Tiny plastic particles long assumed to be chemically inert spontaneously generate cell-damaging free radicals when exposed to water, according to research published in the journal Nature by scientists at Columbia University and the University of California, Berkeley.
The findings offer a potential molecular explanation for how microplastics may harm living organisms, particularly within water-rich environments such as human cells and the bloodstream.
Spontaneous chemical reactions
For decades, plastics have been manufactured for food containers, beverage bottles and medical supplies partly because of their presumed chemical stability. However, the study reveals that fragmentation transforms their chemical behavior. As bulk materials degrade into microscopic shards, their total surface area expands significantly relative to their volume, exposing far more material to the surrounding liquid.
“As plastic fragments into smaller and smaller particles, its surface area increases enormously,” said co-author Wei Min, a Columbia professor of chemistry and biomedical engineering, in a university release. “Then microplastics change the water that surrounds them, generating high-energy, reactive radicals that very likely contribute to biological damage that we see in animals and potentially in humans as a result of microplastic exposure.”
Working across multiple laboratory trials, the researchers tested six widely used commercial plastics, including polystyrene, polyethylene and polypropylene. Using theoretical calculations and dynamic simulations led by Teresa Head-Gordon’s laboratory at UC Berkeley, the team demonstrated that water-repelling plastic surfaces reorganize adjacent water molecules. Hydroxide ions positioned at this interface transfer electrons to dissolved oxygen or hydrogen ions, producing hydroxyl free radicals. Hydroxyl radicals are exceptionally reactive oxygen compounds capable of damaging DNA and other vital biomolecules.
Harm to proteins and blood cells
To examine biological consequences, researchers exposed the microplastic-water mixture to lysozyme, an antibacterial enzyme present in human tears, saliva and mucus. The interaction induced the proteins to clump together in a manner reminiscent of amyloid fibril formation seen in neurodegenerative disorders, ScienceAlert reported. Introducing caffeine, a recognized antioxidant, shielded the protein and halted the clumping during laboratory tests.
The scientists also introduced mouse red blood cells to the reactive solution, observing that the cells warped and fragmented under the oxidative stress.
“Our research found that when microplastics interact with water, as they do when they’re in bottled water, or when they’re absorbed into our bloodstream, they spontaneously generate [these] high energy reactive radicals,” said lead author Naixin Qian, a postdoctoral researcher at Columbia.
Daily exposures and ongoing research
Microplastic shedding occurs routinely through everyday activities. Opening and closing plastic beverage bottles sheds microparticles from bottle caps, while microwave heating, intravenous injections in medical care and sunlight exposure also degrade plastic products, according to co-author Beizhan Yan of the Columbia Climate School.
The study builds on earlier work by the Columbia researchers, who determined in 2024 that bottled water contains roughly 240,000 plastic particles per liter on average. Recent epidemiological studies have linked microplastic accumulation to elevated risks of stroke, heart attack and dementia, though biological mechanisms remained poorly understood until now.
Federal agencies have escalated oversight of the pollutant. Earlier this year, the U.S. Department of Health and Human Services introduced the $144 million STOMP initiative to address microplastics in the human body, while the Environmental Protection Agency placed microplastics on its list of potential drinking water contaminants.
Researchers at Columbia, New York University and Rutgers University are now conducting animal studies to examine how ingested plastic particles migrate across maternal tissue to reach fetal organs during pregnancy. Scientists are also evaluating engineering strategies, such as altering the surface chemistry of commercial polymers or designing specialized laundry filters, to minimize particle emissions.
