Estimating the human health risks associated with exposures to harmful constituents emitted from electronic cigarettes
Creators: name: Son, Yeongkwon
Publisher: name: No Publisher Supplied
Year: 2018

description: The use of electronic cigarettes (e-cigarettes) has been rapidly increased because e-cigarettes are believed to be less harmful to health than conventional cigarettes. In the past five years, a few human and rodent in vivo and in vitro studies have suggested adverse health effects associated with e-cigarette vaping. However, the emission of chemicals and particles from e-cigarettes is still not well understood under “real-world” vaping conditions. This study evaluated the impacts of “real-world” e-cigarette battery power outputs, vaping topographies, and e-liquid compositions on e-cigarette particle size distribution, e-vapor chemical composition, and the vaping-induced human cancer risk.   E-vapors were generated using a smoking machine under various e-cigarette power settings, vaping topographies, and e-liquid compositions. These e-vapor generation conditions reflected the “real-world” e-cigarettes use pattern, and were obtained from the literature and a panel of 23 current e-cigarette users. E-cigarette particle size distributions (10 nm - 5 m) were measured with a portable aerosol mobility spectrometer and an optical particle counter. E-cigarette particle deposition patterns in human airways were estimated using the Multiple-Path Particle Dosimetry (MPPD) Model. Harmful constitutes in e-vapor were characterized for nicotine and nicotyrine (ultraviolet–visible (UV) spectroscopy), hydroxyl radical (UV fluorescence), and carbonyls (high performance liquid chromatography (HPLC)-UV detection). Human cancer risks associated with e-cigarette vaping were also estimated using Monte Carlo simulations.  The count median diameter (CMD) of e-cigarette particles ranged from 116 to 280. The CMD increased by 46%, when the heating power increased from 6.4 watts to 31.3 watts. The CMD of the particles generated from the vegetable glycerin (VG)-based e-liquid was 44% larger than the CMD of the particles generated from propylene glycol (PG)-based e-liquids. Both longer puff duration and smaller puff volume facilitated the formation of bigger e-cigarette particles. This study, for the first time, discovered that e-cigarette particle measurement results are substantially influenced by measurement temperature and humidity.   The amount of nicotine generated from e-cigarette vaping (ranging from 0.37 µg to 249.02 µg per puff) was comparable to cigarette smoking, especially under high e-cigarette power output, large puff volume, and high e-liquid nicotine levels. E-cigarette coil temperature favored the formation of nicotiyrine, the concentration of which in e-vapor were substantially higher than that in cigarette smoke (55-222 ng per puff for e-cigarette vs. 2-13 ng per puff for cigarette).   Higher e-cigarette power and larger puff volume facilitated the formation of hydroxyl radical in e-vapor. An increase in power output and puff volume resulted in significantly higher levels of •OH formation in e-vapor due to the elevated coil temperature and oxygen supply. VG-based e-liquids generated higher amount of •OH than PG-based e-liquids. Furthermore, e-vapor could induce •OH formation, and the co-exposure to transition metal ions accelerated •OH formation. Flavored e-liquids generated larger amount of •OH in e-vapor than non-flavored e-liquids.   Compared with VG-based e-liquid, PG-based e-liquids increased formaldehyde and acetaldehyde emission by 2 - 12 folds. Other potentially harmful chemicals were also identified in e-vapor, including glyoxal, acrolein, diacetyl and acetylpropionyl. An increase in device power output from 6.4 watts to 31.3 watts resulted in the increase in formaldehyde emission by 39.3% (1257.8 ug per puff) and 142.1% (2318.2 ug per puff) for VG and PG e-liquid, respectively. PG-based e-liquid generated higher levels of formaldehyde and acetaldehyde than VG-based e-liquid by a factor of 2 and 12, respectively. In addition, glyoxal and acrolein were detected in e-vapor under high power output conditions. Other potentially harmful carbonyls or their precursors, including diacetyl, acetylpropionyl and acetoin, were observed in e-vapor generated from flavored e-liquids.   Cancer risks associated with e-cigarette vaping ranged from 9.55×106 to 7.51×104, mainly contributed by carbonyls. Vaping under 31.3 watts posed a 2 -3 times higher cancer risk than vaping under 6.4 watts. PG and PG&amp;VG mixture based e-liquids induced 3.9 and 2.3 folds higher cancer risks than VG-based e-liquids. In contrast, if the cancer risks were normalized by e-vapor nicotine concentrations, vaping under 14.7 watts and 31.3 watts posed 7 - 10 folds smaller cancer risks than vaping under 6.4 watts.