The trillions of plastic particles — a “plastic smog,” in the words of the researchers — weigh roughly 2.4 million metric tons and are doubling about every six years, according to the study conducted by a team of international researchers led by Marcus Eriksen of the 5 Gyres Institute, based in Santa Monica, Calif. That is more than 21,000 pieces of plastic for each of the Earth’s 8 billion residents. Most pieces are very small.

“This exponential rise in ocean surface plastic pollution might make you feel fatalistic. How can you fix this?” said Eriksen, a founder of the 5 Gyres Institute, a nonprofit group that works to study and fight ocean plastics pollution.

Only 10 percent of the plastic ever made has been recycled. The material that doesn’t make it into landfills can get swept into rivers or directly into oceans. It slowly breaks down into smaller and smaller pieces, known as microplastics, which are less than 5 millimeters in length and can be eaten by marine life. Plastic has been found near the summit of Mount Everest and inside the deepest point on Earth, the Mariana Trench — as well as in the human bloodstream.

The study examined plastic samples over 40 years starting in 1979. The researchers found a fluctuating amount of plastic in the samples until 2004, when the numbers started to skyrocket. The increase in plastic particles in the oceans corresponds to a previously observed increase of plastic on global beaches over the same time period, they noted.

The data includes samples from the world’s five major gyres, or current systems, which sweep particles from inhabited areas to create large collections of refuse. The best known of these is the Great Pacific Garbage Patch, where plastics float slightly below the surface.

In looking at samples, the researchers concentrated on the North Atlantic and North Pacific ocean basins, partly because they have been studied more frequently over the decades and are where greater concentrations of the world’s population lives. But high concentrations of plastics were found everywhere.

Eriksen, the study’s lead author, said research into plastics pollution had in recent years started to shift away from oceans and move farther upstream, to rivers and other waterways, as advocates struggled to understand the issue at its origin.