If only the answers really were in the envelope.
As he touched on; what happens when, on the molecular-level, plastics contaminate the fish, and thereby our own food supply? What is the long-term health risks, for animal and man? How many years before it degrades to that level? I would guess, not many.
Robert, frightening, isn't it? Here are two articles that address your question. I don't have time to summarize them right now, but they're freely accessible on the web (unlike a lot of my sources which come from University library): http://www.bcise.com/CurrentIssuePapers/Plastic-Continent.pdf, and http://5gyres.org/media/Persistent_organic_pollutants.pdf