Introduction: Electronic cigarettes (commonly referred as e-cigarettes) are designed to generate inhalable nicotine aerosol (vapor). When an e-cigarette user takes a puff, the nicotine solution is heated and the vapor taken into lungs. Although no sidestream vapor is generated between puffs, some of the mainstream vapor is exhaled by e-cigarette user. The aim of the study was to evaluate the secondhand exposure to nicotine and other tobacco-related toxicants from e-cigarettes.
Materials and Methods: We measured selected airborne markers of secondhand exposure: nicotine, aerosol particles (PM2.5), carbon monoxide, and volatile organic compounds (VOCs) in an exposure chamber. We generated e-cigarette vapor from 3 various brands of e-cigarette using a smoking machine and controlled exposure conditions. We also compared secondhand exposure with e-cigarette vapor and tobacco smoke generated by 5 dual users.
Results: The study showed that e-cigarettes are a source of secondhand exposure to nicotine but not to combustion toxicants. The air concentrations of nicotine emitted by various brands of e-cigarettes ranged from 0.82 to 6.23 µg/m3. The average concentration of nicotine resulting from smoking tobacco cigarettes was 10 times higher than from e-cigarettes (31.60±6.91 vs. 3.32±2.49 µg/m3, respectively; p = .0081).
Using an e-cigarette in indoor environments may involuntarily expose nonusers to nicotine but not to toxic tobacco-specific combustion products. More research is needed to evaluate health consequences of secondhand exposure to nicotine, especially among vulnerable populations, including children, pregnant women, and people with cardiovascular conditions.
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Unanswered Questions and Future Research
This study did not test potential health effects associated with secondhand exposure to vapors from e-cigarettes. To date, there are few studies that have tested the acute effects of brief exposure to secondhand e-cigarette vapors. One study by Flouris et al. (2012) found that acute passive “vaping” of e-cigarettes did not influence complete blood count in human subjects. Another study by the same authors found that controlled 1-hr exposure to e-cigarette vapors did not significantly affect lung function in human subjects (Flouris et al., 2013).
We found no publications on the cardiovascular effects of passive exposure to e-cigarette vapors or on the health effects of secondhand exposure to e-cigarette vapors among vulnerable population, including children, pregnant women, and people with cardiovascular conditions.
There is some discrepancy between our findings and results reported recently by Flouris et al. (2013) on secondhand exposure to nicotine. Our data suggest that secondhand exposure to nicotine from e-cigarettes is on average 10 times less than from tobacco smoke. However, Flouris et al. (2013) found that e-cigarettes and tobacco cigarette generated similar effects on serum cotinine levels after 1-hr passive exposure (2.4 ± 0.9 vs. 2.6 ± 0.6 ng/ml, respectively; p < .001). Future research should look for correlation between indoor air levels of nicotine from e-cigarettes and its uptake by passive smokers to explain this discrepancy.
Future research should also study exposure patterns over extended periods of time and the potential health effects of long-term exposure to secondhand e-cigarette vapors. Data are also needed from the field studies conducted in homes and public places where e-cigarettes are in use. Moreover, this study only focused on nicotine and a limited number of chemicals released from e-cigarettes. Further research is needed to explore emission and exposure to other toxicants and carcinogens identified in e-cigarettes, for example, carbonyl compounds (Goniewicz, Knysak, et al., 2013).
It remains unclear whether concentration of PM 2.5 will be a suitable and reliable airborne marker to evaluate emission and exposure to secondhand vapors from e-cigarettes.
Although some studies suggest that e-cigarette vapor and SHS have comparable aerosol particle size distribution and deposition patterns, we found that concentration of e-cigarette aerosol particles tends to decrease rapidly when diluted in the air.
Figure 3 shows that there is a significant particle mass signal from e-cigarette vapor but that it dissipates much more rapidly than cigarette smoke. This may be due to the evaporation of the aerosol in addition to deposition on the surfaces and removal by ventilation. There is a need for developing an accurate methodology to assess e-cigarette vapor indoor concentrations.
Finally, the vapor from e-cigarettes might be easily deposited on surfaces to form “thirdhand” e-cigarette vapor, and studies are needed to assess the deposition rate, potential formation of toxic derivatives, and human exposure.
Implications for Policy Makers
The study showed that e-cigarettes might involuntarily expose nonsmokers and people who do not use e-cigarettes to nicotine.
In the past, secondhand exposure to nicotine has been primarily associated with exposure to ETS. E-cigarettes have created the new scenario under which bystanders might be exposed to low levels of nicotine but not to the other toxins found in tobacco smoke. It remains unclear whether exposure to low levels of nicotine indoors causes any harm to bystanders, including children, pregnant women, and person with cardiovascular conditions.
Besides nicotine, e-cigarette vapor contains significant amounts of propylene glycol and vegetable glycerin. Although both compounds are considered to be safe, there is lack of data on health risk associated with prolonged exposure to their vapors.
Propylene glycol has been shown to cause upper airway irritation (Vardavas et al., 2011). Some volatile carbonyl compounds have been also identified in the vapor of e-cigarettes (Goniewicz, Knysak, et al., 2013). More research is needed about the health risk associated with exposure to toxic constituents of the vapors.
The physicochemical changes may also occur after vapors are released into ambient air. It has been shown that such changes increase toxicity of tobacco smoke two- to four-fold (Schick & Glantz, 2006). These data are needed to inform regulators whether e-cigarettes should be included under smoke-free policies to protect nonusers from inhaling the toxicants.
E-cigarettes are promoted to circumvent smoke-free policies (Grana & Ling, 2013). Exempting e-cigarettes from smoke-free regulations, besides creating secondhand exposure to nicotine, might have additional implications for public health. It remains unclear whether observation of smokers using e-cigarettes, especially by young people, might reverse the denormalization of smoking behavior as a social norm. Cigarette smokers might use e-cigarettes as additional sources of nicotine in places with smoking bans. Data are needed to determine whether dual use of the products (e-cigarettes in addition to tobacco cigarettes) results in reinforcement of nicotine addiction.
This work was supported by the Ministry of Science and Higher Education of Poland (N N404 016939). The study sponsor had no involvement in the study design, collection, analysis, and interpretation of data, the writing of the manuscript, or the decision to submit the manuscript for publication.
DECLARATION OF INTERESTS
MLG received research funding from Pfizer, manufacturer of stop smoking medication, and was funded by the UK Centre for Tobacco Control Studies (UKCTCS) during the study. AS received research funds and travel expenses from Chic Group Ltd., manufacturer of electronic cigarettes in Poland. Other authors declare no conflict of interest.