Airborne microplastic can favor spread of COVID-19, study suggests

Researchers at the University of São Paulo analyzed air samples collected near the hospital complex run by its medical school and found that the more plastic they contained, the higher the viral load. The results of the study suggest SARS-CoV-2 binds to microplastic and more easily enters the upper airways and lungs.

By Maria Fernanda Ziegler  |  Agência FAPESP – There is a correlation between levels of airborne plastic microparticles and transmission of SARS-CoV-2. Early this year researchers at the University of São Paulo (USP) in Brazil collected air filters from the vicinity of Hospital das Clínicas (HC), the hospital complex run by the university’s Medical School (FM-USP), and found that the filters with the most microplastic also had the highest viral loads. 

An article on the study published in Environmental Pollution concludes that SARS-CoV-2 aerosols can bind to suspended plastic microparticles, easily entering our upper airways and lungs as we breathe the polluted air. 

The researchers analyzed samples collected from filters placed at three points in busy streets outside the hospital complex to quantify the airborne particles of microplastic and viral RNA.

“Plastic is known to be a carrier of pathogens. SARS-CoV-2 is no exception. Airborne particulate matter attracts or is attracted by the virus and they can remain stuck together. Our study didn’t show this binding at the molecular level, but we demonstrated a mathematical correlation: the higher the level of plastic microparticles, the higher the viral load,” said Thais Mauad, last author of the article and principal investigator for the study. She is a professor in the Pathology Department at FM-USP.

The study was conducted during the postdoctoral research of Luís Fernando Amato-Lourenço and supported by FAPESP via two projects (19/03397-5 and 19/02898-0).

Microplastic results from a long process of decomposition of plastic materials that can last more than 100 years, the researchers explained. Microparticles steadily fall from curtains, furniture and other objects made of plastic. They are so small that they remain suspended in the air, where they may bind to other microparticles (pollutants or pathogens, for example) and be inhaled.

Previous research by the group showed that viruses can remain viable on plastic surfaces for a long time – up to 72 hours in the case of SARS-CoV-2. “This virus is highly transmissible. Our study suggests viral particles can bind to airborne microplastic, enabling the virus to remain viable for longer with more chances to enter the human body,” Mauad said.

The particulate matter found in the air was analyzed under a fluorescence microscope. Its polymeric composition consisting of different types of plastic was characterized by means of infrared microspectroscopy. Viral load was quantified by real-time PCR, the usual diagnostic test for COVID-19.

Twenty-two out of 38 samples collected near the hospital complex tested positive for SARS-CoV-2 (57.8%). Polyester was the most frequent polymer, detected in 80% of the samples.

Ubiquity of plastic

Past research by Mauad and her group also showed that the city of São Paulo has more airborne microplastic indoors than outdoors. The study, published in Science of The Total Environment, was the first to investigate the quantity, chemical composition and morphological characteristics of airborne microplastic in the megacity’s indoor and outdoor air.

Analysis of 20 samples collected outside FM-USP (near Avenida Dr. Enéas Carvalho de Aguiar, a street with heavy traffic in the west of the city) and a further 20 collected from workspaces inside the building showed higher levels of microplastic in the latter, although the microparticles were found in all 40 samples. 

The researchers also detected differences in composition. Polyester was present in all indoor samples but only 76% of outdoor samples, while polyethylene was found in 59% and 67% respectively. Polypropylene was detected in 26% of the indoor samples, and polyethylene terephthalate in 25% of outdoor samples. 

“These results were expected, in light of studies conducted in other cities showing that airborne plastic microparticles are more abundant indoors. This is because we live in a plasticized world. There’s indoor plastic in packaging, furniture, carpets, curtains and clothes. Everything is synthetic, and many indoor environments are poorly ventilated,” said Amato-Lourenço, currently a researcher at the Free University of Berlin in Germany.

Plastic materials are widely used throughout the world. Their degradation into millimetric fragments of microplastic has become a global environmental hazard, contaminating air, soil and aquatic ecosystems, and endangering human health.

Studies of the effects of microplastic on the human organism are incipient, however, as avoiding sample contamination is a major challenge, Mauad noted. “We’re only just starting to investigate the problem. Plastic is in the air and everywhere else. We need to make sure samples aren’t contaminated,” she said.

Plastic in the lungs

An article published last year in the Journal of Hazardous Materials reported a study by the same group, showing for the first time that airborne microplastic particles can be inhaled. The researchers identified and characterized 33 types of microparticle and four types of polymer fiber in 13 out of 20 human lung tissue samples.

The study was conducted in collaboration with the university’s Institute of Chemistry (IQ-USP) and the São Paulo State Institute of Technological Research (IPT). “We succeeded in proving that there’s plastic in people’s lungs. People are inhaling plastic. Other groups had found microplastic in blood and placenta. Plastic has been found in the wild, in marine birds, whales and the ocean deeps. Plastic is starting to be considered a contaminant rather than a type of waste,” said Amato-Lourenço.

Another front on which progress is needed, according to Mauad, is the creation of indicators pointing to the level at which inhalation of microplastic can be harmful to human health.

“Microplastic has a very significant impact on COVID-19, as we saw more recently. Inhaling plastic evidently has consequences for the biology of lung cells because it takes a long time to degrade in nature and in people. We don’t know exactly how much is dangerous to our health when we inhale it, or the kinds of plastic that do the most damage,” she said.

Toxicological analysis is required to find out how plastic degrades and how it interacts with other compounds, but this kind of research is complex. “Plastic becomes a secondary polymer when it degrades, and its behavior and composition are different in the soil, air, water or living organisms. We don’t know whether the quantities detected are too high or tolerable. We have technology to measure the volumes, but we have yet to understand their real impact,” Mauad said.

The article “Airborne microplastics and SARS-CoV-2 in total suspended particles in the area surrounding the largest medical center in Latin America” is at: www.sciencedirect.com/science/article/pii/S0269749121018819?via%3Dihub. 

The article “Atmospheric microplastic fallout in outdoor and indoor environments in São Paulo megacity” is at: www.sciencedirect.com/science/article/abs/pii/S0048969722005423?via%3Dihub. 

The article “Presence of airborne microplastics in human lung tissue” is at: www.sciencedirect.com/science/article/pii/S0304389421010888.