Each year about 8.8 million tons of plastic ends up in the world oceans, a quantity much higher than previous estimates, according to a new study that tracked marine debris from its source.

That's the equivalent of five grocery bags full of plastic debris dotting each foot of coastline around the world, said study lead author Jenna Jambeck, an environment engineering professor at the University of Georgia.

And if the biggest polluters, mostly developing Asian countries, don't clean up how they throw stuff away, Jambeck projects that by 2025 the total accumulated plastic trash in the oceans will reach around 170 million tons. That's based on population trends and continued waste management disposal problems, although there may be some early signs of change, she said.

More than half of the plastic waste that flows into the oceans comes from just five countries: China, Indonesia, Philippines, Vietnam and Sri Lanka. The only industrialized western country on the list of top 20 plastic polluters is the United States at No. 20. The U.S. and Europe are not mismanaging their collected waste, so the plastic trash coming from those countries is due to litter, researchers said.

While China is responsible for 2.4 million tons of plastic that makes its way into the ocean, nearly 28 percent of the world total, the United States contributes just 77,000 tons, which is less than 1 percent, according to the study published Thursday in the journal Science. This is mostly because developed countries have systems to trap and collect plastic waste, Jambeck said.

"We need to wake up and see our waste," Jambeck said. "I think the problem in some ways has sort of snuck up around us."

The amount of plastics estimated going into the water is equal to how much tuna is fished year, so "we are taking out tuna and putting in plastic," study co-author Kara Lavendar Law said in a press conference at the American Association for the Advancement of Science conference.

Nancy Wallace, who is head of the marine debris program for the National Oceanic and Atmospheric Administration, said plastic waste in the water is a crucial worldwide issue because it is eaten by sea life and it also collects ocean toxins. There's also a clean-up cost and it affects tourism, she said.

Unlike previous studies which looked at the plastic in the oceans, Jambeck used World Bank statistics on 192 countries' waste streams to track and estimate plastic pollution from the source. She examined how much waste is generated and the percentage that to reaches the oceans.

Jambeck's estimates were for 2010 and ranged between 5 and 14 million tons of plastic, with 8.8 million tons the middle scenario estimate.

Previous estimates were less than 1 million tons but those were based on samples. Scientists know that much can be hidden in the bottom of the ocean and in places researchers don't get to. Last year Andrés Cózar of the University of Cadiz in Spain estimated the waste at about 35,000 tons based on samples, but he said the new Jambeck work adds important information to the puzzle of debris. And Cozar said his team acknowledged that "99 percent of the ocean's plastic is missing."