Our previous studies demonstrated that precoating of filter fibers with biologically active tea tree oil (TTO) enhances physical collection efficiency of conventional heating, ventilation, and air conditioning (HVAC) filters, and provides cost effective and rapid inactivation of captured bacterial and fungal particles on the filter surface. The main aim of this study was to investigate the antiviral activity of two natural disinfectants, i.e., TTO and eucalyptus oil (EUO), against the influenza virus captured onto the filter surface. It was found that both tested oils possess strong antiviral properties when used as fiber coating materials, capable of inactivating captured microorganisms within 5–10 min of contact on the fiber surface. The antiviral activity of TTO was also successfully challenged in aerosol form by mixing viable airborne viral particles with oil droplets in the rotational aerosol chamber. The results look very promising for further development of virus inactivating procedures and technologies for air quality applications.



Due to considerable impact on human and animal health, biological aerosols are becoming an increasingly important subject of research investigations all over the world. Removal of microbiological particles from the ambient air with their following inactivation would be one of the most efficient ways to minimize risks of direct exposure to airborne particles or particles re-aerosolized from collecting surfaces. Since filtration remains the most efficient method of the airborne particle removal, it is commonly used for purification of air from microbial particles on its own, or in combination with additional procedures and technological modules enhancing the process efficiency with minimal alteration of the filter hydrodynamics. Such filtration enhancing procedures include utilization of unipolar ions (Huang et al. 2008), electrostatic charging of the filter media (Raynor and Chae 2004), coating of fibers with liquids (Agranovski and Braddock 1998; Boskovic et al. 2007), and others.


Considering the fact that collected microbial aerosols remain on the filter surface, some possibility of their following detachment and re-aerosolization back to the gas carrier could not be neglected. The re-aerosolized particles could still be alive causing substantial risks for residents and environment. This issue could be addressed by adding disinfecting agents into the gas carrier or undertaking some inactivation procedures directly on the filter surface, making microbial particles inactive in the cases of potential re-aerosolization.


There are some technological approaches available for microbial disinfection. They include photocatalytic decomposition of microbes on titanium oxide surface irradiated by ultraviolet (UV; Vohra et al. 2006; Grinshpun et al. 2007), infrared (IR) radiation-based thermal decomposition (Damit et al. 2011), using chemicals directly injected into the air carrier or applied onto the filter surface (Pyankov et al. 2008; Huang et al. 2010), and others. Among variety of various disinfectants, some natural oils look promising due to low or nontoxic nature, especially in diluted form (Carson et al. 2006). During the last decade, a variety of essential oils from plants have been screened to assess their antimicrobial activity (Reichling et al. 2009).


The potential use of oils, such as tea tree oil (TTO) and eucalyptus oil (EUO), as disinfectants was clearly showed in recent in vitro studies regarding antibacterial (Wilkinson and Cavanagh 2005; Carson et al. 2006; Salari et al. 2006; Hayley and Palombo 2009), antifungal (Hammer et al. 2000; Oliva et al. 2003), and antiviral activities (Schnitzler et al. 2001; Cermelli et al. 2008; Garozzo et al. 2011). In addition, it was shown that essential oils are heterogeneous mixtures, with considerable batch to batch variation of constituents, depending on growth conditions at the plantations (Kawakami et al. 1990; Moudachirou et al. 1999). The antimicrobial activity of TTO is attributed mainly to terpinen-4-ol (35–45%) and 1,8-cineole (1–6%); however, other components such as a-terpineol, terpinolene, and a- and c-terpinene are also often present and potentially contribute to microbial disinfection (May et al. 2000). The EUO from different Eucalyptus species contains 1,8-cineole, a-pinene, and a-terpineol as major common compounds (Jemâa et al. 2012). A pharmaceutically graded EUO is commonly enriched up to 70% concentration of 1,8-cineole.


Recently, we suggested a technology based on coating fibrous filters by TTO, and reported the results of feasibility studies on the disinfection of bacteria (Pyankov et al. 2008) and fungal spores (Huang et al. 2010). In these studies, the TTO was used as both, filter efficiency enhancing media and disinfectant on bacterial and fungal aerosols captured on the filter surface. Considering current strong interest toward influenza related research, the present study is logical continuation of our previous investigations with the focus on the assessment of antiviral activity of essential oils (TTO and EUO) on inactivation of airborne influenza virus.


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Post time: Jan-23-2021