For decades, the perceived stability of plastics was a key factor in their popularity. Polyethylene and polystyrene - two of the largest volume synthetic thermoplastics produced today - were created to be long-lasting and easy-to-use (e.g., milk jugs, grocery bags, cutlery) and were therefore considered relatively chemically unreactive in typical daily use scenarios.
Recent research published in Nature ("Intrinsic physicochemical activity at microplastic–water interfaces") from lead authors Teresa Head-Gordon in the College of Chemistry and Wei Min at Columbia University has shown that when bulk polymers become microplastics they are in fact not inert, but rather, the tiny pieces of plastic chemically modify the water around them to generate highly reactive species that may cause damage to living systems.
“As plastic fragments into smaller and smaller particles, its surface area increases enormously. Then microplastics change the water that surrounds them, generating high-energy, reactive radicals that very likely contribute to biological damage that we see in animals and potentially in humans as a result of microplastic exposure,” said Wei Min, a Columbia professor of Chemistry and Biomedical Engineering.
These findings reinforce those from a previous study conducted by Min's team in 2024. In this previous study, Min's team found that a single liter of bottled water contained approximately 240,000 plastic particles - an order of magnitude greater than what was estimated previously.
The recent research published in Nature using theoretical calculations and dynamic simulation techniques developed by UC Berkeley professor Teresa Head-Gordon showed that the microplastics with the greatest degree of hydrophobicity (a molecule’s tendency to repel water) exhibited the greatest degree of electron transfer reactivity to form radicals at their surfaces. This introduced an oxidative stress mechanism to connect increased microplastic exposure to human health consequences such as protein aggregation and lysing of cells observed by the Min lab.
These findings increase awareness of plastic contamination in food and water systems, as microplastic pollution has become a major national concern. The federal government recently launched plans to invest $144 million in fighting toxic microplastics in the human body. In addition, for the first time, microplastics have been added to the U.S. Environmental Protection Agency's list of drinking water contaminants of concern.
This scientific discovery of a possible oxidative stress mechanism provides public health officials, regulatory agencies and clinicians with data-driven evidence for assessing and mitigating potential risks associated with environmental exposures prior to impacts on community health.
In addition to identifying potential biological hazards, the study provides a pathway toward development of environmentally-friendly materials.
By understanding the underlying mechanism behind this phenomenon, scientists can develop next-generation plastics that eliminate these undesirable surface reactions. Prior to this study, environmental concerns related to plastics were largely focused on managing physical waste (i.e., cleaning up waterways, reducing landfill overflow, removing marine debris).
However, this study demonstrates that microplastics induce a reaction in water, significantly expanding our view of plastic pollution in the environment. “Our fundamental work that the most hydrophobic microplastics interacting with water can drive chemical reactivity could ultimately lead to new engineering solutions by redesigning the chemistry of these commodity plastics to reduce the toxic outcomes on health and the environment,” said Head-Gordon.
The discovery exemplifies how interdisciplinary science at our College can provide meaningful contributions towards addressing some of today's most pressing challenges. By combining expertise from theoretical and physical chemistry, environmental monitoring and health sciences, our faculty labs are directly contributing towards two of our College's areas of focus - climate and sustainability and human health - that represent our research priorities over the next decade.