Microplastics Are Chemically Active, and Could Cause Biological Harm

Plastics are supposed to be chemically inert. It’s the reason they’re used so frequently to package food, bottle water, and create children’s toys: They’re safe. 

But something important happens when a large piece of plastic fragments into micro- and nanoparticles. Its surface area increases dramatically relative to its volume. Vastly more of the material is now exposed to its surroundings.

A new study by researchers from Columbia University and the University of California, Berkeley, found that this newly created surface is not necessarily safe, and identified the chemical reasons why.

“As plastic fragments into smaller and smaller particles, its surface area increases enormously. Then microplastics change the water that surrounds them, generating high-energy, reactive radicals (reactive oxygen species, ROS) that very likely contribute to biological damage that we see in animals and potentially in humans as a result of microplastic exposure,” said Wei Min, a Columbia professor of Chemistry and Biomedical Engineering.

The work challenges the common view of microplastics as largely passive fragments of inert material, and contributes to a growing understanding of why the large-scale presence of microplastics is a cause for concern. The research was published today in the journal Nature.

This is particularly noteworthy for human health because human blood is approximately 50% water, and individual human cells are generally 60% to 80% water. The new research suggests that microplastics that enter the bloodstream or cells could remain chemically active in this water-rich biological environment.

Min’s group at Columbia University also led a 2024 study that developed a laser based microscope technology and found that on average, a liter of bottled water contained some 240,000 detectable plastic fragments (mostly nanometer-sized plastic, nanoplastics)—10 to 100 times more fragments than had previously been estimated. That study led to a growing recognition that micro and nanoplastics exist throughout the food system.

The group’s 2024 research on nanoplastics garnered widespread media attention, and combating microplastic has become a public health priority. This year, the U.S federal government launched a $144 million program to combat toxic microplastics in the human body. The U.S. Environmental Protection Agency also recently added microplastics to a federal list of contaminants that may pose a concern for drinking water, the first time microplastics have appeared on the list.

Subsequent research in prominent journals including New England Journal of Medicine, Nature Medicine, and Nature Health have 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 Wei Min’s lab who helped lead the research. “ROS are textbook examples of the kinds of molecules that can 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. 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,” Min said.

The Columbia team conducted the chemical and biological experiments, while collaborators in the lab of Professor 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 that hydroxide ions that are promoted to the immediate water layers near the hydrophobic microplastic interface can more easily lose their electron to create hydroxide 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.

This work has significant implications for environmental and human health,” said co-author Beizhan Yan of Lamont-Doherty Earth Observatory. “In certain environments, such as discharges from plastic manufacturers and laundromats, microplastics can form and enter aquatic environments. This work also indicates that radicals can form on hydrophobic plastic surfaces in water, which could affect ecosystems and human health following exposure. In addition, various uses and processes in our daily lives can generate microplastics, including microwave heating, sunlight exposure of bottled water during storage. This foundational work provides a potential pathway for understanding their health impacts.”