Min stressed, though, that this indicates that microplastics make people sick by generating ROS. While animal studies often point to ROS as possible roots of oxidative stress and chronic inflammation, ROS can be produced in many ways, including through basic metabolic activity.

Min admitted comparing the magnitude of this effect to the impact of ROS our own cells make is rather tricky.

A local problem

“If you are really at the interface, you could be significantly affected by this effect, whereas if you are just a few microns away, you don’t feel it anymore,” Min said. Exposure is another unknown here. Min also emphasized that no one can yet say how many microplastics an average person takes in each year from food, water, and air.

The plastics in the study were mostly fresh, lab-bought powders, unlike weathered particles we encounter in the environment. In the team’s tests, older particles with more oxidized surfaces produced somewhat weaker signals. “This aging process is very heterogeneous,” Min said. “Some microplastic particles were made 50 years ago, some were made five days ago.” Finally, there is the question of size.

Microplastics are usually defined as particles smaller than five millimeters, while the minimum cutoff varies between 100 and 1,000 nanometers. Min’s team did not test how variation in microplastic particle size affects water-interface chemistry, but the researchers suspect it might play a role. The same mass of plastic broken into nanoparticles has far more surface area, which might make the effect larger. “This may be another reason for nanoplastics to be more dangerous,” Min said.

The researchers argue that if water-repellent surfaces drive the water interface chemistry, plastics could be designed to be less water-repellent, either by changing their molecular structure or including additives. First, though, the team wants to focus on the question their study left open. “We definitely want to see how much this effect is directly contributing to disease or biological problems in animals and humans,” Min said.

Nature, 2026. DOI: 10.1038/s41586-026-11141-y