This may be why his team got mixed results in their analysis: more individual microplastics in the intestine, the greater the microbial diversity, but the more mass of microplastics, the lower the diversity. The more particles a bird eats, the more likely these hitchhiking microbes are to take up residence in its gut. But if the bird just ate a higher mass of microplastics — fewer but heavier pieces — it may have consumed fewer microbes from the outside world.
Meanwhile, particularly shredded microplastics could scratch the digestive system of birds, causing trauma that affects the microbiome. Indeed, the authors of the plasticosis paper found significant trauma to the intestines of wild flesh-footed shearwaters, birds that live along the coasts of Australia and New Zealand, which had eaten microplastics and macroplastics. (They also looked at plastic particles as small as 1 millimeter.) “When you ingest plastics, even small amounts of plastics, it changes the structure of the stomach, often in very, very significant ways,” the study says. study co-author Jennifer Lavers, pollution ecologist. at Adrift Lab, which studies the effects of plastic on marine life.
Specifically, they discovered catastrophic damage to the birds’ tubular glands, which produce mucus to provide a protective barrier inside the stomach, as well as hydrochloric acid, which digests food. Without these essential secretions, Lavers says, birds “also cannot digest and absorb protein and other nutrients that keep you healthy and fit. So you are really prone and likely to be exposed to other bacteria, viruses and pathogens.
Scientists call this a “sublethal effect”. Although ingested pieces of plastic do not immediately kill a bird, they can harm it. Lavers calls it the “punch of plastic” because eating the material downright harms birds, then potentially makes them more vulnerable to the pathogens they carry.
A major caveat to today’s article — and the vast majority of microplastics research — is that most scientists haven’t analyzed the tiniest of plastic particles. But researchers using special equipment have recently been able to detect and quantify nanoplastics, on the scale of a millionth of a meter. These are much, much more numerous in the environment. (This is also why the finding that there are 11 billion pounds of plastic floating on the surface of the ocean was likely a major underestimate, as this team only considered particles down to a third of a millimeter. .) But the process of observing nanoplastics remains difficult and expensive, so Fackelmann’s group can’t say how many might have been in the digestive systems of seabirds, and how they, too, might influence the microbiome.
This will probably not be good news. Nanoplastics are so small that they can penetrate and damage individual cells. Experiments on fish show that if you feed them nanoplastics, the particles end up in their brain, causing damage. Other animal studies also found that nanoplastics can cross the intestinal barrier and migrate to other organs. Indeed, another paper Lavers released in January found even microphoneplastics in the kidneys and spleen of flesh-footed shearwaters, where they had caused significant damage. “The harm we demonstrated in the plastics paper is probably conservative because we didn’t treat particles from the nanoplastic spectrum,” Lavers says. “I personally think it’s quite terrifying because the damage from the plasticosis article is quite overwhelming.”
Today, scientists are racing to determine whether ingested plastics can endanger not just individual animals, but entire populations. “Is this harm at the individual level – all these different sublethal effects, exposure to chemicals, exposure to changes in the microbiome, plasticosis – enough to drive population decline?” asks Lavers.
The jury is still out on this, as scientists don’t have enough evidence to form a consensus. But Lavers believes in the precautionary principle. “A lot of the evidence we have now is deeply concerning,” she says. “I think we need to let logic prevail and make a pretty safe and careful assumption that plastics are currently causing the population declines of certain species.”