Research team sheds light on microplastics pollution

A Duke Kunshan University professor-student team has investigated how face masks used widely as protection against COVID-19 degrade in ocean water.

The research, conducted by Professor Weiwei Shi and Class of 2023 undergraduate student Jiayi Shen, has been published in the peer-reviewed scientific journal Langmuir. It offers insight into ocean pollution caused by various forms of commercial face masks.

“During the COVID-19 pandemic, face masks became a feature of daily life for many people,” said Shi, assistant professor of material science at DKU. “While the pandemic may have faded from public attention, the disposal of face masks remains a significant issue, especially in terms of plastics pollution.”

Weiwei Shi, assistant professor of material science at DKU

After the World Health Organization declared the COVID-19 outbreak to be a global pandemic in March 2020, face masks became one of the primary means for stopping the spread of the airborne disease. While their use may have helped to slow the pandemic’s progression, it also led to a surge in global plastic production, from 360m million tons in 2018, to 698 million tons in 2020, according to research, which Shi and Shen refer to in their paper. Much of this increase was due to a rapid rise in the production of face masks, which, although it has dropped since, remains higher than pre-pandemic levels.

“Improper management and disposal of many of these face masks has exacerbated environmental pollution,” said Shi. “This is especially dangerous in the marine environment, where the degradation of face masks could leave behind minute plastic particles called microplastics that absorb pollutants and can be easily ingested by marine organisms, causing severe damage to biological systems.”

Shi and Shen’s research measured how rapidly and to what extent different face masks degrade in ocean water, shedding light on how dangerous they can be to the marine environment. They did this by taking seven different types of commercial face masks, including common surgical ones, N95 masks, PET masks, PU masks, cotton masks, nylon masks and silk masks, and subjecting them to a marine-like environment. This was done by submerging the masks in substitute ocean water under UV lamps and a hot plate turned on and off throughout the day to mimic the natural weathering process as it would take place in the sea. A suite of structural and chemical characterization techniques was also applied to the pristine and treated masks to probe the treatment impact.

DKU student Jiayi Shen, who is due to start a master’s degree at Columbia University in the United States

After 14 days of weathering, weight changes before and after the process were compared to determine to what extent the masks had degraded. The test found PET masks degraded most, followed by the N95 mask, and then the surgical, nylon and silk masks. For the PU and cotton masks there was almost no degradation.

The microstructures of each layer of the masks were then imaged using a scanning electron microscope to check the morphology of the fibers before and after the weathering process. This was followed by x-ray photoelectron spectroscopy analysis of each layer of mask and other tests to gain a more detailed picture of how the masks had degraded in their chemical species and molecular structure.

The research found that the chemical structure and composition of the masks did not change significantly, possibly due to the relatively short artificial aging process, suggesting that degradation takes considerably longer. However, microparticles were found on all the masks, which could be a potential source of environmentally damaging microplastic pollution in the ocean.

“Our findings highlight the potential danger of all types of face masks,” said Shi. “It shows that as they degrade, they are likely to become a source of microplastics and enter the biological web. Ultimately, they could also be damaging to human health, as they will potentially be present in the fish and other seafood we eat.”

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