Cognitively normal human brain samples collected at autopsy in early 2024 contained more tiny shards of plastic than samples collected eight years previously, according to a recently published study.
Overall, cadaver brain samples contained seven to 30 times more tiny shards of plastic than their kidneys and liver, said co-lead study author Matthew Campen, Regents’ Professor and professor of pharmaceutical sciences at the University of New Mexico in Albuquerque.
“The concentrations we saw in the brain tissue of normal individuals, who had an average age of around 45 or 50-years-old, were 4 800 micrograms per gram, or 0.48% by weight,” Campen said.
That’s the equivalent of an entire standard plastic spoon, he added.
“Compared with autopsy brain samples from 2016, that’s about 50% higher,” he said. “That would mean that our brains today are 99.5% brain and the rest is plastic.”
It is possible, however, that current methods of measuring plastics may have over- or underestimated their levels in the body, Campen told CNN: “We’re working hard to get to a very precise estimate, which I think we will have within the next year.”
Researchers also found an additional three to five times the amount of shard-like plastic fragments in the brains of 12 people who had been diagnosed with dementia before their death than with healthy brains. Those shards, smaller than the eye can see, were concentrated in the walls of arteries and veins of brain as well as in the brain’s immune cells.
“It’s a little bit alarming, but remember that dementia is a disease where the blood brain barrier and clearance mechanisms are impaired,” Campen said.
In addition, there are inflammatory cells and atrophy of brain tissue with dementia, which may create “a sort of sink for plastics to go,” he said.
“We want to be very cautious in interpreting these results as the microplastics are probably elevated because of the disease (dementia), and we do not currently suggest that microplastics could cause the disease.”
Finding plastic deposits in the brain does not prove they cause damage, said Phoebe Stapleton, an associate professor of pharmacology and toxicology at Rutgers University in New Jersey, who was not involved in the new study.
“It is unclear if, in life, these particles are fluid, entering and leaving the brain, or if they collect in neurological tissues and promote disease,” she said. “Further research is needed to understand how the particles may be interacting with the cells and if this has a toxicological consequence.”
In fact, researchers did see signs that the body’s liver and kidneys may be capable of flushing some plastics from the body, Campen said. Whether that can happen in the brain, he suggested, is unknown.
Potential health harms
Finding higher levels of microplastics in human tissues today “makes sense” because plastic manufacture, plastic pollution and human exposure to plastics have all been increasing rapidly, said paediatrician and biology professor Dr Philip Landrigan, director of the Programme for Global Public Health and the Common Good and the Global Observatory on Planetary Health at Boston College.
“More than half of all plastic ever made has been made since 2002 and production is on track to double by 2040,” said Landrigan, who was not involved in the new study.
He is lead author of a March 2023 report from the Minderoo – Monaco Commission on Plastics and Human Health, a global consortium of scientists, healthcare workers and policy analysts charged with following plastics from creation to final product.
In the 2023 report, the consortium determined plastics are associated with harms to human health at every single stage of the plastic lifecycle.
“Studies have found these plastics in the human heart, the great blood vessels, the lungs, the liver, the testes, the gastrointestinal tract and the placenta,” Landrigan said.
“The biggest question is, ‘OK, what are these particles doing to us?’ Honestly there’s a lot we still don’t know. What we do know with real certainty is that these microplastic particles are like Trojan horses – they carry with them all the thousands of chemicals that are in plastics and some of these chemicals are very bad actors.”
By invading individual cells and tissues in major organs, nanoplastics can potentially interrupt cellular processes and deposit endocrine-disrupting chemicals such as bisphenols, phthalates, flame retardants, heavy metals and per- and polyfluorinated substances, or PFAS.
Endocrine disruptors interfere with the human reproductive system, leading to genital and reproductive malformations as well as female infertility and a decline in sperm count, according to the Endocrine Society.
“We have some pretty good indications that microplastics and nanoplastics cause harm, even though we are a long way from knowing the full extent of that harm,” Landrigan said.
“I would say we have enough information here that we need to start taking protective action.”
The American Chemistry Council, an industry association, told CNN the FDA says current scientific evidence doesn’t show that microplastics or nanoplastics detected in foods pose a risk to human health.
“Research under way not only helps address current data gaps in our understanding of exposure to microplastics but it also aims to develop improved tools to measure the toxicity of microplastics to humans, said Kimberly Wise White, the council’s vice president of regulatory and scientific affairs.
“This work is important given the unvalidated methods often applied by researchers which can lead to unreliable or misleading outcomes, the complex nature of microplastics, and the many variables that can affect human health,” she said.
Nanoplastics ‘hijack’ their way into the brain
For the study, published in Nature Medicine, researchers examined brain, kidney and liver tissues harvested from people who underwent a forensic autopsy in 2016 and 2024. For comparison, researchers also looked at brains from people who died between 1997 and 2013.
Brain tissue samples were gathered from the frontal cortex, the area of the brain associated with thinking and reasoning. It’s the part of the brain which is most affected by frontotemporal dementia (FTD) and later stages of Alzheimer’s disease.
Microplastics are fragments that can range from less than 0.2 inch (5 millimetres) or about the size of a pencil eraser, to 1 nanometre. A strand of human hair is about 80 000 nanometres wide, according to the US Environmental Protection Agency.
Anything smaller is a nanoplastic that must be measured in billionths of a metre.
“Based on our observations, we think the brain is pulling in the very smallest nanostructures, like 100 to 200 nanometres in length. These are roughly the size of two Covid viruses side by side,” said Campen, who is also the director of the New Mexico Centre for Metals in Biology and Medicine.
Nanoplastics are the most worrisome plastics for human health, experts say, because the minuscule pieces can take up residence inside individual cells.
“Somehow these nanoplastics hijack their way through the body and get to the brain, crossing the blood-brain barrier,” Campen said.
“Plastics love fats, or lipids, so one theory is that plastics are hijacking their way with the fats we eat which are then delivered to the organs that really like lipids – the brain is top among those.”
The human brain is about 60% fat by weight, far more than any other organ. Essential fatty acids, such as omega 3s, are key to the strength and performance of the brain’s cells. Since the human body can’t produce essential fatty acids on its own, they must come from food or supplements.
Diet is the main route of exposure for micro- and nanoplastics, Landrigan said, however some are also airborne: “When people are driving down the highway and their tyres are abrading on the surface of the highway, a certain amount of microplastic particles are thrown into the air.
“If you live near the coast, some of the microplastic particles that are in the ocean get kicked into the air through wave action,” he said. “So ingestion is probably the dominant route, but inhalation is also an important route.”
A March 2024 study found 1 litre of bottled water — the equivalent of two standard-size bottled waters typically purchased by consumers — contained an average of 240,000 plastic particles from seven types of plastics. Some 90% of those were nanoplastics.
This story was originally written in August 2024 based on a preprint, which is an early copy of a paper that had not yet been peer-reviewed. It has been updated to reflect the final peer-reviewed and published paper in Nature.
Study details
Bioaccumulation of microplastics in decedent human brains
Alexander Nihart, Marcus Garcia, Eliane Hayek et al.
Published in Nature Medicine on 3 February 2025
Abstract
Rising global concentrations of environmental microplastics and nanoplastics (MNPs) drive concerns for human exposure and health outcomes. Complementary methods for the robust detection of tissue MNPs, including pyrolysis gas chromatography–mass spectrometry, attenuated total reflectance–Fourier transform infrared spectroscopy and electron microscopy with energy-dispersive spectroscopy, confirm the presence of MNPs in human kidney, liver and brain. MNPs in these organs primarily consist of polyethylene, with lesser but significant concentrations of other polymers. Brain tissues harbour higher proportions of polyethylene compared to the composition of the plastics in liver or kidney, and electron microscopy verified the nature of the isolated brain MNPs, which present largely as nanoscale shard-like fragments. Plastic concentrations in these decedent tissues were not influenced by age, sex, race/ethnicity or cause of death; the time of death (2016 versus 2024) was a significant factor, with increasing MNP concentrations over time in both liver and brain samples (P = 0.01). Finally, even greater accumulation of MNPs was observed in a cohort of decedent brains with documented dementia diagnosis, with notable deposition in cerebrovascular walls and immune cells. These results highlight a critical need to better understand the routes of exposure, uptake and clearance pathways and potential health consequences of plastics in human tissues, particularly in the brain.
Nature Medicine article – Bioaccumulation of microplastics in decedent human brains (Open access)
The Minderoo-Monaco Commission on Plastics and Human Health (Open access)
CNN article – Microplastics found in nose tissue at base of brain, study says (Open access)
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100 times more nanoplastics in water bottles than thought – US study
Microplastics infiltrating brain tissue – ‘nowhere untouched’, warn scientists
Premature birth rate may be linked to plastics – US study