Microplastics Have Been Found in the Human Brain. Now What?

Microplastics have been found in the lungs, liver, blood, and heart. Now, researchers report they have found the first evidence of the substances in human brains.

In a recent case series study that examined olfactory bulb tissue from deceased individuals, 8 of the 15 decedent brains showed the presence of microplastics, most commonly polypropylene, a plastic typically used in food packaging and water bottles.

Measuring less than 5 mm in size, microplastics are formed over time as plastic materials break down but don’t biodegrade. Exposure to these substances can come through food, air, and skin absorption.

While scientists are learning more about how these substances are absorbed by the body, questions remain about how much exposure is safe, what effect — if any — microplastics could have on brain function, and what clinicians should tell their patients.

What Are the Major Health Concerns?

The Plastic Health Council estimates that more than 500 million metric tons of plastic are produced worldwide each year. In addition, it reports that plastic products can contain more than 16,000 chemicals, about a quarter of which have been found to be hazardous to human health and the environment. Microplastics and nanoplastics can enter the body through the air, in food, or absorption through the skin.

As previously reported by Medscape Medical News, a study published in March showed that patients with carotid plaques and the presence of microplastics and nanoplastics were at an increased risk for death or major cardiovascular events.

Other studies have shown a link between these substances and placental inflammation and preterm births, reduced male fertility, and endocrine disruption — as well as accelerated spread of cancer cells in the gut.

There is also evidence suggesting that microplastics may facilitate the development of antibiotic resistance in bacteria and could contribute to the rise in food allergies.

And now, Thais Mauad, MD, PhD, and colleagues have found the substances in the brain.

How Is the Brain Affected?

The investigators examined olfactory bulb tissues from 15 deceased Sao Paulo, Brazil, residents ranging in age from 33 to 100 years who underwent routine coroner autopsies. All but three of the participants were men.

Exclusion criteria included having undergone previous neurosurgical interventions. The tissues were analyzed using micro–Fourier transform infrared spectroscopy (µFTIR).

In addition, the researchers practiced a “plastic-free approach” in their analysis, which included using filters and covering glassware and samples with aluminum foil.

Study findings showed microplastics in 8 of the 15 participants — including in the centenarian. In total, there were 16 synthetic polymer particles and fibers detected, with up to four microplastics detected per olfactory bulb. Polypropylene was the most common polymer found (44%), followed by polyamide, nylon, and polyethylene vinyl acetate. These substances are commonly used in a wide range of products, including food packaging, textiles, kitchen utensils, medical devices, and adhesives.

The microplastic particles ranged in length from 5.5 to 26 microns (one millionth of a meter), with a width that ranged from 3 to 25 microns. The mean fiber length and width was 21 and 4 microns, respectively. For comparison, the diameter of one human hair averages about 70 microns, according to the US Food and Drug Administration (FDA).

“To our knowledge, this is the first study in which the presence of microplastics in the human brain was identified and characterized using µFTIR,” the researchers wrote.

How Do Microplastics Reach the Brain?

Although the possibility of microplastics crossing the blood-brain barrier has been questioned, senior investigator Mauad, associate professor in the Department of Pathology, the University of Sao Paulo, Sao Paulo, Brazil, noted that the olfactory pathway could offer an entry route through inhalation of the particles.

This means that “breathing within indoor environments could be a major source of plastic pollution in the brain,” she said in a press release.

“With much smaller nanoplastics entering the body with greater ease, the total level of plastic particles may be much higher. What is worrying is the capacity of such particles to be internalized by cells and alter how our bodies function,” she added.

Mauad told Medscape Medical News that although questions remain regarding the health implications of their findings, some animal studies have shown that the presence of microplastics in the brain is linked to neurotoxic effects, including oxidative stress.

In addition, exposure to particulate matter has been linked previously to such neurologic conditions as dementia and neurodegenerative conditions such as Parkinson’s disease “seem to have a connection with nasal abnormalities as initial symptoms,” the investigators noted.

While the olfactory pathway appears to be a likely route of exposure the researchers noted that other potential entry routes, including through blood circulation, may also be involved.

The research suggests that inhaling microplastics while indoors may be unavoidable, Mauad said, making it unlikely individuals can eliminate exposure to these substances.

“Everything that surrounds us is plastic. So we can’t really get rid of it,” she said.

Are Microplastics Regulated?

The most effective solution would be stricter regulations, Mauad said.

“The industry has chosen to sell many things in plastic, and I think this has to change. We need more policies to decrease plastic production — especially single-use plastic,” she said.

Federal, state, and local regulations for microplastics are “virtually nonexistent,” reported the Interstate Technology and Regulatory Council (ITRC), a state-led coalition that produces documents and trainings related to regulatory issues.

In 2021, the ITRC sent a survey to all US states asking about microplastics regulations. Of the 26 states that responded, only four said they had conducted sampling for microplastics. None of the responders indicated they had established any criteria or standards for microplastics, although eight states indicated they had plans to pursue them in the future.

Although federal regulations include the Microbead-Free Waters Act of 2015 and the Save Our Seas Act 2.0, the rules don’t directly pertain to microplastics.

There are also no regulations currently in place regarding microplastics or nanoplastics in food. A report issued in July by the FDA claimed that “the overall scientific evidence does not demonstrate that levels of microplastics or nanoplastics found in foods pose a risk to human health.”

International efforts to regulate microplastics are much further along. First created in 2022, the treaty would forge an international, legally binding agreement.

While it is a step in the right direction, the Plastic Health Council has cautioned about “the omission of measures in draft provisions that fully address the impact of plastic pollution on human health.” The treaty should reduce plastic production, eliminate single-use plastic items, and call for testing of all chemicals in plastics, the council argues.

The final round of negotiations for the UN Global Plastic Treaty is set for completion before the end of the year.

What Should Clinicians Know?

Much remains unknown about the potential health effects of microplastic exposure. So how can clinicians respond to questions from concerned patients?

“We don’t yet have enough evidence about the plastic particle itself, like those highlighted in the current study — and even more so when it comes to nanoplastics, which are a thousand times smaller,” Phoebe Stapleton, PhD, associated professor in the Department of Pharmacology and Toxicology at the Ernest Mario School of Pharmacy at Rutgers University, Piscataway, New Jersey, told Medscape Medical News.

“But we do have a lot of evidence about the chemicals that are used to make plastics, and we’ve already seen regulation there from the EPA. That’s one conversation that clinicians could have with patients: about those chemicals,” she added.

Stapleton recommended clinicians stay current on the latest research and be ready to respond should a patient raise the issue. She also noted the importance of exercising caution when interpreting these new findings.

While the study is important — especially because it highlights inhalation as a viable route of entry — exposure through the olfactory area is still just a theory and hasn’t yet been fully proven.

In addition, Stapleton wonders whether there are tissues where these substances are not found. A discovery like that “would be really exciting because that means that that tissue has mechanisms protecting it, and maybe, we could learn more about how to keep microplastics out,” she said.

She would also like to see more studies on specific adverse health effects from microplastics in the body.

Mauad agreed.

“That’s the next set of questions: What are the toxicities or lack thereof in those tissues? That will give us more information as it pertains to human health. It doesn’t feel good to know they’re in our tissues, but we still don’t have a real understanding of what they’re doing when they’re there,” she said.

The current study was funded by the Alexander von Humboldt Foundation and by grants from the Brazilian Research Council and the Soa State Research Agency. It was also funded by the Plastic Soup Foundation — which, together with A Plastic Planet, forms the Plastic Health Council. The investigators and Stapleton reported no relevant financial relationships.