title: Effect of aerosol particles generated by ultrasonic humidifiers on the lung in mouse.
abstract: BACKGROUND
  Ultrasonic humidifiers silently generate water droplets as a cool fog and produce most of the dissolved minerals in the fog in the form of an aerosolized "white dust." However, the health effect of these airborne particles is largely unknown. This study aimed to characterize the aerosol particles generated by ultrasonic humidifiers and to investigate their effect on the lung tissue of mice.
  
  
  METHODS
  An ultrasonic humidifier was operated with tap water, high-silica water, ultrapure water, or other water types. In a chamber (0.765 m3, ventilation ratio 11.5 m3/hr), male ICR mice (10-week-old) were exposed by inhalation to an aerosol-containing vapor generated by the humidifier. After exposure for 7 or 14 days, lung tissues and bronchoalveolar lavage fluid (BALF) were collected from each mouse and examined by microarray, quantitative reverse transcription-polymerase chain reaction, and light and electron microscopy.
  
  
  RESULTS
  Particles generated from the humidifier operated with tap water had a mass concentration of 0.46 ± 0.03 mg/m3, number concentration of (5.0 ± 1.1) × 10(4)/cm3, and peak size distribution of 183 nm. The particles were phagocytosed by alveolar macrophages in the lung of mice. Inhalation of particles caused dysregulation of genes related to mitosis, cell adhesion molecules, MHC molecules and endocytosis, but did not induce any signs of inflammation or tissue injury in the lung.
  
  
  CONCLUSIONS
  These results indicate that aerosol particles released from ultrasonic humidifiers operated with tap water initiated a cellular response but did not cause severe acute inflammation in pulmonary tissue. Additionally, high mineral content tap water is not recommended and de-mineralized water should be recommended in order to exclude any adverse effects.
authors.affiliation: Department of Hygienic Chemistry, Faculty of Pharmaceutical Sciences, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan. masa-ume@rs.noda.tus.ac.jp.
authors.forename: Masakazu
authors.initials: M
authors.lastname: Umezawa
authors.forename: Keisuke
authors.initials: K
authors.lastname: Sekita
authors.forename: Ken-Ichiro
authors.initials: K
authors.lastname: Suzuki
authors.forename: Miyoko
authors.initials: M
authors.lastname: Kubo-Irie
authors.forename: Rikio
authors.initials: R
authors.lastname: Niki
authors.forename: Tomomi
authors.initials: T
authors.lastname: Ihara
authors.forename: Masao
authors.initials: M
authors.lastname: Sugamata
authors.forename: Ken
authors.initials: K
authors.lastname: Takeda
mesh_terms: D000336:Aerosols; D000818:Animals; D001992:Bronchoalveolar Lavage Fluid; D016000:Cluster Analysis; D006813:Humidity; D008168:Lung / Q000378:metabolism*; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D020411:Oligonucleotide Array Sequence Analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014465:Ultrasonics
chemical_list: D000336:Aerosols