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The rapid proliferation of electronic cigarettes (ECs) has raised significant concerns about their potential health effects on both users and bystanders. This study systematically investigates the impact of EC aerosol exposure on human alveolar epithelial cells (A549), considering variations in device parameters, nicotine concentration, and exposure type. Using a gravity-based air–liquid interface exposure system, we assessed cytotoxicity and epithelial barrier integrity by measuring cell viability and transepithelial electrical resistance (TEER). Our results indicate that EC aerosol exposure significantly reduces cell viability and disrupts monolayer integrity in a dose- and device-dependent manner. Notably, VUSE (pod-type) exposure led to a 16% decrease in viability and a 41% reduction in TEER, while VOOPOO (mod-type) exposure caused a 25% viability loss and a 61% reduction in TEER. Power settings played a critical role: at 60 W, cell viability dropped by 48% at 12 mg/mL nicotine concentration compared to 29% at 0 mg/mL. Moreover, under the same number of puffs (30 puffs), firsthand exposure resulted in a 73% viability decrease, whereas secondhand exposure showed a 47% reduction, indicating substantial bystander risks associated with EC usage. These findings underscore the importance of device specifications and exposure conditions in determining EC aerosol toxicity. The observed epithelial barrier disruption suggests increased vulnerability to respiratory diseases. Given the comparable toxicity of firsthand and secondhand aerosols, regulatory measures should extend beyond direct users to include bystander protection. This study highlights the urgent need for comprehensive toxicity assessments to inform public health policies on EC use. 

This study employed high-time-resolution systems to examine the transient properties of aerosols and gases emitted from electronic cigarette (EC) puffs. Using a fast aerosol sizer, we measured particle size distributions (PSDs) across various EC brands (JUUL, VUSE, VOOPOO), revealing sizes ranging from 5 to 1000 nm at concentrations of 107 to 1010 cm–3. Most aerosols were found to be in the ultrafine range (below 100 nm), with JUUL-, VUSE-, and VOOPOO-producing aerosols with geometric mean sizes of 19.9, 47.3, and 29.4 nm, respectively. Applying the International Commission on Radiological Protection (ICRP) deposition model and assuming no further evolution of aerosols in the respiratory system, we estimated particle deposition in different respiratory regions: 45–60% in the alveolar region, 10–25% in the tracheobronchial region, and 20–35% in the extrathoracic region. The highest single-puff deposition was observed with the VOOPOO device at 60 W, depositing 180.1 ± 7.6 μg in the alveolar region. The gas emissions (CO2, NOx, CO, and total hydrocarbons) were measured at different power settings of the VOOPOO EC. Single-puff NOx and CO levels exceeded the permissible exposure limits of the Occupational Safety and Health Administration, indicating potential acute exposure risks. Higher power settings were correlated with increased gas mixing ratios, suggesting more e-liquid vaporization and possible chemical transformations at higher temperatures. These findings demonstrated significant health risks associated with ultrafine particles from high-power ECs and emphasize the need for advanced measurements to accurately assess their physicochemical properties and potential health implications. 

Electronic cigarettes (ECs) emit many toxic substances, including metals, that can pose a threat to users and the environment. The toxicity of the emitted metals depends on their oxidation states. Hence, this study examines the oxidation states of metals observed in EC aerosols. X-ray photoelectron spectroscopy analysis of the filters that collected EC aerosols identified the oxidation states of five primary metals (based on surface sample analysis), including chromium(III) (close to 100%) under low power setting while a noticeable amount of chromium(VI) (15%) at higher power settings of the EC, and copper(II) (100%), zinc(II) (100%), nickel(II) (100%), lead(II) (65%), and lead(IV) (35%) regardless of power settings. This observation indicates that the increased temperature due to higher power settings could alter the oxidation states of certain metals. We noted that many metals were in their lesser toxic states; however, inhaling these metals may still pose health risks. 

Abstract Ultraviolet germicidal irradiation (UVGI) and ozone disinfection are crucial methods for mitigating the airborne transmission of pathogenic microorganisms in high-risk settings, particularly with the emergence of respiratory viral pathogens such as SARS-CoV-2 and avian influenza viruses. This study quantitatively investigates the influence of UVGI and ozone on the viability ofE. coliin bioaerosols, with a particular focus on howE. coliviability depends on the size of the bioaerosols, a critical factor that determines deposition patterns within the human respiratory system and the evolution of bioaerosols in indoor environments. This study used a controlled small-scale laboratory chamber whereE. colisuspensions were aerosolized and subjected to varying levels of UVGI and ozone levels throughout the exposure time (2–6 s). The normalized viability ofE. coliwas found to be significantly reduced by UVGI (60–240μW s cm⁻²) as the exposure time increased from 2 to 6 s, and the most substantial reduction ofE. colinormalized viability was observed when UVGI and ozone (65–131 ppb) were used in combination. We also found that UVGI reduced the normalized viability ofE. coliin bioaerosols more significantly with smaller sizes (0.25–0.5μm) than with larger sizes (0.5–2.5μm). However, when combining UVGI and ozone, the normalized viability was higher for smaller particle sizes than for the larger ones. The findings provide insights into the development of effective UVGI disinfection engineering methods to control the spread of pathogenic microorganisms in high-risk environments. By understanding the influence of the viability of microorganisms in various bioaerosol sizes, we can optimize UVGI and ozone techniques to reduce the potential risk of airborne transmission of pathogens. 

The usage of electronic cigarettes (ECs) has surged since their invention two decades ago. However, to date, the health effects of EC aerosol exposure are still not well understood because of insufficient data on the chemical composition of EC aerosols and the corresponding evidence of health risks upon exposure. Herein, we quantified the metals in primary and secondhand aerosols generated by three brands of ECs. By combining aerosol filter sampling and inductively coupled plasma mass spectrometry (ICP-MS), we assessed the mass of metals as a function of EC flavoring, nicotine concentration, device power, puff duration, and aging of the devices. The masses of Cr, Cu, Mn, Ni, Cu, and Zn were consistently high across all brands in the primary and secondhand aerosols, some of which were above the regulated maximum daily intake amount, especially for Cr and Ni with mass (nanograms per 10 puffs) emitted at 117 ± 54 and 50 ± 24 (JUUL), 125 ± 77 and 219 ± 203 (VOOPOO), and 33 ± 10 and 27 ± 2 (Vapor4Life). Our analysis indicates that the metals are predominantly released from the EC liquid, potentially through mechanisms such as bubble bursting or the vaporization of metal–organic compounds. High metal contents were also observed in simulated secondhand aerosols, generally 80–90% of those in primary aerosols. Our findings provide a more detailed understanding of the metal emission characteristics of EC for assessing its health effects and policymaking.