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Counting All the Plastic in the Ocean Is Really Hard

A recent study counted 5.25 trillion plastic particles floating in the world's oceans.
December 29, 2014, 1:10pm
​A beach in the Azores. Image: Marcus Eriksen

​The huge amount of plastic pollution in the world's seas has led to floating islands​ of trash, ecosystems adapting to a habitat of plastic d​ebris, and birds filling​ their bodies with toxic knick-knacks. Those images are now well-known, but there's still a lot we don't know about the great plastic rubbish heap that is the ocean.

This month, an international team of researchers published a study in PLO​S One that gave the first estimate for the total amount of plastic pollution on the surface of all the world's oceans. They put the figure at around 5.25 trillion plastic particles, weighing 269,000 tons.


Microplastics were found not only in the great gyres where plastic is known to accumulate, but also floating in remote areas. There weren't as many of these tiny particles as expected, however which leads to the question: Where are they all going?

Environmental scientist Marcus Eriksen, director of California-based nonprofit organisation Five Gyr​es Institute and first author of the paper, explained how his team went about modelling the ocean's plastic pollution, and what they're doing with the data.

MOTHERBOARD: So you basically counted how much plastic there was in the ocean. That sounds like quite a mammoth task—how did you start?
Marcus Eriksen: It's a very simple procedure, just very time-consuming. We start with dragging nets behind our boats. We use a very traditional plankton net that scientists have used for almost 100 years to survey the ocean surface. It's a very fine mesh, like one third of a millimetre, and we skim the ocean surface. For two or three miles we'll drag this net, covering an area as big as maybe two soccer fields, and we'll just count the particles. We'll count every single particle, we'll weigh them, we'll divide them into different size classes, we'll divide them by colour, by type—very descriptive data. We get that for thousands of points around the world.

For our study, we combined our data with other colleagues who did the same thing; six other colleagues had data, and two ocean modellers. With all this data, we plugged it into an ocean model that was predicting where trash might come from—coastlines, shipping lanes, big rivers—and we used our data to calibrate the model. And that's where the prediction came from. It was six years of work for a very simple task of counting particles.


What was the hardest part of doing all that?
I think the hardest part is all the logistics of getting to the middle of nowhere. What we've done at the Five Gyres Institute, when we first formed we saw that data on plastic trash in the oceans was really only in the eastern part of the North Pacific and western part of the North Atlantic. There was nothing around Japan, the Marshall Islands, the Azores, or just west of London, in that part of the ocean—or the entire Southern Hemisphere. So we chose to organise expeditions. We don't own the boats; we find boats. Every summer or every spring we find a vessel, and we charter it to go from one point to another. For example, Rio de Janeiro to Cape Town, South Africa, or Perth, Australia to Mauritius, or Chile to Easter Island, or from Bermuda to the Azores and then across to the Bahamas. So long-distance travelling.

You don't see many plastic bags in the middle of the oceans, they just shred into small particles

The way we fundraise, we only charter vessels that have extra seats onboard for crew, and we'll sell those seats to pay for the charter. That got us around the world in 14 expeditions, and that got us out into the middle of the oceans, the middle of nowhere, to see where these garbage patches really are. The sample set is really quite diverse and spread around the world.

Obviously you collated all this data together. What, in a nutshell, did you find out?
What we found was there's a lot of big trash out there; the majority of the 270,000 metric tons is fishing gear. The most persistent material that's filling the oceans is this stuff that's designed to be in the ocean. About half the weight is fishing buoys. The rest is products that are very rapidly breaking down. We also found that the products that leave our coastline and float out to sea are on the fast track to being shredded. Very quickly, a plastic bag gets shredded down to small, micro-class particles. You don't see many plastic bags in the middle of the oceans, they just shred into small particles. So these five subtropical gyres, they're not really accumulation zones that are static, that build up these mountains of trash; they're very dynamic. They shred, they tear plastic apart by two mechanisms.


A sample of microplastic. Image: Stiv Wilson

First of all, the plastic is always moving around, sunlight is always bearing down on the plastics, and lots of fish and even sharks and turtles are nibbling at plastic to tear it apart. What happens is, let's say a plastic bag or a crate, as they float to the oceans they're pulling apart the microplastics. Of that 5.25 trillion microplastic particles worldwide, about 92 percent are smaller than a grain of rice. So when you're out in the middle of the oceans, you see open blue water, you drag your net, and you get a handful of plastic confetti. That's what these garbage patches are—they're very thin, very wide expanses of plastic confetti accumulating in these gyres and very quickly leaving these gyres.

We expected not just 5 trillion particles; we expected 500 trillion particles—[there was] 100 times less than expected. There's something happening on the ocean surface that's making the smallest microplastic particles, the dust-sized particles and fibres, leave the ocean surface. So although plastic products leave our coastlines and migrate to the gyres and shred, they very quickly leave the ocean surface.

We think there are two mechanisms. One is that they sink: little small particles can react to water not by material buoyancy but more by the surface tension of water and they get driven downwards very quickly, and then other currents take them away from the gyres. Also foraging: there are billions of filter-feeding organisms in the oceans that filter out seawater. They're taking in plastics.


So the gyres are these shredders of plastics and redistributors of plastics out to the rest of the world.

I rafted the entire Mississippi River, and I saw an endless trail of trash

How did you get involved with this work in the first place?
I grew up near water, I grew up in New Orleans next to the Mississippi River, and I always watched trash float by. I'd go down to the river and find things to build forts with, as kids do—lots of trash. In 2003 I actually built a raft and rafted the entire Mississippi River, and I saw an endless trail of trash. Soon after I went to Midway Atoll and I saw animals with their chests full of​ trash, albatross birds. I'd find hundreds of piles of bones and feathers and every single one had a pile of trash in its chest. I got interested in the issue and I saw this huge data gap, where no one knew about the southern hemisphere or these parts of the Atlantic and Pacific. So I saw an opportunity to contribute something.

Eriksen on his raft. Image: Marcus Eriksen

What's the next step now?
I think we need to really focus our solution efforts on upstream solutions. There are so many crazy ideas about cleaning up trash in the middle of the ocean—I don't think it's viable, because most of the trash is on the fast track to shredding. I think to focus solutions away from ocean clean up and move it towards resource prevention. To give you an analogy of what this problem looks like, if you look back in the 1970s, when air pollution was plaguing our cities in Europe and the United States, people looked up and saw smoke and smog. There were people who suggested vacuum cleaners on top of buildings and sucking up the air pollution. Everyone said, that's ridiculous—build a better muffler.

It's the same thing with the ocean. Plastic is a cloud of tiny particles globally, and you can't clean it up by going out there and scooping up small particles. What's out there is going to become sediment, and that's the reality. We've got to stop the source, build a better product. We have a few research questions still answering about products' biodegradability, airborne plastics, with important companies.

They become so toxic-laden that we call them hazardous waste

If I could draw your readers to our microbea​d campaign: We did some research a year and a half ago where we pu​blished the first account of plastic microbeads in the Great Lakes in the United States, and these microbeads we traced back to facial scrubs and toothpastes. That opened a huge can of worms; there were companies using small particles of plastic as scrubbers in toothpastes and facial scrubs. We worked with these companies to try to get some legislation in place to stop the use of plastics and go for alternatives that are more ocean friendly.

One last point is that microplastics in the oceans—there's one challenge between scientists and policymakers. Scientists now agree that microplastics at sea really be​come hazardous waste. They absorb so many toxins, they become so toxic-laden that we call them hazardous waste. Policymakers are very hesitant to use those words and the plastic industry is fighting us on terminology, only because of the legal ramifications of it. I argue it's an appropriate term. One colleague found up to a million times higher concentration of [toxins] on a single grain-of-sand-sized piece of plastic in ambient seawater. Plastic's a perfect sponge for hydrophobic compounds.