It seems every few months, we discover microplastics in a new part of the body. We have found them in our livers, kidneys, lungs and guts. They have even shown up in human breast milk and blood. Last week, they turned up again in eight people鈥檚 , a brain structure crucial for smell.
These plastic fragments are so small 鈥� less than 5 millimetres in size 鈥� they can make their way into our bodies through food, water and even the air we breathe. They form when larger pieces of plastic, such as those found in car tyres or food packaging, are broken down by sunlight, water or other forces. Manufacturers also purposely add them to certain goods, such as exfoliating skincare products or cosmetics. While this may sound alarming, it isn鈥檛 clear what, if any, impact microplastics have on our bodies.
So far, the most compelling evidence they can harm our health comes from a study published earlier this year, which detected microplastics in plaques removed from the arteries of 150 out of 257 adults. These plaques are a buildup of cholesterol, fats and blood cells that can reduce blood flow. When the researchers followed up with the study participants 34 months later, they found those whose artery plaques contained microplastics were four times as likely to have died or had a heart attack or stroke as those who did not.
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But the finding doesn鈥檛 prove microplastics cause heart attacks or strokes 鈥� it only establishes a correlation. It is possible other factors could underlie the association. For example, people whose plaques contained microplastics may be exposed to greater amounts of air pollution, which can contain microplastics, than those whose plaques didn鈥檛. And air pollution is a known risk factor for heart disease.
Most of the clues about the potential health harms of microplastics come from animal studies. In 2022, at the University of California, San Francisco and her colleagues reviewed data from 24 rodent studies. They found microplastics had detrimental effects on the of the animals.
For instance, rodents exposed to microplastics through drinking water had more inflammation and fewer mucous-secreting cells in their colon, which are vital for gut health, than those that drank plastic-free water. Male rats also saw reductions in sperm quality and count while female rats had fewer follicles capable of releasing eggs. Woodruff says this indicates microplastics may raise the risk of conditions like colon cancer or infertility.
However, a 2022 report from the (WHO) points out most animal studies use concentrations of microplastics much higher than people are typically exposed to, making it difficult to translate the findings to humans. The report also notes microplastics circulate through our organs differently than they do in rodents, muddying results even further.
Adding to the challenge is microplastics come in a range of shapes, sizes and materials, each of which may have distinct health effects. at the University of Plymouth in the UK and his colleagues found more than half of studies assessing the toxicity of microplastics looked at just two types of common plastics: polystyrene or polyethylene. Most studies also use spherical plastic particles even though most . 鈥淭his is a far more complex range of contaminants than if we were dealing with lead or mercury,鈥� says Thompson.
All of these limitations make it impossible, at least for now, to know if microplastics are detrimental to human health. Yet that doesn鈥檛 mean we should assume they are harmless, especially as they accumulate more. 鈥淲e know that these particles are going to be incredibly difficult to remove,鈥� says Thompson. He recommends we take a precautionary approach to plastics: reducing plastic production 鈥� which is expected to nearly 鈥� and preventing them from entering the environment.
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