Tiny pieces of trash called microplastics are prevalent in the environment, from rivers, lakes and oceans to inside the bodies of animals and humans. In a study published last week in Nature Ecology & Evolution, researchers found seabirds that had ingested more microplastics had more disease-causing and antibiotic-resistant microorganisms in their guts.
The results are “concerning,” Martin Wagner, a biologist at the Norwegian University of Science and Technology who did not contribute to the paper, tells MIT Technology Review’s Jessica Hamzelou. The study “really shows the wide spectrum of adverse effects that we get from plastic pollution and microplastics, in particular.”
By definition, microplastics are less than five millimeters across. Some are designed to be small, such as microfibers from clothing, while others form when larger plastics break down.
“We know that microplastics have reached very remote areas of the deep sea, the Arctic, the Tibetan Plateau,” Gloria Fackelmann, first author of the new study and a microbial biologist at Ulm University in Germany, tells MIT Technology Review. “There are microplastics in rivers … and a lot of research is beginning to look at microplastics in soils as well.”
From the environment, microplastics can enter animals’ bodies. As of 2018, they had been found in at least 114 aquatic species. They’ve also been detected in human blood, breast milk and placentas, writes Linnea Pedersen for the Agence France-Presse (AFP).
As microplastics break down, they can release toxic chemicals. Researchers have found the pollutants clogging the stomachs of birds and linked them to changes in blood chemistry and organ damage in animals, reports James Ashworth for London’s Natural History Museum.
In the new study, scientists looked for a connection between microplastics and the gut microbiome—the collection of bacteria, fungi, viruses and other microorganisms that play an important role in digestion, nutrition and maintaining health—in two species of seabirds. When seabirds eat fish from the ocean’s surface, they also ingest floating plastic.
The team studied 58 Cory’s shearwaters that had died from colliding with buildings in the Azores archipelago in Portugal and 27 northern fulmars that were shot in collaboration with Inuit hunters in Baffin Bay, Canada. In the lab, they analyzed the birds’ gut microbiomes and counted and weighed the microplastics in the animals’ stomachs.
Birds with a greater number of microplastics in their systems had more diverse microbiomes. While microbe diversity can be a good thing, these birds tended to have fewer microbes associated with healthy hosts and more microbes known to be antibiotic-resistant and connected to disease.
“This is a brilliant study that demonstrates yet more ‘hidden effects’ of plastics,” Alex Bond, a conservation biologist at the Natural History Museum in England who did not contribute to the research, tells New Scientist’s Corryn Wetzel.
Notably, the scientists did not examine how these different gut microbes might be affecting the birds’ health. “We can’t say the seabirds that had more plastic were unhealthier,” Fackelmann tells Wired.
“But if you accumulate pathogens and antibiotic-resistant microbes in your digestive system, that’s clearly not great,” Wagner tells MIT Technology Review.
The new gut microbes might enter the birds attached to the plastics. “Microplastics may be able to act as vectors for microbes, so seabirds ingesting more of these particles could have more microbes being shuttled into their body,” Fackelmann tells the Natural History Museum.
The researchers only looked for microplastics that were one millimeter in size or larger, but even smaller plastics exist. These so-called nanoplastics have been shown to cause damage to human cells and fish brains in lab experiments.
Per the AFP, the authors hope future studies will look at how microplastics could be shaping the microbiomes of humans.