For the first time, scientists have discovered the presence of microscopic plastic shards in the human brain — and there’s more in there than you might expect.
Not only were more nano and microplastics detected in the brain than in “filter” organs like the liver and kidneys, researchers found the number of tiny plastic bits in the organ increased “exponentially” over the last decade.
On average, the brains of cadavers who died in 2024 contained an estimated five to seven grams of plastic — about the weight of a credit card or standard plastic spoon, said Marcus Garcia, an ASERT Postdoctoral Fellow at the University of New Mexico who co-led the study.
That’s almost 50 per cent more than was detected in cadavers from just eight years before in 2016.
“Of course, it’s not in one big chunk,” Garcia told the Star. “These are all in the nanoscale, spread throughout the entire brain.”
Furthermore, significantly more plastic shards were found in the brains of dementia patients than healthy subjects, the peer-reviewed study, published this week in Nature Medicine, revealed.
While unaffiliated Canadian researchers praised the study for its novel results, they also warned to take the findings with a grain of salt, citing potential limitations in the authors’ methods. Their results need to be validated in further studies, they said.
Why finding the microplastics was a surprise
The human brain is an remarkably well insulated organ. It’s surrounded by a complex network of blood vessels and tissue called the blood-brain barrier that excels at keeping intruders out, while letting a select list of nutrients in.
That’s why it’s surprising to find not just plastic infiltrators in the human brain, but so many of them — seven to 30 times more than the concentrations detected in the liver and kidneys, according to the study.
Garcia hypothesizes that, because the brain is so well-insulated, plastics that get in might not be able to get out, allowing them to accumulate throughout one’s lifespan. In comparison, the kidney and liver possess powerful clearance pathways that could allow trapped particles to escape.
Micro and nanoplastics (MNP) include particles ranging from 500 micrometres down to 1 nanometre in diameter. The majority of plastics found in the brain were on the nanoscale, Garcia explained — small enough to pass through the gaps in cell membranes.
The team are now working to determine the potential health and cognition implications of their findings, he continued. It’s remains largely unclear how MNPs affect our health.
We do know, however, that microplastics can contain a number of “very hazardous chemicals” linked to long-term health problems, noted Roxana Suehring, an unaffiliated microplastics researcher and assistant professor of chemistry at Toronto Metropolitan University.
These can range from hormonal disruptions and obesity to endometriosis and autoimmune conditions, she explained. “We know that some of these chemicals are associated with cancers,” she continued.
That said, it’s unclear whether these chemicals are present in large enough concentrations in microplastics to cause noticeable symptoms.
Could microplastics cause dementia?
To the surprise of the researchers, people with confirmed dementia had up to 10 times more MNPs in their brains than healthy patients.
That isn’t to say that microplastics cause dementia, Garcia explained. It could easily be the other way around — people with dementia may have a weakened blood-brain barrier, allowing more plastics to enter.
“It’s more of a correlation than causation at this point,” he said.
How are microplastics getting into our brains?
We don’t know exactly how MNPs are entering the brain, but the researchers have some guesses.
The brain has a high metabolism and needs a steady supply of dietary fats to function, Garcia explained. It’s possible plastic particles in our diets are hiding inside these fat supplies, and are smuggled into the brain as a result.
“As we consume products that have plastics in them, those (MNPs) are actually hijacking into those dietary fats and then moving throughout the body — and then, of course, are able to get into the brain and stay there,” he said.
Suehring, at TMU, noted the particles, particularly nanoplastics, are so small they can slip through cell membranes, enabling them to spread throughout the body. Scientists have found MNPs in a long and growing list of human organs, from placentas to the penis. MNPs have also been detected in animal brains.
A rising plastic tide
We live our lives surrounded by plastic — and wherever plastics are found, so are MNPs.
In 1950, the world produced just two million tonnes of plastic. Today, we produce 450 million tonnes every year, a number that continues to grow.
The researchers were curious whether this increase would be reflected in the human brain, and compared cadavers who died in 2016 to those prepared in 2024. It turned out the more modern brains contained 47 per cent more MNPs on average than those eight years before.
Data suggests global plastic production doubled in the last 20 years; it makes sense, then, to see a proportionate increase in the brain in the last decade, Garcia said.
“What ends up happening to plastics after we’re done using them, they usually end up in landfills. And over time, they’ll start to degrade and age,” breaking apart into MNPs, he explained.
“Those plastics will actually leach into our groundwater, and also into our soils. We use that groundwater to irrigate our crops, so of course that gets into the vegetation,” Garcia continued. From there, they can enter our livestock and proliferate throughout our diets, he said: “That seems to be where we see most of our exposure.”
In order to stomp out this trend, we need strong policies and regulations reigning in our plastic production and disposal practices, Garcia said. If not, we may see this trend continue to escalate into the future.
Study limitations
Lindsay Cahill, an unaffiliated microplastics researcher and associate professor of chemistry at the Memorial University of Newfoundland and Labrador, said the study’s results should be approached with “caution.”
“The paper does not provide thorough validation of the analytical methods,” she said over email, noting that “efforts to improve analytical testing methods for microplastics continues to be something a number of groups are still working on worldwide.”
“While we agree that microplastics are likely present in humans, there remains significant uncertainty in the actual concentrations,” Cahill continued.
Suehring agreed the exact numbers should be taken with a “grain of salt,” but added the general trends outlined in the paper — like the increase in MNP concentrations over time, the significantly greater levels of MNPs in the brain compared to other organs and the link with dementia — are novel results that need to be further studied.
Garcia defended his team’s methodology: “We definitely feel that this is a robust technique,” he said, adding that his team sent additional samples to an outside lab to verify their results. “They were able to find the same numbers that we were getting, as well.”
“There’s always more room for improvement. But as far as where we’re at, we feel pretty confident with what we’re seeing.”
