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There is a chance of course that we are just outsourcing the problem with our "recycling" programs. We carefully keep plastic out of our environment by putting them in our recycle bins. The recycle bins get picked up carefully by our Sanitation Engineers. The Sanitation Engineers deliver them to the collection facility. The collection facility bundles everything up and then sells it to China...
I have read other research pointing to a vanishing problem. They filtered sea water through various levels of sieves and plotted the amounts of plastic by size. There is a size of plastic where it stops appearing in the water. One answer is that it is being eaten by animals.
That's an interesting theory Brad, if developed countries are contributing to the 'plastic waste in the oceans' problem to any extent, it is probably through the practice of sending plastic waste abroad for 'recycling'. If the recyclers in developing countries can't make use of all the plastic waste they import, they may just dump the surplus in rivers.
After doing a bit of research, I found that China is the world's predominant recycler of plastic waste:
China and plastic waste recycling
The EU apparently exports 87% of the plastic waste it collects to China, including Hong Kong. But China has recently announced a policy where it intends to cut back substantially on importing foreign waste from next year onwards, and will recycle its own domestic waste instead, so much of the plastic waste collected in developed countries may have nowhere to go. If China recycles its own plastic waste, that will obviously keep some of its own plastic waste out of the rivers.
One country I was expecting to be a big contributor to the 'plastic waste in the oceans' problem was Mexico, but that doesn't seem to be the case. Mexico is notorious for having a litter problem, as discussed in this US newspaper article from ten years ago:
Mexico litter problem
Rubbish gets thrown into rivers in Mexico (the article mentions an incident where the Grijalva River got clogged with trash in a narrow gorge), but it may be that the geography of their rivers is such that not much gets carried into the sea.