June 14 2020 – Varun Sharma
What is Ultraviolet Light?
Ultraviolet light is a component of the electromagnetic spectrum that falls in the region between visible light and X-Rays.
The most natural form of UV light is generated by the sun. About ten percent of sunlight being UV and only about three to four percent penetrating the atmosphere to reach the ground. Of the UV radiation that reaches the earth, 95 percent is made up of UVA and five percent is UVB. No measurable UVC from the sun reaches the earth’s surface. Due to the spectral sensitivity of DNA, only the UVC region demonstrates meaningful germicidal properties. According to LiveSciences, Ultra-violet light also causes black-light posters to glow and is responsible for summer tans — and sunburns.
What is UVC light? How is UVC different from UVA and UVB?
Ultraviolet light is classified into the following three wavelength ranges:
- UVC, from 100 nanometres (nm) to 280 nm
- UVB, from 280 nm to 315 nm
- UVA, from 315 nm to 400 nm
UVC radiation carries a higher amount of energy than UVA or UVB and therefore UVC is more potent in killing bacteria and viruses.
UVC light is germicidal i.e. UVC lighting can kill up to 99.99% of pathogens including bacteria, viruses and other germs. It deactivates the DNA of bacteria, viruses and other pathogens and thus destroys their ability to multiply and cause disease. It does so by causing damage to the nucleic acid of microorganisms by forming covalent bonds between certain adjacent bases in the DNA. The formation of such bonds prevent the DNA from being unzipped for replication, and therefore the organism is unable to reproduce itself. In fact, when the organism tries to duplicate, it dies.
Is UVC effective in Sanitization against Bacteria and Viruses, like Corona Virus?
UV light is highly effective at killing germs. Out of the three main types of UV rays, UVC rays have the shortest wavelength, and therefore highest energy. Science daily quotes "Powerful UVC light has been regularly used to decontaminate surgical tools over time and hospital rooms" This is partly because UVC light can effectively sanitize hard-to-clean nooks and crannies. UVC light also works by destroying the DNA of pathogens, which makes it effective against "superbugs." Killing bacteria and viruses with UV light is especially effective because it kills germs irrespective of drug resistance and without toxic chemicals. It is also effective against all germs, even newly-emerging pathogen strains.
What Scientific Evidence exists that UVC Kills Bacteria and Viruses?
A 2020 study by a team of Columbia University researchers shows that UVC radiation kills airborne viruses, like COVID-19, without damaging human skin or eyes.
Another study funded by the Center for Disease Control and Prevention (CDC) Epicenters Program and published in Infection Control and Hospital Epidemiology, supports and expands on previously published studies confirming the effectiveness of an automatic UVC emitting device to kill the pathogens.
The study data concluded that an automatic UVC system capable of delivering a measured and consistent UVC dose significantly improved the terminal disinfection of patient areas in hospitals.
A 2014 study tested the efficacy of portable UVC wands and found that they killed 100% of commonly-found bacteria within five seconds and inactivated 90% of spore-forming bacteria, which are harder to kill, within 40 seconds. The study found that, compared to a toothbrush that had not been treated with ultraviolet light, the UV-light got rid of 86% more colony-forming units of S. salivarius, lactobacilli, E. coli and other bacteria. These bacteria can cause strep throat, digestive problems, and a number of other illnesses.
A 2016 study comparing the use of UVC Light and Chemicals for Disinfection of Surfaces in Hospital Isolation Units, showed that UVC disinfection significantly reduced the number of bacteria on surfaces directly or indirectly exposed to UVC to a really low number.
UVC light is what's used by sanitizers to kill or inactivate microorganisms by destroying and disrupting their nucleic acids. If the device is properly tested and properly used, it works to kill pathogens, but something that power also has the potential to harm the skin. Some potential problems? It can cause burns and is a known carcinogen (as is all UV light).
Far-UVC technology is an emerging disinfection method that directly kills microorganisms using light. In contrast with conventional UV sterilization, farUVC light has antimicrobial capabilities without apparent harm to mammalian cells.
How does UVC Work?
UVC light is germicidal i.e. UVC lighting can kill up to 99.99% of pathogens including bacteria, viruses and other germs. It deactivates the DNA of bacteria, viruses and other pathogens and thus destroys their ability to multiply and cause disease. It does so by causing damage to the nucleic acid of microorganisms by forming covalent bonds between certain adjacent bases in the DNA. The formation of such bonds prevent the DNA from being unzipped for replication, and therefore the organism is unable to reproduce itself. In fact, when the organism tries to duplicate, it dies. The absorption of UVC energy forms new bonds between nucleotides, creating double bonds or “dimers.” The dimerization of molecules, particularly thymine, is the commonest sort of damage incurred by UVC light in microorganisms. Formation of thymine dimers within the DNA of bacteria and viruses prevents duplication and the ability to infect.
What are the Sources of UVC?
UVC radiation is available to us through artificial sources, such as UVC LEDs or mercury lamps. The University of Liverpool Archive explains that Germicidal UVC is delivered by a mercury-vapour lamp that emits UV rays at the germicidal wavelength. Mercury vapour emits at 254nm. Many known UV bulbs use special transformers to ensure even electrical flow to the bulbs so the correct wavelength is maintained.
There are several different types of germicidal lamps:
- Low-pressure UV lamps offer high efficiencies (approximately 35% UVC) but lower power, typically 1 W/cm³ power density.
- Amalgam UV lamps are a high power version of low-pressure lamps.
They operate at higher temperatures and have a lifetime of up to 16,000 hours. Their efficiency is slightly lower than that of traditional low-pressure lamps (approximately 33% UVC output) and power density is approximately 2-3 W/cm³.
Medium-pressure UV lamps have a broad and pronounced peak-line spectrum and a high radiation output but lower UVC efficiency of 10% or less. Typical power density is 30 W/cm³ or greater.
Another study examines the use of far-UVC light generated from a laser source to be delivered via fibre optics to an optical diffuser element for bactericidal applications.
Princeton university outlines the following as the most likely sources of UV light in the lab setting include:
- Transilluminators (used to visualize DNA bands in gels)
- Germicidal lamps in biological safety cabinets
- Handheld UV lamps
- UV Lasers
- Blue-emitting LEDs used for photocatalysis (some of the emissions fall into the UV range)
- Examples include plasma sources for spectroscopy research, collateral and plasma radiation from cutting and welding processes
Is UVC Approved for Surface Disinfection?
The center for disease control (CDC) has said that the approved use of UVC radiation for health care purposes (i.e., operating rooms, isolation rooms, and biological safety cabinets) is limited to the destruction of airborne organisms or inactivation of microorganisms on surfaces alone.
The International Ultraviolet Association concurs with the CDC, reporting that inactivation of viruses with UVC light has been "demonstrated only under controlled conditions in the laboratory," and that "the effectiveness of UVC light in practice depends on factors such as the exposure time and the ability of the UVC light to reach the viruses in water, air, and in the folds and crevices of materials and surfaces." The Association summarises:
- Don't use any UV light devices directly on your skin.
- Be careful about using UV light devices on in-home surfaces.
- Do your research before going to establishments that have installed UV light fixtures.
- And definitely do not try to get any form of UV light (or any disinfectant, for that matter) inside of your body.
Rising International interest in the use of ultraviolet radiation (UVR) to manage the risk of COVID-19 transmission has made the International Commission on Illumination (CIE) to publish a Position Statement (PS) following on from the two CIE publications related to UVC applications that were recently made freely available.
The CIE summarized their stand with the following points:
- UVC is extremely useful in the disinfection of air and surfaces or sterilization of water. However, CIE and WHO warns against the use of UV disinfection lamps to disinfect hands or any other area of skin (WHO, 2020).
- UVC can be very hazardous to humans and animals and should only be used in carefully controlled circumstances using well-designed products, ensuring that the limits of exposure as specified in ICNIRP (2004)and IEC/CIE (2006) is not exceeded. However, the risk of skin cancer from devices that emit only UVC is considered negligible.
- UVC can cause photodegradation of materials and this should be considered where susceptible materials, such as plastics, are in the exposed environment.
- More research is urgently needed on the safety aspects of novel UVC sources, especially with respect to safety thresholds to avoid photokeratitis (”sunburn” of the cornea).
- For proper UVR assessment and risk management, appropriate UVR measurements are essential.
- UVC products that are aimed at general consumers may not be safe for use or may not be effective for disinfection.
Where is UVC Used?
1. Activation of The Immune System
Many scientific studies have depicted the use of UVC for the activation of components of the immune system and to foster an inflammatory response by a variety of mechanisms. For example, UVC radiation can:
- Directly activate keratinocytes and other cells to release inflammatory mediators such as cytokines and chemokines.
- Cause redistribution and release of sequestered autoantigens from UV-damaged cells.
- Alter self-proteins to make them more immunogenic.
- Chemically alter systemically administered medications whose distribution includes the skin.
2. Disinfection of air in the production area
Clean and fresh air is necessary for the food processing area.
UV technology can be used for preventing the spread of airborne diseases by inhibition of airborne pathogenic microorganisms in the field of production, packaging, cooling, storage and ripening. For this purpose, low-pressure mercury vapour lamps are successfully used as UV light sources. The efficiency of this process depends on the volume of the area and the power of the UV lamp.
3. Disinfection of water used during processing
UVC light has been used to disinfect water for several years and has become a successful process that eliminates several types of microorganisms.
UVC technology is a good alternative to chlorine disinfection.
In the dairy industry, it is possible to use the UV systems for the disinfection of drinking water, process water, wastewater and brine.
4. Packaging materials
In the food industry, the use of UV light for decontamination of the packaging material is becoming widespread. The number of microorganisms on the surfaces of packaging materials such as boxes, cartons, foils, films, wrappings, containers, bottles, caps, closures and lids can be reduced or eliminated by applying the appropriate UV light doses. These packages can be treated with UV light before closing or filling the lid or the packaged food will be exposed to UVC light.
5. Water Disinfection
UV light applications are used to create safe water in pools and spas and eliminate the need for chlorine’s harmful and irritating effects. They are also used in aquaculture, life sciences, and water treatment processes (treating ship ballast water, wastewater, drinking water purification, and water reclamation).
Traditional ways to treat and disinfect water can be unhealthy, hazardous, and environmentally toxic. UV water treatment is safe and environmentally friendly, and, in some cases, more effective.
- Pools & Spas
- Aqua Culture
- Life Sciences
- Water Treatment (wastewater, municipal and residential, drinking water, industrial & commercial process water, and water reclamation)
- Ballast Water in Ships
UVC is widely used for the surface sterilization of many foods, including fruits, vegetables, and processed foods, as well as equipment.
What are the side effects of UVC?
Burning by UVC radiation will occur if too high a dose is used.
Burning can usually be avoided by careful assessment of the minimal erythemal dose before initiating treatment and by avoiding further exposure when signs of erythema from a previous dose are still present.
2. Premature ageing of the skin
Chronic exposure to UVC radiation, including sunlight, is related to premature ageing of the skin. This effect referred to as actinic damage, causes the skin to possess a dry, coarse, leathery appearance with wrinkling and pigment abnormalities. It is thought that these changes are primarily the results of the collagen degeneration that accompanies long-term exposure to UV radiation.
In rare instances of prolonged direct exposure to UVC light, temporary eye and skin damage has been exhibited, like cornea injury (sometimes mentioned as “welder’s eye”) although this generally heals after a couple of days. Therefore, safety recommendations with UVC LEDs include protecting skin (in particular open wounds) and, most significantly, the eyes from UVC radiation. The EU health agency’s safety guidelines on the use of UVC sources can be found here.
Most of the knowledge regarding the carcinogenic effect of UV radiation concerns the effect of prolonged or intense sunlight exposure. Prolonged exposure to UV radiation, as occurs with excessive exposure to sunlight, is taken into account to be a serious risk factor for the event of basal cell and epithelial cell carcinoma and malignant melanoma. A review of the literature on the carcinogenicity of UV phototherapy, with and without psoralens, concluded that the therapeutic use of UVB features a low risk of manufacturing cutaneous cancers, except possibly on the skin of the male genitals; however, there's a particular cutaneous carcinogenic risk from PUVA treatment when oral-systemic psoralens medications are used.
The increased cancer risk with PUVA may be a result of the carcinogenicity of the psoralens or maybe a response specific to the wavelength of UVC radiation used for this treatment application. PUVA treatments can also exacerbate the consequences of previous exposure to carcinogens.
4. Damage to The Eyes
UVC radiation can damage the superficial tissues of the eye and care must be taken to avoid excessive exposures of the eyes. We should note, though, that while eye exposures to UVC may cause extreme discomfort, the symptoms usually subside within a rather short time, and no evidence of any malignant effects has ever been noted.