3.1. Exhaled Aerosol Mass Balance Distribution of Water, Glycerin and Nicotine
The average number of exhaled puffs collected during the water, glycerin and nicotine, phenolic and carbonyl collection sessions were not significantly different between methods as determined by an ANOVA analysis. The average number of exhaled puffs was 30 for three cigarettes and 95 for e-cigarettes during the water, glycerin and nicotine collection sessions.
Nicotine, glycerin and water analysis were used to compare distribution and mass balance of these analytes in exhaled aerosols. Distribution is determined by measuring the amounts of these compounds in exhalate collection sessions for the three products and then dividing by the sum total of the three constituents. The average distributions of exhaled e-cigarette aerosols are shown in
Figure 3.
Figure 3.
Average distributions and mass balances of water, glycerin and nicotine in exhaled e-cigarette aerosols for (a) blu Classic Tobacco Disposable (blu CTD) and (b) blu Magnificent Menthol Disposable (blu MMD).
Figure 3.
Average distributions and mass balances of water, glycerin and nicotine in exhaled e-cigarette aerosols for (a) blu Classic Tobacco Disposable (blu CTD) and (b) blu Magnificent Menthol Disposable (blu MMD).
The exhaled aerosol mass from the two e-cigarettes is primarily water and glycerin, which together comprise greater than 99.9% of the collected aerosol distribution. Average mass balances for water, glycerin and nicotine were fully accounted for in the e-cigarette aerosols at 104% and 101%. Machine-generated mainstream from e-cigarettes contain approximately 86% glycerin and 8% water [
29], which is similar to the e-liquid composition itself. The high concentration of water in the exhaled e-cigarette aerosol has been attributed to water accretion from the respiratory tract by the hydrophilic glycerin aerosol [
31].
Average mass balance for nicotine, glycerin and water in exhaled aerosol from the conventional cigarette was (83% ± 21%). The remaining exhaled aerosol mass for cigarettes samples are attributed to particulates from combustion processes known to comprise more than 70% of mainstream conventional cigarette smoke [
32,
33]. The concentration of nicotine observed in exhaled cigarette smoke was approximately an order of magnitude higher than in the exhaled e-cigarette aerosols (~0.40%
vs. ~0.05%, respectively). Furthermore, the great majority (~85%) of real-world bystander exposures to nicotine and other smoke constituents in smoking environments is derived from the sidestream smoke emitted from the smoldering cigarette rather than from smokers’ exhaled breaths [
14]. Since e-cigarettes do not produce such sidestream emissions, the reductions in most potential bystander chemical exposures that accompany indoor e-cigarette usage as opposed to smoking may be anticipated to be even greater than the differences in exhaled nicotine concentrations of the very different aerosols. The public health impacts of environmental tobacco smoke have been overwhelmingly attributed to chemical constituents other than nicotine, so the simple presence of some nicotine in the exhalate of e-cigarette users does not suggest a basis for concern about bystander exposures.
3.2. Exhaled Phenolics and Carbonyls
The majority of phenolic and carbonyl measurements in exhaled e-cigarette aerosols were either not detectable, below the detection limits or below the quantitation limits. However, these analytes were consistently observed in exhaled cigarette smoke at quantifiable levels. Example data are shown in
Table 3 for hydroquinone and acetaldehyde.
Table 3.
Hydroquinone and acetaldehyde in exhaled aerosol (µg/session) for Marlboro Gold Box (MGB), blu Classic Tobacco Disposable (blu CTD) and blu Magnificent Menthol Disposable (blu MMD).
Table 3.
Hydroquinone and acetaldehyde in exhaled aerosol (µg/session) for Marlboro Gold Box (MGB), blu Classic Tobacco Disposable (blu CTD) and blu Magnificent Menthol Disposable (blu MMD).
MGB | Blu CTD | Blu MMD |
---|
Subject | Acetaldehyde | Hydroquinone | Subject | Acetaldehyde | Hydroquinone | Subject | Acetaldehyde | Hydroquinone |
---|
1 | 227.6 | 70.6 | 11 | <LOQ | <LOD | 21 | 16.7 | <LOD |
186.0 | 60.0 | <LOQ | <LOD | 35.3 | <LOD |
221.0 | 69.1 | <LOQ | <LOD | 38.9 | <LOD |
2 | 134.7 | 41.3 | 12 | <LOQ | <LOD | 22 | <LOQ | <LOD |
129.8 | 33.2 | <LOQ | <LOD | <LOQ | <LOD |
107.7 | 31.9 | <LOQ | <LOD | <LOQ | <LOD |
3 | 131.2 | 32.2 | 13 | <LOQ | <LOD | 23 | <LOQ | <LOD |
169.0 | 47.4 | 86.4 | <LOD | <LOQ | <LOD |
128.1 | 52.5 | 44.2 | <LOD | <LOQ | <LOD |
4 | 115.6 | 48.5 | 14 | <LOQ | <LOD | 24 | 5.4 | <LOD |
119.3 | 47.3 | <LOQ | <LOD | 7.2 | <LOD |
124.1 | 42.5 | <LOQ | <LOD | 9.9 | <LOD |
5 | 195.4 | 18.4 | 15 | <LOQ | <LOD | 25 | <LOQ | <LOD |
122.0 | 13.3 | <LOQ | <LOD | <LOQ | <LOD |
196.3 | 20.0 | <LOQ | <LOD | <LOQ | <LOD |
6 | 208.0 | 99.5 | 16 | <LOQ | <LOD | 26 | <LOQ | <LOD |
116.9 | 103.5 | <LOQ | <LOD | <LOQ | <LOD |
116.0 | 83.9 | <LOQ | <LOD | <LOQ | <LOD |
7 | <LOQ | 22.8 | 17 | <LOQ | <LOD | 27 | <LOQ | <LOD |
88.1 | 8.79 | <LOQ | <LOD | <LOQ | <LOD |
48.1 | 25.9 | <LOQ | <LOD | 6.2 | <LOD |
8 | 380.2 | 29.1 | 18 | <LOD | <LOD | 28 | <LOQ | <LOD |
193.7 | 37.7 | 24.2 | <LOD | <LOQ | <LOD |
189.7 | 30.9 | <LOQ | <LOD | 7.1 | <LOD |
9 | 285.2 | 73.0 | 19 | <LOQ | <LOD | 29 | 6.5 | <LOD |
126.6 | 26.8 | <LOQ | <LOD | 8.9 | <LOD |
104.6 | 81.6 | <LOQ | <LOD | 7.6 | <LOD |
10 | 217.6 | 43.0 | 20 | 6.9 | <LOD | 30 | <LOQ | <LOD |
162.7 | 46.2 | <LOQ | <LOD | <LOQ | <LOD |
114.1 | 64.0 | <LOQ | <LOQ | 5.4 | <LOD |
Avg * | 156.7 | 46.8 | | <9.73 * | <0.421 * | | <8.29 * | <0.367 * |
SD | 68.8 | 24.7 | | 16.5 | 0.3 | | 8.2 | 0.0 |
LOQ | 41.6 | 2.00 | | 5.20 | 2.00 | | 5.20 | 2.00 |
LOD | 0.390 | 0.367 | | 0.390 | 0.367 | | 0.390 | 0.367 |
To simplify data reporting, total phenolic compounds and total carbonyl compounds in exhaled aerosols are presented for each product, along with exhaled breath blanks for comparison. Upper-limit estimates for exhaled aerosol compositions are accomplished by using the method limits for observations below the limits of detection and quantitation. In cases where individual measurements were less than the limits of quantitation, the limit of quantitation values were used and in cases where the measurements were non-detects or less than the limits of detection, the limit of detection values were used to compare analytes in exhaled aerosol between products. ANOVA comparisons were performed to test for differences between exhaled aerosol samples, breath blanks and room air (α = 0.05).
Total exhaled phenolics are shown in
Figure 4 for exhaled aerosol and breaths collected following use of each product. The average number of exhaled puffs was 29 for three cigarettes and 98 for e-cigarettes during the phenolics collection sessions. Phenolics in exhaled breath blanks were all below limits of quantitation or limits of detection for the three products tested. The average total phenolics in exhaled e-cigarette aerosols were not statistically different than in exhaled breaths. In contrast, the average total phenolic compounds in exhaled smoke for cigarette subjects averaged 66 µg/session and ranged from 36 to 117 µg/session, significantly greater than in exhaled e-cigarette aerosol or exhaled breaths. The total phenolics for the ten MGB subjects is comparable, although higher, than data reported by Moldoveanu [
23] for the phenolic compounds reported here, (12.3 µg/3 cigs, range 6–25 µg/3 cigs).
Figure 4.
Total exhaled phenolics for exhaled aerosol and breaths for Marlboro Gold Box (MGB), blu Classic Tobacco Disposable (blu CTD) and blu Magnificent Menthol Disposable (blu MMD).
Figure 4.
Total exhaled phenolics for exhaled aerosol and breaths for Marlboro Gold Box (MGB), blu Classic Tobacco Disposable (blu CTD) and blu Magnificent Menthol Disposable (blu MMD).
Figure 5 summarizes total carbonyl compounds exhaled from each product, exhaled breaths and room blanks. The average number of exhaled puffs was 27 for three cigarettes and 98 for e-cigarettes during the carbonyl collection sessions. Carbonyls in room air blanks and exhaled breath blanks were observed at the levels of quantitation due to the pervasive nature of carbonyls in indoor environments [
20,
21,
22,
23]. Room air blanks, exhaled breath blanks and exhalates from the two e-cigarettes were not statistically different. And as a result, total carbonyls in exhalates from the two e-cigarettes were not distinguishable from exhaled breaths or room air blanks. However, total carbonyls in exhaled smoke from cigarettes were significantly greater than the total carbonyls in exhaled e-cigarette aerosols, exhaled breaths and room blanks (average 242 µg/session, range 136–352 µg/session). The total carbonyls for the ten MGB subjects is comparable to historical data from Moldoveanu [
24], for the carbonyls reported here, (average 183 µg/3 cigs, range 122–309 µg/3 cigs).
The absence of carbonyls and phenolics at quantifiable levels in exhaled e-cigarette aerosols is also demonstrated by comparing acetaldehyde and hydroquinone, as examples, for exhaled aerosol from products, breath blanks and room air as shown in
Table 4. The sample aerosol values for the e-cigarettes are not statistically different than breath blanks, or room blanks.
Figure 5.
Total carbonyls in exhaled aerosol, breaths and room blanks for Marlboro Gold Box (MGB), blu Classic Tobacco Disposable (blu CTD) and blu Magnificent Menthol Disposable (blu MMD).
Figure 5.
Total carbonyls in exhaled aerosol, breaths and room blanks for Marlboro Gold Box (MGB), blu Classic Tobacco Disposable (blu CTD) and blu Magnificent Menthol Disposable (blu MMD).
Table 4.
Hydroquinone and acetaldehyde in exhaled aerosol, breaths and room air (µg/session) for blu Classic Tobacco Disposable (blu CTD) and blu Magnificent Menthol Disposable (blu MMD).
Table 4.
Hydroquinone and acetaldehyde in exhaled aerosol, breaths and room air (µg/session) for blu Classic Tobacco Disposable (blu CTD) and blu Magnificent Menthol Disposable (blu MMD).
Analyte | Blu CTD | Blu MMD |
---|
Aerosol | Breaths | Air | Aerosol | Breaths | Air |
---|
Hydroquinone | Mean | <0.421 * | <0.367 * | ND | <0.367 * | <0.367 * | ND |
SD | 0.3 | 0.0 | ND | 0.0 | 0.0 | ND |
Acetaldehyde | Mean | <9.73 * | <9.58 * | <3.60 * | <8.29 * | <5.20 * | <5.20 * |
SD | 16.5 | 16.0 | 2.3 | 8.2 | 0.0 | 0.0 |
Recent work by Robinson,
et al. characterized the potential for second-hand e-cigarette exposure in indoor air from human subjects using validated air sampling methods (ASTM, EPA, NIOSH and OSHA) for 34 HPHC analytes [
34]. Carbonyls and phenolics were no different than background levels in the room when the study subjects used e-cigarettes. Carbonyls were significantly greater than background when conventional cigarettes were smoked. Phenolics were no different than background for conventional cigarettes. Combustion byproducts were not observed above background for e-cigarettes but were present during conventional cigarette use.
The findings of this study establish the substantial reduction in the complexity and quantities of select chemical constituents in exhaled aerosols from e-cigarettes relative to exhaled smoke from conventional cigarettes. These constituents are expected in mainstream and exhaled conventional cigarette smoke as demonstrated in this study and in extant literature since their formation is a result of combustion and pyrolysis processes. However, the thermal vaporization mode of operation common to e-cigarette designs does not provide a combustion formation pathway for those analytes. Whereas the present work has focused on the smaller, cigarette-like devices that have historically been market leaders in the U.S., the operation of these devices is fundamentally very similar to that of the larger, tank-style products that are increasingly favored by vapers in the U.S. and elsewhere around the world. The emerging technical literature in this area is consistent with an expectation that similarities in emitted and exhaled aerosols across the spectrum of innovative new e-cigarette designs will continue to demonstrate markedly reduced exposures to both users and bystanders relative to those that occur from conventional cigarette smoking.