Microplastics in the intestines of seabirds have another significant impact in addition to negative effects such as the risk of injury and adhering pollutants: the plastic particles change the composition of the bacterial community in the intestines from “good” bacteria to pathogens as well as antibiotic-resistant and plastic-degrading bacteria. A new study by researchers from Germany, Portugal and Canada shows that the more microplastics in birds’ guts, the more their microbial diversity changes.
The research team studied two species of seabirds that frequently ingest plastic: the Northern fulmar, whose distribution extends from temperate northern latitudes to the Arctic and is an established bioindicator of plastic, and the Cory’s shearwater, which occurs throughout the Atlantic. Both species feed on mollusks, crustaceans and fish and migrate thousands of kilometers over the year, allowing global inferences.
In their research, the scientists found that microplastic ingestion alters the microbial community throughout the animals’ digestive tracts. The greater the mass of microplastics, the lower the diversity of the gut microbiome. However, the greater the number of particles, the greater the diversity of microorganisms, which in this case is not at all positive. The more particles they found in the gastrointestinal tract, the more pathogenic and antibiotic-resistant bacteria the researchers detected.
At the same time, the commensal, i.e. “good” intestinal bacteria decreased. But, just as in humans, these are the key to the health of the animal. They contribute to the normal and healthy functioning of the gut and play a critical role in immune modulation and protection against pathogens. If their composition is disturbed, this has an impact on health-related processes and the animal may become ill.
The pathogenic, antibiotic-resistant, and plastic-degrading bacteria enter the birds’ intestines as part of a community of viruses and algae living on the plastic particles called the “plastisphere.” This explains the contrasting results on the diversity of bacteria depending on the mass or number of microplastic particles. Whether the pathogenic microorganisms actually cause disease in the birds was not part of this study and remains to be clarified in future studies. Moreover, each plastic part carries a cocktail of various chemicals (plasticizers, flame retardants, pesticides, fertilizers, environmental toxins,…), which can also have adverse health effects.
The current study shows that microplastic concentrations, such as those found in the environment, can lead to changes in gut flora in animal species that frequently ingest plastic. According to the study, this can have not only short-term individual damage, but potentially long-term cross-species consequences, as the contaminants are expected to accumulate through the food web. “Our conclusions reflect the current situation in the wild. Since humans also uptake microplastics from the environment and through food, this study should act as a warning for us humans,” the authors said.
Julia Hager, PolarJournal
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