Human brain samples collected during an autopsy in early 2024 contained more tiny bits of plastic than samples collected eight years earlier, according to a preprint posted online in May. A preprint is a study that has not yet been peer-reviewed and published in a journal.
“The concentrations we saw in the brain tissue of normal individuals, who had an average age of about 45 or 50 years old, were 4,800 micrograms per gram, or 0.5% by weight,” said lead researcher Matthew Campen, a professor of pharmaceutical sciences at the University of New Mexico in Albuquerque.
“Compared to autopsy brain samples from 2016, that’s about 50% higher,” Campen said. “That would mean that our brains today are 99.5% brain and the rest is plastic.”
However, that increase only shows exposure and does not provide information about brain damage, said Phoebe Stapleton, an associate professor of pharmacology and toxicology at Rutgers University in Piscataway, New Jersey, who was not involved in the preprint.
“It is unclear whether these particles are fluid in life and flow in and out of the brain, or whether they accumulate in neurological tissues and promote disease,” she said in an email. “More research is needed to understand how the particles might interact with cells and whether this has a toxicological consequence.”
According to the preprint, the brain samples contained 7 to 30 times more small pieces of plastic than samples from the kidneys and liver of the cadavers.
“Research has shown that these plastics are present in the human heart, major blood vessels, lungs, liver, testicles, gastrointestinal tract and placenta,” said pediatrician and professor of biology Dr. Philip Landrigan, director of the Program for Global Public Health and the Common Good and the Global Observatory on Planetary Health at Boston College.
“It’s important not to scare people, because the science in this area is still evolving and no one can live without plastic in 2024,” said Landrigan, who was not involved in the preprint.
“I tell people, ‘Listen, there are plastics you can’t avoid. You’re not going to get a cell phone or a computer that doesn’t have plastic in it.’ But try to minimize your exposure to the plastics you can avoid, like plastic bags and bottles.”
The American Chemistry Council, an industry association, told CNN that while “some studies on microplastics have made headlines recently, the FDA noted last month: ‘Current scientific evidence does not show that the amounts of microplastics or nanoplastics found in food pose a risk to human health.’
“Today’s research not only helps address current data gaps in our understanding of microplastic exposure, but also aims to develop better 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 used by researchers that can lead to unreliable or misleading results, 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, researchers examined brain, kidney and liver tissue from 92 people who underwent forensic autopsies in 2016 and 2024 to determine cause of death. Brain tissue samples were collected from the frontal cortex, the area of the brain associated with thinking and reasoning that is most affected by frontotemporal dementia (FTD) and later stages of Alzheimer’s disease.
“Based on our observations, we think that the brain attracts the very smallest nanostructures, ranging from 100 to 200 nanometers in length, while some of the larger particles, which are one micrometer to five micrometers in size, end up in the liver and kidneys,” Campen said.
Microplastics are fragments that can range in size from less than 0.2 inches (5 millimeters), or about the size of a pencil eraser, to 1 nanometer. A strand of hair is about 80,000 nanometers wide, according to the U.S. Environmental Protection Agency. Anything smaller is a nanoplastic, which must be measured in billionths of a meter.
According to experts, nanoplastics pose the greatest threat to human health because the tiny particles can nestle in individual cells.
“Somehow these nanoplastics hijack their way through the body and into the brain, crossing the blood-brain barrier,” Campen said. “Plastics love fats, or lipids, so one theory is that plastics hijack their way with the fats that we eat, which are then delivered to the organs that really love lipids — the brain being at the top of the list.”
The human brain is made up of about 60% fat, far more than any other organ. Essential fatty acids, such as omega 3, are essential for the strength and performance of brain cells. Since the human body cannot produce essential fatty acids, they must come from food or supplements.
According to Landrigan, who is lead author of a March 2023 report from the Minderoo–Monaco Commission on Plastics and Human Health, a global consortium of scientists, health professionals and policy analysts charged with tracking plastics from creation to finished product, food is the main route of exposure for micro- and nanoplastics.
In that report, the consortium found that plastics are harmful to human health at every stage of the plastics life cycle.
“Some microplastics are also airborne,” Landrigan said. “For example, when people drive on the highway and their tires scrape against the road, some amount of microplastic particles are thrown into the air.
“If you live close to the coast, some of the microplastics that are in the ocean are being blown up into the air by the waves,” he said. “So ingestion is probably the dominant route, but inhalation is also a major route.”
Plastics linked to cancer
Polyethylene, which is used in plastic bags, films and bottles and is not biodegradable, was the most common type of plastic in tissue samples. It was found in higher amounts in the brain than in the liver or kidneys, the preprint said.
Polyethylene is also the most common type of polymer in the testicles of humans and dogs, according to an August 2024 study by Campen and his team.
The production of various forms of polyethylene, such as polyethylene terephthalate (PET) plastics, is the largest contributor to emissions of the solvent 1,4-dioxane into the environment, according to industry data collected by Defend our Health, an environmental organization.
The U.S. National Toxicity Program and the International Agency for Research on Cancer consider 1,4-dioxane a possible human carcinogen. In 2023, the EPA published a draft report stating that the solvent poses an “unreasonable risk of health harm” to plastics workers and community residents whose drinking water has been contaminated by discharges from PET plastics plants.
“The biggest question is, ‘OK, what are these particles doing to us?’ And honestly, there’s a lot we don’t know,” Landrigan said. “What we do know for sure is that these microplastic particles are like Trojan horses: They’re carrying all of the thousands of chemicals that are in plastic, and some of them are really bad actors.”
By entering individual cells and tissues in key organs, nanoplastics can potentially disrupt cellular processes and deposit hormone-disrupting chemicals such as bisphenols, phthalates, flame retardants, heavy metals, and per- and polyfluorinated compounds (PFAS).
According to the Endocrine Society, hormone disruptors disrupt the human reproductive system, leading to genital and reproductive malformations, as well as female infertility and decreased sperm quality.
“We have some pretty good evidence that microplastics and nanoplastics are harmful, although we are far from understanding the full extent of that harm,” Landrigan said. “I would say we have enough information here to take protective measures.”
Learn to use less plastic
According to experts, there are many steps people can take to reduce their exposure to plastic and their plastic footprint.
“It’s hard to avoid plastic-wrapped foods, but make sure you remove the food from the plastic wrap before cooking or microwaving it,” Landrigan said. “When you heat plastic, it accelerates the movement of microplastics from the wrapper into the food.
Invest in a cloth zip-up bag and ask your dry cleaner to return your clothes in that instead of those flimsy plastic sheets, suggested the Natural Resources Defense Council, an environmental organization. Bring a travel mug to your local coffee shop for takeout and silverware to the office to cut down on plastic cups and utensils.
“Don’t use plastic bags when you go shopping. Use a cloth bag, a paper bag or a recycled bag. Try to avoid plastic water bottles if possible,” Landrigan said.
A March 2024 study found that 1 liter of bottled water — the equivalent of two standard bottled waters that consumers typically buy — contained an average of 240,000 plastic particles from seven types of plastic. About 90% of those were nanoplastics.
“Use a metal or glass drinking cup instead of a plastic cup. Store your food in glass containers instead of plastic containers,” Landrigan said. “Work in your local community to ban plastic bags, as many communities in the United States have done. There’s a lot you can do.”
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