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The facial coverings utilized and discarded during the COVID-19 crisis have an unpredictable destiny. Their physical impact on the ecosystem and ability to capture organisms within habitats are serious issues, but these are not the sole concerns. Recent studies indicate that the surrounding environment can alter the chemical properties of the mask materials, just as those materials can influence their environment.
Single-use face masks, made from polypropylene, can break down into micro- and nanoplastics when exposed to sunlight, generating reactive oxygen species—powerful oxidizing agents that may oxidize other environmental elements and instigate unforeseen reactions.
Recent investigations by engineers at Washington University in St. Louis, spearheaded by Young-Shin Jun, a professor specializing in energy, environmental, and chemical engineering at the McKelvey School of Engineering, sheds light on the multifaceted pollution issue created by discarded masks.
Ping-I (Dennis) Chou and Zhenwei Gao, both PhD alumni of the McKelvey School of Engineering, are co-first authors of this research published in the Journal of Hazardous Materials. Their study originated from a fundamental inquiry: What becomes of all those discarded masks?
The research provides fresh insights into the crucial chemical alterations that happen when face masks are subjected to sunlight, moisture, and trace metal ions.
Masks degrade into nanoplastics and create reactive oxygen species, Jun noted. These newly formed, highly reactive oxidizing agents engage with metal ions, resulting in rapid formation (within a few hours) of manganese oxide on the plastic fragments, Jun elaborated.
She mentioned that this study focused on manganese ions due to their abundance in various environments and significance to other sensitive trace elements.
“These chemical interactions can modify the reactivity and distribution of these mask materials,” Jun stated, “and consequently, how the materials disperse will also vary—an aspect that has generally been neglected.”
The ecological implications of face masks are alarming, considering the 2020 estimate that 1.56 million of them entered marine environments. Manganese and iron drive numerous biogeochemical reactions and influence the surface chemistry of these materials. The interaction between these “redox elements” and plastic substances can affect the outcomes for both the plastics and trace metal species.
“They could influence the fate of trace metals, and at the same time, trace metals could modify the fate of microplastics,” Jun added.
Additionally, among their findings: sunlight exposure is crucial for the rapid formation of manganese oxide.
Looking ahead, Jun and her research team plan to examine how organic substances in aquatic ecosystems affect the transformation and movement of pollutants emerging from face masks. She is also interested in how microbial biofilms interact with metal-coated nanoplastics and the influence of varied polymer structures in plastic waste on the outcomes and movement of those reactive metal ions.
She highlighted the necessity of awareness, asserting that while trash can be swiftly hidden from view, it should not be forgotten.
“Neglecting and disregarding plastics is not a solution. Plastics not only cause physical destruction, but they also introduce chemical alterations into environmental systems,” Jun remarked.
“A deeper understanding of the reactions at the nanoscale interfaces between plastics and aquatic environments is essential to overcoming this issue, and it could lead to unexpected advantages,” she stated.
The chemical reaction principles uncovered here could assist in developing sustainable energy materials. By comprehending how manganese and polymers engage, it could guide the creation of enhanced supercapacitor energy-storage devices or electrode materials.
Her ultimate objective is to convert the knowledge gained from researching waste into valuable assets, “particularly energy materials that are eco-friendly and energy-efficient,” Jun concluded.
Chou PI, Gao Z, Jung M, Song, M, Jun YS. Photolysis of disposable face masks facilitates abiotic manganese oxide formation. Journal of Hazardous Materials. Online June 2025. https://doi.org/10.1016/j.jhazmat.2025.138246
This research was funded by the National Science Foundation (CHE-1905077). The work performed at the Center for Nanoscale Materials, a U.S. Department of Energy Office of Science User Facility, was supported by the U.S. DOE, Office of Basic Energy Sciences, under Contract No. DE-AC02–06CH11357.
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