Researchers have found that more than 5 trillion pieces of plastic are floating in the world's oceans, with a combined weight of nearly 269,000 tons. In a major study published this week in the journal PLoS One, scientists from the US, France, Chile, Australia, and New Zealand found that the pollution is largely comprised of plastics from food packaging, clothing, and other products. They also observed how plastics spread across the world's oceans, posing serious environmental and health risks throughout the food chain, though they stressed that their estimates are "highly conservative." AsThe Washington Post notes, their findings are equivalent to nearly 700 pieces of plastic per person on Earth.

The study was based on data collected from 24 ocean expeditions conducted between 2007 and 2013, making it the most comprehensive to date. The researchers observed or gathered plastics from 1,571 different locations, before running their data through a model to simulate the volume and distribution of plastics across the globe.

"Bigger fish eat the little fish, and then they end up on our plates."

Most plastics were small in size, measuring less than 5 millimeters. These pieces enter the food chain when ingested by fish, making their way all the way up to humans, along with any toxins or chemicals they carry. Larger pieces, meanwhile, pose more immediate risks to maritime wildlife.

"We saw turtles that ate plastic bags and fish that ingested fishing lines," Julia Reisser, a researcher at the University of Western Australia, tells The Guardian. "But there are also chemical impacts. When plastic gets into the water, it acts like a magnet for oily pollutants. Bigger fish eat the little fish, and then they end up on our plates. It’s hard to tell how much pollution is being ingested but certainly plastics are providing some of it."

The authors say their findings underscore the importance of having a "100 percent recovery plan" for plastics or using environmentally harmless materials, and plastics makers say they agree.

"America’s plastics makers wholeheartedly agree that littered plastics of any kind do not belong in the marine environment," the American Chemistry Council, an organization that represents plastics makers, said in a statement following the study's release. The council added that plastics should be recycled "whenever possible" and that they should be treated as "valuable resources" after they've been used.

Grim as their findings may be, the paper's authors note that their estimates are likely far below the actual volume of plastics circulating the world. Their study doesn't account for the plastics littered along shorelines or already ingested by organisms. And as they point out, the 250,000 tons they estimate represents "only about 0.1 percent of of the world annual production."