Skin and eye protection against ultraviolet C from ultraviolet germicidal irradiation devices during the COVID-19 pandemic

Germicidal efficacy of continuous and pulsed ultraviolet-C radiation on pathogen models and SARS-CoV-2

Ultraviolet radiation's germicidal efficacy depends on several parameters, including wavelength, radiant exposure, microbial physiology, biological matrices, and surfaces. In this work, several ultraviolet radiation sources (a low-pressure mercury lamp, a KrCl excimer, and four UV LEDs) emitting continuous or pulsed irradiation were compared. The greatest log reductions in E. coli cells and B. subtilis endospores were 4.1 ± 0.2 (18 mJ cm-2) and 4.5 ± 0.1 (42 mJ cm-2) with continuous 222 nm, respectively. The highest MS2 log reduction observed was 2.7 ± 0.1 (277 nm at 3809 mJ cm-2). Log reductions of SARS-CoV-2 with continuous 222 nm and 277 nm were ≥ 3.4 ± 0.7, with 13.3 mJ cm-2 and 60 mJ cm-2, respectively. There was no statistical difference between continuous and pulsed irradiation (0.83-16.7% [222 nm and 277 nm] or 0.83-20% [280 nm] duty rates) on E. coli inactivation. Pulsed 260 nm radiation (0.5% duty rate) at 260 nm yielded significantly greater log reduction for both bacteria than continuous 260 nm radiation. There was no statistical difference in SARS-CoV-2 inactivation between continuous and pulsed 222 nm UV-C radiation and pulsed 277 nm radiation demonstrated greater germicidal efficacy than continuous 277 nm radiation. Greater radiant exposure for all radiation sources was required to inactivate MS2 bacteriophage. Findings demonstrate that pulsed irradiation could be more useful than continuous UV radiation in human-occupied spaces, but threshold limit values should be respected. Pathogen-specific sensitivities, experimental setup, and quantification methods for determining germicidal efficacy remain important factors when optimizing ultraviolet radiation for surface decontamination or other applications.

Multi-criteria decision-making for prioritizing photocatalytic processes followed by TiO2-MIL-53(Fe) characterization and application for diazinon removal

Multi-criteria decision-making (MCDM) can introduce the best option based on evidence. We integrated the Analytic Hierarchy Process (AHP) and the Technique for Order of Preference by Similarity to the Ideal Solution (TOPSIS) to prioritize the alternatives for photocatalytic diazinon removal in a bench scale and characterized TiO2-MIL-53(Fe) for this purpose. Criteria and alternatives were listed based on systematic literature reviews and expert opinions. Then, AHP and TOPSIS questionnaires were developed and distributed to an expert panel for pairwise comparisons. We converted the linguistic variables into the corresponding fuzzy values and used R for mathematical calculations. Then, TiO2-MIL-53(Fe) was synthesized and characterized for diazinon removal under LED visible light. The AHP ranked criteria as availability > degradation efficiency > safety for the environment > material cost > energy consumption > mineralization efficiency > photocatalyst reusability > safety for personnel > equipment cost. Based on TOPSIS, the order of alternatives was TiO2-containing/Visible light > ZnO-containing/UV light > TiO2-containing/UV light > ZnO-containing/Visible light > WO3-containing/UV light. With a bandgap of 1.8 eV, TiO2-MIL-53(Fe) could remove 89.35% of diazinon at 10 mg/L diazinon concentration, 750 mg/L catalyst dose, pH 6.8, and 180-min reaction time. Hybrid AHP-TOPSIS identified the best option for photocatalytic diazinon removal from aqueous solutions. Thus, MCDM techniques can use systematic review results to overcome the uncertainty in designing experimental studies.

Systematic evaluating and modeling of SARS-CoV-2 UVC disinfection

The ongoing COVID-19 global pandemic has necessitated evaluating various disinfection technologies for reducing viral transmission in public settings. Ultraviolet (UV) radiation can inactivate pathogens and viruses but more insight is needed into the performance of different UV wavelengths and their applications. We observed greater than a 3-log reduction of SARS-CoV-2 infectivity with a dose of 12.5 mJ/cm² of 254 nm UV light when the viruses were suspended in PBS, while a dose of 25 mJ/cm² was necessary to achieve a similar reduction when they were in an EMEM culture medium containing 2%(v/v) FBS, highlighting the critical effect of media in which the virus is suspended, given that SARS-CoV-2 is always aerosolized when airborne or deposited on a surface. It was found that SARS-CoV-2 susceptibility (a measure of the effectiveness of the UV light) in a buffer such as PBS was 4.4-fold greater than that in a cell culture medium. Furthermore, we discovered the attenuation of UVC disinfection by amino acids, vitamins, and niacinamide, highlighting the importance of determining UVC dosages under a condition close to aerosols that wrap the viruses. We developed a disinfection model to determine the effect of the environment on UVC effectiveness with three different wavelengths, 222 nm, 254 nm, and 265 nm. An inverse correlation between the liquid absorbance and the viral susceptibility was observed. We found that 222 nm light was most effective at reducing viral infectivity in low absorbing liquids such as PBS, whereas 265 nm light was most effective in high absorbing liquids such as cell culture medium. Viral susceptibility was further decreased in N95 masks with 222 nm light being the most effective. The safety of 222 nm was also studied. We detected changes to the mechanical properties of the stratum corneum of human skins when the 222 nm accumulative exposure exceeded 50 J/cm².The findings highlight the need to evaluate each UV for a given application, as well as limiting the dose to the lowest dose necessary to avoid unnecessary exposure to the public.

A systematic scoping review of ultraviolet C (UVC) light systems for SARS-CoV-2 inactivation

A significant amount of epidemiological evidence has underlined that human-to-human transmission due to close contacts is considered the main pathway of transmission, however since the SARS-CoV-2 can also survive in aerosols, water, and surfaces, the development and implementation of effective decontamination strategies are urgently required. In this regard, ultraviolet germicidal irradiation (UVGI) using ultraviolet C (UVC) has been proposed to disinfect different environments and surfaces contaminated by SARS-CoV-2. Herein, we performed a systematic scoping review strictly focused on peer-reviewed studies published in English that reported experimental results of UVC-based technologies against the SARS-CoV-2 virus. Studies were retrieved from PubMed and the Web of Science database. After our criterious screening, we identified 13 eligible articles that used UVC-based systems to inactivate SARS-CoV-2. We noticed the use of different UVC wavelengths, technologies, and light doses. The initial viral titer was also heterogeneous among studies. Most studies reported virus inactivation in well plates, even though virus persistence on N95 respirators and different surfaces were also evaluated. SARS-CoV-2 inactivation reached from 90% to 100% depending on experimental conditions. We concluded that there is sufficient evidence to support the use of UVC-based technologies against SARS-CoV-2. However, appropriate implementation is required to guarantee the efficacy and safety of UVC strategies to control the COVID-19 pandemic.

The value of photomedicine in a global health crisis: Utilizing ultraviolet C to decontaminate N95 respirators during the COVID-19 pandemic

One early problem during the height of the COVID‐19 global pandemic, caused by severe acute respiratory syndrome 2 (SARS‐CoV‐2), was the shortage of personal protective equipment donned by healthcare workers, particularly N95 respirators. Given the known virucidal, bactericidal, and fungicidal properties of ultraviolet irradiation, in particular ultraviolet C (UVC) radiation, our photomedicine and photobiology unit explored the role of ultraviolet germicidal irradiation (UVGI) using UVC in effectively decontaminating N95 respirators. The review highlights the important role of photobiology and photomedicine in this pandemic. Namely, the goals of this review were to highlight: UVGI as a method of respirator disinfection—specifically against SARS‐CoV‐2, adverse reactions to UVC and precautions to protect against exposure, other methods of decontamination of respirators, and the importance of respirator fit testing.