Microplastics are messing with the microbiomes of seabirds.

To determine whether the introduced microbes might be “good” or “bad,” Fakelman and her colleagues analyzed microbiomes and searched databases for individual types of microbes to learn what they do. They found that when there is more plastic, there are more microbes known to break down plastic. There were also many microbes that were resistant to antibiotics and had the potential to cause disease.

Falkman and her colleagues didn’t evaluate the health of the birds, so they don’t know if these microbes are making them sick. “But if you’re accumulating pathogenic and antibiotic-resistant microorganisms in your digestive system, that’s obviously not very good,” says Wagner.

The study, published in the journal Nature Ecology and Evolution, shows that the amount of plastic already in the environment is enough to harm the animal’s microbiomes, Fakelman says. The next step, she says, is to figure out what this means for their health and the health of other animals, including humans.

“When I read [the study], I thought of the whales we find washed ashore with kilograms of plastic debris in their bellies,” says Wagner. “It’s probably comparable to what birds have in their digestive system, so this is what whales, dolphins, [and other marine animals] as well as.”

Plastic people

We don’t yet know whether the amount of plastic humans ingest is enough to shape our microbiomes. Richard Thompson, professor of marine biology at the University of Plymouth in the United Kingdom, says humans ingest less plastic than seabirds. The amount of plastic that enters our body depends on where we live and work. People who work in textile factories, for example, are more exposed than those who work outside the home.

And we do not know the effect of entering the microplastics attached to our body. People are already exposed to many pathogens that aren’t on plastic, Thompson pointed out. For example, we may worry that tiny bits of plastic can pick up bad bugs in wastewater and that these can somehow end up in our bodies. But overflows of sewage regularly contaminate beaches and drinking water directly.

Microbes that break down plastic have a chance to live in our guts. It is difficult to know whether this will affect us or not. Microbes can evolve quickly, and can exchange genes with neighboring bugs. “Are we going to evolve to eat plastic? My answer would be no,” says Fakelman. But the likelihood of our guts harboring microbes that can break down plastic is “not beyond the realm of possibility,” she says.

There is also the possibility that plastic pollution can indirectly harm us. Introducing pathogens to birds and other animals can cause disease outbreaks, and one of the microbes the team found attached to plastic in the birds’ guts is thought to be able to jump from animals to humans. Wagner thinks the microbes seabirds ingest from floating plastic could eventually cause disease outbreaks in humans. But the more we disrupt natural systems, the greater the risk of zoonosis. [a disease jumping from animals to humans]” he added.

Given the place of microplastics, studies like these are sorely needed to help us understand how plastic pollution affects living organisms, including humans, the researchers said.

“We basically made the globe out of plastic,” Wagner said. “Everyone is exposed to microplastics and the chemicals in plastics—it’s only a matter of time before we know what they do to our microbiome. And I can’t see any argument why plastic is useful.