Microplastics in water make their own damaging radicals, and the smaller the fragment the more it produces

Chemists at Columbia University report that microplastics sitting in plain water generate reactive oxygen species on their own, including hydroxyl radicals. The study, published October 14, 2026 in Nature, finds that the effect grows as plastic fragments get smaller, because a small fragment exposes more surface for every unit of volume. It is a laboratory chemistry result, measured in water and in simulation rather than in people.

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Wei Min, a professor of chemistry and biomedical engineering at Columbia who led the group, said in the university’s announcement: “Water is a key active player here, rather than just a spectator.” Naixin Qian, a postdoctoral researcher in Min’s lab who helped lead the work, said: “ROS are textbook examples of the kinds of molecules that can damage animal and human tissue.”

How plastic surfaces and water produce hydroxyl radicals

Plastic is normally treated as chemically inert, but the Columbia news release says the surface of a microplastic becomes reactive on contact with water. Hydroxide ions in the water next to a hydrophobic plastic surface lose electrons more easily, and that loss of electrons is what produces hydroxyl radicals. Teresa Head-Gordon’s group at the University of California, Berkeley, supplied the theory and the computational work, using calculations and simulations of how microplastics interact with water. Head-Gordon said the most hydrophobic microplastics can drive chemical reactivity in water, a finding she suggested could inform the redesign of plastics.

A summary of the paper in News-Medical, which gives the citation as Nature volume 658, pages 650 to 657 and the DOI 10.1038/s41586-026-11141-y, reports that the team tested six common plastics: polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyethylene terephthalate and polymethyl methacrylate. Polymethyl methacrylate was the most hydrophilic and showed the lowest activity, while polypropylene and polyethylene were more reactive than it and than polyethylene terephthalate. Radicals from polystyrene were detected by electron spin resonance with a spin trap and visualized with a fluorescent probe under a confocal microscope.

Why smaller fragments produce more

The size dependence follows from geometry. Cut a plastic particle into smaller pieces and the total volume stays the same while the total surface area rises, so a given mass of small fragments offers many more water-facing surfaces where hydroxyl radicals can form. The Columbia release states that smaller particles have more surface area per unit volume and therefore more reactive sites, and the claim that smaller fragments produce more rests on that reasoning.

The release gives no particle sizes for the experiments in this study, so the exact fragment sizes cannot be stated here. It points instead to earlier work from the same group: a 2024 study of bottled water that used a laser-based microscope and detected about 240,000 plastic fragments per liter, mostly nanoplastics, which was 10 to 100 times earlier estimates. The most numerous fragments in that earlier count were the smallest ones, which are the ones this new chemistry would favor.

What the experiments show about biology, and what they do not

The paper includes biological experiments. News-Medical’s summary says the team exposed mouse red blood cells to the microplastics to measure hemolysis, and that aggregation of the protein lysozyme was tracked with a fluorescent dye, with caffeine used as a radical scavenger to test whether free radicals were involved. It also reports that methyl orange dye degraded by nearly 90 percent within 10 days in water stirred with polystyrene microplastics.

Reading the finding at the right scale matters. A radical forming at a plastic surface in a test tube is a chemical event, and a cell dying in a dish is a biological one, and the paper as summarized links the two only as a hypothesis for further testing. The accurate statement is that microplastics were shown to generate reactive oxygen species in water under laboratory conditions, with more generation expected from smaller fragments, not that people are being harmed at the levels found in drinking water.

The limits are written into that same summary. Cell damage in the laboratory experiments was not shown to be caused directly by radical formation, only polystyrene was used for radical detection, and whether these reactions contribute meaningfully to human disease at typical exposure levels remains unknown. The authors suggest the mechanism could help explain how microplastics might harm health, noting that blood is mostly water, but the release phrases each of those links as a possibility.

Beizhan Yan of Columbia’s Lamont-Doherty Earth Observatory, a co-author, noted that radicals can form on hydrophobic plastic surfaces in water, which could affect ecosystems and human health. The release also ties the mechanism to other research associating micro- and nanoplastic exposure with heart attack, stroke, dementia and brain tumor, but those associations come from separate studies and this paper does not test them. The work was funded by the National Institutes of Health, and the federal government has its own microplastics research program through ARPA-H. Min’s group is described on his Columbia chemistry faculty page.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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