Article

The effect of 222 nm UVC phototesting on healthy volunteer skin: A pilot study

Authors:
  • Toxarus Consulting
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Abstract

Background Frequent topical antiseptic use to hands is now common in healthcare and other work environments. Inevitably, the use of such antiseptics will present an occupational risk for irritancy and allergic dermatitis. New, less irritant and even non-chemical antimicrobial approaches are under investigation.MethodsA Sterilray disinfectant source (222 nm) conventionally used to sterilise equipment and work surfaces was assessed for tolerability in human skin. Using an escalating dosage study methodology, four skin phototype I and II healthy volunteers had their minimal erythema dose (MED) determined. Punch biopsies of irradiated sites were stained for cyclobutane pyrimidine dimers (CPD). The degree of CPD was compared with that in biopsies from unexposed skin and from areas exposed to UVB (280-315 nm) radiation.ResultsCalibrated spectral measurements revealed emission at a peak wavelength of 222 nm with 97% emission at wavelengths less than 250 nm. At low doses below the threshold bacteriostatic effect, the source was capable of inducing both erythema and CPD formation in human skin. In two individuals, cells in the basal layer were not shielded by the overlying tissue.Conclusion The source showed an erythemogenic or CPD potential at lower doses than those required to reach the reported threshold bacteriostatic effect.

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... However, although the peak emission of KrCl* lamps is 222 nm, longer wavelengths emitted by these lamps can potentially cause harm to the skin. It was hypothesised by Woods et al. that erythema on the backs of Fitzpatrick Skin Type (FST) I and II study subjects was caused by these longer wavelengths, and not the dominant 222 nm peak [11]. ...
... The effective irradiances for two KrCl* excimer sources were calculated, one with an optical filter to reduce There have been a number of measurements of Far-UVC induced erythema on human skin, both for filtered Far-UVC lamps [10] and for unfiltered lamps [11]. Eadie et al. delivered an unweighted radiant exposure of 1500 mJ cm -2 from a filtered lamp without inducing visible skin erythema [10]. ...
... Eadie et al. delivered an unweighted radiant exposure of 1500 mJ cm -2 from a filtered lamp without inducing visible skin erythema [10]. By contrast Woods et al. did induce visible erythema at an unweighted radiant exposure of 40 mJ cm -2 using an unfiltered lamp [11]. In the following we relate these two observations to the recommended maximum exposures that can be derived from the various ICNIRP and ACGIH recommendations discussed above and illustrated in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t Specifically, the spectral measurement of each lamp (Fig. 2) was combined with each of the three spectral weighting functions (Fig. 1), and the results compared with the "universal" recommended maximum weighted radiation exposure of 3 mJ cm -2 per 8 hours. ...
Article
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Ultraviolet-C (UVC) radiation can effectively inactivate pathogens on surfaces and in the air. Due to the potential for harm to skin and eyes, human exposure to UVC should be limited within the guideline exposure limits produced by the International Commission on Non-Ionising Radiation (ICNIRP) or the American Conference of Governmental Industrial Hygienists (ACGIH). Both organisations state an effective spectrally weighted limit of 3 mJ cm-2 although the spectral weighting factors of the two organisations diverged following a revision of the ACGIH guidelines in 2022.. Using existing published human exposure data, the effective spectrally weighted radiant exposure was calculated for both unfiltered and filtered, to reduce UV emissions above 230 nm, krypton-chloride (KrCl*) excimer lamps. The effective radiant exposure of the filtered KrCl* lamp was greater than 3 mJ cm-2 when applying ICNIRP or either of the revised ACGIH spectral weightings. This indicates that both guidelines are appropriately conservative for this specific lamp. However the effective radiant exposure of the unfiltered KrCl* lamp was as low as 1 mJcm-2 with the revised ACGIH weighting function that can be applied to the skin if eyes are protected. Erythema has therefore been directly observed in a clinical study at an exposure within the revised ACGIH guideline limits. Extrapolating this information means that a mild sunburn could be induced in Fitzpatrick Skin Types I and II if that particular ACGIH weighting function were applied and an individual received an effective 3 mJcm-2. Whilst it is improbable that such an effect would be seen in current deployment of KrCl* lamp technology, it does highlight the need for further research into skin sensitivity and irradiance-time reciprocity for UVC wavelengths.
... However, although the peak emission of KrCl* lamps is 222 nm, longer wavelengths emitted by these lamps can potentially cause harm to the skin. It was hypothesised by Woods et al. that erythema on the backs of Fitzpatrick Skin Type (FST) I and II study subjects was caused by these longer wavelengths, and not the dominant 222 nm peak [11]. For context, 1 minimal erythema dose (MED) on the back is approximately equal to 1 MED on the face and neck, and 2-2.5 MEDs on the arm [12]. ...
... The effective irradiances for two KrCl* excimer sources were calculated, one with an optical filter to reduce emissions above 230 nm (SafeZone UVC, Ushio Inc., Tokyo, Japan) and the other without such a filter (Sterilray™ Health Environment Innovations, Dover, New Hampshire, USA). Spectral irradiances from 200-400 nm were taken from Woods et al. and Eadie et al. [10,11], which were measured in each study using a calibrated double grating spectroradiometer with traceability to national standards (IDR300, Bentham Instruments Ltd, UK). A normalised comparison is shown in Fig. 2. Each spectral irradiance measurement was weighted for the S(λ) (ICNIRP and ACGIH-2021), S(λ) (ACGIH-2022), and S' (λ) (ACGIH-2022) spectral weighting factors. ...
... There have been a number of measurements of Far-UVC induced erythema on human skin, both for filtered Far-UVC lamps [10] and for unfiltered lamps [11]. Eadie et al. delivered a radiant exposure of 1500 mJ cm -2 from a filtered lamp without inducing visible skin erythema [10]. ...
Preprint
Full-text available
This work considers how recent changes to the ACGIH TLV impact the hazard assessment of two Far-UVC sources - filtered and unfiltered - in the context of the outcomes of two in-human studies.
... Some reports have demonstrated that the bandpass filter reduces the harmful effect of UVC emitted from KrCl excimer lamps by reducing CPD formation in the epidermis of human subjects and a human skin model [11,13,16]. However, the effectiveness of a bandpass filter attached to a KrCl lamp has not been verified in animal experiments. ...
... Using a 3D human skin model, Buonanno et al. reported that radiant exposures as low as 23 mJ/cm 2 from the UVC from unfiltered lamp radiation markedly increased CPD formation [13]. Woods et al. demonstrated that UVC from unfiltered lamp UVC exposure induced CPD formation in not only suprabasal keratinocytes but also germinal keratinocytes in the basal layer in human subjects [16]. However, the effect of UVC from an unfiltered lamp on CPD formation has not been reported in animal experiments. ...
... the lamp spectrum contains 10% of longer-wavelength 230~280-nm UVC, 3% of UVB and 4% of UVA [15]. It has been reported that UVC radiation emitted by an unfiltered KrCl lamp penetrates to the stratum corneum and causes DNA damage in keratinocytes in human skin and a 3D human skin model [13,16]. In the present study, the bandpass filter reduced 230-280-nm UVC and UVB as shown in Fig 1, while the UV radiation emitted by the KrCl lamp without a bandpass filter, which includes UVC and UVB, elicited a harmful effect in mice. ...
Article
Full-text available
It has been reported that 222-nm ultraviolet C (UVC) exerts a germicidal effect on bacteria and viruses as well as UV radiation emitted from a conventional germicidal lamp but is less toxic to the mammalian cells than that from a germicidal lamp. An excimer lamp filled with krypton chloride (KrCl) gas principally emits 222-nm UVC. However, the lamp also emits a wide band of wavelengths other than 222 nm, especially UVC at a longer wavelength than 222 nm and ultraviolet B, which cause DNA damage. There are some reports on the critical role of bandpass filters in reducing the harmful effect of UVC emitted from a KrCl excimer lamp in a human skin model and human subjects. However, the effectiveness of a bandpass filter has not been demonstrated in animal experiments. In the present study, mice were irradiated with UVC emitted from a KrCl excimer lamp with or without a bandpass filter. UVC emitted from an unfiltered KrCl lamp at doses of 50, 150 and 300 mJ/cm2 induced cyclobutyl pyrimidine dimer (CPD)-positive cells, whereas UVC emitted from a filtered lamp did not significantly increase CPD-positive cells in the epidermis. The present study suggested that the bandpass filter serves a critical role in reducing the harmful effect of emission outside of 222 nm to mouse keratinocytes.
...  A Krypton Chloride (KrCl) excimer lamp without restriction of wavelengths above 230 nm (Woods et al. 2015) (11). Two different sunlight exposures were chosen to represent two different scenarios: a moderate UV exposure that is typical of early morning sunshine in a temperate climate from Spring to Autumn and a high UV exposure in a Mediterranean climate (13). ...
...  A Krypton Chloride (KrCl) excimer lamp without restriction of wavelengths above 230 nm (Woods et al. 2015) (11). Two different sunlight exposures were chosen to represent two different scenarios: a moderate UV exposure that is typical of early morning sunshine in a temperate climate from Spring to Autumn and a high UV exposure in a Mediterranean climate (13). ...
... A just perceptible reddening of the skin, defined as the Minimal Erythema Dose (MED), has previously been demonstrated to happen with an unfiltered KrCl lamp at 40-50 mJcm -2 (approximately twice the current TLV). The MED in Fitzpatrick Skin Type I is approximately equivalent to 2 -3 Standard Erythema Dose (SED) which can be achieved in 33 -50 minutes of sunlight exposure when the UV Index is 4(11). In terms of erythema, not CPD, this would equate 10 minutes of sunlight exposure to between 3 -5 hours of an unfiltered KrCl lamp. ...
Article
Full-text available
This study aims to investigate, with computer modeling, the DNA damage (assessed by cyclobutane pyrimidine dimer (CPD) formation) from far‐ultraviolet C (far‐UVC) in comparison with sunlight exposure in both a temperate (Harwell, England) and Mediterranean (Thessaloniki, Greece) climate. The research utilizes the published results from Barnard et al. [Barnard, I.R.M (2020) Photodermatol. Photoimmunol. Photomed. 36, 476–477] to determine the relative CPD yield of unfiltered and filtered far‐UVC and sunlight exposure. Under current American Conference of Governmental Industrial Hygienists (ACGIH) exposure limits, 10 minutes of sunlight at an ultraviolet (UV) Index of 4 – typical throughout the day in a temperate climate from Spring to Autumn ‐ produces equivalent numbers of CPD as 700 hours of unfiltered far‐UVC or more than 30,000 hours of filtered far‐UVC at the basal layer. At the top of the epidermis these values are reduced to 30 and 300 hours respectively. In terms of DNA damage induction, as assessed by CPD formation, the risk from sunlight exposure greatly exceeds the risk from far‐UVC. However the photochemistry that will occur in the stratum corneum from absorption of the vast majority of the high energy far‐UVC photons is unknown, as are the consequences.
... Far-UVC (200 -220 nm) has been proposed as an effective disinfection radiation that is safe to humans 5 . In 2014, Woods et al. undertook a first-in-person study to assess the effect on skin of a 222 nm UVC emitting device (Sterilray disinfectant wand, Healthy Environment Innovations, Dover, NH, USA) 6 . The study concluded that erythema was induced at radiant exposures lower than required for the threshold bacteriostatic effect. ...
... Direct CPD formation was also observed in both the suprabasal (all four volunteers) and basal layer (2 out of 4 volunteers) of the volunteer skin. Woods et al. hypothesised that a small amount of longer wavelength UVC radiation above 250 nm (<3%) may be contributing to the observed effects 6 . We wished to determine why these results contrast with other published studies investigating far-UVC sources 2,5 . ...
... Irradiance of the far-UVC source investigated by Woods et al.6 and MCRT simulated fluence incident on the upper and mid epidermis and basal layer. ...
Preprint
Full-text available
Monte Carlo modelling demonstrating the depth of penetration in the skin of UVC wavelengths used in disinfection. Modelling suggests that previously published evidence indicating harm to the skin from a UVC source was most likely caused by longer wavelength UVC and UVB and not the primary shorter wavelength UVC peak.
... The recent interest in applying Far UV-C to germicidal applications has stimulated investigations of health and safety of Far UV-C. Collectively, the studies demonstrate that exposures of both the eye and skin at wavelengths less than approximately 230 nm are substantially safer than longer UV-C wavelengths (Barnard et al., 2020;Buonanno et al., 2017Buonanno et al., , 2013Buonanno et al., , 2016Buonanno et al., , 2021Cadet, 2020;Fukui et al., 2020;Hanamura et al., 2020;Hickerson et al., 2021;Kaidzu et al., 2019;Woods et al., 2015;Yamano et al., 2020). The experimental data are expected from the biophysical knowledge that Far UV-C radiation has much shorter penetration depths than longer wavelength UV-C radiation (Finlayson et al., 2021). ...
... All but one of the ten recently published experimental, peer-reviewed safety studiesboth in vitro and in vivoof the effects of Far UV-C radiation on human skin and hairless mouse skin showed no measurable negative impacts (Barnard et al., 2020;Buonanno et al., 2017Buonanno et al., , 2016Buonanno et al., , 2021Cadet, 2020;Fukui et al., 2020;Hanamura et al., 2020;Hickerson et al., 2021;Yamano et al., 2020) despite including much larger doses than would be permitted in a human exposure scenario. The one published study (Woods et al., 2015) that did show evidence of skin Figure 6. Effects of UV radiation on human tissues. ...
Article
Full-text available
Far UV-C, informally defined as electromagnetic radiation with wavelengths between 200 and 230 nm, has characteristics that are well-suited to control of airborne pathogens. Specifically, Far UV-C has been shown to be highly effective for inactivation of airborne pathogens; yet this same radiation has minimal potential to cause damage to human skin and eye tissues. Critically, unlike UV-B, Far UV-C radiation does not substantially penetrate the dead cell layer of skin (stratum corneum) and does not reach germinative cells in the basal layer. Similarly, Far UV-C radiation does not substantially penetrate through corneal epithelium of the eye, thereby preventing exposure of germinative cells within the eye. The most common source of Far UV-C radiation is the krypton chloride excimer (KrCl*) lamp, which has a primary emission centered at 222 nm. Ozone production from KrCl* lamps is modest, such that control of indoor ozone from these systems can be accomplished easily using conventional ventilation systems. This set of characteristics offers the potential for Far UV-C devices to be used in occupied spaces, thereby allowing for improved effectiveness for inactivation of airborne pathogens, including those that are responsible for COVID-19. © 2022 The Author(s). Published with license by Taylor & Francis Group, LLC.
... The promising reports on the effects of far-UVC on cells, tissue and pathogens -including coronaviruses -give reason to hope that this radiation might become a very important tool in the fight against airborne pathogens and especially SARS-CoV-2 in the current pandemic. However, there still seems to be only a very limited number of animal or human studies; among them, there exists at least one investigation describing the formation of erythema and cyclobutane pyrimidine dimers (CPD) after 222 nm irradiation [19]. The aim of this study was to collect and analyze the results published to date on the impact of far-UVC in the spectral region between approximately 200 and 230 nm on pathogens, animal and human cells, skin and eyes, as well as to find further information regarding the safety of this kind of radiation and acquire data to determine the necessary doses for pathogen reductions. ...
... In fact, even 100 mJ/cm 2 , the dose necessary to inactivate all listed microorganisms by several orders of magnitude, seems to be harmless according to the majority of investigations. Unfortunately, these investigations stand in contrast to at least five studies in which cell lesions were observed at much lower doses [19], [36], [37], [38], [39], in two of these even for doses below 1 mJ/cm 2 [36], [37]. ...
Article
Full-text available
Background: The ongoing coronavirus pandemic requires new disinfection approaches, especially for airborne viruses. The 254 nm emission of low-pressure vacuum lamps is known for its antimicrobial effect, but unfortunately, this radiation is also harmful to human cells. Some researchers published reports that short-wavelength ultraviolet light in the spectral region of 200–230 nm (far-UVC) should inactivate pathogens without harming human cells, which might be very helpful in many applications. Methods: A literature search on the impact of far-UVC radiation on pathogens, cells, skin and eyes was performed and median log-reduction doses for different pathogens and wavelengths were calculated. Observed damage to cells, skin and eyes was collected and presented in standardized form. Results: More than 100 papers on far-UVC disinfection, published within the last 100 years, were found. Far-UVC radiation, especially the 222 nm emission of KrCl excimer lamps, exhibits strong antimicrobial properties. The average necessary log-reduction doses are 1.3 times higher than with 254 nm irradiation. A dose of 100 mJ/cm2 reduces all pathogens by several orders of magnitude without harming human cells, if optical filters block emissions above 230 nm. Conclusion: The approach is very promising, especially for temporary applications, but the data is still sparse. Investigations with high far-UVC doses over a longer period of time have not yet been carried out, and there is no positive study on the impact of this radiation on human eyes. Additionally, far-UVC sources are unavailable in larger quantities. Therefore, this is not a short-term solution for the current pandemic, but may be suitable for future technological approaches for decontamination in rooms in the presence of people or for antisepsis.
... These laboratory data are being used commercially to intensively promote and sell far-UVC systems to the global public. At the beginning of the COVID-19 pandemic, the only published study investigating a far-UVC system in humans had contradicted the laboratory results, showing skin damage in the form of erythema and cyclobutane pyrimidine dimer (CPD) formation (14). The authors of this study hypothesized that it may be longer wavelengths present in the lamp spectrum that caused the adverse effects, a hypothesis supported by subsequent computer modeling (15). ...
... In the 2015 study by Woods et al., the Minimal Erythema Dose (MED) from exposure to the unfiltered far-UVC device was 40-50 mJ cm À2 ; whereas, in the current report, no erythema was observed with the filtered far-UVC device self-exposure of 1500 mJ cm À2 (or up to 18 000 mJ cm À2 ). This difference would support the hypothesis from Woods et al., and subsequently reinforced by Barnard et al., that longer ultraviolet wavelengths were responsible for the skin damage seen in the 2015 Woods et al. study (14,15). This is proven further in a recent publication by Buonanno et al. (19). ...
Article
Full-text available
***AVAILABLE OPEN ACCESS FROM DOI*** Far‐UVC devices are being commercially sold as “safe for humans” for the inactivation of SARS‐CoV‐2, without supporting human safety data. We felt there was a need for rapid proof‐of‐concept human self‐exposure, to inform future controlled research and promote informed discussion. A Fitzpatrick Skin Type II individual exposed their inner forearms to large radiant exposures from a filtered Krypton‐Chloride (KrCl) far‐UVC system (SafeZoneUVC, Ushio Inc., Tokyo, Japan) with peak emission at 222 nm. No visible skin changes were observed at 1,500 mJcm‐2, whereas skin yellowing that appeared immediately and resolved within 24 hours occurred with a 6,000 mJcm‐2 exposure. No erythema was observed at any time point with exposures up to 18,000 mJcm‐2. These results combined with Monte Carlo Radiative Transfer computer modelling suggest that filtering longer ultraviolet wavelengths is critical for the human skin safety of far‐UVC devices. This work also contributes to growing arguments for the exploration of exposure limit expansion, which would subsequently enable faster inactivation of viruses.
... In terms of current applications, until very recently, there were essentially no photocarcinogenesis data on which to determine an extension of the action spectrum below about 250 nm, and thus current limits on "far-UVC" are based on an abundance of caution. In fact, preliminary data suggest that appropriately filtered 222 nm sources may pose no risk to human skin, and much less to the eye, than does 254 nm (42)(43)(44)(45)(46) Although an initial clinical trial using a device with a Krypton lamp as a source for 222 nm did suggest a hazard, it was noted that accompanying longer wavelengths may well have produced the deleterious changes (42,47). Indeed, subsequent studies have provided evidence that adequate source filtration can eliminate the longer wavelengths, leaving a well-tolerated and germicidal-effective treatment modality (42)(43)(44)(45)(46)(47). ...
... In fact, preliminary data suggest that appropriately filtered 222 nm sources may pose no risk to human skin, and much less to the eye, than does 254 nm (42)(43)(44)(45)(46) Although an initial clinical trial using a device with a Krypton lamp as a source for 222 nm did suggest a hazard, it was noted that accompanying longer wavelengths may well have produced the deleterious changes (42,47). Indeed, subsequent studies have provided evidence that adequate source filtration can eliminate the longer wavelengths, leaving a well-tolerated and germicidal-effective treatment modality (42)(43)(44)(45)(46)(47). Substantial advances in this technology and additions to the resulting body of evidence can be anticipated. ...
Article
Germicidal ultraviolet radiation (GUV) provides a means of dramatically reducing airborne spread of microorganisms in residential and workspace environments. Regarding design and use of GUV, both efficacy and safety data have accumulated over several decades, with a substantial increase of attention during the current COVID‐19 pandemic. Considerations for skin and eye safety previously resulted in guidance on exposures in institutional and workplace settings. This report details the evolution of limits for skin exposures, with particular attention to the risk of skin neoplasia.
... 5 In 2014, Woods et al undertook a first-in-person study to assess the effect on skin of a 222 nm UVC emitting device (Sterilray disinfectant wand, Healthy Environment Innovations, Dover, NH, USA). 6 The study concluded that erythema was induced at radiant exposures lower than required for the threshold bacteriostatic effect. Direct CPD formation was also observed in both the supra-basal layer (all four volunteers) and basal layer (2 out of 4 volunteers) of the volunteer skin. ...
... Woods et al hypothesised that a small amount of longer wavelength UVC radiation above 250 nm (<3%) may be contributing to the observed effects. 6 We wished to determine why these results contrast with other published studies investigating far-UVC sources. 2,5 To determine the depth penetration of UVC in Fitzpatrick Skin Type I and the associated direct CPD formation, we employ Monte Carlo radiation transfer (MCRT) codes previously used to study ultraviolet radiation transport in skin. ...
Article
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NOW OPEN ACCESS BY CLICKING ON DOI It is well understood that ultraviolet‐C (UVC) radiation is effective for the destruction of micro‐organisms and drug‐resistant bacteria and is being investigated for its effectiveness at destroying the virus responsible for the current Covid‐19 global pandemic. Far‐UVC (200 ‐ 220 nm) has been proposed as an effective disinfection radiation that is safe to humans. In 2014, Woods et al. undertook a first‐in‐person study to assess the effect on skin of a 222 nm UVC emitting device (Sterilray disinfectant wand, Healthy Environment Innovations, Dover, NH, USA).
... A 'Sterilray' disinfectant source (222 nm) conventionally used to sterilise equipment and work surfaces was assessed for tolerability in four healthy volunteers with phototype I and II skin (Woods et al., 2015). The MED was determined using an escalating dosage study methodology. ...
... In the study of 4 volunteers using a 'Sterilray' disinfectant source (Woods et al., 2015), described in detail in 7.1.1, the histopathology results showed evidence of CPD formation after irradiation with 'Sterilray' UV-C at 222 nm. ...
Technical Report
Following a request from the European Commission, the Scientific Committee on Health, Environmental and Emerging Risks (SCHEER) reviewed recent evidence to assess health risks associated with UV-C radiation from lamps. The part of the ultraviolet radiation emitted in the wavelength range 280 nm–100 nm is called UV-C; this radiation is used in a growing number of applications, which include disinfection of water and air, food-industry processing, and air-conditioning. Although most appliances are sealed systems there is now increasing use of devices where consumers may be directly exposed to UV-C radiation. Based on the review and assessment of relevant scientific data, the SCHEER concluded that: • Adverse effects to the eye and skin in humans are reported mainly from accidental acute exposure to high levels of UV radiation from UV-C lamps. • Mechanistic studies suggest that there are wavelength-dependent exposure thresholds for UV-C regarding acute adverse effects to human eyes and skin, except for erythema. However, quantitative estimation of these thresholds could not be derived from currently available data. • Due to the mode of action and induced DNA damage similarly to UVB, UV-C can be considered carcinogenic to humans. However, the currently available data do not allow quantitative cancer risk assessment of exposure from UV-C lamps. • UV-C lamps emitting radiation at wavelengths shorter than 240 nm need additional risk assessment of the associated production of ozone in the environment. More data are needed on the exposure of general population and workers from UV-C lamps and generated ozone. • Research is needed on long-term stochastic effects such as cancer.
... Promisingly, the 222-nanometer far UVC lamp has been touted as a safe 2 of 13 solution, in which no pyrimidine dimer formation was observed in human and mouse skin models, and the cell viability of layered cell sheets is retained after irradiation with 222-nanometer far UVC [14]. However, some reports emerged suggesting that 222-nanometer sources may not be as safe, since they are capable of inducing both erythema and cyclopyrimidine dimer (CPD) formation in human skin [16]. ...
Article
Full-text available
Ultraviolet (UV) germicidal tools have recently gained attention as a disinfection strategy against the COVID-19 pandemic, but the safety profile arising from their exposure has been controversial and impeded larger-scale implementation. We compare the emerging 222-nanometer far UVC and 277-nanometer UVC LED disinfection modules with the traditional UVC mercury lamp emitting at 254 nm to understand their effects on human retinal cell line ARPE-19 and HEK-A keratinocytes. Cells illuminated with 222-nanometer far UVC survived, while those treated with 254-nanometer and 277-nanometer wavelengths underwent apoptosis via the JNK/ATF2 pathway. However, cells exposed to 222-nanometer far UVC presented the highest degree of DNA damage as evidenced by yH2AX staining. Globally, these cells displayed transcriptional changes in cell-cycle and senescence pathways. Thus, the introduction of 222-nanometer far UVC lamps for disinfection purposes should be carefully considered and designed with the inherent dangers involved.
... Some UVC lamps can contain UV-A and UV-B. Additional wavelengths that have been shown to penetrate to the skin's basal layer and cause DNA damage [119,121]. UVC irradiation (254 nm) may cause painful eye injury and burnlike skin reactions following a direct exposure. It is recommended to not look directly at a UVC lamp source, even briefly [113]. ...
Article
In December 2019, a severe case of pneumonia of unknown etiology appeared in Wuhan, China. Three months later, the highly contagious coronavirus disease, Covid-19, was declared a pandemic. Covid-19 is caused by a novel coronavirus SARS-CoV-2, that in March 2021 has infected more than 120 million people worldwide and killed more than 2.7 million. Covid-19 has been the deadliest pandemic to arise since the 1918 Spanish flu, shutting down economies and societies worldwide. Covid-19 caused patients to neglect routine visitations to their healthcare providers, out of fear of catching the disease. Fortunately, within our arsenal exist great tools to limit transmission of Covid-19, including face masks and persistent decontamination of surfaces. They have allowed the population to safely return to work and feel safer when visiting their healthcare providers. Arguably, dental workers and patients face a great risk. Although dental workers are appropriately masked during procedures, patients cannot be masked. With 50% of Covid-19 patients presenting as asymptomatic, contamination of dental clinics with SARS-CoV-2 is a genuine concern. An unmasked patient undergoing routine dental procedures can easily spread saliva containing SARS-CoV-2 across dental clinics, which may facilitate transmission of Covid-19. Therefore, an effective decontamination method, such as ultraviolet C (UVC) light, capable of inactivating SARS-CoV-2 on different surfaces as well as within aerosols, may warranted lower the risk of transmission within the dental clinic. In this review, we propose to discuss the studies that have investigated the potential for UVC to decontaminate face masks, surfaces, and aerosols, with a focus on how these may be applied to the dental clinic.
... Multiple recent studies of health effects from Far UV-C exposures of the eye and skin indicate that the wavelengths below about 230 nm are substantially safer than longer UV-C wavelengths. [44][45][46][47][48][49][50][51][52][53][54][55] These experimental observations are consistent with biophysical considerations regarding the much shorter penetration depth of Far UV-C radiation as compared with longer wavelength UV-C radiation. The biophysical background here is that UV-C radiation at wavelengths less than about 230 nm is strongly absorbed by all proteins (particularly through the peptide bond) and by other biomolecules, 45,56,57 and so its ability to penetrate living tissue is quite limited. ...
Technical Report
Full-text available
White Paper, International UV Association Far-UVC Task Force https://www.iuva.org/Projects-Articles-Repository/10503221
... A major attraction of UVC wavelengths below 230 nm is its frequently equivalent efficacy compare with 254 nm UVC but it is characterized by limited penetration in tissue due to its shorter wavelength (19)(20)(21). This suggests that such sources, exemplified by krypton chloride (KrCl) lamps, particularly if modified to remove energy above 230 nm, can be used to inactivate airborne microbes throughout occupied spaces while not posing a health hazard to workers in the lower room (14,(22)(23)(24). Similarly, the limited penetration depth by 254 nm radiation from low-pressure mercury GUV lamps will not pose a health hazard if the in-room exposures are kept within safe levels (25). ...
... Study found that not only is erythema inducible using the UVC emitting Sterilray, but also that DNA damage in the form of the skin cancer-associated CPDs, has also been induced. These events are occurring at Sterilray dosage levels below the threshold for bacteriostatic/bacteriocidal effects suggesting that frequent, several times daily, use of Sterilray irradiation is unlikely to be tolerated as a non-chemical antiseptic for human skin (28). ...
Preprint
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Direct contact and airborne spread are main mechanisms of transmission for SARS-CoV-2, and virus can stay viable for at least 3 hours in aerosols. Initus-V system uses a Far-ultraviolet C (UVC) system, UVC resistant textile and googles to provide virus, bacteria and spore free environments in hospitals, crowded public places and travel environments. Initus-V system may help in prevention of epidemic diseases such as Coronavirus disease-19 (Covid-19), influenza, treatment of airborne viral diseases and spread of hospital-borne resistant infections.
... Ultraviolet radiation is generally considered to be carcinogenic, with UV-B and UV-A parts of the spectrum being known carcinogens (18). Although there is no evidence that UV-C alone causes cancer in humans, it can cause erythema, trigger photokeratitis and some UV-C sources can also emit UV-B and UV-A radiation (19,20). ...
Article
Full-text available
The COVID‐19 pandemic provided a commercial opportunity for traders marketing a range of ultraviolet (UV) radiation products for home use disinfection. Due to concerns about the efficacy of such products and the potential for harmful levels of UV exposure to people, a range of products were purchased from on‐line trading platforms. Spectral irradiance measurements were carried out to determine whether the products could be effective against the SARS‐CoV‐2 virus and whether they were likely to exceed internationally agreed exposure limits. It was concluded that many of the devices were not effective and many of those that were potentially effective presented a risk to users.
... Using, for example, the UVC wavelength of λUVC=222 nm [56] as a minimum wavelength for SARS-CoV-2 destruction, we can calculate the minimum total energy needed to destroy all adsorbed virus, similar to Equation (4) as ...
Article
In this paper, the possible use of graphene oxide (GO) to destroy SARS-CoV-2 of COVID-19 is modeled. A molecular docking approach was first conducted to estimate the binding energy of GO with the spike glycoprotein of SARS-CoV-2 virus (SGCoV). A simple space-limited geometry model is used to set up the maximum limit of SARS-CoV-2 that can be absorbed on the GO surface. Using the GO surface as a hotbed for virus destruction and utilizing the unique properties of GO (the molecular weight, the area to mass ratio, and the specific heat), we build a thermal-based model to explore the possibility of destroying the adsorbed SARS-CoV-2 on the GO-coated cylindrical probe. A hypothetical design of a medical device that could benefit from this model is also proposed here.
... The advantage of KrCl*is that the deactivation efficiency of bacteria and viruses at 222 nm appears to be roughly the same as emission at 270 to 280 nm while the effect of the emission on human skin and appears to be much reduced compared even to the 253.7-nm mercury emission. 8,9 Thus these sources are being considered for disinfection of air and surfaces in occupied areas. However, in the above studies a small but significant emission at around 259 nm and higher, on the order of 20 to 100 times smaller than the main 222-nm emission, became a concern. ...
Article
The COVID‐19 pandemic has generated great interest in reviving an old intervention technology, particularly for air disinfection ‐ ultraviolet germicidal irradiation (UVGI). Since UVGI was developed and refined more than 80‐90 years ago, the ultraviolet source of choice has been almost exclusively the low‐pressure mercury vapor discharge lamp. Today, with new lamp technologies, there has been significant interest in the application of ultraviolet light‐emitting diodes and excimer lamps that emit in the UV‐C (180 ‐ 280 nm) spectral band. This paper reviews these competing technologies with the aim of giving a sound basis for decisions on how to choose and install UV systems for disinfection of air and surfaces given the Covid‐19 pandemic.
... The filter installed in the lamps used in these studies could remove all but the dominant 222 nm emission wavelength. In contrast, skin erythema and CPD formation in basal cells with a smaller dose (less than 1.0 kJ m À2 ) was observed in human skin (37). The lamps in this study, however, have a specificity showing emission peaks at 234 and 257 nm without a filter system. ...
Article
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Biological response and DNA damage following irradiation with shorter wavelengths in the UV‐C range were evaluated to investigate the safety at three wavelengths because of the recent emergence of germicidal equipment emitting short‐wavelength UV‐C for various purposes, including medical uses. To estimate an acceptable safety dose for human skin in the UV‐C range, especially short UV‐C, we studied the biological effects of 207 nm, 222 nm, and 235 nm UV‐C using albino hairless mice and evaluated the inflammatory reactions in the skin. To explore an appropriate indicator to evaluate the biological response, we employed determination of the minimal perceptible response dose (MPRD), by which any subtle cutaneous response; erythema, edema, and scale could be observed by visual inspection. Erythema was rarely observed, but edema and scale formation were evident for short UV‐C wavelengths. The MPRD at 207, 222, and 235 nm was determined to be > 15 kJ/m², 15 kJ/m², and 2.0 kJ/m², respectively. These values could be thresholds and indicators for possible safety assessments. Our data suggest that the current human exposure limits for short UV‐C wavelengths below 254 nm are overly restrictive and should be reconsidered for future disinfection lamps with short UV‐C wavelengths.
... For airborne surface disinfection, a narrow spectrum is highly desirable to precisely trigger biological events for avoiding harmful impact on humans [11]. Therefore, far-UVC LEDs are an ideal disinfectant for occupied spaces when photons in these wavelengths do not penetrate deep into the living cells in the dermis and epidermis layers [12][13][14]. ...
Article
Narrow-band far-ultraviolet C (200-230 nm) light-emitting diodes (far-UVC LEDs) are strongly detrimental to bacteria and viruses while minimally invasive to human health can be used at human-occupied spaces as a disinfectant to suppress the outbreak of infectious diseases. Here, we investigated a design for a narrow band far-UVC LED with a center wavelength222 nm based on AlGaN nanowires. The LED achieves an ultra-narrow full width at half maximum (FWHM) of ~12 nm after an introduced metal-dielectric Fabry-Perot optical bandpass interference filter with three periods of (Al/MgF 2 /Al). This narrow-band far-UVC LED is a promising candidate for airborne surface disinfection to prevent the spread of contagious diseases such as COVID-19. AlGaN nanowires have emerged as a promising candidate for highly efficient UV LEDs due to low threading dislocations, reduced polarization [1, 2], effective strain relaxation, and nearly-free quantum-confined Stark effects [3], compared to thin-film UV LEDs. Herein, using Advanced Physical Models of Semiconductor Devices (APSYS), we numerically demonstrate a far-UVC LED structure. It consists of 300 nm n-AlN/ 40 nm i-AlGaN/ 100 nm p-AlN/ 20 nm p-Al 0.95 Ga 0.05 N on a silicon(111) substrate, shown in Figure 1(a) . The active region is an Al 0.855 Ga 0.145 N single quantum well. Moreover, for efficient airborne surface disinfection, a narrow spectrum is required to effectively trigger biological events for avoiding harmful effects. Toward that end, a far-UVC LED at 222 nm for surface disinfection is preferred because this wavelength is almost harmless to the human body since it is entirely absorbed at the dead skin cell layer [4]. Figure 1(b) presents the narrow electroluminescent spectrum of the far-UVC LED, achieved by the APSYS simulation. The peak emission is at 222 nm with FWHM of ~12 nm. However, the experimentally-obtained far-UVC spectrum from LEDs may be broad, FWHM of larger than 12 nm. Thus, we use OpenFilter [5] to design a 222 nm band-pass filter as a back-up approach for the narrow emission spectrum. Starting with a typical metal-dielectric Fabry-Perot interferometer of three (Al/MgF 2 /Al) stacks, the layers’ thickness is optimized. A relatively high achieved transmission of up to 50% with a FWHM of ~12 nm is shown in the inset of Figure 1(b). Therefore, the proposed nanowire far-UVC LEDs are substantial potential for disinfection applications [6]. In conclusion, the AlGaN nanowire structure presents a novel and remarkable design for high-efficiency far-UVC LEDs which offer a chemical-free, and convenient approach to disinfection applications in human-occupied spaces, with a negligible health concern. References: [1] S. Zhao, H. P. T. Nguyen, M. G. Kibria, and Z. Mi, "III-Nitride nanowire optoelectronics," Progress in Quantum Electronics, vol. 44, pp. 14-68, 2015. [2] Z. Chao, N. Alfaraj, R. C. Subedi, J. W. Liang, A. A. Alatawi, A. A. Alhamoud, M. Ebaid, M. S. Alias, T. K. Ng, and B. S. Ooi, "III-nitride nanowires on unconventional substrates: From materials to optoelectronic device applications ," Progress in Quantum Electronics, vol. 61, pp. 1-31, 2018. [3] X. Li, S. Sundaram, P. Disseix, G. Le Gac, S. Bouchoule, G. Patriarche, F. Réveret, J. Leymarie, Y. El Gmili, T. Moudakir, F. Genty, J-P. Salvestrini, R. D. Dupuis, P. L. Voss, and A. Ougazzaden,"AlGaN-based MQWs grown on a thick relaxed AlGaN buffer on AlN templates emitting at 285 nm," Optical Materials Express, vol. 5, pp. 380-392, 2015. [4] D. Welch, M. Buonanno, V. Grilj, I. Shuryak, C. Crickmore, A. W. Bigelow, G. R. Pehrson, G. Johnson & D. J. Brenner, "Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases" Scientific Reports, vol. 8, pp.1-7, 2018 [5] S. Larouche and L. Martinu, "OpenFilters: open-source software for the design, optimization, and synthesis of optical filters," Applied Optics, vol. 47, pp. C219-C230, 2008. [6] W. Kowalski, Ultraviolet germicidal irradiation handbook: UVGI for air and surface disinfection . Springer science & business media, 2010. Figure 1
... This was emphasized in a study using 222-nm UV-C light which suggests that far-UVC light (207-222 nm) could potentially be used for antimicrobial inactivation without inducing skin damage.42 In 2014, Woods et al found that the 222-nm UV-C-emitting device was able to induce CPD formation on basal layer (of 2 out of 4 volunteers) and hypothesized that a small amount (3%) of contained wavelength UVC above 250 nm may contribute to the observed effect.44 There is a new evidence demonstrating that far-UVC radiation at 222 nm penetrates mostly on the upper epidermis but not into the basal layer.45 ...
Article
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s Hospital-associated infections have led to a significant increment of morbidity and mortality among patients. As a result, the public health had concentrated on preventing the transmission of infection using environmental controls. UV-C radiation or ultraviolet germicidal irradiation (UVGI) had caught interest for decades as it can potentially degrade many kinds of microorganisms. This review aims to highlight the current information regarding the ability of UV-C radiation in terms of disinfection and focuses on its application and safety in the medical field.
... 32 El rango de los rayos UVC se encuentra entre 200 y 280 nm, estudios demuestran que se puede alcanzar una actividad germicida óptima sin rebasar los 220 nm, sin poner en riesgo la salud del personal, ya que esta longitud de onda puede penetrar microorganismos pequeños (<1um) pero no es capaz de ingresar al citoplasma de células de mamíferos ni a las del estrato córneo. 33,34 Una actividad de onda que rebase los 250 nm puede crear eritema y melanomas, también daños en la retina ,cataratas y tumores oculares, el personal de salud no debe encontrarse en la sala al momento de la desinfección. Actualmente en el mercado existen dispositivos controlados que interrumpen su acción cuando se detecta movimiento en el área a desinfectar. ...
Article
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La pandemia por el COVID -19 ha provocado una búsqueda acelerada de diferentes técnicas que aseguren la desinfección completa de las áreas de atención hospitalarias y odontológicas. La presente revisión bibliográfica provee al personal de salud información actualizada sobre las diferentes técnicas de desinfección, haciendo especial énfasis en el uso de la luz ultravioleta, su efecto germicida, diferentes espectros de onda y su posible acción ante el virus SARS-CoV 2. Objetivo: Obtener información que respalde el efecto bactericida y viricida de la luz UV, así como establecer los parámetros recomendados para su uso. Discusión: La implementación de luz UV-C como método de inactivación frente a diferentes esporas, bacterias y virus ha tenido un mayor impacto en los últimos meses debido a la nueva realidad a la que los profesionales de la salud se enfrentan. Conclusión: El empleo de la luz UV-C podría reducir significativamente la carga viral en las áreas de la salud evitando infecciones cruzadas al profesional como también al paciente.
... 50 Other potential uses of far UVC include prevention or reduction of surgical site infections, promotion of wound healing, and hand sanitation. 53,[55][56][57] Both far UVC and 254 nm UVC can be used as low-level decontamination methods as defined by the CDC. 20 Ultraviolet B (290 nm-320 nm) ...
Article
The COVID-19 pandemic has sparked a demand for safe and highly effective decontamination techniques for both personal protective equipment (PPE) and hospital and operating rooms. The gradual lifting of lockdown restrictions warrants the expansion of these measures into the outpatient arena. Ultraviolet C (UVC) radiation has well-known germicidal properties and is among the most frequently reported decontamination techniques used today. However, there is evidence that wavelengths beyond the traditional 254nm UVC – namely far UVC (222nm), ultraviolet B, ultraviolet A, visible light, and infrared radiation – have germicidal properties as well. This review will cover current literature regarding the germicidal effects of wavelengths ranging from UVC through the infrared waveband with an emphasis on their activity against viruses, and their potential applicability in the healthcare setting for general decontamination during an infectious outbreak.
... A built in filter was used to remove essentially all but the dominant 222-nm wavelength emission. A study using an unfiltered 222-nm lamp found significant damage to the skin of human volunteers at doses at the low end of those used here [21]. A UV spectrometer (Photon Control, BC, Canada) sensitive in the wavelength range from 200-360 nm was used to characterize the wavelength spectra emitted by the USHIO lamp, and a deuterium lamp standard with a NIST-traceable spectral irradiance (Newport Corp, Stratford, CT) was used to calibrate the UV spectrometer. ...
Article
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Background Prevention of superficial surgical wound infections from drug-resistant bacteria such as methicillin resistant Staphylococcus aureus (MRSA) currently present major health care challenges. The majority of surgical site infections (SSI) are believed to be caused by airborne transmission of bacteria alighting onto the wound during surgical procedures. We have previously shown that far-ultraviolet C light in the wavelength range of 207–222 nm is significantly harmful to bacteria, but without damaging mammalian cells and tissues. It is important that the lamp be fitted with a filter to remove light emitted at wavelengths longer than 230 nm which are harmful. Aims Using a hairless mouse model of infection of superficial wounds, here we tested the hypothesis that 222-nm light kills MRSA alighting onto a superficial skin incisions as efficiently as typical germicidal light (254 nm), but without inducing skin damage. Methods To simulate the scenario wherein incisions are infected during surgical procedures as pathogens in the room alight on a wound, MRSA was spread on a defined area of the mouse dorsal skin; the infected skin was then exposed to UVC light (222 nm or 254 nm) followed by a superficial incision within the defined area, which was immediately sutured. Two and seven days post procedure, bactericidal efficacy was measured as MRSA colony formation unit (CFU) per gram of harvested skin whereas fixed samples were used to assess skin damage measured in terms of epidermal thickness and DNA photodamage. Results In the circumstance of superficial incisions infected with bacteria alighting onto the wound, 222-nm light showed the same bactericidal properties of 254-nm light but without the associated skin damage. Conclusions Being safe for patient and hospital staff, our results suggested that far-UVC light (222 nm) might be a convenient approach to prevent transmission of drug-resistant infectious agents in the clinical setting.
Article
Due to the changes in pathogenic species and the absence of research on topical skin antibiotics, the therapy of skin and soft tissue infections (SSTIs) is facing more and more severe challenges. It is particularly urgent to look for alternative therapies without induction of drug resistance. UV C (UVC) light within the range of 200 to 280 nm is one of the most common techniques used to kill and/or inactivate pathogenic microorganisms. However, the traditional most commonly used wavelength of 254 nm irradiated from a low-pressure mercury lamp is hazardous to human health, being both carcinogenic and damaging to eye tissues, which limits its applications in vivo. This research aimed to investigate the antimicrobial properties and influence of 275-nm UVC light from a light-emitting diode (UVC-LED light) on wound healing time. Five bacteria, three fungi, and scalded-mouse models combined with SSTIs were used to evaluate the antimicrobial effect in vitro and in vivo. 275-nm UVC-LED light inactivated both bacteria and fungi with a very short irradiation time in vitro and induced neither DNA damage nor epidermal lesions in the mice's skin. Furthermore, in mouse models of SSTIs induced by either methicillin-resistant Staphylococcus aureus (MRSA) or Candida albicans, the 275-nm UVC-LED light showed significant antimicrobial effects and shortened the wound healing time compared with that in the no-irradiation group. UVC-LED light at 275 nm has the potential to be a new form of physical therapy for SSTIs. IMPORTANCE As a common clinical problem, the therapy of SSTIs is facing growing challenges due to an increase in the number of drug-resistant bacteria and fungi. UV C (UVC) light sterilization has been widely used in all aspects of daily life, but there are very few reports about in vivo therapy using UVC light. It is well known that prolonged exposure to UVC light increases the possibility of skin cancer. In addition, it is also very harmful for eyes. UV irradiation with 254-nm UVC light can cause corneal damage, like thinning of the corneal epithelial layer, superficial punctate keratitis, corneal erosion, etc. In this study, we focused on looking for a more accessible light source and safer UVC wavelength, and 275-nm UVC LED light was chosen. We investigated its applicability for SSTIs therapy with relative skin safety and expected that it could be used as a new physical therapy method for SSTIs.
Article
Far UVC light (UVC wavelengths below 235 nm) is a comparatively new modality with significant potential to safely and very efficiently inactivate airborne pathogens in occupied indoor locations. There are now significant accumulations of evidence both in terms of the safety of far‐UVC for direct exposure of occupied indoor locations, and in terms of its efficacy to markedly reduce the levels of active airborne pathogens This article reviews both the safety of far‐UVC, which has a clear mechanistic underpinning, and its efficacy, both in the laboratory and in full‐sized rooms. Highlighted is the paper by Ma et al. in this issue of Photochemistry and Photobiology which addresses the efficacy of far‐UVC light (in this case at 222 nm) against a broad spectrum of common pathogens including SARS‐CoV‐2 and influenza viruses. From their data, and based on our understanding of the largely random nature of UVC‐induced damage within the genome, far UVC would be expected to be effective against the next pandemic virus, if and when it emerges.
Preprint
Ultraviolet (UV) germicidal tools have recently gained attention as a disinfection strategy against the COVID-19 pandemic but the safety profile arising from their exposure have been controversial and impeded larger scale implementation. We compare the emerging 222-nm far UVC and 277-nm UVC LED disinfection modules with the traditional UVC mercury lamp emitting at 254 nm to understand their effects on human retinal cell line ARPE-19 and HEK-A keratinocytes. Cells illuminated with 222-nm far UVC survived while those treated with 254-nm and 277-nm wavelengths underwent apoptosis via JNK/ATF2 pathway. However, cells exposed to 222-nm far UVC presented the highest degree of DNA damage as evidenced by yH2AX staining. Globally, these cells presented transcriptional changes in cell cycle and senescence pathways. Thus, the introduction of 222-nm far UVC lamps for disinfection purposes should be carefully considered and designed with the inherent dangers involved.
Article
Development of antibiotic resistance is a major challenge for antibiotics as an effective treatment approach of infectious diseases and pathogenic microbes with resistance to antibiotics will become difficult to be treated. Therefore, a new therapy method, which is safe and can inactivate pathogenic microbes effectively without developing a resistance, is highly needed. Ultraviolet irradiation is well known for its ability of effective microbial inactivation and it is widely used in sterilization of inanimate objects based on conventional ultraviolet light sources. Meanwhile, applying ultraviolet irradiation in human disinfection application is an emerging and rapidly progressing field. This review focuses on recent studies in ultraviolet based disinfection methods including both animal and human studies. We will introduce different microbial inactivation mechanisms, which are associated with the ultraviolet irradiation wavelength. Relevant research work will be summarized with a focus on their microbial inactivation effect and safety issues.
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This study aims to investigate the DNA damage from far-ultraviolet C (far-UVC) in comparison with daylight in both a temperate (Harwell, England) and Mediterranean (Thessaloniki, Greece) climate. The research utilizes the published results from Barnard et al. [Barnard, I.R.M (2020) Photodermatol. Photoimmunol. Photomed. 36, 476–477] to determine the relative cyclobutane pyrimidine dimer (CPD) yield of unfiltered and filtered far-UVC and daylight. Under current exposure limits, 10 minutes of daylight at an ultraviolet (UV) Index of 4 – typical in a temperate climate from Spring to Autumn - produces the same number of CPD as 750 hours of unfiltered far-UVC or more than 30,000 hours of filtered far-UVC at the basal layer. At the top of the epidermis these values are reduced to 31 and 261 hours respectively. In terms of CPD formation, the risk from daylight exposure greatly exceeds the risk from far-UVC. There are other damage mechanisms which require further investigation as the impact on the stratum corneum from absorption of the vast majority of the high energy far-UVC photons is unknown.
Chapter
Optical radiation consists of the ultraviolet (UV), visible, and infrared (IR) regions of the nonionizing electromagnetic spectrum. The main target organs for optical radiation are the eye and skin. This chapter reviews the basic science of optical radiation, describes characteristics of common broadband optical radiation sources, discusses exposure criteria and methods for the quantitative assessment of optical radiation hazards, describes basic principles for control of these hazards, and provides practical discussion of hazard recognition and control for specific processes or sources, including solar UV, welding, germicidal radiation, and photocuring lamps.
Article
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Far‐UVC radiation is a promising technology that is potentially both effective at killing airborne microbes such as coronaviruses and influenza, and being minimally hazardous to the skin and eyes. Our previous studies on health risks from far‐UVC have employed a krypton‐chloride (KrCl) excimer lamp, emitting principally at 222 nm, supplemented with an optical filter to remove longer wavelength emissions inherent to these lamps. This study explores KrCl lamp health hazards by comparing filtered and unfiltered KrCl lamps using effective spectral irradiance calculations and experimental skin exposures. Analysis of effective irradiances showed a notable increase in allowable exposure when using a filter. Induction of DNA dimers (CPD and 6‐4PP) was measured in human skin models exposed to a range of radiant exposures up to 500 mJ/cm². Compared to sham‐exposed tissues, the unfiltered KrCl lamps induced a statistically significant increase in the yield of both DNA lesions at all the radiant exposures studied. Conversely, filtered KrCl lamps do not induce increased levels of dimers at the current daily TLV exposure limit for 222 nm (23 mJ/cm²). This work supports the use of filters for far‐UVC KrCl excimer lamps when used to limit disease transmission in occupied locations.
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***AVAILABLE OPEN ACCESS BY FOLLOWING THE DOI*** Krypton‐Chloride (Kr‐Cl) excimer lamps have a peak emission wavelength of 222 nm in the ultraviolet‐C (UV‐C) region of the electromagnetic spectrum. Currently Kr‐Cl lamps are the only viable “far‐UV‐C” sources for full‐room inactivation of airborne SARS‐CoV‐2, the virus responsible for the COVID‐19 pandemic¹. Commercially available Kr‐Cl excimer lamps can be retro‐fitted to existing room lamp fittings or mounted at ceiling height independently. Other technologies, such as light emitting diodes (LEDs), are currently neither efficient nor powerful enough for such a task.
Article
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There is growing interest in far‐UVC lighting, defined as wavelengths from 200 to 230 nm, because research has demonstrated these wavelengths to be an effective antimicrobial technology while posing a minimal hazard to human health. Far‐UVC lighting is now being installed to directly irradiate spaces where humans are present, and it will be important to perform measurements to verify far‐UVC lighting installations are operating within widely accepted exposure guidelines. In this work we explore the use of a commercially available film, known as OrthoChromic OC‐1, to measure ultraviolet radiation exposure. The film was tested with a variety of ultraviolet wavelengths and irradiance conditions, and the color change of the film was analyzed for increasing levels of radiant exposure. The film response extended over a dynamic range that was greater than the recommended exposure limits for far‐UVC radiation so it can potentially be useful for health hazard monitoring. The spectrum of the incident ultraviolet radiation strongly affected the response of the film, therefore for accurate measurements we recommend the measured spectrum match the spectrum used for calibration. Overall, dosimetry with this film provides a simple, accurate, and inexpensive method of quantifying ultraviolet radiation exposure that is suitable for far‐UVC measurements.
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Far-UVC devices are being commercially sold as "safe for humans" for the inactivation of SARS-CoV-2, without supporting human safety data. We felt there was a need for rapid proof-of-concept human self-exposure, to inform future controlled research and promote informed discussion. A Fitzpatrick Skin Type II individual exposed their inner forearms to large radiant exposures from a filtered far-UVC source. No visible skin changes were observed at 1,000 mJcm-2 , whereas skin pigmentation that appeared around 2 hours and resolved within 24 hours occurred with an 8,000 mJcm-2 exposure. These results combined with Monte Carlo Radiative Transfer computer modelling suggest that filtering longer ultraviolet wavelengths is critical for the human skin safety of far-UVC devices. 3
Article
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Background UVC has been used to inactivate several pathogens. Unlike the conventional 254-nm UVC, 222-nm UVC is harmless to mammalian cells. Aim To investigate the disinfection efficacy of 222-nm UVC against human pathogens which are commonly found in the environment and healthcare facilities. Methodology Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Salmonella enterica subsp. serovar Typhimurium, Campylobacter jejuni, Bacillus cereus (vegetative cells and endospores), Clostridium sporogenes (vegetative cells and endospores), Clostoridioides difficile (endospores), Candida albicans (yeast), Aspergillus niger (hyphae and spores), Trichophyton rubrum (hyphae and spores), feline calicivirus and influenza A virus were irradiated with 222-nm UVC at various doses. The remaining live bacterial and fungal cells, and the viral infectivity were evaluated. The efficiency of 222-nm UVC germicidal effect was compared to that of the conventional 254-nm UVC. Results The 222-nm UVC showed potent germicidal effect to vegetative bacterial cells, yeast and viruses as efficient as the 245-nm UVC. The 222-nm UVC exhibited more potent germicidal effect to bacterial endospores, compared with the 254-nm UVC. The fungicidal effect of 222-nm UVC against the fungal spores and hyphae was weaker than that of 254-nm UVC. Conclusions The 222-nm UVC is able to inactivate a wide spectrum of microbial pathogens. In comparison with the conventional 254-nm UVC, the germicidal effect of 222-nm UVC to the fungal hyphae and spores is low, but the 222-nm UVC exhibits strong germicidal effect to the bacterial endospores.
Article
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Objective: This study aimed at comparing the ability of low-dose UVC, 0.05% chlorhexidine, and combined UVC with 0.05% chlorhexidine to reduce colony-forming units (CFUs) on select ESKAPE pathogens (Staphylococcus aureus, Klebsiella pneumoniae, and Enterococcus faecium) in a canine skin and muscle model. Background data: Surgical site infections (SSIs) result in increased morbidity and cost. UVC damages DNA, rendering bacteria nonviable and does not discriminate between drug-sensitive and multi-drug-resistant organisms. Materials and methods: Specimens were inoculated with one of three pathogens. Samples were treated with a 254 nm UVC mercury lamp or a 270 nm UVC LED light at 0.015, 0.03, or 0.04 J/cm(2) doses; 0.05% and 2% chlorhexidine were used as positive controls. To evaluate synergism, 0.05% chlorhexidine was used with 0.015 J/cm(2) of UVC. CFUs were counted and compared against the negative control. Results: There were no significant differences in CFU counts between samples of the same tissue type treated with different light sources of the same UVC dose. UVC significantly decreased CFUs when compared against all negative controls in both skin and muscle. There was no consistently superior bactericidal UVC dose identified for individual bacteria or for tissue type. The bactericidal activity of UVC at 0.015 J/cm(2) versus 0.05% chlorhexidine was not different in muscle for any bacteria. The bactericidal activity of UVC at 0.015 J/cm(2) was superior to 0.05% chlorhexidine in skin for S. aureus and K. pneumonia, but not E. faecium. Combination of UVC and 0.05% chlorhexidine showed synergy against E. faecium when evaluated on skin. Conclusions: Low-dose UVC shows promise as a rapid, effective, and synergistic means of reducing bacterial burdens, which may decrease the incidence of SSIs. It should be further evaluated for use when 2% chlorhexidine would be contraindicated or impractical, such as open wounds or surgical sites.
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Wound care is an important area of medicine considering the increasing age of the population who may have diverse comorbidities. Light-based technology comprises a varied set of modalities of increasing relevance to wound care. While low-level laser (or light) therapy and photodynamic therapy both have wide applications in wound care, this review will concentrate on the use of ultraviolet (UV) radiation. UVC (200-280 nm) is highly antimicrobial and can be directly applied to acute wound infections to kill pathogens without unacceptable damage to host tissue. UVC is already widely applied for sterilization of inanimate objects. UVB (280-315 nm) has been directly applied to the wounded tissue to stimulate wound healing, and has been widely used as extracorporeal UV radiation of blood to stimulate the immune system. UVA (315-400 nm) has distinct effects on cell signaling, but has not yet been widely applied to wound care. Penetration of UV light into tissue is limited and optical technology may be employed to extend this limit. UVC and UVB can damage DNA in host cells and this risk must be balanced against beneficial effects. Chronic exposure to UV can be carcinogenic and this must be considered in planning treatments. New high-technology UV sources, such as light-emitting diodes, lasers, and microwave-generated UV plasma are becoming available for biomedical applications. Further study of cellular signaling that occurs after UV exposure of tissue will allow the benefits in wound healing to be better defined.
Article
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Background: 0.5% to 10% of clean surgeries result in surgical-site infections, and attempts to reduce this rate have had limited success. Germicidal UV lamps, with a broad wavelength spectrum from 200 to 400 nm are an effective bactericidal option against drug-resistant and drug-sensitive bacteria, but represent a health hazard to patient and staff. By contrast, because of its limited penetration, ~200 nm far-UVC light is predicted to be effective in killing bacteria, but without the human health hazards to skin and eyes associated with conventional germicidal UV exposure. Aims: The aim of this work was to test the biophysically-based hypothesis that ~200 nm UV light is significantly cytotoxic to bacteria, but minimally cytotoxic or mutagenic to human cells either isolated or within tissues. Methods: A Kr-Br excimer lamp was used, which produces 207-nm UV light, with a filter to remove higher-wavelength components. Comparisons were made with results from a conventional broad spectrum 254-nm UV germicidal lamp. First, cell inactivation vs. UV fluence data were generated for methicillin-resistant S. aureus (MRSA) bacteria and also for normal human fibroblasts. Second, yields of the main UV-associated pre-mutagenic DNA lesions (cyclobutane pyrimidine dimers and 6-4 photoproducts) were measured, for both UV radiations incident on 3-D human skin tissue. Results: We found that 207-nm UV light kills MRSA efficiently but, unlike conventional germicidal UV lamps, produces little cell killing in human cells. In a 3-D human skin model, 207-nm UV light produced almost no pre-mutagenic UV-associated DNA lesions, in contrast to significant yields induced by a conventional germicidal UV lamp. Conclusions: As predicted based on biophysical considerations, 207-nm light kills bacteria efficiently but does not appear to be significantly cytotoxic or mutagenic to human cells. Used appropriately, 207-nm light may have the potential for safely and inexpensively reducing surgical-site infection rates, including those of drug-resistant origin.
Article
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Exposition to ultraviolet (UV) light is involved in the initiation and the progression of skin cancer. The genotoxicity of UV light is mainly attributed to the induction of cyclobutane pyrimidine dimers (CPDs), the most abundant DNA damage generated by all UV types (UVA, B and C). The human cornea is also exposed to the harmful UV radiations, but no UV-related neoplasm has been reported in this ocular structure. The probability that a specific DNA damage leads to a mutation and eventually to cellular transformation is influenced by its formation frequency. To shed light on the genotoxic effect of sunlight in the human eye, we have analyzed CPD induction in the cornea and the iris following irradiation of ex vivo human eyes with UVA, B or C. The extent of CPD induction was used to establish the penetrance of the different UV types in the human cornea. We show that UVB- and UVC-induced CPDs are concentrated in the corneal epithelium and do not penetrate deeply beyond this corneal layer. On the other hand, UVA wavelengths penetrate deeper and induce CPDs in the entire cornea and in the first layers of the iris. Taken together, our results are undoubtedly an important step towards better understanding the consequences of UV exposure to the human eye.
Article
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Since the beginning of the conflicts in the Middle East, US Army physicians have noted a high rate of multidrug-resistant Acinetobacter baumannii infections among US soldiers wounded and initially treated in Iraq. In this study, we investigated the use of ultraviolet C (UVC) light for prevention of multidrug-resistant A. baumannii wound infections using mouse models. Partial-thickness skin abrasions and full-thickness burns in mice were infected with a multidrug-resistant A. baumannii isolate recovered from a wounded US soldier deployed to Iraq. The luxCDABE operon, which was contained in plasmid pMF 385, was cloned into the A. baumannii strain. This allowed real-time monitoring of the extent of infection in mice using bioluminescence imaging. UVC light was delivered to the mouse wounds at 30 minutes after the inoculation of A. baumannii. Groups of infected mouse wounds without being exposed to UVC served as the controls. In vitro studies demonstrated that A. baumannii cells were inactivated at UVC exposures much lower than those needed for a similar effect on mammalian cells. It was observed in animal studies that UVC (3.24 J/cm(2) for abrasions and 2.59 J/cm(2) for burns) significantly reduced the bacterial burdens in UVC-treated wounds by approximately 10-fold compared with nontreated controls (p = 0.004 for abrasions, p = 0.019 for burns). DNA lesions were observed by immunofluorescence in mouse skin abrasions immediately after a UVC exposure of 3.24 J/cm(2); however, the lesions were extensively repaired within 72 hours. These results suggested that UVC may be useful in preventing combat-related wound infections.
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UV radiation is known to cause acute and chronic eye and skin damage. The present case report describes a 90 min accidental exposure to UV-C radiation of 26 medical school students. Germicidal lamps were lit due to a malfunctioning of the timer system. Several hours after irradiation exposure, all subjects reported the onset of ocular symptoms, subsequently diagnosed as photokeratitis, and skin damage to the face, scalp and neck. While the ocular symptoms lasted 2-4 days, the sunburn-like condition produced significant erythema followed by deep skin exfoliation. The irradiation was calculated to be approximately 700 mJ cm(-2) absorbed energy, whereas the actual radiation emitted by the lamps was 0.14 mW cm(-2) (the radiometric measurements confirmed these calculi, because the effective irradiance measured from the height of the autopsy table to about 1 m under the UV-C lamp varied from 0.05 to 0.25 mW cm(-2)) but, more likely, the effective irradiance, according to skin phototype and symptoms, was between 50 and 100 mJ cm(-2). The ocular and skin effects produced by such a high irradiation (largely higher than that accepted by the American Conference of Governmental Industrial Hygienists [ACGIH] threshold limit values [TLVs]) appeared reversible in a relatively short time.
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