Computer Modeling Indicates Dramatically Less DNA Damage from Far-UVC Krypton Chloride Lamps (222 nm) than from Sunlight Exposure.

Ewan Eadie,Sally Helen Ibbotson,Isla Rose Mary Barnard,Kenneth Wood,Paul O’Mahoney,Louise Finlayson

doi:10.1111/php.13477

Abstract

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 etal. [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, 10min 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 700h of unfiltered far-UVC or more than 30000h of filtered far-UVC at the basal layer. At the top of the epidermis, these values are reduced to 30 and 300h, 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.

Highlights

Since the beginning of the COVID-19 pandemic, there has been incredible scientific and commercial endeavor to research and develop technologies to reduce the transmission risk of the SARS-CoV-2 virus
Given this restriction on irradiance, the exposure time required to reach an equivalent number of cyclobutane pyrimidine dimers (CPD) to 10 min of sunlight exposure was calculated for each skin location (Table 1)
This is true in the most critical basal layer, where the computer modeling estimates that approximately 30 000 h of exposure to the Ushio Care222 at current exposure limits would produce the equivalent number of CPD that would occur from 10 min when the UV Index is 4, typical of morning English sunshine from Spring to Autumn [13]

Summary

Introduction

Since the beginning of the COVID-19 pandemic, there has been incredible scientific and commercial endeavor to research and develop technologies to reduce the transmission risk of the SARS-CoV-2 virus One such technology utilizes ultraviolet-C (UVC) wavelengths between 200 nm and 230 nm (often called “far-UVC”) to inactivate viruses in air and on surfaces [1,2,3,4]. Several studies have shown that these wavelengths of UVC appear to induce minimal amounts of deoxyribonucleic acid (DNA) damage in the skin and the damage that is induced is limited to the upper-most non-proliferating skin cells [7, 8] This suggests that long-term exposure to these wavelengths is unlikely to be associated with increased skin cancer risk through induction of cyclobutane pyrimidine dimers (CPD) or 6–4 photoproducts (6–4PP) [8, 9]. We wished to put potential risks into context and convey the message that exposures to UVC wavelengths below 230 nm and to sunlight are distinctly different

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