Scientists from Columbia University have identified a chemical process that may explain how microplastics pose a risk to human health. Their latest study, published on October 14 in the journal Nature, reveals that when water molecules interact with plastic surfaces, they generate reactive oxygen species (ROS)—unstable, high-energy molecules known to damage cells and promote inflammation.

The research challenges the long-held assumption that plastics are chemically inert and resistant to degradation. By examining six common types of plastics—polyethylene, polypropylene, polystyrene, polyvinyl chloride (PVC), poly(methyl methacrylate) (PMMA), and polyethylene terephthalate (PET)—the team found that exposure to water triggered the formation of ROS to varying degrees. Polyethylene and polypropylene produced the highest levels, while PMMA generated the least.

In laboratory tests, the researchers exposed mouse red blood cells to microplastics from these materials. The cells exhibited changes in shape and rupture, with damage correlating to the amount of ROS generated by each plastic type. Wei Min, a chemistry and biomedical engineering professor at Columbia and co-author of the study, noted that ROS can harm nearby molecules such as DNA, potentially causing mutations.

Although the findings do not directly link these reactions to specific diseases in humans, the researchers suggest that increased surface area of plastics as they break down into micro- and nanoplastics could amplify these chemical effects. Since water is present in all human cells, the interaction between microplastics and water could have significant biological implications.

This work builds on earlier research from the same team in 2024, which detected microplastics in commercial bottled water at levels 10 to 100 times higher than previously estimated. The majority of these particles were nanoplastics small enough to cross the blood-brain barrier and enter human cells. Beizhan Yan, a Columbia environmental chemist and co-author, emphasized the ubiquity of microplastic exposure, citing everyday activities such as washing clothes or reheating food as sources of nanoparticles.

Experts caution against drawing premature conclusions about the health consequences of microplastics. Matthew Campen, a pharmaceutical research professor at the University of New Mexico, acknowledged the study’s contribution to understanding plastic-water chemistry while noting that certain substances—such as the surfactant Triton X100 used in the experiments—can inhibit ROS formation, suggesting that other compounds in the human body may mitigate these effects.

The research adds to growing public and governmental concern over microplastic pollution. In April, the U.S. federal government announced a $144 million initiative to investigate the impacts of microplastics in humans and the environment. Tracey Woodruff, a professor of epidemiology and population health at Stanford University, urged caution, arguing that reducing exposure is prudent given current evidence, rather than waiting for definitive proof of harm.