Behavioral Characteristics of Mist Containing PHMG Emitted from Ultrasonic Humidifier

Abstract

Objective: After the outbreak of humidifier disinfectant accident in South Korea, most studies have been focused on the toxicological and epidemiological effects of humidifier disinfectants while the behavior of aerosols emitted from humidifier was rarely evaluated. This study aims to identify the behavior characteristics of aerosols emitted from ultrasonic humidifier including polyhexamethylene guanidine (PHMG) as a representing disinfectant substance, and to determine the effect of water among the aerosols. Methods: After selecting the most appropriate condition among the five water vapor removing conditions using diffusion dryer and thermodenuder, we compared the behavior characteristics of PHMG whether or not the dryer set is used. The scanning mobility particle sizer (SMPS) and the optical particle spectrophotometer (OPS) were utilized to monitor the number concentration and size distribution of aerosols. Filter sampling was conducted simultaneously to confirm the transmission and distribution of PHMG in the air by analyzing with balance and field emission scanning electron microscope with an energy-dispersive X-ray spectrometer (FE-SEM/EDX). Results: The number concentration and the geometric mean of the particles under 10 μm increased as the concentration of PHMG contained in the water tank increased. With the same amount of PHMG added, the number concentration reduced at 1 m, but increased again at 2 m. However, the mean size of the particles continued to increase as the sampling distance is farther from the humidifier outlet. Most of the particles at 0.5 m was nano-sized while 25% of the particles at 2 m measured between 0.3 μm and 10 μm. Through the analysis of FE-SEM/EDX, we observed the aggregated particles containing phosphate in a similar size (40 nm to 70 nm) as measured with real-time monitoring devices. Conclusion: This study aimed to clarify the behavioral characteristics of humidifier disinfectant PHMG. The addition of PHMG in the humidifier water tank produced 10 times more particles in number concentration under 10 μm diameter, compared to the case when only water was added in the humidifier. PHMG was transmitted 2 m from the humidifier, the last measurement distance in the experiment, and remained extensively in the air. The mean size of particles at 2 m was relatively larger than that at closer distance, but still most of them are less than 10 μm which is considered as respirable fraction.