Outbreak of Bioaerosols with Continuous Use of Humidifier in Apartment Room

The effect of continuous humidifier use on the bioaerosol concentration in an indoor environment was investigated. An ultrasonic humidifier was operated for 10 hr per day for 15 days in an apartment room. During this time period, viable bioaerosol samples were taken using a single-stage Andersen sampler containing culture media plates for bacteria and fungi. The culture plates were then incubated at room temperature for 2~7 days depending on the media. The counts for the air sample plates were corrected for multiple impactions using the positive hole conversion method and are reported as the colony forming units per cubic meter of air (CFU/m3). While the bacterial concentration measured using the tryptic soy agar (TSA) did not show any significant change during the first 3 days, the concentration increased from the 6th day (6979 CFU/m3) and reached a maximum on the 9th day (46431 CFU/m3). The concentration then decreased to 2470 CFU/m3 on the 12th day, at which point the fungal concentration increased rapidly to 14424~16038 CFU/m3. Also, while the fungal concentration showed a significant change until the 9th day of humidifier use, fungal growth was observed on the wallpaper and increased rapidly from the 12th day. However, the bacterial concentration increased rapidly after the fungi were removed by remediation. The major fungal species identified in the samples were Penicillium representing 34%, Aspergillus representing 31%, Cladosporium representing 24%, and Alternaria representing 1%. The results also indicated that a relative humidity over 80% was easily achieved with continuous humidifier use. Yet, maintaining a high humidity in a room can cause a rapid outbreak of microbial growth.

Multi-Walled Carbon Nanotube (MWCNT) Dispersion and Aerosolization with Hot Water Atomization without Addition of Any Surfactant

OBJECTIVES: Carbon nanotubes are an important new class of technological materials that have numerous novel and useful properties. Multi-walled carbon nanotubes (MWCNTs), which is a nanomaterial, is now in mass production because of its excellent mechanical and electrical properties. Although MWCNTs appear to have great industrial and medical potential, there is little information regarding their toxicological effects on researchers and workers who could be exposed to them by inhalation during the handling of MWCNTs. METHODS: The generation of an untangled MWCNT aerosol with a consistent concentration without using surfactants that was designed to be tested in in vivo inhalation toxicity testing was attempted. To do this, MWCNTs were dispersed in deionized water without the addition of any surfactant. To facilitate the dispersion of MWCNTs in deionized water, the water was heated to 40degrees C, 60degrees C, and 80degrees C depending on the sample with ultrasonic sonication. Then the dispersed MWCNTs were atomized to generate the MWCNT aerosol. After aerosolization of the MWCNTs, the shapes of the NTs were examined by transmission electron microscopy. RESULTS: The aerosolized MWCNTs exhibited an untangled shape and the MWCNT generation rate was about 50 mg/m3. CONCLUSION: Our method provided sufficient concentration and dispersion of MWNCTs to be used for inhalation toxicity testing.