Smallest plastic particles caused the greatest changes in nasal cells

The nose is one of the body’s first points of contact with substances and particles present in the air. These include microplastics and nanoplastics, which can originate from sources such as synthetic textiles, tyre and road wear, and the degradation of larger plastic objects.

However, relatively little is known about what happens when such particles come into contact with cells in the human airways.

In a new study, researchers at Örebro University investigated how cells from the inside of the human nose respond to plastic particles of different sizes. The cells were exposed to nanoplastics measuring 100 nanometres, microplastics measuring 7 micrometres, and a mixture of the two.

The researchers then examined changes in the cells’ metabolism, the chemical processes that enable cells to generate energy, build up and break down substances, and maintain their functions.

Nanoplastics produced the most pronounced changes

The most pronounced changes were observed in the cells exposed to nanoplastics. Among other things, the levels of several substances important for cell structure, energy use and other fundamental functions were altered. The researchers also observed a marked reduction in several lipids that are important building blocks of cell membranes.

The microplastics produced considerably smaller changes.

“These results show that particle size matters. Nanoplastics can interact with biological systems very differently from larger particles, and in our experiments, nanoplastics were the main drivers of metabolic changes,” says Andi Alijagic, docent in biology at Örebro University.

When the researchers exposed the cells to a mixture of nano- and microplastics, some of the changes were less pronounced than when the cells were exposed to nanoplastics alone. One possible explanation is that some of the small nanoplastic particles became attached to the larger microplastic particles. As a result, fewer free nanoplastic particles were able to come into contact with the cells.

The study does not show that plastic particles cause disease

The study was conducted on cells in a laboratory and does not demonstrate that the quantity of plastic particles people encounter in everyday life causes disease.

“It’s important to distinguish between observing a change in cells in a laboratory experiment and demonstrating that something poses a health risk to humans. We used a comparatively high level of exposure to understand what these particles can do to human cells and which processes are affected,” says Andi Alijagic.

To assess any potential health risks, however, more knowledge is needed about how much micro- and nanoplastics people actually inhale, how much is retained in the airways, and what happens following repeated exposure over longer periods.

Many substances analysed simultaneously

To detect these changes, the researchers used methods known as metabolomics and lipidomics. These techniques make it possible to measure a large number of small molecules and lipids simultaneously, providing a broad picture of what is happening within the cells.

“Using these methods, we can detect molecular changes before we necessarily see more obvious effects in the cells. We observed different patterns depending on which plastic particles the cells were exposed to,” says Tuulia Hyötyläinen, professor of chemistry at Örebro University.

The researchers did not only investigate what happened inside the cells. They also analysed the substances released by the cells into their surroundings. Here too, they observed differences depending on which plastic particles the cells had been exposed to. The changes were linked, among other things, to how the cells respond to chemical stress and break down or transform different substances.

The results provide researchers with clues about which cellular processes may be affected by plastic particles and what should be investigated further.

“The next step is to study exposure levels that more closely reflect real-world conditions and to use more advanced models of the human airways. In the longer term, if we are to assess whether airborne micro- and nanoplastics pose a health risk, we need to understand both how much people are exposed to and what these particles can do to cells,” says Andi Alijagic.