According to the Proceedings of the National Academy of Sciences, only 1% of the plastic calculated to have entered the oceans is still there. The great Pacific Garbage Patch and other maelstroms of floating plastic are only 1% the size they should be. Perhaps polymer-consuming organisms already exist in the oceans and are just waiting to break out on land…
http://www.sciencemag.org/news/2014/06/ninety-nine-percent-oceans-plastic-missing