Abstract
The current fourth generation (“pod-style”) electronic cigarette, or vaping, products (EVPs) heat a liquid (“e-liquid”) contained in a reservoir (“pod”) using a battery-powered coil to deliver aerosol into the lungs. A portion of inhaled EVP aerosol is estimated as exhaled, which can present a potential secondhand exposure risk to bystanders. The effects of modifiable factors using either a prefilled disposable or refillable pod-style EVPs on aerosol particle size distribution (PSD) and its respiratory deposition are poorly understood. In this study, the influence of up to six puff profiles (55-, 65-, and 75-ml puff volumes per 6.5 and 7.5 W EVP power settings) on PSD was evaluated using a popular pod-style EVP (JUUL® brand) and a cascade impactor. JUUL® brand EVPs were used to aerosolize the manufacturers' e-liquids in their disposable pods and laboratory prepared “reference e-liquid” (without flavorings or nicotine) in refillable pods. The modeled dosimetry and calculated aerosol mass median aerodynamic diameters (MMADs) were used to estimate regional respiratory deposition. From these results, exhaled fraction of EVP aerosols was calculated as a surrogate of the secondhand exposure potential. Overall, MMADs did not differ among puff profiles, except for 55- and 75-ml volumes at 7.5 W (p < 0.05). For the reference e-liquid, MMADs ranged from 1.02 to 1.23 μm and dosimetry calculations predicted that particles would deposit in the head region (36–41%), in the trachea-bronchial (TB) region (19–21%), and in the pulmonary region (40–43%). For commercial JUUL® e-liquids, MMADs ranged from 0.92 to 1.67 μm and modeling predicted that more particles would deposit in the head region (35–52%) and in the pulmonary region (30–42%). Overall, 30–40% of the particles aerosolized by a pod-style EVP were estimated to deposit in the pulmonary region and 50–70% of the inhaled EVP aerosols could be exhaled; the latter could present an inhalational hazard to bystanders in indoor occupational settings. More research is needed to understand the influence of other modifiable factors on PSD and exposure potential.
Highlights
IntroductionElectronic cigarette, or vaping, products (EVPs) heat liquids (“eliquids”) using a battery-operated coil and deliver the aerosolized particles to the lungs
Toxicological studies have reported evidence of deleterious health effects on heating e-liquids in pod-style EVP design—either prefilled in JUUL R or simulated JUUL R -like e-liquids, the PSD of emitted EVPs aerosol as a significant determinant for their regional respiratory depositions has not been addressed adequately [28, 65]
For all puff profiles with the reference e-liquid, the dosimetry analysis predicted that 40–43% of total respiratory depositions of particles were in the pulmonary regions where toxicological implications have been reported
Summary
Electronic cigarette, or vaping, products (EVPs) heat liquids (“eliquids”) using a battery-operated coil and deliver the aerosolized particles to the lungs. By 2014, EVPs were the most popular tobacco product among youth in the USA. The evolution of internal design and external appearance of EVPs have occurred with each consequent modification, referred to as “generations” [1–3]. The current, fourth generation, EVPs or “pod-mod” or “pod-style” device type includes two parts: a heating coil/eliquid reservoir assembly and a flow-activated, rechargeable battery. The coil/e-liquid reservoir assembly is referred to as a “pod” and is either a prefilled disposable pod or refillable pod. For consistency in our study, the fourth generation EVP design type is described as pod-style. A pod-style design such as JUUL R brand has been popular for its sleek design, user-friendly function, desirable flavors, and ability to be used for “stealth vaping” [4–14]
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