A daunting quest to map the reach and risk of nanoplastics

Abstract

After researchers documented plastic debris floating in the Sargasso Sea in the early 1970s, a spate of similar discoveries followed suit in other marine waters and within a growing list of aquatic creatures.¹ When more recent studies began turning up evidence of microplastics and even smaller nanoplastics in human tissues and organs—blood, lungs, liver, placenta, and testicles among them—worried scientists started asking how much might be accumulating.

Then in 2024, researchers led by Matthew Campen, PhD, MSPH, director of the New Mexico Center for Metals in Biology and Medicine at the University of New Mexico in Albuquerque, delivered a bombshell.² For the first time, several independent experts told CytoSource, Dr Campen’s team had provided solid evidence that nanoplastics could cross the blood-brain barrier. Megan Wolff, PhD, MPH, executive director of the Physician and Scientist Network Addressing Plastics and Health in New Paltz, New York, calls it the “last frontier” of the human body.

“We did the math and said, well, we see about 5000 micrograms per gram,” Dr Campen recalls. “The brain is about 1400 grams so that works out to—my gosh, there’s about 7 grams of plastic in the brain!” It is the approximate weight of a plastic spoon, he explains. That analogy generated multiple headlines as well as blowback from critics who argued that the numbers could have been inflated by the inclusion of lipid contaminants.

Dr Campen has urged caution over what he concedes is an initial estimate, even as his research has since estimated that the brain may harbor an average of 100 million or more shard-like nanofragments. “We’re comparing it against fresh plastics, and we know we’ve got old plastics in our body,” he says. Because they are so small, nanoplastics also are notoriously difficult to measure.

To quantify them, some researchers extract and burn them and capture the chemical signatures of the various plastics. Gas chromatography–mass spectrometry can isolate and differentiate among those signatures, but the method is not foolproof. Polyethylene plastics and lipid molecules have comparable architectures that can yield deceptively similar signatures, Dr Campen says. In the brain and other high-lipid tissues, tiny fat globules might not fully digest or wash away with existing methods and could be inadvertently added to the plastics tally.

Even so, a collaborator at Oklahoma State University reported similar results when he tested human brain samples, and Dr Campen found significantly more accumulation in brain and liver tissues collected in 2024 than in tissues dating back to 2016. “The trend of increasing over time was captivating and something we had a lot of confidence in, even if the total magnitude was adjusted up or down because of the way we digest the samples,” he says.

Dr Campen’s study also documented an even greater accumulation of nanoplastics in 12 preserved brains from individuals with documented dementia. That makes sense, he says, because the blood-brain barrier impairment and inflammation associated with dementia may aid nanoplastics’ uptake. “We have a lot of confidence that there’s more compared to normal brains, but we can’t really say whether it’s cause or effect,” he says.

Once he had convinced himself that the numbers were real, Dr Campen admits to feeling deep concern. “Nobody’s shown this before. This is very clear in our data, no matter how we revisit the data,” he says. “What next? Is this going to continue? Does our body eventually put up some kind of a defense to stop these things from getting in?” If the amount remains uncertain, Dr Wolff agrees that the trend is ominous.

In the human body, few plastic particles are larger than 500 nanometers, and some scientists believe that the gut may provide an initial barrier to larger ones. Intriguingly, Dr Campen and other researchers suspect that some larger bits labeled microplastics, such as those found in the placenta, may instead be nanoplastic accumulations that have lined up or have been packaged together as the body’s machinery attempts to move or clear them.

“Our first clue comes from the liver, where we see these haystacks, if you will, of particles in the lipid droplets of the liver,” he says. Similar groupings have appeared in the kidneys. “Those are clearance organs, and they have a way of handling lipids and other materials, and maybe they’re not efficient at getting rid of plastics, but they’re trying,” he says.

Nanoplastics, in other words, might hitch a ride on the lipid delivery system to the lipid-rich brain. “We might be showing plastics as high in fatty regions because we’re just measuring fats and we’re wrong,” he says. “Or they’re probably there because they are lipophilic.” Other evidence supports the latter alternative. In whale blubber, with a fat content of approximately 80%, the Campen laboratory has measured a concentration of nanoplastics roughly 10-fold lower than that in the human brain, with its 40%–60% fat content (depending on the region). “So it’s not just fats; there’s something more to it than just interference,” he says.

For Alan Workman, MD, an assistant professor of rhinology and skull-based surgery at Harvard Medical School and Massachusetts Eye and Ear in Boston, the complex exposure questions, even if resolved, lead to an even bigger one: So what? Even if microplastics and nanoplastics are definitively linked to cancer-causing pathways such as inflammation, “What can we even do about it at this point?” he asks. “How can we limit our exposure if they are causing problems?”

As with other chemicals of concern, experts such as Dr Wolff say that the best way to reduce the risk is to “turn off the tap.” Such efforts, however, have drawn fierce opposition by the oil and gas industry, including a proposal in the International Plastics Treaty to cap plastic production, and even limited bills in many US jurisdictions that would ban single-use plastic bags.³

Dr Campen is skeptical that any meaningful production caps will be enacted in the near future. “That’s an absurdity,” he says. Instead, he suggests that an overhaul of how we manage plastic waste might make a difference. “The whole concept of recycling is a joke,” he says, referring to recent studies suggesting that less than 5% of plastic is actually recycled.⁴ Instead, he points to countries such as Switzerland that are reducing their overall volume through initiatives such as waste-to-energy incineration.

Evidence-based regulations could be aided by more data about exposure routes and comparisons of nanoplastic levels in different populations, though their sheer ubiquity in everything from irrigation water to fertilizer and soil could make such comparisons difficult. “My fear is that so much of our agricultural system is hamstrung by a process that magnifies the plastics into our food chain,” Dr Campen says.

That ubiquity also complicates the task of calculating relative risk because exposure rates are already 100% for most people. Toxicology studies in animal models may help, says Genoa Warner, PhD, an assistant professor of chemistry and environmental science at the New Jersey Institute of Technology in Newark, especially with nanoplastics that are hard to measure on their own. “We feed our animals plastics, we have a control group, and we look to see what kind of health effects we see,” she says. “It’s just one piece of the puzzle, but we don’t necessarily have to be able to see [the nanoparticles] to figure that out.”

What the field really needs, Dr Campen says, is a reliable metric that can link the relative amount of nanoplastics in particular tissues with a higher risk of consequences such as cancer—another admittedly tall order. Since his recent publication, though, multiple research groups have proposed collaborations, including ones on glioblastoma and breast, colorectal, and appendiceal cancers. By working with cancer experts to apply his laboratory’s measurement capabilities, he says, “I think the next few years will be really telling, and we’ll learn a lot.”