Microplastics can reach the brain through the nose – 10/02/2024 – Balance and Health

Tiny plastic particles are everywhere: in the soil where our food is grown, in the water we drink and in the air we breathe. They ended up there because of the plastic that we throw away and that ends up in landfills, rivers and seas. In these places, plastic waste slowly decomposes, releasing even tinier particles, called microplastics and nanoplastics, into the environment.

Microplastics are also increasingly being found throughout the human body. We’re not sure how they get there, although there are three likely routes. We can ingest microplastics when we eat and drink, breathe them in through our lungs, or absorb them through our skin. Recently, another route has been suggested, whereby microplastics enter our noses and then go directly to our brains.

For a long time, it was thought that the human brain existed in splendid isolation from the rest of the body. The so-called blood-brain barrier, a special layer of cells, protects the brain from all types of pathogens and harmful substances. We now know, however, that the blood-brain barrier can be breached, as small plastic particles have been found in the human brain.

New research suggests that the blood-brain barrier has at least one vulnerable point through which microplastics can enter the brain. This possible entry point was suggested by researchers at Freie Universität Berlin and the University of São Paulo (USP). This point is in the nose, where there are special nerves, the olfactory nerves, which detect odors.

The olfactory nerves run from inside the nose, through the skull and go directly to a part of the brain called the olfactory bulb. The researchers suggest that microparticles breathed in through the nose may somehow be transported by olfactory nerves to the brain.

The researchers reached their conclusions by analyzing tissue samples from São Paulo residents who had died and had undergone routine autopsies by medical examiners. They removed the olfactory bulbs from these brains and analyzed them using a variety of techniques.

Eight of the 15 brains studied had microplastics in their olfactory bulbs. These eight positive samples, however, only had 16 microplastic particles between them in total, which is perhaps a little reassuring for us.

These 16 microplastic particles included fragments, beads and fibers, and were made from polypropylene, nylon and other types of plastic. Some of the fibers may have come from clothing. This makes sense because washing clothes made with synthetic fibers is a significant source of microplastics present in the environment.

Even more dangerous particles

This new study is just one of many that have reported the presence of small plastic particles in the human body. Most of these studies are about microplastics, particles up to five millimeters in size. Very few studies have investigated the presence of nanoplastics in the human body.

Nanoplastics are less than a thousandth of a millimeter in size — so small that they are difficult to detect without special equipment, and few scientists have easy access to such equipment.

The reason nanoplastics are a major concern is that, unlike microplastics, they are proven to be harmful to living cells. This is because nanoplastics are small enough to enter cells. And, once inside, they can lead the cell to death.

Nanoplastics have already been shown to kill cells in animal embryos. This can lead to birth defects in animals if the embryo is exposed to a high dose of plastic nanoparticles.

Fortunately, there is no evidence that humans have suffered a large increase in birth defects in recent years. Perhaps the human placenta is capable of preventing microplastics and nanoplastics from reaching the fetus.

We need to know much more about the presence of microplastics — and especially nanoplastics — in the human body. And we need to know how they get there in the first place.

This makes the new study carried out in collaboration between Berlin and São Paulo so interesting. It suggests a possible new entry point for microplastics into the human body, from the nose to the brain. Which leaves us with the following question: what are the possible risks that microplastics and nanoplastics pose to our health? The jury is still out on its verdict, but perhaps it is a little more nervous about this issue than before.

This article was published on The Conversation and republished here under a Creative Commons license. Click here to read the original version.