UV light can be broadly classified into the higher energy waves of the EM spectrum.
The sun emits three different types of UV radiation: UVA, UVB, and UVC. The three types of UV radiation are classified according to their wavelength/frequency. The higher the frequency, the higher the energy and dangerous the radiation.
Let’s have look at what World health organization has to say about UV radiation exposure.
The best known acute effect of excessive UV exposure is ‘erythema’, the familiar skin reddening termed sunburn. UVA rays, which account for 95 percent of radiation that reaches the earth’s surface, cause wrinkles, “sun spots,” and other types of premature aging. A further, less obvious adaptive effect is the thickening of the outermost layers of the skin.
Medium-wavelength UVB is very biologically active but cannot penetrate beyond the superficial skin layers. It is responsible for delayed tanning and burning; in addition to these short-term effects it enhances skin aging and significantly promotes the development of skin cancers such as non-melanoma skin cancers, malignant melanoma.
Most solar UVB is filtered by the ozone layer. WHO estimates suggest that up to 20 percent of cataracts may be caused by overexposure to UVB radiation and are therefore avoidable. UVB radiation also appears to reduce the effectiveness of the immune system.
However one need not panic, seeing the frightening effects of UV radiation in our system. Only prolonged exposure or acute high doses such as unprotected viewing of a solar eclipse pose a significant risk; on the contrary, a minimum amount of dose is essential for the synthesis of a type of Vitamin (vitamin D3) in our body.
Among the three types of UV radiation mentioned, UVC is by far the most energetic – having a higher frequency (shorter wavelength) and the most damaging. Because of the higher energy, they react with ozone high in our atmosphere and don’t reach the ground at all.
This article tries to explore how this lethality of the UVC can be redirected to our fight against SARS COV2 aka the novel Corona Virus which causes COVID19.
Ultraviolet light kills microbes by a completely different mechanism from the way the drugs kill them, so ultraviolet light is just as capable of killing a drug-resistant microbe as any other microbe.
In fact the potential use of ultraviolet light for airborne disinfection is by no means new and was first demonstrated more than 80 years ago.
Ultraviolet light destroys cells by damaging their DNA. The light initiates a reaction between two molecules of thymine, one of the bases that make up the DNA, the DNA can repair this, but a prolonged enough exposure can override the repair mechanism making the DNA impaired.
If the damage is moderate, cancer will result, if it is extensive apoptosis will result- the programmed cell death.
However our villain of the day, the Coronavirus, doesn’t have a DNA, it has an RNA.
The exact molecular mechanism how UV light affects RNA is not fully understood, (although UVC irradiation has been shown to induce mainly pyrimidine dimers and uridine hydrates and, less frequently, unspecific chain breaks), but the damage to the RNA and the virus inactivation is categorically proven.
UVC light can inactivate aerosolized viruses like the SARSCOV2; In this context, we should remember that Corona Virus is suspected to be transmitted airborne in addition via respiratory droplets.
However, the use of UVC as a germicide in public spaces are severely limited due to the health hazards, as mentioned above.
This severe limitation of UV has been overcome by the new kid in the corner-‘The far UVC’
Far-UVC light has a shorter wavelength, higher frequency, higher energy than UV-C, making its effect on microorganisms different from the regular germicidal UV.
Far UVC has to be generated artificially, since none of those occurring naturally penetrate the ozone layer.
We do have the necessary technology to make this kind of radiation in the spectrum.
A study by David Welch et.al from Colombia University in paper details how the spectrum, of far UVC can be used to effectively counter microbial growth with zero harm to the human tissue.
Far UVC light having a wavelength of 222 nanometers and a comparatively low dose of 2 milli Joules/ Cm3 is shown to inactivate all aerosolized SARS-COV-2.
The coolest thing about this particular spectrum of ultraviolet light (207–222 nm) is that efficiently inactivates the virus without any harm to exposed human cells.
This particular wavelength cannot penetrate the outer layer of the skin, even the thickness of tear layer on the outer surface of the eye is larger than the ability of far UVC light to penetrate; neither of which contain living cells.
Viruses are typically of micron or smaller dimensions, far-UVC light can still effectively penetrate and inactivate them by messing with their RNA mechanisms as discussed above.
This study has been reported by the Nature Magazine.
This ability of the far UVC light makes it the most potent candidate in using in Public spaces where the virus can possibly linger around and spread.
Airports, Railway stations, Bus Stands, Schools, Theatre halls can be potentially and safely be irradiated without causing cellular damage to humans which hazards inherent with conventional germicidal UV lamps.
This is a powerful, yet inexpensive approach for prevention of airborne viral infections and has the potential to revolutionise public health.
India is also geared towards using Ultraviolet light in its fight against COVID19.
Defence Institute of Physiology & Allied Sciences (DIPAS) and Institute of Nuclear Medicine & Allied Sciences (INMAS), DRDO laboratories in Delhi have designed and developed Ultraviolet C Light based sanitisation box and hand held UV-C (ultraviolet light with wavelength 254 nanometres) device.
The UV-C box is designed for disinfecting personal belongings like mobile phone, tablets, purse, currency, cover of office files, etc.
The hand-held device having eight-watt UV-C lamp disinfects office and household objects like chairs, files, postal delivered items etc.
This measure can reduce the transmission of Coronavirus in office and public environment which is required to work in all conditions.
Southern Naval Command (SNC), has also designed and fabricated an Ultra Violet Disinfection Unit, at Kochi, as part of its efforts to contain the spread of COVID – 19.
The unit built at a cost of Rs 5000/-, comprises a metallic container, two UV lamps one each on opposite side, with aluminium foil pasted on its internal surfaces to facilitate UV radiation to reach every corner of the chamber.
The efficacy of the equipment has been validated by a team of medical experts from SNC.
The above-mentioned devices use regular Germicidal UV and human contact is nil. The technique usage and applications of far UVC is under active research internationally.
Until, International Protocols are established for the usage of far UVC , exposure to any kind of ultraviolet radiation by human tissue is hazardous and be avoided.
DV Vinod Kumar
Deputy Director(PIB Goa)