Headed out to sea. AP Photo/Julio Cortez

It's important to illuminate the volume and the origin of marine plastic.

Trillions of microscopic plastic bits litter the oceans of Earth, converging in huge trash vortexes before becoming lodged in the seabed and getting gobbled up by tiny fish. But since countries don’t report how much plastic they’re flushing, it’s been impossible to tell how much there is—or where it’s all coming from.

This map from a groundbreaking new study (paywall) in Science finally gives us a sense of the biggest culprits—specifically which countries heap the most plastic into poorly managed coastal dumps or landfills. The study, led by Jenna Jambeck of the University of Georgia, estimates that between 15 and 40% of that precariously placed plastic is swept into the ocean via inland waterways, storm water or the wind. In 2010, between 4.8 million and 12.7 million tons (5.3 million-14 million tons) of plastic entered the sea.

Global map with each country shaded according to the estimated mass of mismanaged plastic waste [millions of tons (MT)] generated in 2010 by populations living within 50 km of the coast. Countries not included in the study are shaded white. ("Plastic waste inputs from land into the ocean," Jambeck et al. 2015)

And as you can see from the map above, China likely contributed a hefty share of the total—nearly 28%. According to the authors’ forecasts, its share will fall only slightly by 2025. By then, China another other countries will flush as much as 28 million tons into the ocean each year—adding up to 155 million tons accumulated since 2010.

The generally high share of plastic waste from China and other Asian countries is consistent with where scientists have found marine plastic debris, says Andrés Cózar, a marine ecologist at the University of Cadiz, who was not involved in the study. And this makes sense. Thanks to sprawling metropolises like Shanghai, Guangzhou, and Tianjin, China also has the biggest, densest coastal population on the planet.

However, China’s plastic debris contributions don’t only come down to its huge size, says Daniel Hoornweg, associate professor at University of Ontario Institute of Technology and an expert in Asia’s waste management systems.

“China generates a lot of garbage—per unit of GDP, more than India or Indonesia,” he says. (Though on a per capita basis, China generates less trash than the U.S.).

While Shanghai, for example, boasts a coastal landfill that Hoornweg says is “reasonably well managed,” the swift growth of Chinese plastic consumption is outpacing most municipal governments’ capacity to manage it. Part of the problem is simply the cultural preference for excessive packaging. “You go into a store in China and there are individually wrapped oranges,” says Hoornweg.

Those orange wrappers and other plastic bits that wind up in the ocean are typically worn by seawater into small pellets called “microplastics.”

What toothbrushes, shampoo bottles, and other plastic stuff turns into at sea. (Flickr/U.S. Fish and Wildlife Services via CC License)

What confounds scientists like University of Cadiz’s Cózar—who recently led an important investigation into the global distribution of plastic debris—is that the share of floating plastic found bobbing near the surface only makes up a minute portion of that thought to have entered the ocean. Put another way, 99% of marine plastic is effectively missing. A huge amount is likely embedded in sediment, many fathoms deep. Scientists also suspect that tiny lanternfish snack heavily on plastic.

But by helping illuminate both the volume and origin of marine plastic, says Cózar, the research by Jambeck and her colleagues “add a relevant piece to the puzzle of marine plastic pollution.”

This post originally appeared on Quartz, an Atlantic partner site.

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