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Plastics pollute each of the world’s oceans. About 92 per cent of all floating marine plastics are microplastics. That means they are less than 5 millimetres in diameter. This is about the size of a grain of rice. But whatever their size, marine plastics are a huge problem. Tiny bits can poison even the smallest forms of marine life, while larger pieces can choke or tangle large animals. Plastics may pose problems in the ocean, but it’s important to remember where they come from: land.

Did you know? Most marine plastics in world’s oceans come from on land, but not from people littering. They escape out of sewer pipes and flow down rivers.

Scientists estimate that there are more than 5.25 trillion plastic pieces floating on the surface of oceans. Altogether, they weigh over 250 million kilograms. And that’s just what’s on the surface! About half of all plastics, including expanded Styrofoam and the high-density polyethylene used in plastic bags, are less dense than water. This means that they float. The other half, including nylon and the PVC used in piping, are dense enough to sink. It is expensive and time-consuming to do research underwater. Because of this, little is known about plastics on the ocean floor.

Most plastics found in the ocean start out as larger objects you would easily recognize, like plastic bags and toothbrushes. Over time, they break into tiny microplastics. That's because plastics don’t decay into different molecules the way organic substances do. While some microorganisms and fungi have been found to eat plastic, they do so in tiny quantities that do not break down the plastic entirely. Instead of decomposing, plastics break or crack into smaller and smaller pieces. However, they are still 100 per cent plastic polymers because the molecular bonds that hold them together are so strong. You may have heard people say there is a plastic island in the middle of the ocean. As you can see, this isn’t really true. It’s more like a plastic “smog” of tiny particles, even in places where plastics accumulate the most.

Seas of plastic (2009)
Charles Moore, TED Talks

Microplastics can be easily eaten by a wide variety of marine life, from microscopic organisms to sea birds and mammals. Some plastic fragments are small enough for plankton to eat. Plastic has even been found circulating in the blood of mussels. Some larger animals can choke on plastics. For example, some turtles eat plastic bags that look like jelly fish. However, the bigger concern is the oily chemicals attached to plastics. When animals eat the plastics, they’re eating these chemicals, too. Examples include brominated flame retardants (BFRs) and bisphenol A (BPA). BPA is a chemical that makes polycarbonate plastics like water bottles clear and strong.

If you’ve ever done dishes after eating leftover spaghetti or curry, you know that orange colour that’s so hard to scrub off plastic Tupperware. That orange is an example of one of these oily substances attracted to plastics. In the ocean, a small plastic fragment can absorb more than a million times more chemicals than the surrounding water. This makes the piece of plastic very toxic. Scientists nickname ocean plastics “poison pills” because when an animal eats the plastic, the chemicals move into its body as well. These chemicals continue to build up as larger organisms eat smaller ones (bioaccumulation). They also become more concentrated as they move up the food chain (biomagnification).

Did you know? Many ocean plastics are so tiny that they can be eaten by plankton, or even circulate in the blood of mussels.

Scientists are concerned that humans, who are at the top of the food chain, are also affected by animals eating microplastics. Most of these chemicals are endocrine disruptors, which mimic hormones in the body. They can affect brain development and reproductive health. They can also cause diabetes, obesity and cancer. The danger is especially serious in fetuses and young children.

Other problems caused by marine plastics include animals getting tangled. This is an especially big problem with “ghost fishing” nets that have been lost at sea but continue to catch fish. Floating plastics also serve as habitats for microbes and larger animals. So, when plastics wash up on new shores, they might be bringing living creatures with them. This means that floating plastics they can introduce invasive species. Plastics that sink into sediments can reduce the transfer of oxygen that organisms like worms need to breathe. Finally, plastics get tangled in engines, water intakes, and other parts of ocean infrastructure like boats and power plants.

Be a citizen scientist!

The Marine Debris Tracker is an online tool that lets you report marine debris or litter anywhere in the world.
You can also view the data collected via the Tracker.

Scientists and governments first became concerned about ocean plastics in the 1990s. At the time, they thought that people were dumping garbage straight into the ocean and on beaches. In fact, most marine plastics come from land. For example, researchers often find nurdles in the water and on beaches. These tiny spheres of plastic are feedstock pellets designed to be melted down to make plastic products. They get blown out of trucks or shipping containers, or spilled from ships. Likewise, plastic bags and other plastics that you put in the garbage can fly out of garbage trucks and get into sewage systems that lead to the sea.

The sea is downhill from everything. Plastic lasts a long time, so it can travel long distances. Two of the newest forms of marine plastic scientists are concerned about get into the ocean from wastewater treatment plants. The first is microbeads, which are found in face scrubs and toothpaste. They are small and slip through filters. The other is microfibers, which are even smaller. They’re the microscopic lint that comes off clothes when you wash them.

Because of where marine plastics come from, solutions to the problem need to start upstream: on land. Reducing the production of disposable plastics is the most important step. Five to 10 per cent of disposable plastics in North America are recycled. About half end up in landfills. What about the rest? A lot of them end up in the ocean, break into fragments, and become part of the world’s aquatic plastic smog.

This article was updated by Let's Talk Science staff on 2016-07-13 to improve readability by reducing the reading grade level.

Learn more!

Websites with a variety of information and resources related to ocean plastics, including videos and worksheets:

Plastic Oceans
Digital Explorer

Marine debris program
US National Oceanic and Atmospheric Administration (NOAA)

More Ocean. Less Plastic. 
5 Gyres

Scientific articles on how plastics break down:

Biological degradation of plastics: A comprehensive review (2008)
A. A. Shah, F. Hasan, A. Hameed & S. Ahmed, Biotechnology Advances 26
Link to abstract. Registration or subscription required to view full text.

Assessment of Environmental Biodegradation of Synthetic Polymers (1994)
Anthony L. Andrady, Journal of Macromolecular Science, Part C: Polymer Reviews 34
Link to abstract. Registration or subscription required to view full text.

Scientific articles on how plastics collect on beaches and in the ocean, and on the environmental effects of marine plastics:

Plastic pollution in the world’s oceans: More than 5 trillion plastic pieces weighing over 250,000 tons afloat at sea (2014)
M. Eriksen et al., PloS ONE 9

Microplastic pollution in the surface waters of the Laurentian Great Lakes (2013)
M. Eriksen et al., Marine pollution bulletin 77
Link to abstract. Registration or subscription required to view full text.

Accumulation of Microplastic on Shorelines Worldwide: Sources and Sinks (2011)
M. A. Browne et al., Environmental Science & Technology 45
Link to abstract. Registration or subscription required to view full text.

Accumulation and fragmentation of plastic debris in global environments (2009)
D. K. A. Barnes, F. Galgani, R. C. Thompson & M. Barlaz, Philosophical Transactions of the Royal Society B: Biological Sciences 364

Environmental implications of plastic debris in marine settings—entanglement, ingestion, smothering, hangers-on, hitch-hiking and alien invasions (2009)
Murray R. Gregory, Philosophical Transactions of the Royal Society B: Biological Sciences 364

Scientific articles and reports on how plastics collect toxic substances and on related health concerns:

The Impact of Endocrine Disruption: A Consensus Statement on the State of the Science (2013)
A. Bergman et al., Environmental health perspectives 121

Ingested plastic transfers hazardous chemicals to fish and induces hepatic stress (2013)
C. M. Rochman, E. Hoh, T. Kurobe & S. J. Teh, Scientific reports, 3

State of the science of endocrine disrupting chemicals - 2012 (2013)
World Health Organization & United Nations Environmental Program

Plastics, the environment and human health: current consensus and future trends (2009)
R. C. Thompson, C. J. Moore, F. S. vom Saal & S. H. Swan, Philosophical Transactions of the Royal Society B: Biological Sciences 364

Transport and release of chemicals from plastics to the environment and to wildlife (2009)
E. Teuten et al., Philosophical Transactions of the Royal Society B: Biological Sciences 364

Plastic resin pellets as a transport medium for toxic chemicals in the marine environment (2001)
Y. Mato et al., Environmental Science & Technology 35
Link to abstract. Registration or subscription required to view full text.

Ingested microscopic plastic translocates to the circulatory system of the mussel (2008)
M. A. Browne, A. Dissanayake, T. S. Galloway, D. M. Lowe & R. C. Thompson, Environmental science & technology 42
Link to abstract. Registration or subscription required to view full text.

Max Liboiron

I'm a professor at Memorial University of Newfoundland, where my students and I create citizen science technologies for monitoring marine plastics. I thought that making inexpensive, open-source, do-it-yourself environmental monitoring technologies was so important that I founded Civic Laboratory for Environmental Action Research (CLEAR) (http://civiclaboratory.nl/). I came to Newfoundland after 15 years in New York City, where I got my Master's degree and PhD, because Memorial University valued doing research that impacted local people and their concerns.  http://maxliboiron.com/

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