Influence of electronic cigarette vaping on the composition of indoor organic pollutants, particles, and exhaled breath of bystanders

Particulate matter in aerosols produced by two last generation electronic cigarettes: a comparison in a real-world environment

The design of e-cigarettes (e-cigs) is constantly evolving and the latest models can aerosolize using high-power sub-ohm resistance and hence may produce specific particle concentrations. The aim of this study was to evaluate the aerosol characteristics generated by two different types of electronic cigarette in real-world conditions, such as a sitting room or a small office, in number of particles (particles/cm3). We compared the real time and time-integrated measurements of the aerosol generated by the e-cigarette types Just Fog and JUUL. Real time (10s average) number of particles (particles/cm3) in 8 different aerodynamic sizes was measured using an optical particle counter (OPC) model Profiler 212-2. Tests were conducted with and without a Heating, Ventilating Air Conditioning System (HVACS) in operation, in order to evaluate the efficiency of air filtration. During the vaping sessions the OPC recorded quite significant increases in number of particles/cm3. The JUUL e-cig produced significantly lower emissions than Just Fog with and without the HVACS in operation. The study demonstrates the rapid volatility or change from liquid or semi-liquid to gaseous status of the e-cig aerosols, with half-life in the order of a few seconds (min. 4.6, max 23.9), even without the HVACS in operation. The e-cig aerosol generated by the JUUL proved significantly lower than that generated by the Just Fog, but this reduction may not be sufficient to eliminate or consistently reduce the health risk for vulnerable non e-cig users exposed to it.

Exposure to secondhand aerosol from electronic cigarettes at homes: A real-life study in four European countries

Electronic cigarette (e-cigarette) use emits potentially hazardous compounds and deteriorates indoor air quality. Home is a place where e-cigarettes may frequently be used amid its increasing prohibition in public places. This study assessed the real-life scenario of bystanders' exposure to secondhand e-cigarette aerosol (SHA) at home. A one-week observational study was conducted within the TackSHS project in four countries (Greece, Italy, Spain, and the United Kingdom) in 2019 including: 1) homes of e-cigarette users living together with a non-user/non-smoker; and 2) control homes with no smokers nor e-cigarette users. Indoor airborne nicotine, PM2.5, and PM1.0 concentrations were measured as environmental markers of SHA. Biomarkers, including nicotine and its metabolites, tobacco-specific nitrosamines, propanediol, glycerol, and metals were measured in participants' saliva and urine samples. E-cigarette use characteristics, such as e-cigarette refill liquid's nicotine concentration, e-cigarette type, place of e-cigarette use at home, and frequency of ventilation, were also collected. A total of 29 e-cigarette users' homes and 21 control homes were included. The results showed that the seven-day concentrations of airborne nicotine were quantifiable in 21 (72.4 %) out of 29 e-cigarette users' homes; overall, they were quite low (geometric mean: 0.01 μg/m3; 95 % CI: 0.01-0.02 μg/m3) and were all below the limit of quantification in control homes. Seven-day concentrations of PM2.5 and PM1.0 in e-cigarette and control homes were similar. Airborne nicotine and PM concentrations did not differ according to different e-cigarette use characteristics. Non-users residing with e-cigarette users had low but significantly higher levels of cotinine, 3'-OH-cotinine and 1,2-propanediol in saliva, and cobalt in urine than non-users living in control homes. In conclusion, e-cigarette use at home created bystanders' exposure to SHA regardless of the e-cigarette use characteristics. Further studies are warranted to assess the implications of SHA exposure for smoke-free policy.

Assessment of worker chemical exposures in California vape shops

E-cigarettes are battery-operated devices that heat a liquid mixture to make an aerosol that is inhaled, or vaped, by the user. Vape shops are retail environments designed to fulfill customer demand for diverse e-liquid flavors and hardware options, which create unique worker exposure concerns. To characterize exposures to vape shop workers, especially to flavoring chemicals associated with known respiratory toxicity, this study recruited vape shops from the San Francisco Bay Area. In six shops, we measured air concentrations for volatile organic compounds, formaldehyde, flavoring chemicals, and nicotine in personal and/or area samples; analyzed components of e-liquids vaped during field visits; and assessed metals on surface wipe samples. Interviews and observations were conducted over the course of a workday in the same six shops and interviews were performed in an additional six where sampling was not conducted. Detections of the alpha-diketone butter flavoring chemicals diacetyl and/or 2,3-pentanedione were common: in the headspace of purchased e-liquids (18 of 26 samples), in personal air samples (5 of 16), and in area air samples (2 of 6 shops). Two exceedances of recommended exposure limits for 2,3-pentanedione (a short-term exposure limit and an 8-hr time-weighted average) were measured in personal air samples. Other compounds detected in the area and personal air samples included substitutes for diacetyl and 2,3-pentanedione (acetoin and 2,3-hexanedione) and compounds that may be contaminants or impurities. Furthermore, a large variety (82) of other flavoring chemicals were detected in area air samples. None of the 12 shops interviewed had a health and safety program. Six shops reported no use of any personal protective equipment (PPE) (e.g., gloves, chemical resistant aprons, eye protection) and the others stated occasional use; however, no PPE use was observed during any field investigation day. Recommendations were provided to shops that included making improvements to ventilation, hygiene, use of personal protective equipment, and, if possible, avoidance of products containing the alpha-diketone flavoring chemicals. Future research is needed to evaluate the long-term health risks among workers in the vape shop retail industry and for e-cigarette use generally. Specific areas include further characterizing e-liquid constituents and emissions, evaluating ingredient health risks, evaluating the contributions of different routes of exposure (dermal, inhalation, and ingestion), and determining effective exposure mitigation measures.

Thirdhand smoke from tobacco, e-cigarettes, cannabis, methamphetamine and cocaine: Partitioning, reactive fate, and human exposure in indoor environments

A source of chemical exposure to humans, thirdhand smoke (THS) refers to the contamination that persists indoors following the cessation of a smoking event. The composition of thirdhand smoke depends on the type of substance from which it originates. Although past studies have investigated the effects of tobacco THS on indoor air quality and human health, few have focused on the chemical composition and health impacts of other sources and components of THS. Here we review the state of knowledge of the composition and partitioning behavior of various types of indoor THS, with a focus on THS from tobacco, e-cigarettes, cannabis, and illicit substances (methamphetamine and cocaine). The discussion is supplemented by estimates of human exposure to THS components made with a chemical fate and exposure model. The modeling results show that while very volatile THS compounds (i.e., aromatics) are likely to be taken up by inhalation, highly water-soluble compounds tended to be dermally absorbed. Conversely, minimally volatile THS compounds with low solubility are predicted to be ingested through hand-to-mouth and object-to-mouth contact.

Prediction of potential passive exposure from commercial electronic nicotine delivery systems using exhaled breath analysis and computational fluid dynamic techniques

Use of computational fluid dynamic (CFD) modeling to predict temporal and spatial constituent exposure for non-electronic nicotine delivery systems (ENDS) users (passive exposure) provides a more efficient methodology compared to conducting actual exposure studies. We conducted a clinical study measuring exhaled breath concentrations of glycerin, propylene glycol, nicotine, benzoic acid, formaldehyde, acetaldehyde, acrolein, menthol and carbon monoxide from use of eight different commercial ENDS devices and a non-menthol and menthol cigarette. Because baseline adjusted levels of other constituents were not consistently above the limit of detection, the mean minimum and maximum per puff exhaled breath concentrations (N= 20/product) of glycerin (158.7-260.9µg), propylene glycol (0.941-3.58µg), nicotine (0.10-1.06µg), and menthol (0.432-0.605µg) from use of the ENDS products were used as input parameters to predict temporal and spatial concentrations in an environmental chamber, office, restaurant, and car using different ENDS use scenarios. Among these indoor locations and ENDS use scenarios, the car with closed windows resulted in the greatest concentrations while opening the car windows produced the lowest concentrations. The CFD predicted average maximum glycerin and propylene glycol concentration ranged from 0.25 to 1068µg m^-3and 1.5 pg m^-3to 13.56µg m^-3,respectively. For nicotine and menthol the CFD predicted maximum concentration ranged from 0.16 pg m^-3to 4.02µg m^-3and 0.068 pg m^-3to 2.43µg m^-3, respectively. There was better agreement for CFD-predicted nicotine concentrations than glycerin and propylene glycol with published reports highlighting important experimental and computational variables. Maximum measured nicotine levels from environmental tobacco smoke in offices, restaurants, and cars exceeded our maximum average CFD predictions by 7-97 times. For all the measured exhaled breath constituents and CFD predicted constituents, except for propylene glycol and glycerin, concentrations were less from use of ENDS products compared to combustible cigarettes. NCT number: NCT04143256.

Analysis of furans and pyridines from new generation heated tobacco product in Japan

Background

In recent years, heated tobacco products (HTPs), which are widely used in Japan, have been sold by various brands using additives such as flavors. It has been reported that the components of mainstream smoke are different from those of conventional cigarettes. In this study, we established an analytical method for furans and pyridines in the mainstream smoke, which are characteristic of HTPs and particularly harmful among the generated components, and investigated the amount of component to which the smokers are exposed.

Methods

We established a simple analytical method for simultaneous analysis of gaseous and particulate compounds in the mainstream smoke of HTPs (IQOS, glo, ploom S) in Japan by combining a sorbent cartridge and glass fiber filter (Cambridge filter pad (CFP)). Both the sorbent cartridge and CFP were extracted using 2-propanol and analyzed via GC-MS/MS to determine the concentration of furans and pyridines generated from each HTP.

Results

The results showed that the levels of target furans such as furfural, 2-furanmethanol, 2(5H)-furanone, and 5-methylfurfural tended to be higher in the mainstream smoke of glo than in standard cigarettes (3R4F). Pyridine, which is generated at a high level in 3R4F as a combustion component, and 4-ethenylpyridine (EP), which is a known marker of environmental tobacco smoke, were detected. Among these components, 2-furanmethanol and pyridine are classified as Group 2B (possibly carcinogenic to humans) by the International Agency for Research on Cancer (IARC). Therefore, it is possible that they will contribute to the health effects caused by use of HTPs.

Conclusions

Using the new collection and analytical method for furans and pyridines in the mainstream smoke of HTPs, the level of each compound to which smokers are exposed could be clarified. By comprehensively combining information on the amount of ingredients and toxicity, it will be possible to perform a more detailed calculation of the health risks of using HTPs. In addition, the components detected in this study may be the causative substances of indoor pollution through exhaled smoke and sidestream smoke; therefore, environmental research on the chemicals generated from HTPs would be warranted in future studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12199-021-01008-1.

Environmental and individual exposure to secondhand aerosol of electronic cigarettes in confined spaces: Results from the TackSHS Project†

Secondhand electronic cigarette (e-cigarette) aerosol (SHA) might impair indoor air quality and expose bystanders. This study aims to investigate exposure to SHA in controlled conditions of enclosed settings simulating real-world scenario. An experiment was performed in a car and in a room, in which SHA was generated during a 30-minute ad libitum use of an e-cigarette. The experiment was replicated on five consecutive days in each setting. We measured PM_2.5 , airborne nicotine concentrations, and biomarkers of exposure to SHA, such as nicotine metabolites, tobacco-specific nitrosamines, propylene glycol, and glycerol in bystanders' saliva samples before, during, and after the exposure period. Self-reported health symptoms related to exposure to SHA were also recorded. The results showed that the highest median PM_2.5 concentration was recorded during the exposure period, being 21 µg/m³ in the room setting and 16 µg/m³ in the car setting-about twofold increase compared to the baseline. Most concentrations of the airborne nicotine and all biomarkers were below the limit of quantification in both settings. Bystanders in both settings experienced some short-term irritation symptoms, expressed as dry throat, nose, eyes, and phlegm. In conclusion, short-term use of an e-cigarette in confined spaces increased indoor PM_2.5 level and caused some irritation symptoms in bystanders.

Electronic cigarettes, vaping-related lung injury and lung cancer: where do we stand?

Electronic cigarettes have been considered a promising alternative to nicotine replacement products to help heavy tobacco smokers quit smoking. They work thanks to a heating coil causing evaporation of the liquid rapidly followed by cooling, thus creating an aerosol, a completely different mechanism from the combustion of tobacco in traditional cigarettes. The term 'vaping' indicates the use of electronic cigarettes or other devices to inhale heated, aerosolized nicotine, or other substances like cannabidiol, tetrahydrocannabinol, or butane hash oils together with solvents, mainly propylene glycol and vegetable glycerine or their combination. A very fast increase of vaping among adolescents has been observed since electronic cigarettes and other vaping devices first appeared. Although electronic cigarettes have been advocated as a short-term cessation aid for tobacco smokers or as a long-term alternative, there is the concrete risk that they can be perceived by young nonsmokers as a less dangerous alternative to tobacco smoking, thus stimulating nonsmokers to start smoking rather than helping heavy tobacco smokers to quit smoking. Moreover, several cases of exogenous lipoid pneumonia and diffuse alveolar hemorrhage with proven alveolar injury, as well as vaping-associated bronchiolitis obliterans, have been recently reported among electronic cigarette smokers, with severe clinical impact, thus posing the risk of the life-threatening toxic potential of vaping. At the moment, no definitive assessment can be made about the efficacy of electronic cigarettes as a smoking cessation aid, and further studies are required about vaping-related life-threatening acute lung injury.

Toxicology of flavoring- and cannabis-containing e-liquids used in electronic delivery systems

Electronic cigarettes (e-cigarettes) were introduced in the United States in 2007 and by 2014 they were the most popular tobacco product amongst youth and had overtaken use of regular tobacco cigarettes. E-cigarettes are used to aerosolize a liquid (e-liquid) that the user inhales. Flavorings in e-liquids is a primary reason for youth to initiate use of e-cigarettes. Evidence is growing in the scientific literature that inhalation of some flavorings is not without risk of harm. In this review, 67 original articles (primarily cellular in vitro) on the toxicity of flavored e-liquids were identified in the PubMed and Scopus databases and evaluated critically. At least 65 individual flavoring ingredients in e-liquids or aerosols from e-cigarettes induced toxicity in the respiratory tract, cardiovascular and circulatory systems, skeletal system, and skin. Cinnamaldehyde was most frequently reported to be cytotoxic, followed by vanillin, menthol, ethyl maltol, ethyl vanillin, benzaldehyde and linalool. Additionally, modern e-cigarettes can be modified to aerosolize cannabis as dried plant material or a concentrated extract. The U.S. experienced an outbreak of lung injuries, termed e-cigarette, or vaping, product use-associated lung injury (EVALI) that began in 2019; among 2,022 hospitalized patients who had data on substance use (as of January 14, 2020), 82% reported using a delta-9-tetrahydrocannabinol (main psychoactive component in cannabis) containing e-cigarette, or vaping, product. Our literature search identified 33 articles related to EVALI. Vitamin E acetate, a diluent and thickening agent in cannabis-based products, was strongly linked to the EVALI outbreak in epidemiologic and laboratory studies; however, e-liquid chemistry is highly complex, and more than one mechanism of lung injury, ingredient, or thermal breakdown product may be responsible for toxicity. More research is needed, particularly with regard to e-cigarettes (generation, power settings, etc.), e-liquids (composition, bulk or vaped form), modeled systems (cell type, culture type, and dosimetry metrics), biological monitoring, secondhand exposures and contact with residues that contain nicotine and flavorings, and causative agents and mechanisms of EVALI toxicity.

Nicotine, Cotinine, and Tobacco-Specific Nitrosamines Measured in Children's Silicone Wristbands in Relation to Secondhand Smoke and E-cigarette Vapor Exposure

INTRODUCTION

Simple silicone wristbands (WB) hold promise for exposure assessment in children. We previously reported strong correlations between nicotine in WB worn by children and urinary cotinine (UC). Here, we investigated differences in WB chemical concentrations among children exposed to secondhand smoke from conventional cigarettes (CC) or secondhand vapor from electronic cigarettes (EC), and children living with nonusers of either product (NS).

METHODS

Children (n = 53) wore three WB and a passive nicotine air sampler for 7 days and one WB for 2 days, and gave a urine sample on day 7. Caregivers reported daily exposures during the 7-day period. We determined nicotine, cotinine, and tobacco-specific nitrosamines (TSNAs) concentrations in WB, nicotine in air samplers, and UC through isotope-dilution liquid chromatography with triple-quadrupole mass spectrometry.

RESULTS

Nicotine and cotinine levels in WB in children differentiated between groups of children recruited into NS, EC exposed, and CC exposed groups in a similar manner to UC. WB levels were significantly higher in the CC group (WB nicotine median 233.8 ng/g silicone, UC median 3.6 ng/mL, n = 15) than the EC group (WB nicotine median: 28.9 ng/g, UC 0.5 ng/mL, n = 19), and both CC and EC group levels were higher than the NS group (WB nicotine median: 3.7 ng/g, UC 0.1 ng/mL, n = 19). TSNAs, including the known carcinogen NNK, were detected in 39% of WB.

CONCLUSIONS

Silicone WB show promise for sensitive detection of exposure to tobacco-related contaminants from traditional and electronic cigarettes and have potential for tobacco control efforts.

IMPLICATIONS

Silicone WB worn by children can absorb nicotine, cotinine, and tobacco-specific nitrosamines, and amounts of these compounds are closely related to the child's urinary cotinine. Levels of tobacco-specific compounds in the silicone WB can distinguish patterns of children's exposure to secondhand smoke and e-cigarette vapor. Silicone WB are simple to use and acceptable to children and, therefore, may be useful for tobacco control activities such as parental awareness and behavior change, and effects of smoke-free policy implementation.

Room air constituent concentrations from use of electronic nicotine delivery systems and cigarettes using different ventilation conditions

To assess potential exposure of non-users to exhaled constituents from pod and cartridge electronic nicotine delivery systems (ENDS) products, an environmental clinical study was conducted with (n = 43) healthy adult smokers. Room air concentrations of 34 selected constituents (nicotine, propylene glycol, glycerin, 15 carbonyls, 12 volatile organic compounds, and 4 trace metals) and particle number concentration (0.3 to 25 µm) were compared from use of two ENDS products and conventional cigarettes using room ventilations representative of a residential, an office or a hospitality setting over a 4-h. exposure period. Products used were JUUL ENDS, Virginia Tobacco flavor (Group I), VUSE Solo, Original flavor (Group II) (5.0 and 4.8% nicotine by weight, respectively) and subjects' own conventional cigarettes (Group III). Cumulative 4-h room air sampling and particle counting were performed during prescribed (Groups I and II) and ad libitum product use (all Groups). Conventional cigarette use resulted in significantly more constituents detected and higher 4-h cumulative constituent concentrations compared to use of the ENDS products tested, except for the predominant ENDS ingredients, propylene glycol and glycerin. Use of conventional cigarettes also resulted in greater total particle number concentration than either prescribed or ad libitum use of either of the ENDS used in this study.

Breath analysis of smokers, non-smokers, and e-cigarette users

Solid phase micro extraction-Gas Chromatography/Mass Spectrometry (SPME-GC/MS) analysis was performed in exhaled breath samples of 48 healthy volunteers: 20 non-smokers, 10 smokers and 18 e-cigarette (EC, vape) users. Each volunteer provided 1 L of exhaled breath in a pre-cleaned Tedlar bag, in which an SPME fiber was exposed to absorb the emitted breath volatile organic compounds (VOCs). The acquired data were processed using multivariate data analysis (MDA) methods in order to identify the characteristic chemicals of the three groups. The results revealed that the breath of non-smokers demonstrated inverse correlation with a variety of molecules related to the breath from smokers including furan, toluene, 2-butanone and other organic substances. Vapers were distinguished from smokers by the chemical speciation of the e-liquids, such as that of esters (e.g. ethyl acetate), terpenes (e.g. α-pinene, β-pinene, d-limonene, p-cymene, etc.) and oxygenated compounds (e.g. 3-hexen-1-ol, benzaldehyde, hexanal, decanal, etc). Two classification models were developed (a) using principal component analysis (PCA) with hierarchical cluster analysis (HCA) and (b) using partial least squares-discriminant analysis (PLS-DA). Both models were validated using 8 new samples (4 vapers and 4 smokers), collected in addition to the 48 samples of the calibration set. The combination of GC/MS breath analysis and MDA contributed successfully in classifying the volunteers into their respective groups and highlighted the relevant characteristic VOCs. The respective dynamic combination (SPME-GC/MS and MDA) provides a means for long term non-invasive monitoring of the population's health status for early detection purposes.

Organic Air Quality Markers of Indoor and Outdoor PM2.5 Aerosols in Primary Schools from Barcelona

Airborne particulate matter with an aerodynamic diameter smaller than 2.5 µg, PM2.5 was regularly sampled in classrooms (indoor) and playgrounds (outdoor) of primary schools from Barcelona. Three of these schools were located downtown and three in the periphery, representing areas with high and low traffic intensities. These aerosols were analyzed for organic molecular tracers and polycyclic aromatic hydrocarbons (PAHs) to identify the main sources of these airborne particles and evaluate the air quality in the urban location of the schools. Traffic emissions were the main contributors of PAHs to the atmospheres in all schools, with higher average concentrations in those located downtown (1800-2700 pg/m3) than in the periphery (760-1000 pg/m3). The similarity of the indoor and outdoor concentrations of the PAH is consistent with a transfer of outdoor traffic emissions to the indoor classrooms. This observation was supported by the hopane and elemental carbon concentrations in PM2.5, markers of motorized vehicles, that were correlated with PAHs. The concentrations of food-related markers, such as glucoses, sucrose, malic, azelaic and fatty acids, were correlated and were higher in the indoor atmospheres. These compounds were also correlated with plastic additives, such as phthalic acid and diisobutyl, dibutyl and dicyclohexyl phthalates. Clothing constituents, e.g., adipic acid, and fragrances, galaxolide and methyl dihydrojasmonate were also correlated with these indoor air compounds. All these organic tracers were correlated with the organic carbon of PM2.5, which was present in higher concentrations in the indoor than in the outdoor atmospheres.

Passive Exposure to Pollutants from a New Generation of Cigarettes in Real Life Scenarios

The use of electronic cigarettes (e-cigarettes) and heat-not-burn tobacco (HNBT), as popular nicotine delivery systems (NDS), has increased among adult demographics. This study aims to assess the effects on indoor air quality of traditional tobacco cigarettes (TCs) and new smoking alternatives, to determine the differences between their potential impacts on human health. Measurements of particulate matter (PM₁, PM_2.5 and PM₁₀), black carbon, carbon monoxide (CO) and carbon dioxide (CO₂) were performed in two real life scenarios, in the home and in the car. The results indicated that the particle emissions from the different NDS devices were significantly different. In the home and car, the use of TCs resulted in higher PM₁₀ and ultrafine particle concentrations than when e-cigarettes were smoked, while the lowest concentrations were associated with HNBT. As black carbon and CO are released by combustion processes, the concentrations of these two pollutants were significantly lower for e-cigarettes and HNBT because no combustion occurs when they are smoked. CO₂ showed no increase directly associated with the NDS but a trend linked to a higher respiration rate connected with smoking. The results showed that although the levels of pollutants emitted by e-cigarettes and HNBT are substantially lower compared to those from TCs, the new smoking devices are still a source of indoor air pollutants.

Effects of flavoring compounds used in electronic cigarette refill liquids on endothelial and vascular function

Electronic cigarette refill liquids are commercially provided with a wide variety of flavoring agents. A recent study suggested that several common flavors may scavenge nitric oxide (NO) and cause endothelial dysfunction. It was the aim of the present study to investigate the effects of these flavors on NO/cyclic GMP-mediated signaling and vascular relaxation. We tested the flavoring agents for effects on Ca²⁺-induced cGMP accumulation and NO synthase activation in cultured endothelial cells. NO scavenging was studied with NO-activated soluble guanylate cyclase and as NO release from a NO donor, measured with a NO electrode. Blood vessel function was studied with precontracted rat aortic rings in the absence and presence of acetylcholine or a NO donor. Cinnamaldehyde inhibited Ca²⁺-stimulated endothelial cGMP accumulation and NO synthase activation at ≥0.3 mM. Cinnamaldehyde and diacetyl inhibited NO-activated soluble guanylate cyclase with IC₅₀ values of 0.56 (0.54–0.58) and 0.29 (0.24–0.36) mM, respectively, and caused moderate NO scavenging at 1 mM that was not mediated by superoxide anions. The other compounds did not scavenge NO at 1 mM. None of the flavorings interfered with acetylcholine-induced vascular relaxation, but they caused relaxation of pre-contracted aortas. The most potent compounds were eugenol and cinnamaldehyde with EC₅₀ values of ~0.5 mM. Since the flavors did not affect endothelium-dependent vascular relaxation, NO scavenging by cinnamaldehyde and diacetyl does not result in impaired blood vessel function. Although not studied in vivo, the low potency of the compounds renders it unlikely that the observed effects are relevant to humans inhaling flavored vapor from electronic cigarettes.