Researchers from the College of Engineering-Swansea University and the, Division of Infection & Immunity-Cardiff University have in a new study demonstrated that Ozone gas is effective as a SARS-CoV-2 disinfectant.
he study evaluated the inactivation of SARS-CoV-2 coronavirus, the pathogen responsible for COVID-19, by ozone using virus grown in cell culture media either dried on surfaces (plastic, glass, stainless steel, copper, and coupons of ambulance seat and floor) or suspended in liquid.
The Ozone-SARS-CoV-2 study findings showed that treatment in liquid reduced SARS-CoV-2 at a rate of 0.92 ± 0.11 log10-reduction per ozone CT dose (mg min/L); where CT is ozone concentration times exposure time.
The study findings were published in the peer reviewed Journal of Hazardous Materials. https://www.sciencedirect.com/science/article/pii/S0304389422000395
SARS-CoV-2 spreads from person-to-person through inhalation of contaminated droplets and aerosols or by touching contaminated surfaces (i.e. fomites) (Mohan et al., 2021, Alimohammadi and Naderi, 2021). The virus remains viable in aerosols for up to 3 h, while on surfaces, it can remain viable up to 24 h (van Doremalen et al., 2020).
By changing from winter to spring/fall environmental conditions, Kwon et al. showed that SARS-CoV-2 remains infectious on surfaces for up to 21 days and 7 days respectively, while it remained infectious for up to 3–4 days under indoor conditions (Kwon et al., 2021).
In another study, Riddell et al. (2020) isolated viable virus from common surfaces after 28 days at 20 °C. Thus, these studies demonstrate the remarkable persistence of SARS-CoV-2 on surfaces under different environmental conditions highlighting the potential risk of contaminated surfaces as a driver of virus spread.
Controlling the transmission of SARS-CoV-2 by eliminating the virus on surfaces and in liquid droplets and aerosols in the air is an important measure to curb COVID-19 disease.
In the recent year, a variety of methods have been studied to eliminate SARS-CoV-2 from the environment, including heat sterilisation, chemical disinfection, non-thermal plasma, and ultraviolet irradiation (Kwok et al., 2021, Martins et al., 2021, Volkoff et al., 2021, Welch et al., 2021, Oral et al., 2020, Murata et al., 2021).
In these studies, the virus was inoculated onto a variety of hard and porous surfaces or in liquids before being exposed to the treatment. However, airborne virus studies are rare, due to the difficulty in safely handling aerosolised virus. Generally, the chemical disinfectants were either used in gas (e.g. ozone, hydrogen peroxide vapour) or liquid (e.g. chlorine-based agents, hydrogen peroxide) forms, with each offering advantages and disadvantages (Table 1).
Being a gas and a strong oxidant, which can easily be produced from oxygen, ozone is more effective as compared to other chemical disinfectants. Ozone can also easily be applied in large and small areas and decompose back to safe oxygen after treatment. Ozone is particularly lethal against viruses through peroxidation of their surface lipids and subsequent damage to the lipid envelope and proteins (Murray et al., 2008), and can also damage the capsid and genome (Kim et al., 1980, Wigginton and Kohn, 2012).
Generally, the susceptibility of viruses to ozone depends on the type of virus, with enveloped viruses being more susceptible to ozone attack than non-enveloped viruses; this is due to the high reactivity of ozone with the lipid layer of the envelope (Tseng and Li, 2006, Tizaoui, 2020). Being an enveloped virus, SARS-CoV-2 is therefore vulnerable to ozone attack through reactions with reactive oxygen species (ROSs) including molecular ozone and its decomposition products such as hydroxyl radicals and singlet oxygen (Tizaoui, 2020, Li et al., 2016).
Table 1. Summary of effective disinfectants against SARS-CoV-2.
|Technique||Advantages||Disadvantages||Potential areas of use||Typical doses for SARS-CoV-2 inactivation||References|
|Ozone||•A powerful disinfectant•Produced on site from oxygen in air•Can be easily converted back to oxygen using catalysts integrated in ozone generators•Gas, thus it can be distributed easily in space.•Low energy demand||•Inhalation at low concentration may increase health risk•Applied only in unoccupied environment•May generate by-products•High relative humidity is required when treating surfaces||Air, water, and surfaces||•Wide range of CT values from 100 s to 1000 s mg min/m3 for surfaces•CT < 1 mg min/L for water.||(Martins et al., 2021, Volkoff et al., 2021, Murata et al., 2021, Tizaoui, 2020, Zucker et al., 2021, De Forni et al., 2021)|
|UV||•Easy to operate•Chemical-free•Leaves no chemical residues•Damages the genomic system of microorganisms||•Unlikely to be feasible in large spaces indoor, hence with low impact•Light shielding•Sensitive to material type and ambient conditions (e.g. RH and T)•May generate ozone, if not controlled,•May present a risk to unprotected skin and eyes||Air, water, and surfaces||3–10 mJ/cm2||(Raeiszadeh and Adeli, 2020, Minamikawa et al., 2021, Kitagawa et al., 2021)|
|Non thermal plasma||•Local disinfection||•High voltage•Reactive species may be toxic if not controlled (e.g. NOx, O3)•Limited action in gas phase||Surfaces, liquids||< 20 min exposure time||(Bisag et al., 2020, Chen et al., 2020, Capelli et al., 2021)|
|Heat treatment||•Common method of disinfection in an autoclave||•Not suitable for materials sensitive to heat•Not suitable for indoor areas||Surfaces, liquids||30 min at 56 °C, < 10 min at > 70 °C||(Kwok et al., 2021, Xiling et al., 2021, Pastorino et al., 2020)|
|Sodium hypochlorite (chlorine bleach)||•Inexpensive•Widely available||•May attack materials, furniture, and electronic equipment•Hazardous to the environment•Sensitive to pH•Laborious to apply over large areas||Liquids, surfaces||150 ppm for 5 min||(Xiling et al., 2021, Brown et al., 2021, Subpiramaniyam, 2021)|
|Chlorine dioxide (liquid or gas)||•Can be produced onsite•Stronger disinfectant than sodium hypochlorite||•Inactivation takes place in wet state only•Requires high relative humidity in gas phase•Requires unoccupied spaces•Can be explosive||Liquids, surfaces, and air||~ 10 mg.min/L in water||(Kaly-Kullai et al., 2020, Morino et al., 2009)|
|Hydrogen peroxide (liquid or vapour)||•Safe at very low concentrations•Breaks down into molecular oxygen and water•Easily available (e.g. pharmaceutical grade solutions at 3% w/w)||•Modest virucidal activity•Acidification and additives are required•Long contact times and high concentrations are often necessary||Liquid or vapour||3% H2O2 + acetic acid for 5 min||(Mileto et al., 2021, Goyal et al., 2014, Schinkothe et al., 2021)|
The efficacy of ozone gas to inactivate surface or airborne viruses depends on several operating factors including the product ozone concentration times exposure time (i.e. CT value – see Supplementary Information S1), the relative humidity (RH) (Hudson et al., 2009, Dubuis et al., 2020), the chemical composition of the media carrying the virus (i.e. water, biological fluid, aerosol, or dried/wet virus-adhered surface) (Araújo et al., 2013), and the type and texture of the surface (Szpiro et al., 2020). Although ozone has recently been studied to eliminate SARS-CoV-2 (Martins et al., 2021, Volkoff et al., 2021, Murata et al., 2021, Zucker et al., 2021, Yano et al., 2020, Uppal et al., 2021), these studies have only concerned with a narrow range of ozone dose and RH, and have mostly used surrogates instead of authentic SARS-CoV-2 virus (Zucker et al., 2021, Uppal et al., 2021).
In addition, the effect of the media on virus inactivation has not been studied, and the CT values reported varied widely; for example, for a virus inactivation of 93% ± 3%, the reported CT values spanned over the range 0.1–40 g.min/m3 (Murata et al., 2021, Zucker et al., 2021, Percivalle et al., 2021, Criscuolo et al., 2021). Furthermore, the effect of RH on inactivation has not been fully clarified, and there are no clear kinetic data on ozone-mediated inactivation of the virus.
To address these knowledge gaps and support possible large-scale field implementation of ozone for the elimination of SARS-CoV-2 from surfaces and in liquid medium, this paper aims to provide novel quantitative evidence on ozone inactivation of the causative virus of COVID-19.
In particular, we used authentic SARS-CoV-2 virus to evaluate the synergistic effect of both CT and RH, and developed a unified basis to quantify their joint effect on virus inactivation by ozone. We evaluated the kinetics of virus inactivation and calculated rate constants in liquid and at different RH values.
The effect of virus matrix was evaluated in liquid and dried media through reaction and mass transfer studies benchmarked against a probe of known reactivity with ozone, and the findings allowed us to suggest possible routes explaining the role of virus medium in interfering with the inactivation process.