First published study in 40 years estimating the amount of plastic going into our oceans, and expected to go into the ocean. Things are unfortunately not looking good.
Key excerpts – “5% to 40% of [plastic] littered or dumped plastic enters the ocean each year.” “About 4 million to 12 million metric tons of plastic washed offshore in 2010 alone.” 

http://news.sciencemag.org/earth/2015/02/here-s-how-much-plastic-enters-ocean-each-year