Ultrasonic humidifier aerosols: Observed high heavy metal enrichment and a new emission control method.

Ultrasonic humidifiers are commonly used in households to maintain indoor humidity and generate a large number of droplets or spray aerosols. However, there have been various health concerns associated with humidifier use, largely due to aerosols generated during operation. Here, we investigated the size distribution, chemical composition, and charged fraction of aerosol particles emitted from commercial ultrasonic humidifiers. Heavy metals in water used for humidifiers were found to be highly enriched in the ultrasonic humidifier aerosols (UHA), with the enrichment factors ranging from 102 to 107. This enrichment may pose health concerns for the building occupants, as UHA concentrations of up to 106 particles/cm3 or 3 mg/m3 were observed. Furthermore, approximately 90% of UHA were observed to be electrically charged, for the first time according to our knowledge. Based on this discovery, we proposed and tested a new method to remove UHA by using a simple electrical field. The designed electrical field in this work can efficiently remove 81.4% of UHA. Therefore, applying this electrical field could be an effective method to significantly reduce the health risks by UHA.

Ultrasonic Levitation for Airway Humidification.

This study employs the transmitter part of an ultrasonic proximity sensor to generate a powerful ultrasonic field for medical humidification. This field is created using an arrangement of small ultrasonic transmitter transducers configured in an acoustic levitator-style setup. As droplets pass through this ultrasonic field, they undergo disintegration, leading to an accelerated evaporation process. The research findings highlight a significant change in droplet size distribution due to ultrasonics, resulting in a notable increase in the rate of evaporation. As a result, this study presents a conceptual framework for reimagining humidification devices for lung therapeutic purposes through the utilization of simple sensor technology.

Ultrasonic humidifier lung with a reversed halo sign: A case report.

The reversed halo sign was initially reported as a representative computed tomography scan finding of cryptogenic organizing pneumonia. Since then, however, it has been reported in various diseases and is now considered a nonspecific finding. However, there are no cases of humidifier lung with the reversed halo sign. An 82-year-old Japanese male patient presented with moving difficulties 48 days after starting darolutamide treatment for prostate cancer. He was admitted to the hospital due to acute pneumonia, which presented as bilateral extensive nonsegmental ground-glass opacities in the peripheral regions and extensive areas of ground-glass opacity with a circumferential halo of consolidation, with the reversed halo sign on computed tomography scan. After darolutamide discontinuation with the concomitant administration of antibiotics, the patient's pneumonia improved, and he was discharged from the hospital. However, within a few days, he was again admitted to the hospital due to pneumonia. He was found to have been using an ultrasonic humidifier at home and was then diagnosed with humidifier lung based on the bronchoscopy and provocative testing findings. Hence, ultrasonic humidifier lung should be considered as a differential diagnosis in patients presenting with the reversed halo sign, and a detailed medical history must be taken.

Environmental risks from consumer products: Acceptable drinking water quality can produce unacceptable indoor air quality with ultrasonic humidifier use.

The commonly used consumer product of an ultrasonic humidifier (e.g., cool mist humidifier) emits fine particles containing metals from tap water used to fill the humidifier. The objectives are: 1) predict emitted indoor air inhalable metal concentrations produced by an ultrasonic humidifier filled with tap-water containing As, Cd, Cr, Cu, Mn, and Pb in 33 m3 or 72 m3 rooms with varying air exchange rates; 2) calculate daily ingestion and 8-h inhalation average daily dose (ADD) and hazard quotient (HQ) for adults and children (aged 0.25-6 yr); and 3) quantify deposition in respiratory tract via multi-path particle dosimetry (MPPD) model. Mass concentrations of indoor air metals increase proportionally with aqueous metal concentrations in fill water, and are inversely related to ventilation. Inhalation-ADDs are 2 magnitudes lower than ingestion-ADDs, using identical water quality for ingestion and fill-water. However, in the 33 m3, low 0.2/h ventilated room, inhalation-HQs are >1 for children and adults, except for Pb. HQ inhalation risks exceed ingestion risks at drinking water regulated levels for As, Cd, Cr, and Mn. MPPD shows greater dose deposits in lungs of children than adults, and 3 times greater deposited doses in a 33 m3 vs 72 m3 room. Rethinking health effects of drinking water and consumer products to broaden consideration of multiple exposure routes is needed.

Exposure at the indoor water-air interface: Fill water constituents and the consequent air emissions from ultrasonic humidifiers: A systematic review.

This systematic review investigates the emissions from ultrasonic humidifiers (e.g., cool mist humidifiers) within indoor air environments, namely soluble and insoluble metals and minerals as well as microorganisms and one organic chemical biocide. Relationships between ultrasonic humidifier fill water quality and the emissions in indoor air are studied, and associated potential adverse health outcomes are discussed. Literature from January 1, 1980, to February 1, 2022, was searched from online databases of PubMed, Web of Science, and Scopus to produce 27 articles. The results revealed clear positive proportional relationships of the concentration of microorganisms and soluble metals/minerals between fill water qualities and emitted airborne particles, for both microbial (n = 9) and inorganic (n = 15) constituents. When evaluating emissions and the consequent health outcomes, ventilation rates of specific exposure scenarios affect the concentrations of emitted particles. Thus, well-ventilated rooms may alleviate inhalation risks when the fill water in ultrasonic humidifiers contains microorganisms and soluble metals/minerals. Case reports (n = 3) possibly due to the inhalation of particles from ultrasonic humidifier include hypersensitivity pneumonitis in adults and a 6-month infant; the young infant exhibited nonreversible mild obstructive ventilator defect. In summary, related literature indicated correlation between fill water quality of ultrasonic humidifier and emitted particles in air quality, and inhalation of the emitted particles may cause undesirable health outcomes of impaired respiratory functions in adults and children.

Portable ultrasonic humidifier exacerbates indoor bioaerosol risks by raising bacterial concentrations and fueling pathogenic genera.

Portable ultrasonic humidifiers are frequently used in heating rooms to ease air dryness. However, it has also posed serious health concerns such as "humidifier fever" because the bioaerosol concentration and community in the humidified space may alter quickly before the occupants could even notice. We compared the microbial proliferation rates in the humidifiers' reservoirs filled with three commonly used water types and investigated the impacts of the ultrasonic humidifiers on the temporal concentration, size distribution, and community variations of indoor bacterial and fungal aerosols during two-week humidification. The concentration of indoor bacterial aerosols increased exponentially, concentrating in the respiratory size ranges (≤1.1 µm), and was proportional to the humidification level, which soon exceeded 1000 CFU/m3 in one week (at RH = 70%), while the fungal concentration always remained low (≤177 CFU/m3 ). The indoor bioaerosol community, significantly associated with the humidifier water, was substantially distorted after humidification and dominated by the pathogenic Pseudomonas spp. (40.50%), Brevundimonas spp. (3.02%), Acinetobacter spp. (0.98%) and Legionella spp. (0.69%). Our results show that ultrasonic humidification contaminates indoor air by raising bacterial concentrations and fueling the pathogenic genera. To minimize the exposure risks, occupants should avoid long-term and excessive humidification (RH ≥ 70%) and clean the ultrasonic humidifier weekly.

Risks to children from inhalation of aerosolized aqueous manganese emitted from ultrasonic humidifiers can be greater than for corresponding ingestion.

The essential trace element manganese (Mn) can cause neurotoxicity with inhalation acknowledged as a more severe health and cognition threat than ingestion. METHODS: Over a range of aqueous Mn concentrations present in tap water, this research characterizes exposures and risks for adults and 0.25, 1, 2.5, and 6 yr old children who ingest the water and inhale respirable particles produced by a room-sized ultrasonic humidifier filled with the same water. Aqueous Mn concentrations evaluated included 50 µg/L USEPA esthetic guideline, 80 µg/L WHO infant guideline, and 120 µg/L Canadian regulatory level. Airborne-particle-bound Mn concentrations were generated for water filling an ultrasonic humidifier under four realistic room conditions (33 m3 small or 72 m3 large) with varying ventilation rates from 0.2/h -1.5/h. Average daily doses (ADD) and reference intake doses were calculated for ingestion and 8-h inhalation of humidified air. Hazard quotients (HQ) compared the intake doses and reference doses. Multi-path particle dosimetry (MPPD) model quantified the particle deposition and deposited dose in children's and adults' respiratory tracts. RESULTS: At only 11 µg/L Mn, the resulting humidified air Mn exceeds USEPA's reference concentration of 0.05 µg/m3 Mn in small room with low, energy-efficient ventilation. Inhalation ADD are 2 magnitudes lower than ingestion ADD for identical water Mn concentrations and daily exposure frequency. Even so, ingestion HQs are approximately 0.2 but inhalation risk is significant (HQ>1) for children and adults when breathing Mn-humidified air under most small room conditions at 50, 80 or 120 µg/L Mn. MPPD model indicates inhaled Mn deposits in head and pulmonary regions, with greater Mn dose deposits in children than adults. CONCLUSION: Inhalation of Mn-particles produced from ultrasonic humidifiers can pose greater risks than ingestion at the same water concentration, especially for children. Aqueous Mn concentration and room size influence risks. Limiting manganese exposures and setting regulations requires consideration of both ingestion and inhalation of water.

Ammonia Generation System for Poultry Health Research Using Arduino.

An ammonia gas (NH3) generator was developed to maintain a set concentration of ammonia gas in a controlled environment chamber to study poultry physiological responses to sustained elevated levels of ammonia gas. The goal was to maintain 50 parts per million (ppm) of ammonia gas in a 3.7 m × 4.3 m × 2.4 m (12 ft × 14 ft × 8 ft) controlled environment chamber. The chamber had a 1.5 m3/s (3000 cfm) recirculation system that regulated indoor temperature and humidity levels and a 0.06 m3/s (130 cfm) exhaust fan that exchanged indoor air for fresh outdoor air. The ammonia generator was fabricated by coupling ultrasonic humidifiers with an Arduino-based microcontroller and a metallic oxide MQ-137 ammonia gas sensor. Preliminary evaluation under steady conditions showed the average MQ-137 gas sensor accuracy was within 1.4% of the 65.4 ppm concentration measured using a highly accurate infrared gas analyzer. Further evaluation was performed for a setpoint concentration of 50 ppm where ammonia generator reservoirs were filled with 2% or 10% ammonia liquid. For the system tested, it was found that two generators operating at the same time filled with 3.8 L (1.0 gallon) of 2% ammonia cleaning liquid each (7.6 L or 2.0 gallons total) could maintain a gas level of 49.45 ± 0.79 ppm in the chamber air for a duration of 30 h before refilling was required. One generator filled with 3.8 L of 10% ammonia cleaning liquid could maintain 51.24 ± 1.53 ppm for 195 h. Two ammonia generators were deployed for a six-week animal health experiment in two separate controlled environment chambers. The two ammonia generators maintained an average ammonia concentration of 46.42 ± 3.81 ppm and 45.63 ± 4.95 ppm for the duration of the experiment.

Ultrasonic humidifier lung as a mimic of COVID-19.

Chest computed tomography (CT) has been used to complement coronavirus disease 2019 (COVID-19) diagnosis due to its high sensitivity. However, owing to the low specificity of CT findings, differential diagnosis is essential. The typical CT findings of COVID-19 include ground-glass opacifications and consolidations with predominant distribution in bilateral, peripheral, and subpleural parts of the lung. These imaging findings are non-specific and may resemble other lung conditions, including ultrasonic humidifier lung, which is a condition that develops on inhaling aerosols generated by ultrasonic humidifiers. We present two patients with initial symptoms similar to COVID-19. CT examination revealed centrilobular nodules and consolidations with upper lobe-predominant distribution, although atypical for COVID-19, but key findings for ultrasonic humidifier lung. Therefore, ultrasonic humidifier lung could be a differential diagnosis for COVID-19 in dry environments. Characteristic CT findings and a history of ultrasonic humidifier use are critical to the final diagnosis.

An overlooked route of inhalation exposure to tap water constituents for children and adults: Aerosolized aqueous minerals from ultrasonic humidifiers.

Fine particulates and aerosols emitted by commonly used, room-sized ultrasonic humidifiers may pose adverse health effects to children and adults. The literature documents adverse effects for children exposed to minerals emitted from humidifiers. This study performs novel and comprehensive characterization of bivariate particle size and element concentrations of emitted airborne aerosols and particles from ultrasonic humidifiers filled with tap water, including size distribution from 0.014 to 10 µm by scanning mobility particle sizer and AeroTrak; corresponding metal and elemental concentrations as a function of particle size by inductively coupled plasma mass spectrometer; and calculations of deposition fraction in human lungs for age-specific groups using the multi-path particle dosimetry model (MPPD). Deposition fraction is the ratio of mass deposited to total mass inhaled. When filled with tap water, water evaporated from emitted aerosols to form submicron particles that became essentially "dried tap water" with median size 146 nm and mean concentration of 211 µg-total elements/m3-air including 35 µg-calcium/m3-air in a room of 33.5 m3 and air exchange rate at ∼0.8 hr-1. Approximately 90% of emitted particles deposited in human lungs were <1 µm as shown by MPPD model. The smaller particles contained little water and higher concentration of minerals, while larger particles of >1 µm consisted of lower elemental concentrations and more water due to low evaporation. Deposition fraction in pulmonary region was ∼2-fold higher, and deposited particulate mass was 3.5-fold higher for children than adults, indicating greater inhalation exposure to children compared to adults. Modeled data of total particles mass per body weight (BW) that will deposit in adult and child lungs after 8-h humidifier exposure were respectively 2.8 µg/kg-BW and 9.8 µg/kg-BW, where calcium contributes 0.4 µg/kg-BW and 1.6 µg/kg-BW. This comprehensive study of bivariate inorganic chemical composition as a function of particle size expanded, quantified, and modeled exposure for children and adults to aerosolized calcium and other inorganic constituents in water.

Human exposure to particles at the air-water interface: Influence of water quality on indoor air quality from use of ultrasonic humidifiers.

Ultrasonic humidifiers provide indoor relief to symptoms caused by dry air and produce aerosols containing both water and minerals that are present in the water that fills the humidifier. This study investigated the spatial distributions, concentrations, and metal and mineral composition of aerosols emitted when an ultrasonic humidifier was filled with deionized water (DI), low mineral tap water (LL), high total dissolved solids (TDS)/high hardness water (HH), and high TDS/low hardness water (HL). Aerosol/particle sizes and counts were obtained at six horizontal distances in both the plume and near floor for each water quality. Results are that water quality significantly affects particle size distributions which become uniform after 0.9 m from the humidifier outlet, and are independent of vertical distance from the humidifier. The mean count median diameters were 64 nm for DI, 129 nm for LL, 234 nm for HH, and 260 nm for HL; the particle counts and total mineral solids concentrations were 2,194 #/cm3 (16 µg/m3) for DI, 21,070 #/cm3 (113 µg/m3) for LL, 38,353 #/cm3 (438 µg/m3) for HH, and 43,880 #/cm3 (521 µg/m3) for HL. The µg/m3 values for LL, HH, and HL exceeded PM2.5 ambient air standards. Model predictions are that the deposition mass in the human respiratory system from inhaling particles emitted from HH and HL water exceed 135 µg for a 1 to 3-month old child and 600 µg for an adult over an 8-hr period. Mineral water quality significantly affects the distribution and concentration of emitted and inhaled indoor air particles. Consumers may unknowingly be degrading their indoor air quality when using tap water of acceptable drinking water quality as humidifier fill water.

Behavioral characteristics of polyhexamethyleneguanidine (PHMG) particles in aqueous solution and air when sprayed into an ultrasonic humidifier.

Polyhexamethyleneguanidine (PHMG) is widely used as a disinfectant to prevent microbial contamination in ultrasonic humidifiers in Korea; however, sales have been prohibited by the government after an outbreak of severe lung injury among humidifier disinfectant users. This study was therefore conducted to determine the characteristics of PHMG particles in aqueous solution and to investigate the behavior of airborne particles generated when using PHMG as a humidifier disinfectant. Three types of PHMG were selected (manufactured in Korea, USA, and China), with dynamic light scattering (DLS) used to determine their behavioral characteristics in aqueous solution. To determine the airborne behavioral characteristics, PHMG was diluted to obtain high (62.5-65 ppm) and low (6.25-6.5 ppm) concentrations, and then real-time monitoring instruments were used to measure the effect of using a diffusion dryer and thermodenuder to control moisture in a cleanroom. A polycarbonate filter sample was analyzed by field emission-scanning electron microscope-energy dispersive spectrometry (FE-SEM-EDS) to determine the particle morphology. The DLS intensity results for the three products showed a slightly right-shifted (~100 nm) bimodal distribution relative to the airborne particle size distribution. The size of the airborne PHMG particles increased during the spraying due to aggregation, with the particle size of aggregated particles confirmed by FE-SEM to be approximately 20 nm or more. As the PHMG concentration increased by 10 times, the airborne concentrations measured by the real-time monitoring instrument increased by 2-3 times for nanoparticles, and by 45-85 times for 1-10 µm particles during humidifier operation; however, 99% of the particles generated could be classified as PM1. Without ventilation, even after operating the humidifier, the PHMG particles could be airborne for about 2 h until the background concentration was reached. Therefore, we found that the airborne behavior was affected by PHMG concentration. Products from different manufacturers had no effect on the airborne behavior.

Human exposure to polyhexamethylene guanidine phosphate from humidifiers in residential settings: Cause of serious lung disease.

Exposure to the humidifier disinfectant, polyhexamethylene guanidine phosphate (PHMG), in mists generated from ultrasonic humidifiers was studied in a simulation chamber and apartment rooms. PHMG is suspected as a causative agent of lung disease in Korea residences. In the simulation-chamber study, the amount of disinfectant discharged from three different ultrasonic humidifiers was measured. Mists generated at 1, 2, and 4 times the recommended amount of disinfectant were sampled with an impinger, and the effect of relative humidity (RH) on airborne disinfectant concentration was studied by changing RH from 60%-70% to 90%-100%. In addition, particle size distribution (PSD) in mists was measured by scanning mobility particle sizer (SMPS), aerodynamic particle sizer (APS), and Mastersizer. In the apartment study, mists generated from ultrasonic humidifiers were sampled for 6 h in small and large rooms during fall ( n = 10) and winter ( n = 15). In the simulation study, the humidifiers discharged 205 ± 24.6 ml/h of mist at maximum capacity. Concentrations of airborne disinfectant increased with increasing concentration of disinfectant. RH affected airborne disinfectant concentration in the chamber, with increasing concentration with increasing RH. Below RH 70%, no airborne PHMG was detected. PHMG-containing mists generated from ultrasonic humidifier showed various sizes ranging from 149-157 nm to 690-740 nm to larger than 5.4 µm by SMPS, APS, and Mastersizer, respectively. Surface area mean diameter measured by Mastersizer ranged from 5.39 µm to 5.72 µm. In the apartment study conducted during the fall, the geometric mean (GM) and geometric standard deviation (GSD) and arithmetic mean (AM) and standard deviation (SD) of airborne PHMG concentration were 3.22 + 5.13 µg/m3 and 8.26 ± 12.18 µg/m3, respectively. In the winter, GM + GSD and AM ± SD of airborne PHMG concentration were 0.21 + 2.11 µg/m3 and 0.35 ± 0.62 µg/m3, respectively. RH and temperature in the apartment rooms for fall and winter were 22.5 ± 1.7°C, 74.5 ± 15.6% and 22.0 ± 2°C, 51.1 ± 12.9%, respectively. Different RHs in the fall and winter resulted in very different airborne concentrations of disinfectant in the apartment rooms. Exposure levels and PSD of mists generated from ultrasonic humidifiers in apartments are not sufficient to conclude that PHMG causes lung disease in Korean residences.