Northern Europe, and by that I mean from the Bay of Biscay northwards receives so much marine pollution for three main reasons. One we are producing it ourselves, finding it hard to dispose of and allow a lot to enter our water systems. Secondly prevailing winds are from the west and south west so anything that makes the ocean in the North Atlantic, and by that it includes the whole of the east of the USA and Canada makes its way over to us. And finally, the North Atlantic Currents, surface and sub surface currents (not deep water) all move west to east, so you chuck a Maccas container or a Coke bottle into the sea in Florida, and there is a possibility that it washes up in Ireland or ends up in the garbage patch in the Bay of Biscay.
Simply we’re at the end of our own waste but also potentially everything else that enters the North Atlantic from Eastern North America as well.