About eight million tonnes of plastic waste wound up in the world's oceans in 2010, a study says, warning that the annual input increases every year.
So the cumulative amount could increase more than tenfold in the next decade unless the international community improves its waste management practices, the researchers said.
They identified that China and the United States are among 20 major sources of ocean-bound plastic.
Uncaptured waste - trash that is littered or lost from waste management systems - is the biggest source of ocean-bound plastic debris in the world, the findings showed.
"Our estimate of eight million metric tonnes going into the oceans in 2010 is equivalent to five grocery bags filled with plastic for every foot of coastline in the world," said Jenna Jambeck from the University of Georgia.
"This annual input increases each year, so our estimate for 2015 is about 9.1 million metric tonnes," Jambeck added.
She noted that in 2025, the annual input would be about twice the 2010 input, or 10 bags full of plastic per foot of coastline.
"So the cumulative input by 2025 would equal 155 million metric tonnes," Jambeck said.
The researchers studied the sources of ocean-bound plastic around the world and developed models to estimate their annual contributions.
They combined data on solid waste from 192 different coastal countries with factors such as population density and economic status.
According to the researchers' models, a country's population size and the quality of its waste management systems largely determine the amount of mismanaged waste that it generates.
"This mismanaged waste goes uncaptured, meaning that it then becomes available to enter marine environments," Jambeck said.
"Our mismanaged waste is a function of both inadequate management - open dumping, for example - and litter," she said.
The findings appeared in the journal Science.
