Plastic of the smallest size is now everywhere. It’s in the air we breathe, the water we drink – and the food we eat. According to current estimates, some people eat plastic the size of a credit card every week. Microplastics have already been found in human blood, in women’s placenta and, of course, in feces. But we still don’t know exactly what all those tiny bits of plastic are doing to us — and other living things.
New studies on seabirds now suggest that the foreign bodies they eat could affect the gut microbiome – the trillions of microorganisms that colonize the gut and play an important role in health. Seabirds ingest the plastic from the sea, which we know can accumulate in their stomachs. The latest study shows that as a result, the birds have more potentially harmful microorganisms in their guts, including some that can break down plastics.
“The study broadens our view of the impact of plastic pollution on wildlife,” says Martin Wagner, a biologist who studies the impact of plastic on ecosystems and human health at the Norwegian University of Science and Technology and is familiar with the work. He finds the results “worrying”. It has long been known that plastics can cause toxicity and physical harm to animals. The fresh evidence that the microbiome of animals is also affected shows the wide range of negative effects that come from plastic pollution and microplastics in particular, says Wagner.
Plastic planet
Microplastics, tiny bits of plastic less than five millimeters in diameter, are a type of pollution that has reached ecosystems around the world. “We know that microplastics have reached very remote areas of the deep sea, the Arctic and the Tibetan Plateau,” says Gloria Fackelmann, a microbiologist at Ulm University. “There are also microplastics in rivers. And more and more research is starting to look at microplastics in soils.” Scientists don’t yet know exactly how much plastic most animals get. But it is clear that seabirds are particularly vulnerable. Because these species spend a large part of their time at sea and eat fish near the water surface. They also eat a lot of floating plastic.
Previous studies have shown that these plastics can be extremely harmful to seabirds. Animals with stomachs full of plastic can become so full that they don’t eat enough and eventually starve. The chemicals that escape from the plastic fragments can also be harmful, such as causing inflammation. Because microorganisms can attach themselves to the surfaces of plastics, Fackelmann and her colleagues wondered if microplastics could also affect the species that make up the animals’ microbiome. To date, few studies have examined the potential impact of plastics in this area. These often involved experimental setups in which mice were fed plastic in a laboratory. Instead, the Ulm researcher Fackelmann and her colleagues wanted to find out what happens in a real environment.
Fackelmann’s colleagues studied seabirds from Canada and Portugal. Twenty-seven fulmars were collected by the scientists working with Inuit hunters near Qikiqtarjuaq in Nunavut, Canada. 58 Cory’s shearwaters that died after collisions with buildings were collected from the Azores archipelago. The scientists then took samples from both ends of each bird’s digestive tract to get an idea of what the microbiome was like.
Section of a seabird’s gastrointestinal tract where microplastic particles can be seen with the naked eye.
(Image: Yasmina Rodríguez, University of the Azores)
Plastic parts count – and microbes
The team also flushed the birds’ gastrointestinal tracts to count the pieces of plastic present and weigh the total amount in each animal’s intestines. The birds that had more pieces of microplastic in their guts had more diversity in their microbiome than others. A greater diversity of gut microbes has actually traditionally been considered good. But that’s not always the case, says Fackelmann. If the introduced bacteria are harmful to the animal, greater diversity wouldn’t be beneficial, she says.
To find out whether the introduced microbes are “good” or “bad,” Fackelmann and her colleagues analyzed the microbiomes and searched databases for individual microbes to learn what they’re doing. They found that with more plastic, there were more microorganisms known to break down plastic. There were also more microbes known to be resistant to antibiotics and more microbes with the potential to cause disease.
However, Fackelmann and her colleagues did not examine the health status of the birds, so they do not know whether parts of the microbiome could have made the birds sick. “But of course, if pathogens and antibiotic-resistant microbes accumulate in the digestive system, that’s not good,” says Wagner.
According to Fackelmann, the study, published in the journal Nature Ecology and Evolution, shows that the amounts of plastic already present in the environment are sufficient to influence the animals’ microbiome. The next step now is to find out what this might mean for animal health and the health of other living beings, including humans, she says. “If I [die Studie] “When I read it, it made me think of whales stranded with pounds of plastic in their bellies,” says Wagner. “It’s probably similar to what birds have in their digestive systems, so it would be interesting to know if whales do the same , dolphins [und anderen Meerestieren] occurs.”
What happens in humans?
We don’t yet know if the amount of plastic humans eat is enough to change our microbiome. Humans ingest far less plastic than seabirds, says Richard Thompson, a professor of marine biology at the University of Plymouth in the UK. The amount of plastic that enters our bodies also depends on where we live and work. For example, people working in textile factories are exposed to higher levels of exposure than those working outdoors.
Nor do we know the consequences of ingesting microbes that attach themselves to the microplastics that enter our bodies. Thompson points out that humans are already exposed to many disease-causing microbes that aren’t found on plastics. For example, we might worry that tiny bits of plastic in sewage could pick up problematic germs, which would then somehow enter our bodies. But overflowing sewage regularly contaminates beaches and drinking water directly, without any plastic.
There’s a chance that microbes that break down plastic may also take up residence in our guts. It’s hard to say how – or if – this is affecting us negatively. Microbes can evolve rapidly and exchange their genes with those of neighboring creatures. “Are we going to develop in the direction of digesting plastic? My answer would probably be no,” says Fackelmann. But the possibility that more microbes that can break down plastic colonize our guts is “not beyond the realm of possibility,” she says.
(jl)