Two new chemicals of concern have been connected to electronic cigarettes: Glycidol, a probable carcinogen, is found in e-cigarette vapor; and propylene oxide, a respiratory irritant and possible carcinogen, is found in the flavored liquid heated by the device to produce the vapor. Hugo Destaillats of Lawrence Berkeley National Laboratory and his colleagues also confirmed the presence of the probable carcinogens formaldehyde and acetaldehyde, as well as the strong respiratory and eye irritant acrolein, in the vapor (Environ. Sci. Technol., DOI: 10.1021/acs.est.6b01741).
Notably, the researchers conclude that several of these compounds come from heating the liquid’s solvents, propylene glycol and glycerin. Glycidol, acrolein, and formaldehyde are thermal by-products of glycerin, and propylene glycol degrades into acetaldehyde and formaldehyde.
The team tested two different brands of e-cigarettes with three different liquids, analyzing the liquid and vapor using gas chromatography-mass spectrometry and high-performance liquid chromatography. Propylene oxide was not detectable in the vapor in their HPLC analysis, but because it was found at relatively high levels in the liquid, the researchers speculate that it may be present in the vapor.
Several factors increased the amount of thermal degradation products delivered per puff, including repeated puffs within a half hour and increasing the e-cigarette voltage, both of which result in heating the liquid at a higher temperature. “As you increase the temperature, the amount of acrolein formed increases almost exponentially,” Destaillats says—by an order of magnitude for a voltage increase from 3.3 to 4.8 V. Minimizing the voltage could help e-cigarette users limit their exposure to these compounds, he says.
Most compounds of concern were detected at 0.3 to 70 μg per puff. The researchers estimate that e-cigarettes emit a quarter or less acrolein than a conventional cigarette for the equivalent number of puffs. However, the team’s calculations also indicate that at least two compounds in e-cigarette vapor exceed limits for chronic exposure—both secondhand and for vapers themselves—set by the California Office of Environmental Health Hazard Assessment by up to an order of magnitude or more, Destaillats says. The team’s conclusions on health implications will appear in a forthcoming paper.