Jenna Jambeck and colleagues combined data on waste generation, population density and waste management quality for 192 coastal countries to estimate how much plastic reaches the sea from land.
They found that between 4.8 and 12.7 million tonnes of plastic entered the ocean in 2010, with a middle estimate of 8 million tonnes. They warned that, without better waste management, the total amount of plastic waste that could reach the sea from land would grow about tenfold by 2025. This is a build-up over time, not a yearly figure.
This is one of the most cited papers in the field and the source of the 'garbage truck of plastic every minute' image. It established that mismanaged waste in fast-growing coastal economies, not ocean dumping, was the main source of marine plastic.
It is routinely misquoted as a current annual figure. It describes 2010, covers land-based sources only, and has been followed by estimates ranging from 0.5 million tonnes (buoyant plastic, measured) to 19–23 million tonnes (all aquatic environments). Always give the year.