High levels of microplastics found in human brains

A new study has found high concentrations of tiny plastic particles in human brain samples,  with levels appearing to climb over time.

The paper, published Monday in the journal Nature Medicine, found nanoplastics in each of the brain samples studied, and found a potential link between the presence of the plastics and several types of dementia.

“There’s much more plastic in our brains than I ever would have imagined or been comfortable with,” said Matthew Campen, a doctor and researcher at the University of New Mexico who is  the lead author of the study.

The median concentration in brain samples collected from people who died in 2024 was nearly 5,000 micrograms of plastic per gram of brain tissue, tallying almost 0.5% by weight.

This total was 50% higher than it was just eight year prior, from brain samples acquired in 2016 (for various reasons, most brain samples become available these two years). This suggests the concentration of microplastics found in human brains is going up as plastic waste and microplastic pollution increases.

“You can draw a line — it’s increasing over time. It’s consistent with what you’re seeing in the environment,” Campen said.

The paper also looked at 12 brains from patients who died with different types of dementia; half of them had been diagnosed with Alzheimer’s disease. These brains all contained more plastic by weight than healthy samples — roughly three to five times more, on average.

“That’s a little bit alarming,” Campen said, but he emphasized that a causal relationship cannot be established yet, in part because the brain’s normal clearance mechanisms are often impaired in dementia. That being said, this potential link between microplastics and dementia needs to be further explored.

Most of the organs came from the Office of the Medical Investigator in Albuquerque, New Mexico, which investigates untimely or violent deaths. A total of 28 brain tissue samples were collected in 2016, and 24 in 2024. From these bodies, liver and kidney samples were also analyzed. They contained a median plastic concentration about 10 times lower than the brain.

The 12 brains from dementia patients came from the same source, and date to between 2019 and 2024. The team also examined 27 brain samples from people without dementia from other locations on the East Coast dating to between 1997 and 2013. These contained significant less plastic on average than the later samples, further supporting the idea that levels of plastics are rising in this organ.

“The evidence here is concerning,” said Bethanie Carney Almroth, an ecotoxicologist at the University of Gothenburg in Sweden who studies microplastics but wasn’t involved in the paper.

When it comes to these insidious particles, “the blood-brain barrier is not as protective as we’d like to think,” Almroth said, referring to the series of membranes that keep many chemicals and pathogens from reaching the central nervous system.

Some of the particles appeared to be too big to make it into the brain, or even the blood. “Yet there they are.”

Nanoplastics are a subset of microplastics with a diameter smaller than one micron. Larger microplastics are too large to make their way into the brain. Most of the nanoplastic particles found in the brain are made up of polyethylene, the study found.

This is the most commonly-made plastic and is used in plastic bags, films, and many types of bottles used to store liquids and food.

The researchers used a technique called pyrolysis gas chromatography–mass spectrometry to measure plastic in samples of the prefrontal cortex from various brains. This technique heats up materials and then identifies its chemical makeup.

The study also involved a variety of imaging techniques to find and characterize the tiny bits of plastics, which primarily consisted of nanoplastic shards.

This study received a lot of press attention in September after The New Lede reported on a pre-print that hadn’t yet been peer-reviewed. The now published paper is very similar to that version previously reported on.

The Food and Drug Administration states on its website that “current scientific evidence does not demonstrate that levels of microplastics or nanoplastics detected in foods pose a risk to human health.”

The American Chemistry Council, which represents plastic and chemical manufacturers, said in a statement that “the global plastics industry is dedicated to advancing the scientific understanding of microplastics.”

The study also examined a number of brain samples collected before 2016 at various locations on the East Coast; these all contained plastics as well, though in slightly smaller concentrations.

Previous research will need to look at other parts of the brain besides the white matter of the prefrontal cortex, Campen said. Preliminary work on this has already found, however, that tiny plastic shards are “fairly ubiquitous” throughout the brain, he said.

(Featured image by Getty Images for Unsplash+.)