A team led by Jeroen Sonke at the University of Toulouse built an independent model of how plastic moves through land, rivers, oceans and air, then ran the Organisation for Economic Co-operation and Development (OECD)'s own policy scenarios through it.
They estimated the marine plastic pool at 263 million tonnes in 2015, with 14 million tonnes a year moving from land to sea, several times the OECD's figure. By 2060, land-to-sea transport reaches 43 million tonnes a year under business as usual, 22 million tonnes under 'Global Ambition' and 18 million tonnes under 'System Change'. Marine accumulation reaches 1,500 million tonnes (business as usual) or about 1,200 million tonnes (ambitious policy).
The key message is that even the most ambitious policies only slow accumulation, because the plastic already in the environment keeps fragmenting into microplastics for decades.
This is one model among several, and estimates of ocean inflow vary widely depending on scope and method.