Abstract
The formation of carbonyls and epoxides in e-cigarette (EC) aerosol is possible due to heating of the liquid constituents. However, high background levels of these compounds have inhibited a clear assessment of exposure during use of ECs. An EC containing an e-liquid replaced with 10% of 13C-labeled propylene glycol and glycerol was used in a controlled use clinical study with 20 EC users. In addition, five smokers smoked cigarettes spiked with the described e-liquid. Seven carbonyls (formaldehyde, acetaldehyde, acrolein, acetone, crotonaldehyde, methacrolein, propionaldehyde) were measured in the aerosol and the mainstream smoke. Corresponding biomarkers of exposure were determined in the user’s urine samples. 13C-labeled formaldehyde, acetaldehyde and acrolein were found in EC aerosol, while all seven labeled carbonyls were detected in smoke. The labeled biomarkers of exposure to formaldehyde (13C-thiazolidine carboxylic acid and 13C-N-(1,3-thiazolidine-4-carbonyl)glycine), acrolein (13C3-3-hydroxypropylmercapturic acid) and glycidol (13C3-dihydroxypropylmercapturic acid) were present in the urine of vapers indicating an EC use-specific exposure to these toxicants. However, other sources than vaping contribute to a much higher extent by several orders of magnitude to the overall exposure of these toxicants. Comparing data for the native (unlabeled) and the labeled (exposure-specific) biomarkers revealed vaping as a minor source of user’s exposure to these toxicants while other carbonyls and epoxides were not detectable in the EC aerosol.
Highlights
The use of e-cigarettes (ECs) has increased over the past several years (Beard et al 2020; Cullen et al 2019; Dai and Leventhal 2019; Kapan et al 2020)
The aerosol is formed by heating the e-liquid and during this process propylene glycol (PG) and G may be decomposed into toxicants such as the carbonyls formaldehyde (FA), acetaldehyde (AA), acrolein (ACR), and crotonaldehyde (CR) as well as the epoxides glycidol (GLY) or propylene oxide (PO), to which vapers might be exposed (Fig. 1) (Flora et al 2016; Sleiman et al 2016; Sodhi and Khanna 2015; Uchiyama et al 2020)
This study demonstrates the potential utility of the stable isotope labeling approach by comparing biomarker data for unlabeled and labeled compounds from cigarette smoke and EC aerosols
Summary
The use of e-cigarettes (ECs) has increased over the past several years (Beard et al 2020; Cullen et al 2019; Dai and Leventhal 2019; Kapan et al 2020). As use of ECs become more prevalent, it becomes more important to understand the potential exposure to harmful chemicals during use of these products. One area of focus is the potential formation of carbonyls, epoxides, and aromatic amines by thermal degradation of e-liquid constituents, despite the much lower. The major constituents of e-liquids are propylene glycol (PG), glycerol (G), nicotine, water and flavors. The aerosol is formed by heating the e-liquid and during this process PG and G may be decomposed into toxicants such as the carbonyls formaldehyde (FA), acetaldehyde (AA), acrolein (ACR), and crotonaldehyde (CR) as well as the epoxides glycidol (GLY) or propylene oxide (PO), to which vapers might be exposed (Fig. 1) (Flora et al 2016; Sleiman et al 2016; Sodhi and Khanna 2015; Uchiyama et al 2020).
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