Aqueous lithium chloride solution as a non-toxic bactericidal and fungicidal disinfectant for air-conditioning systems: Efficacy and mechanism

Abstract

Airborne pathogenic bacteria and fungi transmitted through air-conditioning (AC) systems have been identified as a major public health risk. Air scrubbing is a promising liquid-based air disinfection technique that captures and inactivates airborne pathogens in liquid disinfectants. However, owing to the drawbacks of irritating odor and toxicity, the commonly-used chemical disinfectants cannot be employed for AC systems. This study aimed to unveil the inactivation performance and mechanism of non-toxic and chemically stable aqueous lithium chloride (LiCl) solution-the popular liquid desiccant in the AC systems-as a user-friendly disinfectant. Four prominent airborne pathogenic bacteria and fungi were exposed to the LiCl solution under various conditions. The inactivation effects were quantified with fluorescence-staining-based confocal microscopy and verified with the pathogens' membrane integrity variations, intracellular substance leakage, and morphological changes. Results showed that LiCl solution was remarkably efficient in inactivating the pathogens within 60 min, with an efficacy of 35.2-96.2%. The solution's inactivation ability was promoted by increasing the temperatures and concentrations; however, it appeared insensitive to exposure time over 30 min. We then explored the inactivation mechanism of LiCl solution by assessing cellular protein leakages and compared the inactivation rates with those of NaCl solution. The extracellular protein increased by over 470% after being exposed to LiCl solution. The inactivation rate was also considerably higher than in NaCl solution under the same osmotic pressure (24.79 MPa). We suggest that apart from osmotic pressure, the inactivation is reinforced by Li⁺-specific properties, including its strong water attraction that deprived the solvation shells of microbial protein and caused protein denaturation. We propose that aqueous LiCl solution may act as a user-friendly disinfectant for air-scrubbing due to its attractive characteristics, including its non-toxicity, odorless nature, and chemical stability. These findings may open up a "green" way to disinfect airborne pathogens and safeguard public health.

Keywords: Air-scrubbing; Bacteria; Fungal spore; Inactivation; Lithium chloride.