Microplastics in water aren't inert and make damaging chemicals on their own

Researchers show that common microplastics are not chemically inert in water but actively generate reactive oxygen species (ROS) at their water-plastic interfaces, challenging the idea that fragmented plastics are just passive particles. Inspired by microdroplet chemistry, experiments found hydroxyl radicals forming on the surfaces of six widely used plastics; the most water-repellent materials (polyethylene and polypropylene) produced the most radicals, while PET and acrylic produced the least. Reactive chemistry concentrated at particle surfaces and broke down a dye (methyl orange) and induced protein aggregation, indicating the radicals can damage biomolecules.

Multiple detection methods - electron spin resonance, a ROS-activated fluorescent sensor, and surfactant suppression tests - support that the effect arises from altered water structure and surface charge rather than simple contamination. Biological tests showed lysozyme aggregation and fragmentation of mouse red blood cells scaling with radical production. Aging of particles reduced but did not eliminate the signal, and smaller particles with greater surface area likely amplify it. The health impact is not yet quantified: exposure levels, particle sizes in people, and the contribution of this interface chemistry to disease remain open, but the findings point toward designing less water-repellent plastics or additives to mitigate ROS generation.