Influence of the E-Cigarette Emission Profile by the Ratio of Glycerol to Propylene Glycol in E-Liquid Composition

Abstract

The use of electronic cigarettes (E-cig) is popular because of the perception that they are less addictive and safer compared to the traditional cigarettes. Nevertheless, there are still harmful effects associated with chemicals emitted from E-cig. Identifying the sources of the emitted compounds can be challenging because of the differences in the design of E-cig devices and the variability in the composition of E-cig liquids used in these devices. In this study, the emission profiles from impurity-free E-liquids containing only propylene glycol and glycerol in various percentage ratios along with two commercially available E-liquids were evaluated using gas chromatography–mass spectrometry (GC–MS). This study approach allows the elucidation of the transformation pathways of the major emitted compounds without the confounding effects of existing impurities or flavor ingredients added to E-liquids. Analysis of the vapor phases of E-cig emissions detected toxicants such as acetaldehyde, acrolein, benzaldehyde, as well as benzene, toluene, ethylbenzene, and xylene (BTEX) compounds. The amount of glycerol in the E-liquids has a major effect on the concentration of these hazardous compounds emitted because the concentration of these chemicals increased with increasing glycerol percentage in the E-liquid. Acetaldehyde and acrolein increased by 175-fold and 28-fold, respectively, when the glycerol composition was increased from 0 to 80%. Benzaldehyde, naphthalene, diphenyl ether, and glycerol along with menthol and nicotine that were present in the commercial E-liquids were also detected in the aerosol condensates. The cascade impactor data on the distribution of the nicotine and menthol in different size fractions from >2.5 to <2.5 μm allow the estimates of the extent of toxicant deposition in different parts of the pulmonary system including the oropharynx region, the trachea as well as inside the alveoli and bronchioles. In summary, users of E-cig are exposed to harmful chemicals even if the E-liquids contain only propylene glycol and glycerol without flavorings, nicotine, or impurities. Furthermore, this study shows that E-liquids containing higher percentages of glycerol will produce higher levels of toxicants compared to E-liquids with similar percentages of propylene glycol. This finding has important implications to E-cigarette vendors and manufacturers, consumers, and regulatory agencies.

Reducing toxic reactive carbonyl species in e-cigarette emissions: testing a harm-reduction strategy based on dicarbonyl trapping

“…Bekki et al 51 attributed the formation of carbonyls and dicarbonyls in e-cigarette aerosols to the oxidation of the e-liquid, when it becomes in contact with the heated atomiser coil in the presence of atmospheric oxygen. The present study suggests that the compounds observed by Ooi et al 52 are formed in the e-liquid of our model system prior to vaping, in part or in the whole. The difficulty in quantifying the concentration of these adducts prevented a fuller assessment of the role of each phenol compounds in reducing carbonyl formation.…”

Vaper, Beware: The Unique Toxicological Profile of Electronic Cigarettes

“…The solvents in e-liquid are typically a mixture of propylene glycol (PG) and vegetable glycerol (VG) at variable ratios. 10 Researchers have raised concern about the inhalation toxicity of these solvents alone, even without nicotine and flavoring chemicals. 35 When PG and VG are exposed to heat, breakdown products include three aldehydes: formaldehyde, acrolein, and acetaldehyde.…”

“…53,55 Solvent mixtures on the current market span the range from 100% PG, to 50/50, to 100% VG. 10 Studies showed that e-liquids with a higher VG content produce more formaldehyde and acrolein than those with more PG, especially at high power settings. This might expose e-cigarette users to higher aldehyde levels than smokers 10,56,57,58 and is a concern for "cloud chasers," who prefer VG-heavy e-liquids for the large visible clouds they produce.…”

“…18 Conjugating nicotine with a weak acid produces nicotine salt, which creates a much more palatable aerosol than the harshtasting alkaline free-base (unprotonated) nicotine. 10 There is also evidence that nicotine salt formulations are associated with increased nicotine yields or exposure 19,20 and faster nicotine absorption. 21 Much of the decline in U.S. smoking in the last few decades has been attributed to tobacco control measures such as cigarette taxes, smoking bans, and health educational campaigns.…”

The Effects of E-Cigarette Vapor Components on the Morphology and Function of the Male and Female Reproductive Systems: A Systematic Review

“…However, when e-liquids are heated, a number of harmful compounds—including formaldehyde, acetaldehyde, methylglyoxal, acrolein, acetone, benzaldehyde, and the so-called BTEX compounds (benzene, toluene, ethylbenzene, and xylenes)—are found in the inhaled vapor. These are produced primarily by the oxidation and thermal decomposition of the two main components of e-fluid, glycerol and PG [ 31 ]. Moreover, e-liquids contain a range of flavorings, such as fruit and sweet flavors sold under names such as “Candy Corn”, “Chocolate Fudge”, and “Berry Splash”; in 2014, and the number of e-liquid flavors exceeded 7500, and it continues to increase [ 32 , 33 ].…”