Assessment of the potential vaping-related exposure to carbonyls and epoxides using stable isotope-labeled precursors in the e-liquid

Arch Toxicol. 2021 Aug;95(8):2667-2676. doi: 10.1007/s00204-021-03097-x. Epub 2021 Jun 22.


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.

Keywords: Biomarkers of exposure; Carbonyls; Electronic cigarettes; Epoxides; Mercapturic acids; Stable isotope-labeled constituents.

Publication types

  • Controlled Clinical Trial

MeSH terms

  • Adult
  • Aerosols / analysis
  • Aldehydes / analysis*
  • Biomarkers / analysis
  • Carbon Isotopes
  • Electronic Nicotine Delivery Systems*
  • Epoxy Compounds / analysis*
  • Humans
  • Male
  • Smoke / analysis
  • Vaping*


  • Aerosols
  • Aldehydes
  • Biomarkers
  • Carbon Isotopes
  • Epoxy Compounds
  • Smoke