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.

Water-rich tissues raise health concerns
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.