Despite the hundreds of millions of metric tons of plastic floating in our oceans—not to mention the microplastics in our saliva, blood, breast milk, and semen—researchers have been unable to account for all the plastic ever produced. A new study has just tracked down a large portion of it.

Researchers from the Royal Netherlands Institute for Sea Research (NIOZ) and Utrecht University claim to be the first to provide a real estimate of ocean-polluting nanoplastics. Their research indicates that the North Atlantic Ocean alone hosts 27 million tons of floating plastic particles less than 1 micrometer (μm) in size.

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Unfortunately, there are a number of ways nanoparticles can end up in the oceans. While some likely arrive via rivers, others fall out of the sky with rain or on their own as “dry deposition.” (Yes, we’ve even found plastic pollution in the sky). Nanoparticles can also form when large pieces of plastic already in the ocean are broken down by waves and/or sunlight, according to the researchers. The question now is how this pollution is impacting the world and its creatures—including us.

“It is already known that nanoplastics can penetrate deep into our bodies. They are even found in brain tissue. Now that we know they are so ubiquitous in the oceans, it’s also obvious that they penetrate the entire ecosystem; from bacteria and other microorganisms to fish and top predators like humans,” said Helge Niemann, a geochemist at NIOZ and another co-author of the study. “How that pollution affects the ecosystem needs further investigation.”