Microplastics May Generate Reactive Oxygen at Water Interfaces, Study Finds

Microplastics can generate reactive oxygen species (ROS) at the boundary between plastic and water, according to research published in Nature. However, Professor Min stressed that the findings do not yet show how strongly this effect affects human health.

Animal studies often identify ROS as a potential source of oxidative stress and chronic inflammation. ROS are also produced through many normal biological processes, including basic metabolic activity. Min acknowledged that it remains difficult to compare the amount of ROS generated at a microplastic–water interface with the ROS produced naturally by human cells.

The effect may be concentrated at the plastic–water interface

“If you’re actually at the interface, you can be really affected by this, but if you’re just a few microns away, you don’t feel it anymore,” Min said.

Human exposure is another unresolved question. Researchers cannot yet determine how much microplastic the average person ingests through food, water and air each year.

Weathering may change how microplastics behave

The plastic used in the study was primarily fresh powder purchased for laboratory experiments, rather than the weathered particles found in the environment. In the researchers’ tests, older particles with more oxidized surfaces produced a slightly weaker signal.

“This aging process is very uneven,” Min said. “Some microplastic particles were created 50 years ago, while others were created five days ago.”

Particle size could affect the chemical reaction

Microplastics are generally defined as plastic particles smaller than 5 millimeters, although the minimum size cutoff varies from 100 to 1,000 nanometers. Min’s team has not yet tested how particle size changes the chemistry at the water interface, but the researchers suspect size plays an important role.

Breaking the same mass of plastic into nanoparticles creates a much larger surface area, which could increase its chemical impact. “This may be another reason why nanoplastics are more dangerous,” Min said.

Could less water-repellent plastics reduce the effect?

The researchers suggest that if water-repellent surfaces promote chemical reactions at the water interface, plastics could potentially be engineered to be less water-repellent. This might be achieved by changing their molecular structure or adding specific substances to the material.

Before drawing conclusions about health risks, the team wants to investigate how directly this chemical effect contributes to disease and biological problems in animals and humans.

“We would love to know how directly this effect contributes to disease and biological problems in animals and humans,” Min said.

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