Scientists suspect that the plastics can be linked to a host of medical conditions, but clear evidence is elusive without appropriate biomarkers for clinical laboratory testing
Recent research indicates that microplastics and nanoplastics (MNPs) are accumulating in human organs at an increasing rate. The health impact is not entirely clear, but the research suggests that clinical laboratories could someday find themselves testing for levels of MNPs in patients.
In one study, scientists at the University of New Mexico and Oklahoma State University analyzed autopsy samples of liver, kidney, and frontal cortex brain tissue collected in 2016 and 2024. “Brains exhibited higher concentrations of MNPs than liver or kidney samples,” they wrote. However, “all organs exhibited significant increases from 2016 to 2024.”
The study, titled, “Bioaccumulation of Microplastics in Decedent Human Brains Assessed by Pyrolysis Gas Chromatography-Mass Spectrometry,” was published as a preprint by the National Institutes of Health (NIH) and has not yet been peer reviewed.
“The concentrations we saw in the brain tissue of normal individuals, who had an average age of around 45 or 50 years old, were 4,800 micrograms per gram, or 0.5% by weight,” lead author Matthew Campen, PhD, Regents’ Professor, Pharmaceutical Sciences, University of New Mexico, and Director of the New Mexico Center for Metals in Biology and Medicine (CMBM), told CNN. “Compared to autopsy brain samples from 2016, that’s about 50% higher.”
Researchers have not yet uncovered clear evidence of specific health risks, but “what scientists worry about is several trends in disease prevalence that have been unexplained—Alzheimer’s disease and dementia, colorectal cancer in people under 50, inflammatory bowel disease, and global reductions in sperm count,” Campen told Everyday Health.
In another recent study, a different team of researchers at the University of New Mexico found high levels of microplastics in human and canine testicular tissue.
“At the beginning, I doubted whether microplastics could penetrate the reproductive system,” said lead author Xiaozhong Yu, MD, PhD, Professor, University of New Mexico College of Nursing in a university news story. “When I first received the results for dogs I was surprised. I was even more surprised when I received the results for humans.”
That study appeared in the journal Toxicological Sciences titled, “Microplastic Presence in Dog and Human Testis and Its Potential Association with Sperm Count and Weights of Testis and Epididymis.”
“The rate of increase in microplastics in the environment is exponential and we have every reason to believe that the concentrations in our bodies will continue to increase in the coming years and decades,” Matthew Campen, PhD (above), of the University of New Mexico told Everyday Health. As studies continue to produce evidence that nanoplastics affect human health, testing companies may develop biomarkers for clinical laboratory tests that measure the amount of microplastics in different organ locations. (Photo copyright: University of New Mexico.)
How They Get Into the Body
“Studies have found these plastics in the human heart, the great blood vessels, the lungs, the liver, the testes, the gastrointestinal tract, and the placenta,” epidemiologist Philip J. Landrigan, MD, pediatrician, public health physician, and professor in Boston College’s Department of Biology, told CNN. He also serves as director of the Program for Global Public Health and the Common Good and the Global Observatory on Planetary Health at Boston College.
Landrigan told CNN that most people are exposed to MNPs through their diet, “but inhalation is also an important route.”
However, he added, “it’s important not to scare the hell out of people, because the science in this space is still evolving, and nobody in the year 2024 is going to live without plastic.”
CNN noted that experts consider nanoplastics to be the biggest concern [as opposed to microplastics] because they can infiltrate human cells.
“Somehow these nanoplastics hijack their way through the body and get to the brain, crossing the blood-brain barrier,” Campen told CNN. “Plastics love fats, or lipids, so one theory is that plastics are hijacking their way with the fats we eat which are then delivered to the organs that really like lipids—the brain is top among those.”
The US Food and Drug Administration (FDA) states that microplastics typically measure less than 5mm, whereas nanoplastics are less than a micron (micrometer). However, the agency notes that “there are currently no standard definitions for the size of microplastics or nanoplastics.”
What Are the Health Risks?
Scientists suspect that MNPs could be associated with cancer, cardiovascular disease, kidney disease, Alzheimer’s disease, and infertility, The Washington Post reported, but that they “still don’t have a clear sense of what these materials are doing to the human body.”
One challenge is that microplastics come in different forms, such as polyethylene, polypropylene, and polyethylene terephthalate, often with chemical additives.
“In a 2021 study, researchers in Switzerland identified more than 10,000 chemicals used in the manufacture of plastic—of which over 2,400 were potentially ‘of concern’ for human health,” The Post noted.
“To be able to say we have a health impact, we need to have a direct correlation between a product and a health outcome,” Phoebe Stapleton, PhD, Associate Professor at the Rutgers University Ernest Mario School of Pharmacy (EMSOP), told The Post. “It’s very narrow, that straight line. And there’s so many different health outcomes there could be, and we’re finding these particles in so many different tissues.”
One study published in the New England Journal of Medicine (NEJM) suggested that MNPs in arteries could be risk factors for heart attacks or strokes. But even here, the authors wrote, “direct evidence that this risk extends to humans is lacking.”
Yu suspects that MNPs could be a factor in a global decline in sperm count, along with other environmental contaminants such as heavy metals and pesticides. His study found that polyethylene was the most prevalent plastic in dogs, followed by polyvinyl chloride (PVC). Higher levels of PVC correlated with lower sperm count, but there was no correlation with polyethylene.
“PVC can release a lot of chemicals that interfere with spermatogenesis, and it contains chemicals that cause endocrine disruption,” he said in the UNM news story.
Clinical laboratory managers should recognize that interest in identifying micro- and nanoplastics in every organ of the human body will increase. At some point, physicians may want labs to test their patients for microplastic levels in certain organ sites. This will likely be when enough published studies show a correlation between high levels of microplastics in certain locations of the body and specific disease states.
—Stephen Beale
Related Information:
UNM Researchers Find Microplastics in Canine and Human Testicular Tissue
Microplastics Are Infiltrating Brain Tissue, Studies Show: ‘There’s Nowhere Left Untouched’
Microplastics Found in Every Human Testicle in Study
Minuscule Plastic Pieces Found in Human and Dog Testicles
What Are the Health Risks of Microplastics in Our Bodies?
With Microplastics, Scientists Are in a Race Against Time
Tiny Shards of Plastic Are Increasingly Infiltrating Our Brains, Study Says