Summary
In lab models of the human airway, HOCl gas below 500 ppb did not harm cell viability or cilia. Very little reached the model's lungs at low concentrations. Four of the five authors work for Panasonic Ecology Systems, which makes HOCl air devices.
Key points
- Human airway tissue showed no loss of viability or ciliary activity at 100 ppb for 8 hours or 500 ppb for 5 days.
- In an artificial airway model, about 47% of the chamber concentration reached the lung space, and close to none below 20.5 ppb, because HOCl sticks to surfaces.
- Lab models only; no animals or people.
- Four of five authors work for Panasonic Ecology Systems.
Abstract
During the disinfection of indoor spaces using gaseous hypochlorous acid (HOCl(g)), inhalation is the most common route of exposure for humans. In this study, an artificial human respiratory tract model was exposed to 12-140 ppb HOCl(g) at an aspiration flow rate of 800 mL/s for 15 h in a 1 m3 chamber. The respiratory tract model was equipped with 5th order bronchi and all gas-contact parts were made of silicone rubber with no other chlorine-consuming substances. The concentration of HOCl(g) reaching the lung pseudo-space was approximately 47.4% of the HOCl(g) concentrations in the chamber and was calculated to be very close to zero when the chamber concentration was less than 20.5 ppb. The disappearance of HOCl(g) during inhalation is likely due to the adsorption of HOCl(g) on the gas-contact silicone rubber surfaces. The cytotoxicity of HOCl(g) on respiratory epithelial cells was also examined using human air-liquid-interface airway tissue models. Human nasal epithelium and bronchiolar epithelium were exposed to 100 ppb and 500 ppb HOCl(g) for 8 h and 5 d, respectively. No significant effects of HOCl(g) on cell viability and ciliary activity were observed in any cell type, indicating that low concentrations of HOCl(g）, less than 500 ppb, had no cytotoxic effect.
**Keywords: ** bronchiolar epithelium; gaseous hypochlorous acid; human respiratory tract model; inhaled concentration; nasal epithelium.
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