Have you ever heard of microplastics? See what they can do with the brain

Every year, 8 million tons of plastic waste are produced. With inadequate disposal, a significant part of this production goes through constant exposure to ultraviolet rays and ends up in the oceans, turning into very small particles, known as microplastics (MPs). The understanding of its effects on the brain is still limited, which prompted a new study coordinated by scientists in South Korea. The initial discovery is that MPs can accumulate in the region, where they are toxic.

It may seem strange that such a small substance “lost” in the oceans can harm humans, but they may be closer than we think. That’s because, at sea, microplastics are consumed by plankton and can become a threat to mammals closer to the top of the food chain, such as humans.

Microplastics can be toxic to the brain of mammals, according to a South Korean study (Image: Reproduction/IciakPhotos/Envato)

That’s why the South Korean study is so important. During the tests, the effects of microplastics on the brain of rodents and also on brain tissue cells were evaluated. “The study shows that MPs, especially MPs with a size of 2 micrometers [2 milionésimos de metro] or less, begin to deposit in the brain even after short-term ingestion, within 7 days, resulting in apoptosis [morte celular programada] and changes in immune responses and inflammatory responses,” explained researcher Seong-Kyoon Choi, from the Daegu Gyeongbuk Institute of Science and Technology (DGIST), in a statement.

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In addition, Choi commented that the results of the study, published in the journal Science of the Total Environment, open doors for new research on the relationship of these substances in mammals. “Based on the results of this research, we plan to conduct additional research that may further reveal the accumulation of MPs in the brain and the mechanism of neurotoxicity,” he added.

How can microplastics affect the brain?

“Despite several reports on the impact of small MPs on the brain and behaviors in aquatic animals, it is still unclear how small MPs affect the brain and its underlying cellular physiology in terrestrial animals,” explain the authors in the article. To assess the impact of microplastics on the brain, their effects were tested in vivo with rodents and in vitro with human cells.

In rodents, microplastics can pass beyond the blood-brain barrier (Image: Reproduction/Twenty20photos/Envato Elements)

In the case of mice, the scientists administered, orally, microplastics for 7 days. After analysis, the team found that microplastics with sizes of 2 micrometers or less can pass through the blood-brain barrier (BHE) of animals. It is this protection that prevents the brain from absorbing harmful substances, but it is apparently vulnerable to microplastics.

In addition, the team also revealed that MPs accumulate in samples of microglial cells — they are part of the Central Nervous System (CNS) and have a similar function to that of leukocytes (white blood cells) in the bloodstream — in the human brain. In the experiment, the team tested MPs of different sizes, reaching a maximum size of 10 micrometers.

According to the researchers, microplastics equal to or smaller than 2 micrometers accumulated in the cytoplasm of microglial cells and significantly decreased the ability of cell proliferation. Furthermore, these CNS cells recognize MPs as an external threat, leading to microglial phagocytosis, which causes apoptosis, that is, they lead the body to program cell death in brain tissues.

It is not yet known for sure whether it is possible that MPs can naturally reach the brain of mammals, but a Brazilian study, by the University of São Paulo (USP), has already detected the presence of microplastics in the human lung.

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