategies. • Surface current dynamics shows marked seasonality in the Mediterranean. • Accumulation and distribution of floating particles follow currents patterns. • Floating litter accumulates in diverse areas during different seasons. • Lagrangian model helps to identify beaches impacted by floating litter. [ABSTRACT FROM AUTHOR]