The fate of selected electronic nicotine delivery systems (ENDS) constituents in adolescents and young adults

Electronic nicotine delivery systems (ENDS) use is prevalent among adolescents and young adults. While there have been several efforts to estimate the exposure and dose of ENDS puff constituents in adults, no study to date has focused on younger ENDS users. Given the non-uniformity of lung growth with age, the lungs of young people cannot be considered miniature versions of those of adults; in addition, breathing profiles and flow rates may substantially differ with age. Thus, inhalation dosimetry models developed for adults cannot be directly applied to youth without proper modifications. We extended a previously developed ENDS aerosol deposition model for adults to younger ages (10–21 years) by developing age-specific lung geometries based on available data on lung morphometry and using relationships such as the volume of the oral cavity of adults based on the relevant trachea dimensions, using relationships for volume of the oral cavity for inhaled puff volume, and functional residual capacity (FRC) at different ages. We then used the age-specific deposition model to predict the fate of an ENDS puff with selected constituents (nicotine, propylene glycol, vegetable glycerin, benzaldehyde, and vanillin). Model predictions showed similar patterns of deposition to those of adults in terms of droplet deposition versus vapor uptake. Total deposition and deposition per surface area of individual constituents in the lung decreased with age. The age-specific deposition model is a useful tool to predict lung deposition of ENDS aerosol constituents and compare results across different age groups.