Researchers Find Specific UV Light Wavelength Safe for Humans but Harmful to COVID-19 Virus

A new study from the University of Colorado Boulder informs that a particular wavelength of ultraviolet (UV) light is not only very effective at destroying the virus which causes COVID-19 but can also be safely used in public spaces.

Researchers Find Specific UV Light Wavelength Safe for Humans but Harmful to COVID-19 Virus.
Different wavelengths of UV light, measured here in nanometers, can penetrate the skin down to different layers. The farther down into the skin these wavelengths go, the more harm they can cause. Image Credit: “Far UV-C Radiation: Current State-of Knowledge,” published by the International UV Association in 2021.

The study, published recently in Applied and Environmental Microbiology, is the first to expansively investigate the effects of various wavelengths of UV light on SARS-CoV-2 and other respiratory viruses, including the only wavelength harmless for humans to be exposed to without a shield.

The results, which the authors call a “game changer” for UV light application, could lead to new economical, safe and very effective systems for decreasing viral spread in congested public spaces like concert venues and airports.

Of almost every pathogen we have ever studied, this virus is one of the easiest, by far, to kill with UV light. It takes a very low dose. This indicates that UV technology could be a really good solution for protecting public spaces.

Karl Linden, Senior Study Author and Professor of Environmental Engineering, University of Colorado Boulder

UV light is naturally produced by the sun, and the majority of forms are unsafe for both living beings and microorganisms, like viruses. This light could be absorbed by the genome of an organism, tie knots in it and stop it from breeding. The ozone layer, however, filters out these destructive wavelengths from the sun before they touch the earth’s surface.

Some everyday products, such as fluorescent tube lamps, use manmade UV light, but a coating of white phosphorous on the inside safeguards people from the UV rays.

“When we take that coating off, we can emit those wavelengths, and they can be harmful for our skin and our eyes — but they can also kill pathogens,” said Linden.

Hospitals already utilize UV light technology to sanitize surfaces in spaces where there are no people, employing robots that can stream UV light into patient and operating rooms between uses.

A number of tools currently in the market clean numerous items from cell phones to water bottles with UV light. But safety conventions are still being formulated by the EPA and FDA. Linden warns against employing any personal or “germicidal" devices in which a person can be exposed to UV light.

The results are exceptional, he said, because they are a balance between UV light that is comparatively safe for humans and destructive for viruses, particularly the one that causes COVID-19. 

This can be a game changer for the public use of UV light in indoor spaces.

Karl Linden, Senior Study Author and Professor of Environmental Engineering, University of Colorado Boulder

Death by Exposure

For the research, Linden and his team compared various UV wavelengths alongside each other using uniform methods formulated across the UV light sector.

We thought, let's come together and make a definitive statement on what UV exposure is required to kill off SARS-CoV-2. We wanted to make sure that if UV light is being used to control disease, you're delivering the right dose that's protective of human health and human skin, but also going to be killing off these pathogens.

Karl Linden, Senior Study Author and Professor of Environmental Engineering, University of Colorado Boulder

The chance to perform this kind of work is uncommon, as there are very rigorous safety stipulations required for experimenting with SARS-CoV-2. Therefore, Linden and Ben Ma, postdoctoral scientists in Linden’s research group, teamed up with virologist Charles Gerba at the University of Arizona, at a lab sanctioned to work with the virus and its variants.

The scientists learned that while the virus was quite vulnerable to UV light, a specific wavelength of Far ultraviolet-C, at 222 nanometers, was especially effective. Formed by a krypton chloride excimer lamp, powered by molecules moving between various states of energy, this wavelength is extremely high energy.

Thus, it is able to cause greater viral protein and nucleic acid destruction to the virus compared to other UV-C tools while hindered by the top-most layers of the human skin and eyes — meaning that it has little-to-no harmful health effects at doses that are capable of completely destroying viruses.

“Not only is it safe, it's also the most effective,” said Linden.

The Role of UV Disinfection Today

UV light in different forms has been used extensively since the early 20th century to sanitize air, water and surfaces. As early as the 1940s, it was used to lessen the transmission of tuberculosis in classrooms and hospitals, by directing the light at the ceiling to purify the air as it circulated all over the room.

At present, it is employed not only in hospitals but also in some airplanes and public bathrooms when people are not in those spaces.

In a new white paper published by the International UV Association, “Far UV-C Radiation: Current State-of Knowledge,” which complements the new study, Linden and co-authors debate that this safer wavelength of Far UV-C light could act as a central mitigation measure against the current and future pandemics, along with mask-wearing, better ventilation and vaccination.

Linden envisages systems that could either cycle on and off in indoor spaces to regularly sanitize the air and surfaces, or form an ongoing, invisible barricade between teachers and students, customers and service workers, and people in spaces where social distancing is not viable, to sanitize the air.

Disinfection using UV light can even rival the advantages of better indoor ventilation by providing the same protection of better air changes per hour inside a room. It is also far cheaper to fix UV lights than to upgrade a complete HVAC system.

There is an opportunity here to save money and energy while protecting public health in the same way. It’s really exciting.

Karl Linden, Senior Study Author and Professor of Environmental Engineering, University of Colorado Boulder

Other authors of this paper include Patricia Gundy and Charles Gerba of the University of Arizona; Ben Ma of CU Boulder; and Mark Sobsey of the University of North Carolina, Chapel Hill.

Journal Reference:

Ma, B., et al. (2021) UV Inactivation of SARS-CoV-2 across the UVC spectrum: KrCl* excimer, mercury-vapor, and LED sources. Applied and Environmental Microbiology. 10.1128/AEM.01532-21.

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