By linking worldwide data on solid waste, population density, and economic status, Jenna R. Jambeck and co-authors writing in the Journal Science estimated that 275 million metric tons of plastic waste were generated worldwide in 192 coastal countries in 2010, with 4.8 to 12.7 million tons entering the ocean (Science 13 February 2015: Vol. 347 no. 6223 pp. 768-771) The authors noted that world plastic production increased by 620% in the last 40 years, and without waste management infrastructure improvements, the cumulative quantity of plastic waste available to enter the ocean from land is predicted to increase by an order of ten by 2025.
A trash-covered creek in Manila, Philippines. Francis R. Malasig/U.S. EPA. http://www.theguardian.com/environment/gallery/2009/jun/05/waste-world-environment-day.