A sliver of human brain in a small vial starts to melt as lye is added to it. Over the next few days, the caustic chemical will break down the neurons and blood vessels within, leaving behind a grisly slurry containing thousands of tiny plastic particles.
Toxicologist Matthew Campen has been using this method to isolate and track the microplastics — and their smaller counterparts, nanoplastics — found in human kidneys, livers and especially brains. Campen, who is at the University of New Mexico in Albuquerque, estimates that he can isolate about 10 grams of plastics from a donated human brain; that’s about the weight of an unused crayon.
Microplastics have been found just about everywhere that scientists have looked: on remote islands, in fresh snow in Antarctica, at the bottom of the Mariana Trench in the western Pacific, in food, in water and in the air that we breathe. And scientists such as Campen are finding them spread throughout the human body.
Detection is only the first step, however. Determining precisely what these plastics are doing inside people and whether they’re harmful has been much harder. That’s because there’s no one ‘microplastic’. They come in a wide variety of sizes, shapes and chemical compositions, each of which could affect cells and tissues differently.
This is where Campen’s beige sludge comes into play. Despite microplastics’ ubiquity, it’s difficult to determine which microplastics people are exposed to, how they’re exposed and which particles make their way into the nooks and crannies of the body. The samples that Campen collects from cadavers can, in turn, be used to test how living tissues respond to the kinds of plastic that people carry around with them.
“Morbidly speaking, the best source I can think of to get good, relevant microplastics is to take an entire human brain and digest it,” says Campen.
The world is hungry for data — German consumers rated microplastics in food as their top environmental-health concern in 2023, for example. And negotiations on a global treaty that could cap plastics production are under way. Findings have trickled out slowly, hampered by insufficient analytical methods, contamination risks and a lack of collaboration between scientists in different fields. “There’s no cookbook at this point. There’s no manual of standard operating procedures,” says Kathleen Egan, a cancer researcher at Moffitt Cancer Center in Tampa, Florida. “We’re having to make them up as we go, and it’s a process.”
But there are signs that scientists are ironing out these kinks, and that the field is maturing. Campen is one of a cadre of researchers developing unconventional methods and forming teams of interdisciplinary scientists. They are caught in a race against time. Plastics production, which began less than a century ago, reaches an all-time high each year, and the material takes hundreds, if not thousands, of years to degrade, which will create trillions of microplastics in the process.
“There are microplastics everywhere,” says Bart Koelmans, an environmental chemist at Wageningen University in the Netherlands. “We cannot run away from them.”
Piling up
The term microplastics was coined 20 years ago, but only in the past 10 years have researchers progressed from studying the particles in the environment and animals to gauging their effects on human health, says Martin Wagner, a biologist at the Norwegian University of Science and Technology in Trondheim. “It’s a young field,” he says.
Campen’s team has already found grim results: as the number of plastics created has increased sharply, so too has the concentration of microplastics found in the brain, liver and kidneys, according to his group’s results published in Nature Medicine this month1. On average, microplastic levels were about 50% higher in brain samples from 2024 than in 2016 samples. And brain samples contained up to 30 times more microplastics than samples from a person’s liver and kidneys.
Another study published in January2 might offer clues as to how the particles congregate. Researchers fed mice water laced with microplastics and tracked the movements of the particles through the bodies of the mice. The researchers found that the plastics were gobbled up by immune cells, and ended up piling up in and blocking small blood vessels in the brain.
What plastics do to human organs is subject to intense study. When scientists add microplastics to human tissue samples in the laboratory, it can result in cell death, immune reactions and tissue damage. And hundreds of studies have exposed animals — mainly aquatic organisms — to microplastics and found that the particles can clog their guts or hinder their ability to reproduce. On the basis of these findings, researchers suspect that these particles could be linked to cancer3, heart4 and kidney disease5, Alzheimer’s disease6 or fertility issues7 in people.
But there is no evidence yet that microplastics directly cause poor health in humans — only data that show a link. A landmark study4, published in March 2024, reported that nearly 60% of about 250 people who were undergoing heart surgery had micro- or nanoplastics in a main artery. Those who did were 4.5 times more likely to experience a heart attack, a stroke or death in the three years after the surgery than were those whose arteries were plastic-free.
But, as the authors of the study acknowledge, the presence of plastic might correlate with other factors that would influence health, such as diet or socio-economic status.
Shifting sands
The field has grown in the past decade: for example, in 2014, there were 20 papers published that include the keyword ‘microplastics’ listed in Elsevier’s Scopus database. Nearly 6,000 were published in 2024. The US National Institutes of Health (NIH) issued its first grant with the word ‘microplastics’ only seven years ago — in 2018. Since then, the agency has funded more than 45 projects.
But as money comes in and interest grows, researchers are still developing methods. This burst of innovation is exciting, says Phoebe Stapleton, a toxicologist at Rutgers University in Piscataway, New Jersey, who studies the effects of plastics during pregnancy. But it also means that each team of scientists is developing and using different analytical approaches to detect and characterize microplastics. And there haven’t been many studies analysing each method’s reliability or validity.
This lack of standardization makes it difficult to do a head-to-head comparison of studies by different groups, says Eliseo Castillo, a mucosal immunologist at the University of New Mexico in Albuquerque who studies the particles’ effects on the digestive and immune systems.
For example, many studies use pristine microplastics — such as small spheres — that are not representative of the diversity of particles found in the environment. Some researchers argue that they are the most readily available and standardized set of microplastics available to use, whereas others say that they’re a waste of money because they are so different from what people are exposed to. “We defend our areas like crazy”, Campen says, and that can ultimately hinder the search for conclusive data. There are numerous variables in the plastics themselves, including size, shape and composition. And many are coated with one of more than 10,000 chemical additives to make them more flexible, flame retardant or degradable. Furthermore, plastics might affect each organ or cell type differently. A sharp microplastic fragment might be more damaging in the fragile lung environment than in the throat, for example.
The dose matters, too, as well as the route of ingestion, says Alison Elder, an inhalation toxicologist at the University of Rochester Medical Center in New York. “The inhalation route is a major concern because if inhaled plastics can get into the deep lung and cause an inflammatory reaction, they don’t need to go anywhere to cause health outcomes,” she says.
While the field develops tools and works out the strengths and weaknesses of each one, it will be important for researchers to use multiple methods to confirm the characteristics of the particles that they’re finding, Stapleton says.
Continue reading atwww.nature.com
