Microplastics can generate highly reactive chemicals simply by interacting with water, according to a peer-reviewed study that challenges a longstanding assumption about the chemical stability of common plastics.
Researchers at Columbia University and the University of California, Berkeley, found that the surfaces of several widely used plastic polymers can spontaneously produce reactive oxygen species, including hydroxyl radicals. These short-lived chemicals can react with biological molecules, potentially helping explain some harmful effects associated with microplastic exposure.
The study, published in Nature on October 14, 2026, shows that this activity can occur without sunlight, prior environmental weathering, or externally added oxidizing chemicals. The findings identify a possible mechanism of microplastic toxicity, although they do not establish that the reactions cause specific diseases in humans.
How Microplastics Generate Reactive Chemicals in Water
Plastics are generally considered chemically resistant under ordinary conditions. Their durability is one reason they are widely used in packaging, manufacturing, and consumer products.
However, the new research suggests that their behavior can change significantly when plastic materials fragment into tiny particles and interact with water.
The key is the interface where the plastic surface meets the surrounding liquid. Researchers observed that this boundary can support the formation of hydroxyl radicals, highly reactive molecules capable of altering other chemical substances.
These radicals belong to a broader category known as reactive oxygen species, or ROS. Although ROS also occur naturally in living organisms, excessive or poorly controlled production can contribute to oxidative damage.
The researchers found that radical generation was associated with two important surface characteristics: hydrophobicity and interfacial electrostatics.
Hydrophobic materials tend to repel water. At their surfaces, interactions involving water molecules and electrical charge can differ from those in ordinary bulk water.
The team's molecular simulations and quantum-mechanical calculations suggest that these interfacial conditions can make the oxidation of hydroxide ions energetically more favorable, providing a possible explanation for the observed hydroxyl radical production.
Importantly, the calculations help explain the experimental findings; they are not a substitute for the laboratory measurements themselves.
What the Experiments Actually Showed
One of the study's experiments involved polystyrene, a common plastic used in packaging and other products, and methyl orange, a dye that can break down when exposed to certain reactive chemicals.
When researchers stirred polystyrene microplastics into water containing methyl orange, the solution gradually changed from light yellow to nearly colorless over 10 days. The study reported approximately 90% dye degradation under those experimental conditions.
By comparison, the researchers did not observe comparable degradation when the plastic was tested with the dye in several common organic solvents.
This difference suggested that water was playing an essential role in the chemical process, rather than the plastic particles simply releasing a substance that would behave similarly in every solvent.
To investigate further, the team used electron spin resonance spectroscopy and chemical probes designed to detect reactive species. Fluorescence microscopy also helped locate hydroxyl radical activity near the surfaces of the particles.
The researchers estimated a lower-bound hydroxyl radical production rate of approximately 0.1–1 nanomolar per minute under the relevant laboratory conditions. That estimate describes the experimental system, not a measured production rate in drinking water or human tissue.
The study also examined six common plastics: polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyethylene terephthalate, and polymethyl methacrylate.
All six demonstrated radical-generating activity in the experiments, but the strength varied. More hydrophobic plastics, including polyethylene and polypropylene, generally showed greater activity than some of the less hydrophobic materials.
As Chemical & Engineering News explained in its October 2026 coverage, the results point to surface properties as an important factor in determining how chemically active different microplastics become in water.
Why Smaller Plastic Particles Matter
Microplastics are generally defined as plastic particles smaller than five millimeters. They can originate from manufactured small particles or from the breakdown of larger plastic objects.
As a piece of plastic breaks into smaller fragments, its total exposed surface area increases relative to its volume.
That matters because the reactions described in the new study occur at the boundary between plastic and water. More exposed surface can potentially create more opportunities for this chemistry to take place.
The finding therefore adds another dimension to concerns about plastic fragmentation. Breaking a plastic object into smaller pieces does not necessarily change only its size, distribution, or ability to enter biological systems. It can also increase the importance of chemical processes occurring at its surfaces.
However, the results should not be interpreted as evidence that every intact plastic container generates harmful amounts of radicals under normal use. Particle size, surface properties, water chemistry, and environmental conditions can influence the reactions.
In its October 14 research announcement, Columbia University emphasized that fragmentation creates substantially more exposed plastic surface, potentially increasing interactions between plastic particles and their surroundings.
Could These Reactions Help Explain Microplastic Health Risks?
The discovery could help scientists investigate why microplastics sometimes produce harmful effects in biological experiments.
Hydroxyl radicals are particularly reactive and can interact with proteins and other biological molecules. When reactive oxygen species overwhelm protective biological processes, they can contribute to oxidative stress and cellular damage.
The Nature researchers examined consequences extending beyond radical generation, including biomolecular adsorption, protein aggregation, and cellular damage.
These experiments support the possibility that chemical reactions at microplastic surfaces contribute to biological harm, rather than all effects arising solely from physical particle interactions or chemicals already present in plastics.
Still, there is a critical distinction between identifying a plausible damage mechanism and demonstrating that it causes disease in humans.
Laboratory systems allow scientists to control particle concentration, polymer type, solution composition, and exposure conditions. Human bodies contain complex biological environments, protective mechanisms, and many simultaneous chemical processes that can affect the consequences of exposure.
As discussed in The Washington Post's October 25 reporting, the new chemistry may help explain how microplastics interact with living tissue, but establishing the health significance of these reactions requires additional evidence.
The findings do not establish that microplastics cause cancer, cardiovascular disease, Alzheimer's disease, or any other specific human illness through this mechanism.
What Scientists Still Need to Establish
Several questions remain before researchers can determine how important this newly identified chemistry is in everyday environments or human health.
One is whether hydroxyl radicals are generated at comparable rates when microplastics are present at the concentrations typically encountered in natural waters, food, or human tissues.
Another concerns the influence of environmental conditions. The researchers found that surface properties and surrounding chemistry affect radical production, but real-world microplastics encounter changing temperatures, dissolved substances, biological material, and different degrees of surface ageing.
Scientists also need to determine how much these reactions contribute to biological damage compared with other proposed mechanisms, including inflammation, particle interactions, and exposure to plastic additives or pollutants carried on particle surfaces.
Independent replication and further studies involving realistic exposures will be important for assessing whether the laboratory findings translate into measurable environmental or health consequences.
The research also opens questions for materials science. If polymer surface chemistry influences radical generation, understanding those relationships could eventually help researchers investigate ways to design plastics with less undesirable interfacial activity.
For now, the central finding is a chemical one: common microplastics are not necessarily passive when they encounter water. Their surfaces can participate in reactions that generate highly reactive species, offering scientists a new mechanism to investigate as they work to understand the broader consequences of plastic pollution.
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