Microplastics are starting to turn up in all kinds of places, from the heights of Mount Everest, to the sea ice in the Antarctic, to the organs and tissues of the human body. In an effort to better understand how these tiny fragments of plastic are absorbed by organisms in aquatic environments, scientists have carried out a study that shows how a coating of biomolecules can act as a "Trojan horse" that sneaks them into living cells.
Researchers are beginning to shine a light on just how widespread microplastic pollution is, and how it can affect living organisms. These tiny pieces of plastic measure less than 5 mm in size and are therefore very difficult to trace through the environment, though recent studies have found them in sea turtles, sea bass and crustaceans. One study on Japanese medaka fish demonstrated how microplastics can cause aneurysms, as well as reproductive changes.
A team of scientists from Germany's University of Bayreuth set out to explore how microplastics can make their way into living organisms after some time in the marine environment, which is where a huge portion of plastic waste ends up. The team worked with microplastics measuring around three micrometers in size, which they say are similar to those often found in the environment, and drew up a couple of experiments to study their behavior.
Some of the particles were placed in fresh water from an artificial pond, while others were placed in salt water from an aquarium. Within two weeks, both groups of microplastic particles developed coatings made up of biomolecules.
"Spectroscopic examinations indicate that these biomolecules are carbohydrates, amino acids, nucleic acids, and proteins," explains first author of the study, Anja Ramsperger. "We are talking about an 'eco-corona' that forms on the microplastic particles in a natural environment."
From here, the team wanted to investigate whether living cells internalized these coated particles, or if they simply stuck to the outside of the cells. They did this by staining key components of cells, called actin filaments, and then studying them under a microscope, where internalized particles did indeed show up as dark holes.
"The fluorescent labeling of the actin filaments enabled us to see exactly which particles were internalized by the cells," says. Dr. Holger Kress, Professor of Biological Physics at the University of Bayreuth. "Based on spectroscopic methods, we verified that these particles were indeed microplastics – or more precisely: polystyrene particles – and not accidental impurities."
As part of the experiments, the team used a control group of microplastic particles that were instead incubated in ultra pure water, which didn't develop the coating of biomolecules. These particles were occasionally taken up by the living cells, but far less frequently than those incubated in the impure water.
"Our study supports the assumption that microplastics which were exposed to the natural environment – and are therefore coated with biomolecules – not only pass through the digestive tract when ingested with food, but may also be incorporated into tissue," says Dr. Christian Laforsch from the University of Bayreuth. "The coating of biomolecules may act as a kind of Trojan horse that allows plastics to be internalized into living cells. The precise damage that the particles can cause here has not yet been sufficiently investigated. It is also still largely unclear which of the properties of microplastics are actually responsible for any negative effects."
Herein lies the great unknown regarding plastic pollution. While studies have began to explore its effects on living organisms such as fish, as mentioned above, the impacts on human health are yet to be properly explored. The World Health Organization launched a health review in 2018 after finding plastic particles in 93 percent of bottled water, and other research groups are shifting their focus toward the health outcomes of plastic pollution, so it is an increasingly active area of scientific inquiry.
The research was published in the journal Science Advances.
Source: University of Bayreuth