We often hear that plastic is chemically inert. That means it does not react with other things. This is why companies use it for food packaging, water bottles, and toys for children. But a big change happens when a large piece of plastic breaks into tiny bits. These bits are called microplastics and nanoplastics. As the pieces get smaller, their surface area grows considerably compared to their volume. Much more of the plastic now touches the world around it.
A new study from Columbia University and the University of California, Berkeley, shows that this new surface is not always safe. The team also found out why. The work appeared in the journal Nature.
Wei Min, a Columbia professor of chemistry and biomedical engineering, explained the main idea. He said that tiny plastic pieces change the water around them. This creates highly reactive molecules called radicals. These radicals very likely add to the harm seen in animals. They may also harm people.
The result matters for human health because blood is mostly water. If microplastics get into the blood or into cells, they could remain chemically active there. Water is everywhere in the body.
Beizhan Yan, a co-author and environmental geochemist at Lamont-Doherty Earth Observatory, said the work has major meaning for people and nature. Microplastics can enter waterways through factory discharge and laundromats. Daily life also makes them. Heating food in a microwave, leaving bottled water in the sun, and giving IV injections in hospitals can all release them. He called the study a basic step toward understanding how they affect health.
The same researchers led a study in 2024. They built a laser-based microscope. With it, they found that one liter of bottled water holds about 240,000 detectable pieces of plastic on average. Most were nanoplastics. That is 10 to 100 times more than earlier estimates. The study showed that tiny plastics are found all through our food supply.
That study drew wide attention. Fighting microplastics is now a public health goal. This year, the U.S. government started a $144 million program to tackle harmful microplastics in the human body. The Environmental Protection Agency also placed microplastics on its list of possible drinking water contaminants. It was the first time they had appeared there.
Later studies in top journals, including the New England Journal of Medicine, Nature Medicine, and Nature Health, linked exposure to heart attack, stroke, dementia, and brain tumors. Yet nobody knew how the plastics could cause these illnesses, since plastic was thought to be inert. The new study points to a mechanism that people had missed.
Here is how it works. Plastic repels water. When water touches it, the setting helps electrons move around. This process leads to reactive radicals. Smaller particles have more surface area for the reaction to happen. So more fragments mean more reactive spots.
Naixin Qian, a postdoctoral researcher in Min’s lab, said microplastics make these radicals on their own when they meet water. This phenomenon can happen in bottled water or in the bloodstream. She said these molecules are classic examples of what can damage animal and human tissue. Min added that water is not just a bystander. It plays a key part in making microplastics reactive.
The Columbia team ran the chemical and biological experiments. Teresa Head-Gordon’s lab at Berkeley ran theory calculations and simulations. Her group showed that hydroxide ions move into the water layers right next to the plastic surface. There, they lose an electron more easily and form hydroxyl radicals.
Head-Gordon said the findings could lead to safer plastics. Engineers could redesign plastic chemistry to reduce harm. Yan studies how particles spread in tissue and ways to cut emissions.
