Carbonyl Emissions in E-cigarette Aerosol: A Systematic Review and Methodological Considerations

Abstract

Carbonyl emissions from tobacco cigarettes represent a substantial health risk contributing to smoking-related morbidity and mortality. As expected, this is an important research topic for tobacco harm reduction products, in an attempt to compare the relative risk of these products compared to tobacco cigarettes. In this study, a systematic review of the literature available on PubMed was performed analyzing the studies evaluating carbonyl emissions from e-cigarettes. A total of 32 studies were identified and presented. We identified a large diversity of methodologies, with substantial discrepancies in puffing patterns, aerosol collection and analytical methods as well as reported units of measurements. Such discrepancies make comparisons difficult, and in some cases the accuracy of the findings cannot be determined. Importantly, control for the generation of dry puffs was not performed in the vast majority of studies, particularly in studies using variable power devices, which could result in testing conditions and reported carbonyl levels that have no clinical relevance or context. Some studies have been replicated, verifying the presence of dry puff conditions. Whenever realistic use conditions were ensured, carbonyl emissions from e-cigarettes were substantially lower than tobacco cigarette smoke, while newer generation (bottom-coil, cotton wick) atomizers appeared to emit minimal levels of carbonyls with questionable clinical significance in terms of health risk. However, extremely high levels of carbonyl emissions were reported in some studies, and all these studies need to be replicated because of potentially important health implications.

Daily exposure to formaldehyde and acetaldehyde and potential health risk associated with use of high and low nicotine e-liquid concentrations

“…Our results suggest that aerosol yield and liquid consumption per day were the main determinants of the differences in daily formaldehyde and acetaldehyde exposure between conditions. This finding is in agreement with studies reporting that while aldehydes levels per puff are dependent on power settings, aldehydes levels per gram liquid consumption are independent of power settings when the devices are used in realistic conditions 15,18 . Still, a limitation of this particularly analysis is that there may not be enough statistical power to detect differences between conditions in aldehyde exposure per g of liquid consumption.…”

“…These studies clearly illustrate that when nicotine is reduced, vapers are likely to engage in compensatory behavior by increasing the power on their devices and/or puffing more intensively. Both power 8,15 and puffing topography 30 may affect toxicant emissions, but the extent to which such compensatory behavior affects daily toxicant exposure and subsequent health risk is unknown.…”

Carbonyl emissions from a novel heated tobacco product (IQOS): comparison with an e‐cigarette and a tobacco cigarette

“…However, these findings have been questioned with replication studies showing either lower carbonyl emissions or unrealistic testing conditions that created overheating and dry puffs . A recent systematic review of carbonyl emissions from e‐cigarettes identified several methodological issues which could result in reporting findings with questionable clinical context .…”

A Comparison of Flavorless Electronic Cigarette-Generated Aerosol and Conventional Cigarette Smoke on the Planktonic Growth of Common Oral Commensal Streptococci

“…In contrast, E-liquids are comprised of only a few ingredients (i.e., propylene glycol (PG) or vegetable glycerin (VG) ± nicotine and flavorings), of which the myriad of available flavors [40] appear to provide most of the detriment to the ECIG user [41][42][43][44][45] when inhaled. Regardless of the apparent "harm reduction" provided by ECIGs, more research is needed to determine additional health related risks [34], especially since it is known that vaporization of E-liquid can induce chemical alterations yielding substances (such as carbonyl emissions) that could potentially cause lung injury [46,47]. In contrast to generic ECIG-generated aerosol, inhalation of aerosol containing cannabis products, especially those bought on the black market, are known to contain vitamin E acetate, a chemical that has been shown to be extremely dangerous, resulting in serious lung injury and even death [48].…”