Plastics are widely considered chemically inert, which is why they’re so common in food packaging, water bottles and children’s toys. But new research from Columbia University and the University of California, Berkeley, suggests that once plastic breaks into micro- and nano-particles, its newly exposed surfaces can react with water in ways that may help explain how microplastics harm biological systems.
Fragmenting a large piece of plastic dramatically increases its surface area relative to its volume, exposing far more of the material to its surroundings. Columbia professor Wei Min and his team found that when microplastics contact water, they spontaneously generate reactive oxygen species (ROS)—the kind of high-energy, reactive radicals known to damage animal and human tissue.
“Water is a key active player here, rather than just a spectator. It’s integral to making these microplastics reactive,” said Min, a professor of chemistry and biomedical engineering. “Water molecules become chemically active when they come into contact with plastic, which is hydrophobic. Contact between the water and plastic creates an environment that facilitates electron transfer, and the formation of reactive radicals. When plastics fragment into smaller particles, their increasing surface-to-volume ratio creates more of these chemically active areas.”
The study’s findings, published in Nature, challenge the common view of microplastics as passive fragments—which especially matters for human health since blood is largely water. The researchers say microplastics that enter the bloodstream or cells could remain chemically active in that water-rich environment.
Min’s group also led a 2024 study that found, on average, a liter of bottled water contained 240,000 detectable plastic fragments—10 to 100 times more than had previously been estimated. That study led to a growing recognition that micro- and nano-plastics exist throughout the food system. Subsequent research has found links between micro and nanoplastic exposure and heart attack, stroke, dementia, and brain tumor. But, given its supposed inertness, the mechanism by which microplastics could contribute to these illnesses had been unclear.
This new study specifies a previously overlooked mechanism that might help bridge this gap.
“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 (ROS),” said Naixin Qian, a postdoctoral researcher in Min’s lab who helped lead the research. “ROS are textbook examples of the kinds of molecules that can damage animal and human tissue.”
The Columbia team conducted the chemical and biological experiments, while collaborators in the lab of Teresa Head-Gordon at the University of California, Berkeley, created theoretical calculations and dynamical simulations to identify how the microplastic interacted with water.
Head-Gordon’s lab led the theory that showed hydroxide ions that are promoted to the immediate water layers near the hydrophobic microplastic interface can more easily lose their electron to create hydroxyl radicals.
“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 to reduce the toxic outcomes on health and the environment,” said Head-Gordon.
Data from Columbia University