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And that's a highly conservative estimate, say scientists.

We know the oceans are home to tons of plastic garbage, from discarded nylon fishing nets that ensnare sea turtles to packing straps that strangle the life out of marine mammals. But because all that plastic is coming from everywhere, it's difficult to tell how much of it, exactly, is floating around—an important question, given its pernicious effects on the ecosystem and possible toxic repercussions to humanity's dinner plate.

Thanks to an international research effort spanning six years, we now have a much better idea of the sheer bulk of plastic water pollution. The minimum count is 5.25 trillion plastic particles littering the seas, say scientists in a new study in PLOS ONE. All those teeny bits—the result of the gradual breakdown of larger plastics, as well as escaped nurdles and microbeads used in cosmetics—add up to 269,000 tons, or about the weight of 2,150 adult blue whales.

The researchers arrived at these figures after analyzing two-dozen expeditions in five "subtropical gyres," large, swirling zones in the South Pacific, Indian Ocean, and elsewhere. The numbers were smaller than they expected to see at the water's surface, which they put down to removal processes that could include "UV degradation, biodegradation, ingestion by organisms, decreased buoyancy due to fouling organisms, entrainment in settling detritus, and beaching." In regards to "ingestion," they theorize that fish and other animals are gulping up the plastic because they believe it's food, and then pooping it out in "fecal pellets" that sink into lower waters where it's harder to detect.

Interestingly, the size of the debris was not uniform over the world. That could be due to the gyres acting like mulching disposals, the scientists explain:

Large plastics appear to be abundant near coastlines, degrading into microplastics in the 5 subtropical gyres, [and] the smallest microplastics were present in more remote regions, such as the subpolar gyres, which the authors did not expect. The distribution of the smallest microplastics in remote regions of the ocean may suggest that gyres act as 'shredders' of large plastic items into microplastics, after which they eject them across the ocean.

"Our findings show that the garbage patches in the middle of the five subtropical gyres are not the final resting places for the world's floating plastic trash. The endgame for micro-plastic is interactions with entire ocean ecosystems," says Marcus Eriksen, PhD, Director of Research for the 5 Gyres Institute.

More about the spread of this pollution: The Northern Hemisphere appears to have more plastic gunk than the Southern (at about 57 percent of total oceanic mass). And below the Equator, the Indian Ocean seems rife with debris, accounting for more particles than the South Pacific and South Atlantic taken together. Here's a map the scientists put together showing the measured count for various sizes of plastic particles (upper left is tiniest, bottom right biggest):

Eriksen et al./PLOS ONE

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