The Smelly Science of Tracking the Movements of Microplastics

Posted Wed, 02/06/2019 - 08:24

Where does plastic go once it enters the ocean? This is a harder question to answer than it may seem. When we think of plastic pollution, most of us think of large pieces of plastic floating at the surface of the ocean, but that’s only a piece of the puzzle. Plastic can be found at every depth in the ocean. Some of that plastic does float, but some drifts underwater, and some sinks all the way down to the ocean floor. It is especially hard to keep track of the smallest pieces of plastic, microplastics less than 5mm in size. Recent research is revealing that those microplastics are being moved not just by currents and weather, but by animals through their digestive tracts.

We know animals out in the ocean are eating plastic, and many of us have seen the pictures of plastic in the bellies of sea birds, sea turtles, and whales. Larger pieces of plastic can become stuck in an animal’s stomach, making it hard for them to eat, while microplastics tend to pass right on through the animal.

Sample of microplastics.
Tiny microplastics like these easily end up in the guts of all sorts of marine life (Photo Credit: Will Parsons, Chesapeake Bay Program)

Sea birds are especially prone to snacking on plastic. More than 100 species of sea birds have been confirmed to eat plastic. A recent study of seabirds of the coast of Canada’s Labrador peninsula has found that they are also pooping out plastic, and about half of the birds studied had microplastics in their poop. This is potentially an issue because of where the birds are pooping. These birds feed all over the north Atlantic, and then return to their rocky island roosts. Tens of thousands of birds gather together, and poop together. In essence, these birds are collecting microplastics from wide swaths of the ocean, and concentrating them in one place. These plastic-eating birds could be creating rings of plastic pollution around their colonies.

Bird on beach surrounded by plastic trash.
Seabirds such as this masked booby are exposed to plastic marine debris daily, even in remote locations such as the NWHI. (Photo Credit: NOAA)

It’s not just birds that are eating and pooping plastic. Some of the smallest animals in the ocean, zooplankton, could also be moving plastic as they move their bowels. Researchers looked at zooplankton living in the Monterey Bay off the coast of California. With their small, nearly transparent bodies, it was easy for researchers to see brightly colored plastic in the zooplankton’s guts. Researchers also examined the fecal pellets expelled by the small creatures, and once again found microplastics. Zooplankton habits may also be influencing how these microplastics move through the ocean. The specific type of zooplankton studied, larvaceans, tend to have poop that sinks rapidly at an estimated 1,000 feet per day, when they are microplastic free. Scientists are still researching how microplastics affect the rate at which the poo drops. In this particular study, they did find that although the microplastics themselves didn’t sink, the microplastic-rich fecal pellets had no problem dropping to the bottom of the zooplankton’s holding container. This means that these little critters could be transporting microplastics from near the ocean’s surface down to the briney depths of the ocean floor.


Sample of microplastics under a microscope. Fish visible.
This sample of plastics collected from the Gulf of Mexico also contains life. Animals all over the ocean and Great Lakes are consuming and excreting plastics. (Photo Credit: NOAA)

Zooplankton, sea birds, and hundreds other species of animals are eating, and presumably pooping, plastic every day. It is going to take a lot more research and looking at animal feces to figure out how this affects the plastic pollution problem that is imperiling our ocean and Great Lakes. But there is one thing that’s certain: you can help keep plastic out of the ocean and out of animals’ bellies! Join a cleanup, reduce the amount of single-use plastic you use, and always to remember to dispose of any plastic waste properly, no matter where you live. Together we can make the seas, and also animal’s intestines, free of debris.