A new study from Lawrence Berkeley National Laboratory (Berkeley Lab) has pinpointed the source of the toxic compounds emitted by electronic cigarettes (or e-cigarettes) and discovered two new probable carcinogens.
The study found the thermal decomposition of propylene glycol and glycerin, two solvents found in most "e-liquids" (the substance vaporized by e-cigarettes), leads to emissions of toxic chemicals such as acrolein and formaldehyde.
"Advocates of e-cigarettes say emissions are much lower than from conventional cigarettes, so you're better off using e-cigarettes," said Berkeley Lab researcher and study author Hugo Destaillats.
"I would say, that may be true for certain users -- for example, long time smokers that cannot quit -- but the problem is, it doesn't mean that they're healthy. Regular cigarettes are super unhealthy. E-cigarettes are just unhealthy," he said.
Destaillats and a team of researchers simulated vaping using three types of e-liquids in two different vaporizers operated at various battery power settings.
The two e-cigarettes were quite different: one fairly cheap with one heating coil; the other more expensive with two heating coils in parallel. Researchers used gas and liquid chromatography to determine what was in the vapor, looking at the first puffs and later puffs after the device heated up and reached a "steady state."
One finding was that the first and last puffs produce widely varying emissions. Emissions levels between the first few puffs and the steady state increased by a factor of 10 or more in some cases, depending on the device, the battery voltage and the emitted compound.
For example, for acrolein (a severe eye and respiratory irritant) a single-coil e-cigarette operated at 3.8 volts emitted 0.46 micrograms per puff in the first five puffs. It emitted 8.7 micrograms per puff at a steady state, however.
"When you apply the same voltage to the double-coil e-cigarette you see a lot less emissions," said co-author and Berkeley Lab researcher Lara Gundel. "We think it has to do with lower temperatures at each of the coil surfaces."
Conventional cigarettes emit 400 to 650 micrograms of acrolein per cigarette. Assuming 20 puffs on an e-cigarette is equivalent to smoking a conventional cigarette, Gundel said total emissions of acrolein for an e-cigarette are about 90 to 100 micrograms.
Emissions of formaldehyde, acetaldehyde and acrolein -- all either carcinogens or respiratory irritants -- increased with usage. In some case, researchers saw aldehyde levels increase 60 percent between cycles 1 and 9, said co-author and Berkeley Lab researcher Mohamad Sleiman.
The study also found the accumulation of the sort of residues often referred to as "coil gunk" or "caramelization" are a secondary source of volatile aldehydes when heated.
The researchers vaporized liquids consisting solely of the solvents propylene glycol and glycerin to verify they were the source of the emissions. They detected significant levels of 31 harmful chemical compounds, including two that had never been previously found in e-cigarette vapor -- propylene oxide and glycidol, both of which are probable carcinogens.
The study, "Emissions from electronic cigarettes: Key parameters affecting the release of harmful chemicals," was published in Environmental Science & Technology.
It also shows factors such as the temperature, type and age of the device play a role in the severity of emission levels. This information might be valuable to both manufacturers and regulators seeking to minimize the health impacts of these popular tobacco alternatives.