A major new study of the world’s oceans has reached a shocking conclusion: Thanks to humans, there are now over 5 trillion pieces of plastic, weighing more than 250,000 tons, floating in water around the world.

With a global population of about 7.2 billion, that’s nearly 700 pieces per person.

The study, published in the journal PLOS One by Marcus Eriksen of the Five Gyres Institute in Los Angeles and a large group of colleagues, is based on data from 24 separate ocean expeditions, conducted between 2007 and 2013, to sample plastic pollution. Plastic was either observed from boats, or hauled up from the ocean by nets, in 1,571 locations. The data were then used to run an ocean model to simulate the amount and distribution of plastic debris.

The result not only yielded the estimate of over 5 trillion pieces of plastic in the global ocean – it also cast light on how plastic changes within the ocean (breaking down into smaller pieces) and circulates around the globe. Pieces between 1 millimeter and 4.75 millimeters in size were by far the most prevalent class of plastic in the ocean. However, by weight, really large pieces of plastic, greater than 200 millimeters in size, were the most significant.

“What we are witnessing in the global ocean is a growing threat of toxin-laden microplastics cycling through the entire marine ecosystem,” commented lead study author Eriksen of the Five Gyers Institute.

Worryingly, even though there are far fewer people living in the Southern Hemisphere, the research found that its oceans have about the same amount of plastic, suggesting that winds and ocean currents may transport our trash all around the world.

The authors stress that they suspect their estimate is “highly conservative” – there could be a lot more plastic out there than that. For as they note, there is also a “potentially massive amount of plastic present on shorelines, on the seabed, suspended in the water column, and within organisms.”

Once in the oceans, plastic plastic breaks into smaller pieces and circulates – traveling into five major ocean gyres.