Scientists have long known that seabirds ingest microplastics, mistaking them for food. And according to a study published on Monday, this waste not only clogs or passes through the stomach, but also disrupts the balance of the entire digestive system, reports AFP.

By studying the digestive tracts of two species of Atlantic seabirds (such as the gray heron), researchers found that small particles of plastic disrupt their microbiome – a complex array of microorganisms, including good and bad bacteria.

In general, the more microplastics a bird consumes, the more the mostly beneficial gut bacteria decreases, while potentially pathogenic agents multiply.

The study, published in the journal Nature Ecology & Evolution, also shows an increase in antibiotic-resistant microbes and shows that some types of microplastics can also release chemicals that disrupt the gut microbiome of birds.

Microplastics, which are produced by the breakdown of plastic products in the environment, are found all over the world, from the deepest ocean trenches to the top of Mount Everest, and in most animal food chains. In humans, traces have been found in blood, breast milk and placenta.

The study supports previous findings that long-term consumption of microplastics causes an imbalance between healthy and harmful bacteria in the digestive tract.

The implications of this could be far-reaching because, like birds, many species, including humans, have a large microbiome in their digestive system.

“It’s a whole symbiosis that takes place in both birds and humans,” Gloria Fackelmann of the University of Ulm (Germany), lead author of the study, told AFP.

The diversity of this intestinal flora is often the key to good digestion and helps strengthen the immune system. But some of these bacteria and microbes can also have a harmful effect on health and cause disease, although the exact effect of each of them on the body is still not clear.

In general, however, there is growing evidence that microplastics – less than five millimeters in diameter – are harmful to animal health.

In humans, their presence can cause allergic reactions and cell damage, and the chemicals they contain have also been linked to an increased risk of cancer, reproductive problems, and DNA mutations.