Polluting microplastics harm both animals and ecosystems

The tiny bits may post risks to everything from mussels and microbes to birds and more

Plastic bits picked up from a beach. This pollution appears to threaten a broad swath of aquatic life. But new work also shows this debris can provoke harmful changes in soil ecosystems.

doble-d/iStock/Getty images Plus

People around the world discard tons of tiny bits of plastic every year. Those bits can break down into pieces no bigger than a sesame seed or piece of lint. Much of that waste eventually will wind up loose in the environment. These microplastics have been found throughout the oceans and locked in Arctic ice. They can end up in the food chain, showing up in animals big and small. Now a host of new studies show that microplastics can break down rapidly. And in some cases, they can alter entire ecosystems. 

Scientists have been finding these plastic bits in all kinds of animals, from tiny crustaceans to birds and whales. Their size is a concern. Small animals low on the food chain eat them. When larger animals feed on the small animals, they can end up also consuming large amounts of plastic.

And that plastic can be toxic.

Nashami Alnajar is part of a team at the University of Plymouth in England that has just examined the effect of microfibers on marine mussels. Animals exposed to plastic-tainted dryer lint had broken DNA. They also had deformed gills and digestive tubes. The researchers say that it’s not clear the plastic fibers caused these problems. Zinc and other minerals leached out of the microfibers. And these minerals, they now argue, likely damaged the mussels’ cells.

a photo of a Northern fulmar flying above the sea
Northern fulmars are seabirds that fly long distances in search of food. And they may get poisoned by plastics and related chemicals they pick up while hunting down food.Jan van Franeker/Wageningen Marine Research

Mussels aren’t the only animals that eat plastic. And often not on purpose. Consider Northern fulmars. These seabirds eat fish, squid and jellyfish. As they scoop their prey from the water’s surface they may pick up some plastic, too. In fact, some plastic bags look like food — but aren’t.

The birds fly long distances in search of a meal. To survive those long treks, a fulmar stores oil from recent meals in its stomach. This oil is lightweight and energy rich. That makes it a quick source of fuel for the bird.

Susanne Kühn in the lab extracting plastic additives from oil
Sitting beside jars filled with seabird stomach oil and plastic fragments, Susanne Kühn extracts plastic additives from stomach oil.Jan van Franeker/Wageningen Marine Research

Some plastics contain additives, chemicals that give them features that help that last longer or function better. Some plastic chemicals dissolve in oils. Susanne Kühn wanted to know if those additives might end up in the birds’ stomach oil. Kühn is a marine biologist at Wageningen Marine Research in the Netherlands. Might these chemicals seep into the stomach oil of a fulmar?

To find out, she teamed up with other researchers in the Netherlands, Norway and Germany. They gathered different types of plastic from beaches and crushed it into microplastics. The researchers then extracted stomach oil from fulmars. They pooled the oils and poured it into glass jars.

They left some jars alone. In others, they added the microplastics. The researchers then placed the jars in a warm bath to mimic the temperatures inside a bird’s stomach. Again and again over hours, days, weeks and months, they tested the oils, looking for the plastic’s additives.

a pile of teeny tiny pieces of plastic in a disk shape
Plastic pieces filtered out of the jars of stomach oil at the end of Kühn’s experiment.Jan van Franeker/Wageningen Marine Research

And they found them. A variety of these additives leached into the oil. They included resins, flame retardants, chemical stabilizers and more. Many of these chemicals are known to harm reproduction in birds and fish. Most entered the stomach oil quickly.

Her team described its findings August 19 in Frontiers in Environmental Science.

Kühn was surprised that “within hours, plastic additives can leach from plastic to fulmars.” She also hadn’t expected so many chemicals to enter the oil. The birds may expose themselves to these additives again and again, she says. A bird’s muscular gizzard grinds up the bones and other hard bits of its prey. It also can grind up plastic, she notes. That could expose even more plastic to the birds’ stomach oil.

Smaller pieces, bigger problems

As plastic pieces break down, the total surface area of the plastic increases. This larger surface area allows for more interactions between the plastic and its surroundings.

Until recently, scientists thought sunlight or crashing waves were needed to break plastics down. Such processes could take years to release microplastics into the environment.

a close-up photo of an amphipod on some duckweed
An amphipod clings to duckweed at the start of Mateos-Cárdinas’s study.A. Mateos-Cárdinas/University College Cork

But a 2018 study discovered that animals play a role as well. The researchers found that Antarctic krill can pulverize microplastics. These small ocean-dwelling crustaceans break microplastics down into even smaller nanoplastics. Nanoplastics are so tiny they can get inside cells. Last year, researchers at the University of Bonn, Germany, showed that once there, those nanoplastics can damage proteins.

Microplastics are common in streams and rivers, too. Alicia Mateos-Cárdenas wanted to know if freshwater crustaceans also break down microplastics. She’s an environmental scientists who studies plastic pollution at University College Cork in Ireland. She and her colleagues collected shrimp-like amphipods from a nearby stream. These critters have toothed mouthparts to grind up food. Mateos-Cárdenas thought they might also grind plastic.

To test this, her team added microplastics to beakers containing amphipods. After four days, they filtered pieces of that plastic from the water and examined them. They also checked each amphipod’s gut, looking for swallowed plastic.

a nano-sized piece of plastic inside amphipod
Mateos-Cárdinas used fluorescent plastic in her experiment, making this nano-sized piece easy to spot inside an amphipod.A. Mateos-Cárdinas/University College Cork

In fact, almost half the amphipods had plastic in their guts. What’s more, they had turned some microplastics into tiny nanoplastics. And it took just four days. That’s a serious concern, Mateos-Cárdenas now says. Why? “It is believed that the negative impacts of plastics increase as particle size decreases,” she explains.

Exactly how those nanoplastics could affect an organism remains unknown. But these chopped up nanobits will likely move through the environment once created. “Amphipods did not defecate them, at least not during the length of our experiments,” Mateos-Cárdenas reports. But that doesn’t mean nanoplastics stay in the amphipod’s gut. “Amphipods are prey for other species,” she says. “So they can be passing these fragments through the food chain” to their predators.

Not just a water problem

Much of the research on microplastics has focused on rivers, lakes and oceans. But plastics are a major problem on land, too. From water bottles and grocery bags to car tires, discarded plastics pollute soils around the world.

Dunmei Lin and Nicolas Fanin were curious how microplastics might affect soil organisms. Lin is an ecologist at Chongqing University in China. Fanin is an ecologist at France’s National Research Institute for Agriculture, Food and Environment, or INRAE. Created in January 2020, it’s in Villenave-d’Ornon. Soils teem with microscopic life. Bacteria, fungi and other tiny organisms thrive in the stuff we call dirt. Those microscopic communities involve food-web interactions like those visible in larger ecosystems.

Lin and Fanin decided to mark off plots of forest soil. After mixing up the soil at each site, they added microplastics to some of those plots.

More than nine months later, the team analyzed samples collected from the plots. They identified lots of larger organisms. These included ants, fly and moth larvae, mites and more. They also examined microscopic worms, called nematodes. And they didn’t overlook soil microbes (bacteria and fungi) and their enzymes. Those enzymes are one sign of how active the microbes were. The team then compared their analysis of the plots with microplastics to soils without the plastic.

The microbial communities didn’t seem much affected by the plastic. At least not in terms of sheer numbers. But where plastics were present, some microbes ramped up their enzymes. That was especially true for enzymes involved in the microbes’ use of important nutrients, such as carbon, nitrogen, or phosphorous. Microplastics may have changed the available nutrients, Fanin now concludes. And those changes may have altered the enzyme activity of the microbes.

Larger organisms fare even less well with the microplastics, the study showed. Nematodes that eat bacteria and fungi were fine, perhaps because their prey was not affected. All other types of nematodes, however, became less common in the plastic-tainted soil. So did mites. Both animals play a role in decomposition. Losing them could have major impacts on the forest ecosystem. Numbers of the larger organisms, such as ants and larvae, also decreased. It’s possible the plastic poisoned them. Or they might simply have moved to less polluted soils.

These new studies “continue to demonstrate that microplastics are everywhere,” says Imari Walker Karega. She is a plastic-pollution researcher at Duke University in Durham, N.C. Each study leads to new questions requiring additional research, she says. But even now, she says, it’s clear that microplastics can have an impact on ecosystems everywhere. That includes our food crops, she says.

“I believe that anybody, regardless of their age, can tackle the issue with plastic pollution by making better choices,” says Mateos-Cárdenas. “We need to take care of [the planet] for our future selves and everyone who is coming after us.”

Alison Pearce Stevens is a former biologist and forever science geek who writes about science and nature for kids. She lives with her husband, their two kids and a small menagerie of cuddly (and not-so cuddly) critters.

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