Microplastics are a source of extreme concern for health: the presence of these tiny pieces of plastic has been linked to heart attacks, stroke, dementia and brain tumors. But what drives these associations is unclear. Now a study published in Nature offers a tantalizing clue: microplastics interact with water, generating highly reactive molecules.
When microplastics come into contact with water, the water near their surface can become chemically active, generating highly reactive species that can modify nearby substances, including biologically important molecules.
As plastics wear down to microscopic sizes, their surface-to-volume ratio increases dramatically. For example, when a credit card is fragmented into particles some 10 microns in diameter, there is a more than 200-fold increase in its surface area, says Wei Min, a chemist at Columbia University and one of the senior authors of the study. As a result, any chemical activity is amplified.
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Min and his colleagues examined various microplastics—including polystyrene, polyethylene, polyvinyl chloride, polypropylene and polyethylene terephthalate. Plastic surfaces are hydrophobic, meaning they repel water, Min says. Thus, water molecules cannot form the hydrogen bonds they maintain in liquid form. That changes molecular arrangements, and, in turn, the change influences the local electrical environment and chemical reactivity.
The presumed chemical inertness of bulk plastics overlooks the toxicity of their fragmented microscale forms. “For microplastics, this is especially important because fragmentation creates enormous amounts of new surface area,” Min says.
In past research, microplastics have been shown to cause inflammation, oxidative stress and decreased mitochondrial activity. The new study provides a possible mechanism for this, showing that plastic-water interfaces can perturb proteins, cell membranes, and more.
How this might contribute to damage in living tissues in humans is still unclear, Min says. “Ultimately, we hope to connect fundamental interfacial chemistry with quantitative measurements of biological effects, which would help us better understand potential health risks,” he adds.
Martin Wagner, a toxicologist and a biologist at the Norwegian University of Science and Technology, who was not involved in the new work, says the study’s findings are exciting. The paper gives scientists a new way to look at the effects of plastic pollution, Wagner says. “It implies microplastics themselves are a source of oxidative species … and oxidative stress is not a secondary effect of exposure.”
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