Not to mention that there are rivers runningthrough many of those landlocked countries, which surely would take some plastic waste along for the ride (for example Vienna with over a million inhabitants and a tourist destination surely has the odd plastic cup/bag/wrapping ending up drifting downstream in the Danube) but that seems to be left out.
Unrelated, from a flyer (unknown source):
View attachment 462792
Even if this is meant to be a globe and as such the curvature has to be taken into account there are still things not adding up (like the total lack of Africa south of Somalia and eastern Asia in general)