Monday, September 26, 2022

The type of ultraviolet light most effective at killing coronavirus is also the safest to use around people.

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Scientists have long known that ultraviolet light can kill pathogens on surfaces, air and water. UV robots are used to disinfect empty hospital rooms, buses and trains; UV lamps in heating, ventilation and air conditioning systems eliminate pathogens in the building air; UV lamps kill insects in drinking water.

You may have seen UV sticks, UV LEDs, and UV air purifiers advertised as silver bullets for coronavirus protection. While decades of research have examined the ability of UV light to kill many pathogens, there are no set standards for UV disinfectants for coronavirus. These products may work to kill SARS-CoV-2, the virus that causes COVID-19, but they also cannot.

I am an environmental engineer and UV disinfection specialist. In May 2021, my colleagues and I set out to accurately test various UV systems and see which one is most effective at killing – or inactivating – SARS-CoV-2.

When ultraviolet light enters a cell, it breaks the bonds that hold DNA or RNA together.
NASA / David Herring via WikimediaCommons

How does UV light kill the virus?

Light is classified by wavelength – the distance between the peaks of a light wave – and is measured in nanometers. UV wavelengths range from 100 to 400 nanometers – they are shorter in wavelength than violet shades in visible light – and are invisible to the human eye. As the wavelength decreases, the photons of light contain more energy.

UV light at different wavelengths works better than others for inactivating viruses, and this depends on how well the wavelengths are absorbed by the DNA or RNA of the virus. When UV light is absorbed, the photons of the light transmit their energy and damage the chemical bonds of the genetic material. In this case, the virus cannot multiply or cause infection. The researchers also showed that proteins that viruses use to attach to a host cell and initiate infection – such as the spike proteins on coronavirus – are also vulnerable to ultraviolet radiation.

The dose of light also matters. Light can vary in intensity – bright light is more intense and has more energy than dim light. Short-term exposure to bright light can result in the same amount of UV radiation as prolonged exposure to dim light. You need to know the correct dose that can kill coronavirus particles at each UV wavelength.

A man with tanned shoulders sits on the beach.
Sunburns are caused by ultraviolet radiation damaging skin cells.
Ian Hooton / Science Photo Library via Getty Images

Making UV radiation safe for humans

Traditional UV systems use wavelengths around 254 nm. At these wavelengths, light is harmful to human skin and eyes, even in small doses. Sunlight includes ultraviolet light around these wavelengths; Anyone who has ever suffered a severe sunburn knows how dangerous ultraviolet radiation can be.

However, recent studies have shown that at certain UV wavelengths – in particular below 230 nanometers – high energy photons are absorbed by the top layers of dead skin cells and do not penetrate the active layers of the skin, where damage can occur. Likewise, the tear layer around the eyes also blocks these germicidal ultraviolet rays.

This means that with UV light wavelengths below 230 nanometers, people can move more freely while the air around them is disinfected in real time.

Diagram showing a lamp over a water sample containing coronavirus.
The researchers used this setup to test several different UV rays at different doses to see what it takes to kill SARS-CoV-2.
Karl Linden, CC BY-ND

Testing different wavelengths

My colleagues and I tested the five most commonly used UV wavelengths to see which ones are best for inactivating SARS-CoV-2. Specifically, we tested how large a dose is needed to eliminate 90% to 99.9% of the viral particles present.

We ran these tests at a Biosafety Level 3 facility at the University of Arizona, which is built to fight deadly pathogens. There, we tested a variety of UV light sources, including UV LEDs emitting light at 270 and 282 nm, traditional UV lamp bulbs at 254 nm, and a new technology called excited dimer or excimer UV light source at 222 nm. …

To test each device, we added millions of SARS-CoV-2 viruses to a water sample and coated a Petri dish with a thin layer of this mixture. We then shone UV light onto the Petri dish until we reached a certain dose. Finally, we examined the viral particles to see if they could still infect human cells in culture. If viruses could infect cells, then the dose was not high enough. If the viruses did not cause infection, the UV source at this dose successfully killed the pathogen. We have carefully repeated this process for a range of UV doses using five different UV devices.

While all the wavelengths we’ve tested can inactivate SARS-CoV-2 at very low doses, the lowest doses required systems emitting ultraviolet light at 222 nanometers. In our experiment, it took less than 2 millijoules of energy per square centimeter to kill 99.9% of the viral particles. This means it takes about 20 seconds to disinfect the space, receiving low intensity shortwave UV light similar to that used in our test.

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These 222nm systems are nearly twice as efficient as conventional tubular UV lamps, which are often used in UV disinfection systems. But what is important, the winning lamp also turns out to be the safest for humans. With the same ultraviolet light intensity required to kill 99.9% of SARS-CoV-2 in 20 seconds, a person can safely be exposed to 222 nm light for one hour and 20 minutes.

This means that widely available types of UV lamps can be used to safely reduce coronavirus levels in the presence of people.

Best use of existing technologies

Many places or organizations – from the US Air Force to the Space Needle in Seattle and Boeing – are already using or exploring ways to use ultraviolet light in the 222 nanometer range to protect public health.

I believe our results are important because they quantify the exact doses required to achieve various levels of control of SARS-CoV-2, whether it be 90% or 99.9% elimination of viral particles.

Imagine coffee shops, grocery stores, classrooms, restaurants and concert venues are now safe with this technology. And this solution is not only for SARS-CoV-2. These technologies can help protect public health in times of crisis in the future, as well as during periods of relative normalcy, by reducing exposure to everyday viral and bacterial threats.

This article is republished from – The Conversation – Read the – original article.

Nation World News Desk
Nation World News Deskhttps://nationworldnews.com
Nation World News is the fastest emerging news website covering all the latest news, world’s top stories, science news entertainment sports cricket’s latest discoveries, new technology gadgets, politics news, and more.

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