Small plastic particles are everywhere: in the soil where our food is grown, in the water we drink and in the air we breathe. They get there from the plastic we throw away, which ends up in landfills, rivers and seas. There, the plastic waste slowly decomposes, releasing tiny particles called microplastics and even smaller ones called nanoplastics into the environment.
HMH provides a paraphrase of the study, which was published by Michael Richards, professor of animal development at the Leiden University, and Meiru Wang, researcher in developmental biology, molecular biology and nanotoxicology at the Leiden University, in The Conversation.
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Microplastics inside the human body
Microplastics are also increasingly being found in the human body. We do not know how it gets there, although there are three possible ways. We can swallow microplastics when we eat and drink, inhale them through our lungs, or absorb them through our skin. Recently, another pathway has been proposed for microplastics to reach our noses and from there to our brains.
For a long time, it was believed that the human brain exists in complete isolation from the rest of the body. The so-called blood-brain barrier, a special layer of cells, protects the brain from all kinds of pathogens and harmful substances. However, we now know that the blood-brain barrier can be compromised, as small plastic particles have been found in the human brain.
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How microplastics get inside
New research has shown that the blood-brain barrier has at least one vulnerability through which microplastics can enter the brain. This potential entry point was proposed by researchers from the Free University of Berlin and the University of São Paulo. This place is located in the nose, where special nerves are located, the olfactory nerves that recognise smells.
The olfactory nerves run from inside the nose, through the skull and then directly to a part of the brain called the olfactory bulb. Researchers suggest that the microparticles we inhale through our nose may somehow be transported along the olfactory nerves to the brain.
The researchers came to their conclusions by analysing tissue samples from deceased residents of São Paulo. They removed the olfactory bulbs from their brains and analysed them using various methods.
Eight of the 15 brains examined had microplastics in the olfactory bulbs. However, there were only 16 microplastic particles in these eight samples.
The 16 plastic particles included fragments, balls and fibres and were made of polypropylene, nylon and other plastics. Some of the fibres may have come from clothing. This makes sense, as the washing of synthetic fibre clothing is a significant source of microplastics in the environment.
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What is the danger of nanoplastics
The new study is just one of many that have reported the presence of small plastic particles in the human body. Most of these studies have focused on microplastics, i.e. particles up to five millimetres in size. Very few studies have looked for nanoplastics in the human body.
Nanoplastics are less than one thousandth of a millimetre in size – so tiny that they are difficult to detect without special equipment.
The danger of nanoplastics lies in the fact that, unlike microplastics, their harmfulness to living cells is well documented. This is because nanoplastics are small enough to penetrate cells. Once inside, they can kill the cell.
Nanoplastics have been shown to kill cells in animal embryos. This can lead to birth defects in animals if the embryo is exposed to high doses of nanoparticles.
Fortunately, there is no evidence that the number of birth defects in humans has increased significantly in recent years. The placenta may be able to stop microplastics and nanoplastics from reaching the fetus.
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