A recent study found microplastics in brain tissue above the nose. Scientists say that this could be a passage for microscopic plastic shards and fibre to enter the brain. Earlier, microplastics were discovered in almost every organ in the human body including the bloodstream and plaque that clogs arteries. The study was published in the journal JAMA Network Open and conducted by included researchers from the University of São Paulo Medical School in Brazil.

The study looked at the olfactory bulb which is a part of the brain that processes information about smell. Humans have two olfactory bulbs, one above each nasal cavity which connects the olfactory bulb and the nasal cavity is the olfactory nerve. Researchers say that the olfactory pathway can be an entry point for microplastics to enter the brain.

Dr Thais Mauad, lead author of the study and associate professor of pathology at the University of São Paulo Medical School in Brazil said, “Previous studies in humans and animals have shown that air pollution reaches the brain and that particles have been found in the olfactory bulb, which is why we think the olfactory bulb is probably one of the first points for microplastics to reach the brain.”

Mauad and her team took samples of olfactory bulb tissue from 15 cadavers of people who died between the ages of 33 and 100. Samples from eight of the cadavers contained microplastics — tiny bits of plastic that ranged from 5.5 micrometres to 26.4 micrometres in size.

The researchers found 16 plastic fibre and particles in the tissues. The smallest were slimmer than the diameter of a human red blood cell, which measures about 8 micrometres. The most common type of plastic they found was polypropylene, followed by polyamide, nylon and polyethylene vinyl acetate.

Mauad said, “Propylene is everywhere, in furniture, rugs, clothes. We know the place we are most exposed to particles is indoors because all of our homes are full of plastic.”

According to a report in NBC News, Matthew Campen, a toxicologist at the University of New Mexico who has studied microplastics in the brain, said the presence of microplastics in the olfactory bulb “is unique but not terribly surprising.”

Campen wrote in an email, “The nose is a major point of defense to keep particles and dust out of the lungs.

“So seeing some plastics in the olfactory system, especially given how they are being found everywhere else in the body, is completely expected.”

While it wasn’t noted in the study, Campen said he believes the samples likely also contained many nanoplastics, which range in size from 1 to 1,000 nanometers. A strand of human DNA is about 2.5 nanometers thick. (One micrometre is 1,000 times larger than a nanometer.)

The presence of microplastics in the olfactory bulb doesn’t automatically mean there are microplastics elsewhere in the brain, such as regions related to cognition. Whether these particles can actually reach these parts of the brain through the olfactory bulb is still not clear.

“There is evidence that very small airborne particles can move to the brain via the olfactory bulb, but this is not known to be a major route of trafficking material to the brain,” Campen said.

The olfactory system is the pathway between the nose and the brain. Although rare, amoebas such as Naegleria fowleri which is larger than the size of the microplastics found in the study can get into the brain through the olfactory nerve. Mauad said, ‘We thought that if bacteria can pass through this pathway, microplastics might be able to, too.”

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