One reason plastic is so widespread is its chemical stability; it does not easily react with surrounding substances, which is why it is used for food packaging and water bottles. The same stability was assumed for microplastics, the tiny fragments that break off larger plastic items and have been detected in virtually every ecosystem on Earth. New research from Columbia University and the University of California, Berkeley, however, shows that water can make the surfaces of microplastics chemically active, turning them into a possible health hazard.
The study, published in Nature, reports that this activity can spontaneously generate chemicals capable of altering other molecules, including those essential for life. The authors emphasize that the reaction occurs under normal environmental conditions, without sunlight or other agents that normally degrade plastic.
Why do microplastics behave differently from larger plastics? The scientists point to the much larger surface area that tiny particles provide. “As plastic fragments into smaller and smaller particles, its surface area increases enormously,” said Wei Min, professor of chemistry and biomedical engineering at Columbia University, in a press release. “Then microplastics change the water that surrounds them, generating high‑energy, reactive radicals that very likely contribute to biological damage that we see in animals and potentially in humans as a result of microplastic exposure.”
Among the reactive chemicals produced are reactive oxygen species, especially hydroxyl radicals. These radicals can strip electrons from proteins and fats in cell membranes, compromising their structure and function. “They are textbook examples of the kinds of molecules that can damage animal and human tissue,” noted Naixin Qian, a postdoctoral researcher in Min’s lab who co‑led the work.
The body’s natural defense against such damage comes from antioxidants, which neutralize reactive chemicals. If the amount of reactive compounds exceeds the capacity of antioxidants, oxidative stress can develop, leading to cellular injury. Earlier studies have linked oxidative stress to microplastic exposure, but the precise mechanisms have remained unclear.
How much microplastic actually accumulates in human tissue is still debated, and some sensational claims have been questioned. Nonetheless, even a small presence in the body could allow the particles to react with bodily water. The researchers were especially concerned about blood, which is largely water. If microplastics become chemically active in this fluid, they could pose risks beyond the pollutants they may carry.
In experiments, red blood cells taken from mice were exposed to various microplastics. The cells deformed and burst—a process known as hemolysis. The damage was more pronounced with plastics that reacted more strongly with water, indicating that the chemical activation was responsible for the cellular injury.
Past research on microplastics has focused mainly on chemicals leaching from the particles or on their physical effects, often treating the plastic itself as chemically inert. While larger pieces of plastic are generally inert, these new findings challenge the assumption that the same holds true for the microscopic fragments they break into.