Plastic is the most pervasive pollutant in the ocean today. But researchers have struggled to estimate just how much of the 6 billion tons of plastic that has been manufactured since the mid-20th century ultimately winds up in the ocean.
Now a carefully vetted estimate of our oceans’ plastic burden shows that the answer is not pretty. Based on the calculations, at least 5.25 trillion pieces of plastic—weighing nearly 269,000 tons—are currently bobbing around in the ocean. A team of researchers from six countries reported the finding today in PLOS ONE.
Revealing this disturbing figure required the team to conduct 24 garbage-collecting expeditions between 2007 and 2013. Those trips to sea included visits to all five sub-tropical gyres—large systems of constantly rotating currents infamous for their roles in creating garbage patches—plus the Mediterranean Sea, the Bay of Bengal and Australia. At all of the sites, teams collected water samples for estimating the amount of microplastic, pieces of plastic smaller than 4.75 millimeters. They also tallied up larger pieces using standardized visual surveys. These data represent the most comprehensive tally yet done for ocean plastic pollution.
With their field data in hand, the researchers created a computer model to estimate the total quantity and weight of the world’s marine plastic. The model assumed that plastic entered the ocean via rivers, coastlines and ships, and it took factors like wind-driven vertical mixing, currents and the amount of plastic that winds up on the ocean floor into account. The team also corroborated their estimates with field tests.
In addition to the weight estimate, the team made an important and frightening observation: Large pieces of plastic tended to be most concentrated near coasts, but the smallest particles they measured—from the size of a grain of sand to a grain of rice—accounted for about 90 percent of the total garbage count. It seems that plastic gets chewed into microplastic once it hits an ocean gyre, where it is broken down by a combination of waves, ultraviolet radiation from the sun, oxidation and nibbling fish. Given these findings, ocean garbage patches may be more aptly named garbage blenders.
To make matters worse, the newly created microplastic doesn't stay put, but instead gets spewed from the gyre into the greater ocean. Every water sample the researchers took, no matter how remote, was laced with some amount of microplastic. The team was shocked to discover multitudes of microplastic near the subpolar gyres, for example, corroborating recent findings that high amounts of the humanmade material can also be found in sea ice.
The extreme reach of plastic pollution is a problem, because those barely noticeable pieces can bind to pollutants and, when ingested by marine animals, can act as mini toxic bombs, gut-clogging confetti or both. As Marcus Eriksen, director of research for the 5 Gyres Institute and lead author of the study, told PLOS: “The endgame for micro-plastic is interactions with entire ocean ecosystems.”