Microplastics are far from chemically inert, according to a Columbia University study that found the tiny particles spontaneously generate damaging molecules when they meet water. Researchers reported that contact between water and the surface of microplastics produces reactive oxygen species, a family of highly reactive radicals known to damage cells and tissue. The discovery, published in the journal Nature, offers a long-sought chemical explanation for how the particles, now found everywhere from bottled water to human blood, could harm living organisms.
Microplastics Turn Water Into a Chemically Active Player
The study was led by Wei Min, a professor of chemistry and biomedical engineering at Columbia, together with postdoctoral researcher Naixin Qian, who helped lead the experimental work. Theoretical calculations and dynamical simulations identifying the mechanism were contributed by the laboratory of Teresa Head-Gordon at the University of California, Berkeley. The team found that water is not a mere spectator in the process but a key active player: water molecules become chemically active when they touch hydrophobic plastic surfaces, creating an environment that facilitates electron transfer and the formation of reactive radicals.
“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 what we call reactive oxygen species,” Qian said. “ROS are textbook examples of the kinds of molecules that can damage animal and human tissue.” In the proposed mechanism, hydroxide ions near the plastic interface more easily lose an electron, creating hydroxide radicals.
The effect grows stronger as plastic fragments shrink. When plastics break into smaller and smaller pieces, the surface-to-volume ratio rises enormously, creating far more chemically active area. The researchers also found that the most hydrophobic plastics they tested, such as polyethylene and polypropylene, showed stronger radical-generating activity than more hydrophilic ones such as PET, the plastic commonly used in beverage bottles.
The biological implications are direct, because human blood is largely water. If microplastics enter the bloodstream or cells, the same chemistry could plausibly occur inside the body. The researchers noted one mitigating factor: adding a surfactant, a substance that weakens the forces holding water molecules together, dampened radical generation. Some lipids in the body act as natural surfactants, which may limit the reaction in certain biological settings.
Microplastics Research Builds on Growing Health Concerns
Min’s group previously led a 2024 study that used a laser-based microscope to detect an average of about 240,000 plastic fragments, mostly nanoplastics, in a single liter of bottled water, far more than earlier estimates. Since then, micro and nanoplastic exposure has been linked in studies published in prominent journals to heart attack, stroke, dementia, and brain tumors, but the mechanism had been unclear given the long-standing view of plastic fragments as passive, inert debris.
“Our fundamental work that the most hydrophobic microplastics interacting with water can drive chemical reactivity could ultimately lead to new engineering solutions by redesigning the chemistry of these commodity plastics,” Head-Gordon said. The team suggests the findings could guide the design of safer materials that keep the useful properties of plastics while reducing toxic outcomes.
Public concern is rising in parallel. This year, the U.S. federal government launched a $144 million program to combat toxic plastic particles in the human body, and the Environmental Protection Agency recently added microplastics to a federal list of contaminants that may pose a concern for drinking water, the first time they have appeared on the list.
The new study does not by itself prove that microplastics cause disease in people. The researchers describe the biological damage as very likely rather than certain, and say more work is needed to determine actual health effects and exposure levels. Still, by showing that the particles change the water around them into a source of reactive radicals, the work supplies a concrete mechanism that scientists can now test, and it reframes them from passive debris to chemically active agents. For the public, the findings sharpen the case for reducing unnecessary plastic use while scientists work to quantify real-world risk.