Plastic plastic everywhere. Over five trillion pieces floating in the ocean, to be exact. And together, they weigh over a quarter of a million tons. The findings were published in PLOS ONE this week.
Buoyant and durable, plastics and other synthetic polymers can be found in every ocean, bay, gulf, and sea, and their impact on marine wildlife is well known. To estimate the extent of plastic pollution in the oceans, an international team led by Marcus Eriksen from the Five Gyres Institute analyzed data from 24 expeditions between 2007 and 2013 across the Bay of Bengal, the Mediterranean Sea, coastal Australia, and all five subtropical gyres—that is, the massive rotating currents in the North Pacific, South Pacific, North Atlantic, South Atlantic, and Indian Ocean.
The work totaled 680 surface tows using mesh nets and 891 visual survey transects of large debris. That’s when someone looks at the ocean surface from one side of the boat out to 20 meters, while taking note of all the large plastic debris during a set time frame. Then they used data to populate an oceanographic model of debris pollution, taking into account factors such as currents, circulation, and winds. They arrived at this staggering number: A minimum of 5.25 trillion particles weighing 268,940 tons are afloat in our world’s oceans.
According to their estimates, the amount of plastic in those massive gyres in the northern and southern hemispheres were similar in magnitude: The two northern hemisphere ocean regions contain 55.6 percent of particles and 56.8 of plastic mass. The North Pacific, in particular, contains 37.9 percent and 35.8 percent by particle count and mass, respectively. In the southern hemisphere, the Indian Ocean has a bigger particle count and accounts for more of the weight than the South Atlantic and South Pacific ocean regions combined.
The team separated the plastic debris into four size classes: small microplastics (0.33-1.00 millimeter in diameter), large microplastics (1.01-4.75 mm), mesoplastics (4.76-200 mm), and macroplastics (greater than 200 mm), the majority of which were derelict fishing buoys.
Their calculations show that 75.4 percent of the total weight of plastic pollution is due to macroplastic. Mesoplastic made up 11.4 percent, and the two microplastic size classes made up 10.6 percent and 2.6 percent, respectively. In fact, microplastics together weigh only about 35,540 tons, which was surprising because the researchers expected to see more of these tiny bits. The missing microplastics, Science reports, may have sunk below the surface, become stranded on shorelines, eaten by animals, or broken down under UV rays from the sun.