One of the main arguments that e-cig advocates have used is that the aerosol is much less toxic than cigarette smoke because it contains many fewer chemicals. For example, the article “Balancing consideration of the risks and benefits of e-cigarettes” organized by Ken Warner says “The number of chemicals in cigarette smoke, greater than 7000, exceeds that of e-cigarette aerosol by more than 2 orders of magnitude.” To support this statement they cite a paper that identified 31 compounds in e-cigarette aerosol. The paper they cite is fine as far as it goes, but, like other studies of e-cig aerosol to date, it only looked for a limited number of compounds. (Even so, it concluded, “Glycidol and acrolein were primarily produced by glycerin degradation. Acetol and 2-propen-1-ol were produced mostly from PG, while other compounds (e.g., formaldehyde) originated from both. Because emissions originate from reaction of the most common e-liquid constituents (solvents), harmful emissions are expected to be ubiquitous when e-cigarette vapor is present.”)
Now Mina Tehrani and colleagues from Johns Hopkins have published a much broader non-targeted analysis of e-liquids and aerosols produced by four widely available tobacco flavor e-cigarettes (Blu, Juul, Mi-Salt Smok, Vuse) and the polypropylene glycol/vegetable glycerine (PG/VG) base without any nicotine or flavorings. As the title of their paper “Characterizing the Chemical Landscape in Commercial E-Cigarette Liquids and Aerosols by Liquid Chromatography-High-Resolution Mass Spectrometry” indicates (figure above), they used liquid chromatography-high-resolution mass spectrometry together with chemical fingerprinting to count the number of chemical compounds in the e-liquids and aerosols.
Depending on the product, the number of compounds in the e-liquid varied from 769 to 2129 and the number of compounds in the aerosol varied from 828 to 2140.
They also found that the number of compounds in the aerosol varied by how many puffs had been taken on the e-cig. These results can also depend on the precise electrical characteristics of the device and nicotine content of the e-liquid. Also, all the e-cigs used were tobacco flavor; other flavors have other chemicals.
The Johns Hopkins press release noted, “They found thousands of unknown chemicals in the e-liquid, and the number of compounds increased significantly in the aerosol. Furthermore, they detected [condensed] hydrocarbon-like compounds, typically associated with combustion, which manufacturers say is not happening during vaping. In traditional cigarettes, the condensed hydrocarbons generated during combustion are toxic [emphasis added].”
They also found caffeine in some of the aerosols.
One interesting finding was that the number of compounds was generally higher in the PG/VG only e-cigs than the commercial brands that had tobacco flavor and nicotine. I emailed Carsten Prasse, the senior author, asking him how this could be the case given that all the commercial brands use a PG/VG base. Here is what he told me:
You are raising a good question. As we describe in our paper, we purchased propylene glycol and glycerol for the preparation of the in-house PG/VG e-liquid base solution. One potential reason for the higher number of compounds in the control compared to the e-liquids is that the presence of other constituents in the commercial e-liquids such as emulsifiers leads to the formation of compounds that cannot be detected with our method. I know that this might seem counterintuitive at first but these matrix effects are a known phenomenon for the analytical approach that we used. Please also keep in mind that while our method is very comprehensive, we are not able to detect all chemicals that are present (which would require a number of different analytical approaches). Every method has a certain ‘analytical window’.
The main take home from our study is that a large number of unknown compounds are present and that there is also a clear indication that compounds are forming during the vaping process. Further studies will have to show what these compounds are and whether they pose a risk for consumers.
Here is the abstract:
The surge in electronic cigarette (e-cig) use in recent years has raised questions on chemical exposures that may result from vaping. Previous studies have focused on measuring known toxicants, particularly those present in traditional cigarettes, while fewer have investigated unknown compounds and transformation products formed during the vaping process in these diverse and constantly evolving products. The primary aim of this work was to apply liquid chromatography-high-resolution mass spectrometry (LC-HRMS) and chemical fingerprinting techniques for the characterization of e-liquids and aerosols from a selection of popular e-cig products. We conducted nontarget and quantitative analyses of tobacco-flavored e-liquids and aerosols generated using four popular e-cig products: one disposable, two pod, and one tank/mod. Aerosols were collected using a condensation device and analyzed in solution alongside e-liquids by LC-HRMS. The number of compounds detected increased from e-liquids to aerosols in three of four commercial products, as did the proportion of condensed-hydrocarbon-like compounds, associated with combustion. Kendrick mass defect analysis suggested that some of the additional compounds detected in aerosols belonged to homologous series resulting from decomposition of high-molecular-weight compounds during vaping. Lipids in inhalable aerosols have been associated with severe respiratory effects, and lipid-like compounds were observed in aerosols as well as e-liquids analyzed. Six potentially hazardous additives and contaminants, including the industrial chemical tributylphosphine oxide and the stimulant caffeine, were identified and quantified in the e-cig liquids and aerosols analyzed. The obtained findings demonstrate the potential of nontarget LC-HRMS to identify previously unknown compounds and compound classes in e-cig liquids and aerosols, which is critical for the assessment of chemical exposures resulting from vaping.
The full citation is: Tehrani MW, Newmeyer MN, Rule AM, Prasse C. Characterizing the Chemical Landscape in Commercial E-Cigarette Liquids and Aerosols by Liquid Chromatography-High-Resolution Mass Spectrometry. Chem Res Toxicol. 2021 Oct 5. doi: 10.1021/acs.chemrestox.1c00253. Epub ahead of print. PMID: 34610237. It is available here.