A study in Nature from Columbia University and the University of California, Berkeley reports that common plastic particles spontaneously produce hydroxyl radicals, highly reactive forms of oxygen, at their interface with water. In laboratory tests the particles clumped proteins and ruptured mouse red blood cells. The work offers a possible chemical explanation for how microplastics might harm living tissue. It does not show harm in people.
Plastics have long been regarded as chemically inert, which is one reason they are used to package food and medicines. Concern about microplastics has therefore focused on what they carry: additives, absorbed pollutants and microbes, plus the physical effects of particles lodged in tissue. A paper published in Nature on 14 October suggests a more direct mechanism. The plastic surface itself, in contact with water, may be chemically active.
The study, titled “Intrinsic physicochemical activity at microplastic–water interfaces”, was led by the laboratory of Wei Min, professor of chemistry and biomedical engineering at Columbia University. Postdoctoral researcher Naixin Qian is first author. Theoretical calculations and simulations came from Teresa Head-Gordon’s group at UC Berkeley, and co-authors include Beizhan Yan of Columbia’s Lamont-Doherty Earth Observatory and Phoebe A. Stapleton.
“Water is a key active player here, rather than just a spectator,” Min said in the university’s announcement.
What the researchers found
According to the paper’s abstract, commodity microplastics “exhibit intrinsic physicochemical activity in water”: they spontaneously generate reactive oxygen species (ROS). The amount increases with the surface’s hydrophobicity, meaning how strongly it repels water, and tracks the electrical charge at the interface.
A detailed account of the paper by Earth.com reports that six common plastics were tested: polypropylene, polyethylene, polystyrene, PVC, PET and acrylic. All six produced radicals, with polyethylene and polypropylene, the most water-repellent, producing the most and acrylic the least. The radicals were identified as hydroxyl radicals using a chemical trap and a fluorescent probe, and the fluorescence appeared mainly at particle surfaces. In one test, polystyrene in water degraded nearly 90% of a dye over ten days. Coating the particles with a surfactant that neutralised their surface charge largely stopped radical formation. No external trigger such as ultraviolet light was needed. NSH has not read the full paper and relies on that account for these experimental details.
The proposed mechanism
The Berkeley team’s calculations suggest why. At a hydrophobic surface, water molecules cannot arrange themselves as they do in bulk liquid. Hydroxide ions (OH⁻) pushed into this interfacial layer are only partly surrounded by water and sit in a strong local electric field. Under these conditions, the abstract says, oxidation of hydroxide is more favourable: the ion can lose an electron and become a hydroxyl radical (•OH), one of the most reactive and damaging molecules in chemistry.
The finding is consistent with a growing body of research showing that water behaves unusually at interfaces. Microdroplet studies have shown, for example, that the surfaces of tiny droplets can drive reactions that do not occur in bulk water.
Size matters too. Smaller fragments have far more surface area per unit of mass. Grinding a plastic card into one-micrometre particles would increase its surface area more than 2,000-fold, so the same mass of plastic, broken down further, would have more reactive sites. That matters because real-world exposure is dominated by small particles: a 2024 study from Min’s laboratory detected about 240,000 plastic fragments per litre of bottled water, most of them nanoplastics.
Biological effects in the laboratory
The team then asked whether this chemistry could affect biological molecules. According to the accounts of the paper:
- Radicals continued to form on polystyrene in blood-serum-like liquids.
- Charged proteins and short DNA strands accumulated on plastic surfaces.
- A protein clumped at particle surfaces, a sign of structural damage, and the radical scavenger caffeine largely prevented this.
- Mouse red blood cells broke apart after contact with polystyrene particles, with the most active plastics rupturing the most cells.
Weathering may reduce the effect: polystyrene whose surface had already oxidised repelled water less and produced fewer radicals.
“ROS are textbook examples of the kinds of molecules that can damage animal and human tissue,” Qian said. Oxidative stress caused by ROS is implicated in inflammation and cell damage.
Independent views and limitations
Independent researchers contacted by the Science Media Centre network were broadly positive but cautious:
- June-Woo Park of the Korea Institute of Toxicology said the work explains how microplastics generate ROS, where earlier studies had only linked ROS to toxicity. He noted that only microscale particles, not nanoplastics, were examined.
- Vanessa Morris of the University of Canterbury said it challenges the idea that plastics are inert. She noted that the proteins tested were not those directly linked to Alzheimer’s or Parkinson’s disease.
The limitations are significant:
- The experiments used clean plastic powders from chemical suppliers, not weathered environmental particles, which carry coatings, additives and biofilms.
- The blood-cell tests used mouse cells outside the body.
- Radical formation inside a living organism has not been measured, and no health effect in people has been demonstrated.
The work offers a possible chemical explanation for observed harms, not a measured health effect.
Why it matters for India
India is among the world’s largest producers and consumers of plastics, and microplastics have been reported in its rivers, coastal waters, salt and bottled water. If the radical-forming activity is confirmed in real-world particles and living systems, regulators may need to consider surface chemistry as well as particle counts when they assess risk. Head-Gordon suggested the work could eventually help redesign commodity plastics to be less harmful.
What comes next
Testing with weathered and nanoscale particles, measurements in living cells and tissues, and studies of whether biological coatings switch the effect off.
