While plastic has transformed modern life, improving everything from food packaging to medical devices, research shows that over time, plastic waste can degrade into particles so small that they become invisible — and increasingly, unavoidable. These micro- and nanoplastics (MNPs) can be found not only throughout the environment but also in the human body, raising important questions about their potential health effects.

NIEHS grantee Matthew Campen, Ph.D., from the University of New Mexico, is tackling such questions with innovative research. In a study published Feb. 3 in Nature Medicine, he used cutting-edge tools to assess MNP accumulation in human liver, kidney, and brain tissues collected postmortem. Campen identified MNPs in all three tissues, but the brain stood out. It contained significantly higher concentrations of the plastic particles. Even more striking, brain tissues from individuals with dementia harbored substantially greater levels of MNPs.

Recently, I spoke with Campen to dive deeper into these findings and MNPs more broadly. How do they pass through biological barriers and accumulate in places like the brain? Could their presence in inflamed or diseased tissues point to a role in chronic illness, or are they simply bystanders? We discussed these and other important aspects of MNPs during our conversation, and Campen also shared what inspired him to pursue a research career.

Plastics break down over many years

Rick Woychik: Let’s start with the basics. What exactly are MNPs?

Matthew Campen: They are the breakdown products of plastics. We use plastic in nearly every part of daily life, and eventually, we throw it away. Once it ends up in a landfill or, unfortunately, in the ocean, it starts to degrade. For many plastics, that process can take decades.

Their surfaces get exposed to heat, oxygen, and other elements, which causes oxidation and chemical changes. Over time, the particles get smaller and smaller. First, they reach micro size — less than five millimeters down to about one micrometer. Then they keep going, into the nanoscale: just hundreds of nanometers, even smaller. At that size, you need electron microscopy to detect them. Our recent work shows they can be as small as viruses.

Making their way back to humans

RW: Are there certain types of plastic we should be especially concerned about?

MC: Chemically, MNPs seem to be a mix of everything. We see polyethylene most often. But we also see PVC, polypropylene, and, to a lesser extent, polycarbonate and polyurethane. That said, we think MNPs are decades-old degradation products. So, a new water bottle might not be a problem for you — but it could be for your grandchildren.

The concern is that when you discard these materials, they slowly break down and eventually re-enter the ecosystem. There’s already about half a ton of plastic per person on this planet that’s been sent to landfills. It’s already started the long degradation process, and we haven’t tracked exactly where those plastic particles are going. For example, a lot of those particles could be making their way back into groundwater, which is then used to irrigate crops.

Causing other chemicals to enter body

RW: Can you comment on how MNPs can carry bisphenol A and other chemicals?

MC: The particles we’re seeing in the brain, liver, and kidneys look really small — and really old. Some of these may be just 20 to 30 nanometers thick. The idea that those particles might still be carrying other organic chemicals seems unlikely. If plastic additives were going to leach out, they probably would have done so long before the material degraded to that size.

At the same time, we’re exposed to lots of larger microplastics that are less likely to reach the brain but still present in the GI tract. And yes, those can contain phthalates, bisphenols, and other plasticizers — putting them in direct contact with our gastrointestinal lining, enterocytes, gut macrophages, and other cells in that environment.

Plastics love fats

RW: How do these particles actually get into the body?

MC: There’s still a lot we don’t know. But it seems that the bulk of exposure comes through the gastrointestinal route. The amount we’re seeing in the air is in nanogram quantities — very small. And in truth, most of the particles you inhale are cleared from the lungs by the mucociliary escalator, meaning you end up swallowing them anyway. So even what you breathe in often ends up entering the body through the GI tract.

A lot of food we eat contains plastics. And plastics love fats. If you’ve ever tried to clean a Tupperware bowl that had butter or bacon grease in it, you know it takes hot water and a lot of soap. What we’re thinking now — and we have some data to support this — is that the smallest of these nanoparticles may get absorbed through the lipid uptake system of the small intestine.

In the gut, enterocytes [cells that absorb nutrients, including fats] form what are called chylomicrons, which are tiny lipid-filled particles that allow fats to circulate in the bloodstream. We think that when you eat these plastics, they’re already coated in a lipid corona [layer of fat molecules], so they’re mistaken for fat. That’s how the body handles them: it distributes them through the blood to different parts of the body, since lipids are used for both energy and growth. So, we think they kind of slip in — almost protected by those lipid coronas.

Where MNPs accumulate

RW: Once the particles are in the bloodstream, where do they go?

MC: We think they go everywhere, but where they accumulate seems to depend on tissue metabolism — and, to some extent, the amount of fat in a tissue. What’s interesting is that we see surprisingly high quantities in the brain. There’s still a lot we’re trying to figure out in terms of how much is getting into the brain, but we don’t see nearly that much in adipose tissue.

For instance, we looked at whale blubber, and the concentration of particles there — and in other animal fats — is about one-tenth of what we see in the human brain. So, something else is going on. We think it has to do with metabolism — that the brain is actively drawing in lipids not just for storage, but for energy and function.

We have also found these particles in the liver and kidneys. They tend to show up in regions associated with filtration and clearance. So, even if the process is slow, it looks like the liver and kidneys are doing their best to help rid the body of MNPs.

Getting rid of these tiny particles

RW: What do we know about the body’s ability to excrete these particles?

MC: The honest answer is that we don’t know, but the way these particles are distributed in organs gives us some clues. In the kidney, for example, they show up in areas associated with filtration — suggesting the kidney is helping remove them via urine. In the liver, it looks like the particles are being handled like lipids and packaged into lipid droplets.

In dementia brains, we see greater amounts of plastic, especially along the blood vessel walls. That suggests a leaky blood-brain barrier in patients with dementia may play a role in allowing more particles to enter. We also see the particles inside macrophages in inflamed brain regions. Those immune cells appear to be doing their job — engulfing the particles — which is probably a good thing.

In the brain, there are mechanisms for pulling things out of cells and the interstitial space — they can be taken up by macrophages or glial cells. The brain is constantly generating waste, and it does have systems to eliminate it. So, like any other organ, there is some kind of waste disposal process. But it’s probably slower than in other organs. The brain is more contained and isolated — and it also has a higher concentration of lipids. That might create a kind of affinity for these plastics to remain in brain tissue.

By the way, there’s a question that I’ve been thinking about recently: Can these plastics actually degrade inside the body? If you’ve got a particle that’s only 60 molecules thick, it’s possible those molecules could slowly peel off over months or years while embedded in tissue. So rather than staying whole, these particles might be shedding long polymer chains — individual molecules — into the surrounding cells or lipids. I think that’s entirely possible. And if that’s happening, then we’re dealing with a much more complex challenge: tracing those long carbon chains, which might be 60 to 600 molecules long.

Potential to change how the body functions

RW: You have identified increased concentrations of plastics in patients with Alzheimer’s disease. Can you expand on that?

MC: In our recent study, we had 12 dementia patients — six with Alzheimer’s, three with vascular dementia, which is probably related, and three with another classification. But all of them had high levels of these plastics compared to normal brains. So, the question becomes: Is this a chicken-or-egg situation?

When we think about the natural history of the disease, dementia is often characterized by a leaky blood-brain barrier. That barrier breakdown leads to inflammation in the brain and helps drive the progression of the disease. So, we think it may simply be that dementia creates a more permissive environment for plastics to enter and persist in the brain.

And I should add a note of caution. Dr. Alzheimer diagnosed exactly one person with what we now call Alzheimer’s disease. That one case, from the early 1900s, clearly predates widespread plastic use. In other words, we know dementia can occur without plastics. We also know it’s age-related, and the rising prevalence of Alzheimer’s is tied to an aging population. So, I tend not to believe that plastics are causing or worsening that disease directly.

That said, there are other conditions that are increasing globally — and we don’t have good explanations. For instance, multiple sclerosis is becoming more common worldwide. Some of that increase is due to better recognition and diagnosis, but not all of it. Autism is another example. Fertility rates are declining. Global sperm counts are going down. And certain cancers — like early-onset colorectal cancer in people under 50 — have been climbing since the mid-1990s in this country. Breast cancer also appears to be rising globally.

So, while it’s hard to pin all these trends on one specific mechanism, we know that exposure studies — whether in cells, animals, or tissues — consistently show that MNPs, especially nanoparticles, can change how the body functions. More research in this area will be critical.