The cluster model of ultraviolet disinfection explains tailing kinetics

Abstract

Aims To develop a new mathematical model derived from first principles to define the kinetics of ultraviolet disinfection and to explain the phenomenon known as tailing. The theory presented interprets tailing as the result of photoprotection due to cumulative Mie scattering effects in clustered populations of micro‐organisms. Methods and Results Mie scattering effects at ultraviolet wavelengths are used to compute a shielding constant for each micro‐organism based on the average projected diameter. An intrinsic rate constant, hypothesized to be a characteristic property of the microbial genome alone, is computed. The cluster model is fitted to tailing data from 30 ultraviolet inactivation studies and results are compared with the classic two stage multihit model. Conclusions The cluster model demonstrates a statistically significant improvement in the mean adjusted R2 values of the tested data sets (P < 0·0001). Tailing in survival curves is the direct consequence of the Gaussian distribution of cluster sizes and the intrinsic rate constant is a real and critical parameter that defines ultraviolet susceptibility. Significance and Impact of the Study The ultraviolet dose–response behaviour of micro‐organisms can now be explained in terms of parameters that have physical meaning and provide deep insight into the disinfection process.

Inactivation times from 290 to 315 nm UVB in sunlight for SARS coronaviruses CoV and CoV-2 using OMI satellite data for the sunlit Earth

“…S1 to S4 ). This inactivation dose is similar to that of the Berne virus Coronaviridae (Weiss and Horzinek 1986 ; Lytle and Sagripanti 2005 ; Kowalski et al 2020a , b ), which we estimate to be 7.1 J/m 2 (Fig. S2 ).…”

“…When D = D 90 (J/m 2 ), it is an exposure representing 10% survival, N / N O = 0.1. More complicated two-slope inactivation models have been used when the inactivation vs. D show two log-linear slopes (Kowalski et al 2020a , b ) for inactivation times greater than T 90 .…”

“…S3 ) based on laboratory studies by Darnell et al ( 2004 ). Kowalski et al ( 2020a , b ) obtained different values of D 90 = 134 J/m 2 and 2410 J/m 2 , respectively. https://avdc.gsfc.nasa.gov/pub/DSCOVR/JayHerman/COVID-19/ ).…”

“…While both viruses are in the coronavirus family, their UV inactivation sensitivity may not be representative of either the SARS-CoV or MERS-CoV variants. Inactivation of CoV-P9 by UVC (Duan et al 2003 ) showed undetectable amounts of virus after 60 min of irradiation to 0.9 W/m 2 , which, in a company report, Kowalski et al ( 2020a , b ) estimated D 90 = 40 J/m 2 . Evaluation of a laboratory study by Kariwa et al ( 2004 ) on SARS CoV (Hanoi) gives 46 J/m 2 (Fig.…”

“…S1 to S4 , items 1-6) and later section for items 7–8 Item D 90 (J/m 2 ) Data reference 1 7.1 Berne-CV (Weiss and Horzinek 1986 ). 2 40 CoV-P9 by UVC (Duan et al 2003 ; Kowalski et al 2020a , b ) 3 46 SARS CoV (Hanoi) (Kariwa et al 2004 ) 4 1826 SARS-CoV (Urbani) (Darnell et al 2004 ) 5 95 Murine Hepatitis Coronavirus (MHV) (Liu et al 2003 ) 6 6.6 Murine Hepatitis Coronavirus (MHV) Airborne (Walker and Ko 2007 ) 7 3.2 SARS CoV-2 dried on steel mesh UVC D 90 estimated 8 6.5 SARS CoV-2 in growth medium UVC D 90 estimated …”