University of New Mexico Health Sciences researchers have detected microplastics in human brains at much higher concentrations than in other organs – and the plastic accumulation appears to be growing over time, having increased 50% over just the past eight years.
Microplastics – tiny bits of degraded polymers that are ubiquitous in our air, water and soil – have lodged themselves throughout the human body, including the liver, kidney, placenta and testes, over the past half century.
Now, University of New Mexico Health Sciences researchers have found microplastics in human brains, and at much higher concentrations than in other organs. Worse, the plastic accumulation appears to be growing over time, having increased by 50% over just the past eight years.
In a new study published in Nature Medicine , a team led by toxicologist Matthew Campen, PhD, Distinguished and Regents' Professor in the UNM College of Pharmacy, reported that plastic concentrations in the brain appeared higher than in the liver or kidney, and higher than previous reports for placentas and testes.
The rate of accumulation mirrors the increasing amounts of plastics waste on this planet, Campen said. "This really changes the landscape. It makes it so much more personal," he said. Additionally, they observed that much of the plastic appears to be much smaller than previously appreciated – in the nanometer scale, about two to three times the size of viruses.
The findings should trigger alarm, he said.
Complicating matters, brain tissue from people who had been diagnosed with dementia had up to 10 times as much plastic in their brains as everyone else, Campen said. But while there is a clear correlation, the study design cannot show whether higher levels of plastic in the brain caused the dementia symptoms – they may simply accumulate more due to the disease process itself, he said.
The new research builds on a novel method devised by the UNM researchers to specify and quantify the microplastics in tissue, which has previously been used to document quantities of plastics in human placentas and both human and canine testes.
In the current study, they analyzed brain tissue samples donated by the New Mexico Office of the Medical Investigator, which by law must retain tissue from autopsies for seven years before disposing of it. The older brain tissue dated back to 2016, on average, and was compared with tissue from 2024. All of the samples were collected from the frontal cortex, the brain region above and behind the eyes, Campen said.
The researchers chemically dissolved the tissue, creating a kind of slurry, then ran it through a centrifuge, which spun out a small pellet containing undissolved plastic. The pellet was then heated to 600 degrees Celsius, a process known as pyrolysis. The researchers captured gas emissions as the plastics burned. Ions derived from the combusted polymers were separated chromatographically and identified with a mass spectrometer.
The technique detected and quantified 12 different polymers, the most common of which was polyethylene, which is widely used for packaging and containers, including bottles and cups.
The team also used transmission electron microscopy to visually examine the same tissue samples that had high polymer concentrations – and found clusters of sharp plastic shards measuring 200 nanometers or less – not much larger than viruses. These are small enough to cross the blood-brain barrier, although Campen says it is unclear how the particles are actually being transported into the brain.
It is also unclear what effects plastic, which is considered to be biologically inert and used in medical applications like heart stents and artificial joints, might be having, he said. The physical characteristics of these particles may be the real problem, as opposed to some sort of chemical toxicity.
"We start thinking that maybe these plastics obstruct blood flow in capillaries," Campen said. "There's the potential that these nanomaterials interfere with the connections between axons in the brain. They could also be a seed for aggregation of proteins involved in dementia. We just don't know."
He suspects that most of the microplastics in the body are ingested through food – particularly meat, because commercial meat production tends to concentrate plastics in the food chain.
"The way we irrigate fields with plastic-contaminated water, we postulate that the plastics build up there," Campen said. "We feed those crops to our livestock. We take the manure and put it back on the field, so there may be a sort of feed-forward biomagnification." The team has found high concentrations of plastic in meat bought at grocery stores, he added.
Microplastics tend to accumulate in fat cells in the brain's insulating myelin sheath, which wraps around neurons and helps to regulate signal transmission. That, in turn, might help explain the higher concentrations of plastic in the brain.
Plastic production around the world continues unabated, but even if it were halted tomorrow, it would be a ticking timebomb. Because it can take decades for existing polymers to decay into microscopic particles, concentrations of micro- and nano-plastics in the environment will continue to grow for years to come.
Campen, who often cites the toxicologist's maxim, "Dose makes the poison," says the new results should give rise to alarm about a global threat to human health. He acknowledges it can be hard to motivate consumers, who often shrug when warned about environmental contaminants that tend to be measured in parts per billion.
But the new findings might finally get their attention, he said. "I have yet to encounter a single human being who says, 'There's a bunch of plastic in my brain and I'm totally cool with that.'"
