Finding microplastics in human body parts is not new: Scientists have uncovered the minuscule waste products in human blood, lungs, brains, hearts and testicles.

But a new study, published Monday in the journal Nature Medicine, shows a lockstep relationship between the amount of plastic found in tissues harvested from human cadavers and the amount being produced by the plastic industry.

As global plastic production has ramped up in the last 20 years, so too has the concentration of these shredded, fossil fuel-derived polymers in human tissue samples.

The findings are “pretty striking,” said Phil Landrigan, director of the Program for Global Public Health and the Common Good at Boston College, who was not affiliated with the research.

The study also showed a concerning correlation between patients who had received a dementia diagnosis before they died and the amount of plastic particles found in their brains — adding to a growing body of research indicating that the presence of these particles in the human body can potentially cause harm.

The study was published by a team of researchers at the University of New Mexico, Oklahoma State University, Duke University and Universidad del Valle, in Colombia.

The team acquired brain, liver and kidney tissue samples from patients who had undergone autopsies between 2016 and 2024 at the University of New Mexico.

To determine both the concentration and kinds of plastic in the samples, the team visually inspected the samples and applied pyrolysis-gas chromatography–mass spectrometry — a technique that allowed them to analyze the tissue’s chemical composition.

They found that the concentrations of particles in kidney and liver samples were comparable, with an average of 433 micrograms of microplastic per gram of tissue in the liver samples and 404 micrograms per gram of the kidney samples.

But the levels seen in the brain samples — all taken from the frontal lobe — dwarfed those numbers, and showed a jump over time. In the samples they harvested from people who died in 2016, they found average concentrations of 3,345 micrograms/gram. In the 2024 cohort, the average was 4,917.

“I never would have imagined it was this high,” said Matthew Campen, professor of pharmaceutical sciences at the University of New Mexico. “I certainly don’t feel comfortable with this much plastic in my brain, and I don’t need to wait around 30 more years to find out what happens if the concentrations quadruple.”

The concentrations of microplastics the researchers found were independent of the biological age of the deceased person — it didn’t matter if the person was young or old when they died. What mattered was the year they died — the more recent the death, the more accumulated plastic in the body.

Intrigued by this increase in plastic concentration over time, the researchers obtained more brain tissue samples. This time, they examined brains from people who died between 1997 and 2013. They made sure the cadavers were similarly aged to the ones they had already examined — but could not control for geography. The second cohort all came from people who had died on the East Coast.

Again, the researchers found “significantly increasing trends for total plastics” over time in this second group of samples.

Polyethylene — a plastic polymer used to make things such as plastic bags, milk jugs, shampoo bottles, etc. — was the most common microplastic found in the brain. It comprised 75% of the plastic shards observed in the brain tissue samples. But the researchers also detected polypropylene (the plastic used to make yogurt cups and rigid takeout food containers), polyvinylchloride (which is used in most water pipes), and styrene-butadiene rubber (found in some pneumatic tires, shoe soles, brake pads and electrical insulation).

The concentration of all of these plastics increased from 2016 to 2024, irrespective of the biological age of the cadaver.

They also noted that brain tissue harvested from patients who’d been diagnosed with dementia had higher concentrations of microplastics than those who hadn’t. Although it was a concerning observation, they noted that their sample size was small, and that hallmarks of dementia include brain tissue atrophy, impaired blood-brain barrier integrity, and poor brain clearance mechanisms — which could themselves lead to microplastic buildup.

Therefore, they could make no claims to causation — just correlation.

Landrigan said the work reinforces our knowledge “that we’re all exposed, that these things actually get into our bodies, into people of all ages” and that it “appears to be getting worse with time.”

He said it adds to the urgency of a Global Plastics Treaty — to cap plastic production — and which reached an impasse at the last round of negotiations in South Korea, in 2024. He said negotiators plan to reconvene later this year.

According to Landrigan, it’s unclear how the United States, under President Trump, would approach the treaty. If Trump follows the advice of the fossil fuel proponents in his administration, it’s likely the U.S. will vote the deal down — or not even show up.

But if the Robert F. Kennedy Jr. element gets a seat at the table, the U.S. is a wild card, Landrigan said. Kennedy was openly critical of the Biden administration for not doing enough to stanch the flow of microplastics into the environment, and he penned a detailed plan that would ban most hazardous chemicals, reform the recycling infrastructure and curtail the production of plastics.

Landrigan said he has known Kennedy for decades, and would happily sit down with him to present this research and the growing number of studies showing the harms these particles — and the chemicals they carry — cause in the human body.

“I’m a pediatrician with the American Academy of Pediatrics, and we’ve always taken the position that the academy will do what it has to do to protect children’s health. We will always stand up for children. So, if there’s an opening there for conversation with Bobby, why not?” he said.