Microplastics have long been found everywhere in the environment - in the ocean and in bodies of water, in the soil and in the air. However, the consequences of this contamination for living beings are hardly known. A study of seabirds is now providing the first answers. It shows that the intake of microplastics changes the intestinal flora of the animals - helpful, healthy bacteria become fewer, pathogens increase. Accordingly, these changes already occur at the microplastic concentrations that are common in the environment.
Pollution of the environment from microplastics – plastic particles smaller than five millimeters – is an ongoing and growing problem. This plastic - often formed by the disintegration of larger pieces of plastic - is now popping up everywhere. Microplastics have also been found in the deep sea and in remote areas like Antarctica. The tiny plastic particles can also be found in the food chain and microplastics can even be found in our tissues and in our faeces.
A look inside the guts of two seabird species
But what are the consequences if we or other animals swallow the small plastic particles? There are initial indications from laboratory tests that microplastics of certain sizes and types of plastic can damage cells and possibly also trigger inflammation. Whether this also happens in everyday life and what consequences microplastic contamination has for wild animals, for example, has not yet been clarified. "Currently there is little systematic evidence that the amounts of microplastics already present in the environment have a negative impact on the health of affected species," explains lead author Gloria Fackelmann from the University of Ulm.
To learn more about this, Fackelmann and her colleagues studied the gut contents and gut-dwelling bacterial communities of two common seabird species, the fulmar (Fulmarus glacialis) and the cory's shearwater (Calonectris borealis). Both species live mainly in high seas and feed on marine molluscs, crabs and fish. In addition, both species migrate thousands of kilometers over the course of the year. For the study, the researchers examined the amount of microplastics in the gut of 85 birds and analyzed their gut microbiome using high-throughput sequencing.
Significant shift in bacterial species
The analyzes showed that the seabirds, which had more microplastics in the gastrointestinal tract, showed significant changes in the intestinal flora. The more microplastics were present in the birds' digestive tract, the more the composition of the bacterial community was shifted compared to normal conditions. The proportion of pathogens, as well as antibiotic-resistant and plastic-degrading microbes increased, while the number of commensals - beneficial bacteria - decreased. The latter make a decisive contribution to nutrient metabolism and healthy digestion, but also play an important role in the immune system.
"These results confirm that the microplastic pollution already present in the environment also affects the intestinal microbiome of seabirds," report Fackelmann and her colleagues. In their opinion, the changes found in the animals could impair health-related processes and even cause diseases. In the long term, this could also have cross-species consequences because an accumulation of pollutants through the food chain is to be expected. It is not yet clear why the microplastic changes the intestinal flora. "In addition to the consequences of mechanical injuries, pathogens carried over with the microplastics or chemical disturbances caused by the plastic polymers could also be considered," says Fackelmann's colleague Simone Sommer.
Despite some questions that are still unanswered, the researchers see a clear warning sign in their results: "Since humans also absorb microplastics from the environment and through food, these studies should also serve as a warning sign for us humans," emphasizes the research team.
Source: University of Ulm; Specialist article: Nature Ecology & Evolution, doi: 10.1038/s41559-023-02013-z