Assessing electronic cigarette emissions: linking physico-chemical properties to product brand, e-liquid flavoring additives, operational voltage and user puffing patterns

Abstract

Users of electronic cigarettes (e-cigs) are exposed to particles and other gaseous pollutants. However, major knowledge gaps on the physico-chemical properties of such exposures and contradictory data in published literature prohibit health risk assessment. Here, the effects of product brand, type, e-liquid flavoring additives, operational voltage, and user puffing patterns on emissions were systematically assessed using a recently developed, versatile, e-cig exposure generation platform and state-of-the-art analytical methods. Parameters of interest in this systematic evaluation included two brands (A and B), three flavors (tobacco, menthol, and fruit), three types of e-cigs (disposable, pre-filled, and refillable tanks), two puffing protocols (4 and 2 s/puff), and four operational voltages (2.2-5.7 V). Particles were generated at a high number concentration (10-10 particles/cm). The particle size distribution was bi-modal (∼200 nm and 1 µm). Furthermore, organic species (humectants propylene glycol and glycerin, nicotine) that were present in e-liquid and trace metals (potassium and sodium) that were present on e-cig heating coil were also released into the emission. In addition, combustion-related byproducts, such as benzene and toluene, were also detected in the range of 100-38,000 ppbv/puff. Parametric analyzes performed in this study show the importance of e-cig brand, type, flavor additives, user puffing pattern (duration and frequency), and voltage on physico-chemical properties of emissions. This observed influence is indicative of the complexity associated with the toxicological screening of emissions from e-cigs and needs to be taken into consideration.

Metal/Metalloid Levels in Electronic Cigarette Liquids, Aerosols, and Human Biosamples: A Systematic Review

“…The total SD was estimated because it accounts for the SD within the groups as well as among the groups (Sharma 2006). For some studies, there were insufficient data to estimate the SD because only means were reported, with no estimation of variability around those point estimates (Beauval et al 2017;Dunbar et al 2018;Margham et al 2016;Palazzolo et al 2017;Song et al 2018;Williams et al 2013;Williams et al 2017;Zhao et al 2018). The study by Olmedo et al (2018) reported medians instead of means (SDs) in the original publication, but we calculated them directly from the original data.…”

“…The study by Olmedo et al (2018) reported medians instead of means (SDs) in the original publication, but we calculated them directly from the original data. For the study that reported two aerosol size fractions of particulate matter (PM 0:1 and PM 0:1-2:5 ), we kept only the PM 0:1 , because it is likely inhaled deep into the lungs, and metals/metalloids were not detected in the PM 0:1-2:5 (Zhao et al 2018).…”

“…Most studies of e-liquids reported metals/metalloids in micrograms per kilogram. For easy comparison, for studies reporting e-liquid metal/metalloid levels in micrograms per liter (Beauval et al 2017;Hess et al 2017;Palazzolo et al 2017;Talio et al 2015Talio et al , 2017Zhao et al 2018) and parts per billion (ppb) (Beauval et al 2016;Dunbar et al 2018;Song et al 2018), those concentrations were converted to micrograms per kilogram, assuming the e-liquid density was 1:16 g=ml (Sleiman et al 2016). Most studies of aerosols reported metals/metalloids in ng per puff.…”

“…Most studies of aerosols reported metals/metalloids in ng per puff. For studies reporting aerosol metal/metalloid levels in other units (Beauval et al 2017;Goniewicz et al 2014;Mikheev et al 2016;Olmedo et al 2018;Palazzolo et al 2017;Williams et al 2013Williams et al , 2015Williams et al , 2017Zhao et al 2018), we converted them to ng per puff. For the study by Mikheev et al (2016) that reported aerosol metal/metalloid levels in nanograms per milligram of total PM (TPM), we used the average mass of TPM per puff of 2 mg to convert nanograms per milligram TPM to ng per puff.…”

“…For the study by Olmedo et al (2018) that reported aerosol metal/metalloid levels in micrograms per kilogram, we first converted micrograms per kilogram to milligrams per cubic meter using the equation described in the original paper (C i = h i × m tot Vair ), and then converted milligrams per cubic meter to nanograms per puff using the conversion factor of 6:67 × 10 −5 m 3 =puff (Olmedo et al 2018). The study by Zhao et al (2018) reported aerosol metal/metalloid levels (nanograms per milligram) in PM with an aerodynamic diameter of ≤0:1 lm (PM 0:1 ). To facilitate comparison with the other studies, we estimated the mass of metals/metalloids per puff from the total aerosol mass (measured in PM 0:1 ) collected in 10 min divided by the number of puffs (17.65 puffs based on an inter-puff time of 30 s and puff duration of 4 s provided by their study) and multiplied by the metals/metalloids mass fraction (Zhao et al 2018).…”