Evaluation of electronic cigarette liquids and aerosol for the presence of selected inhalation toxins

Abstract

Introduction: The purpose of this study was to evaluate sweet-flavored electronic cigarette (EC) liquids for the presence of diacetyl (DA) and acetyl propionyl (AP), which are chemicals approved for food use but are associated with respiratory disease when inhaled.

Methods: In total, 159 samples were purchased from 36 manufacturers and retailers in 7 countries. Additionally, 3 liquids were prepared by dissolving a concentrated flavor sample of known DA and AP levels at 5%, 10%, and 20% concentration in a mixture of propylene glycol and glycerol. Aerosol produced by an EC was analyzed to determine the concentration of DA and AP.

Results: DA and AP were found in 74.2% of the samples, with more samples containing DA. Similar concentrations were found in liquid and aerosol for both chemicals. The median daily exposure levels were 56 μg/day (IQR: 26-278 μg/day) for DA and 91 μg/day (IQR: 20-432 μg/day) for AP. They were slightly lower than the strict NIOSH-defined safety limits for occupational exposure and 100 and 10 times lower compared with smoking respectively; however, 47.3% of DA and 41.5% of AP-containing samples exposed consumers to levels higher than the safety limits.

Conclusions: DA and AP were found in a large proportion of sweet-flavored EC liquids, with many of them exposing users to higher than safety levels. Their presence in EC liquids represents an avoidable risk. Proper measures should be taken by EC liquid manufacturers and flavoring suppliers to eliminate these hazards from the products without necessarily limiting the availability of sweet flavors.

Figure 1.

Chemical structures of diacetyl (DA) and acetyl propionyl (AP).

Figure 2.

Box-plots of the estimated daily exposure to diacetyl (A) and acetyl propionyl (B) from the liquid samples tested. The box represents the 25th and 75th percentiles, with the line inside the box showing the median value. The error bars represent the 10th and 90th percentiles. The dotted line represents the maximum acceptable levels of daily exposure estimated from the NIOSH limit for occupational exposure.

Figure 3.

Correlation between the expected (based on liquid consumption during aerosol production) and the measured concentrations of diacetyl (DA) and acetyl propionyl (AP) in aerosol. A strong correlation was observed, while the expected and measured values were almost identical, verifying that DA and AP are readily delivered from the liquid to the aerosol and that no additional DA and AP are produced during the evaporation process.