Vaping’s toxic vapors come mainly from e-liquid solvents

April 12, 2022 | Janet Raloff

Vaping’s toxic vapors come mainly from e-liquid solvents

Over the last three years, growing evidence has shown that electronic cigarettes are not the harmless alternative to smoking that many proponents have argued. Now, a new study traces a large share of e-cigs’ toxic gases to a heat-triggered breakdown of the liquids used to create the vapors. And the hotter an e-cig gets — and the more it’s used — the more toxic compounds it emits, the study shows.

“There is this image that e-cigarettes are a lot better than regular cigarettes, if not harmless,” says Hugo Destaillats, a chemist at Lawrence Berkeley National Laboratory in California. But after his team’s new analyses, published July 27 in Environmental Science & Technology, “we are now definitely convinced that they are far from harmless.”

Electronic cigarettes draw liquids over one or more hot metal coils to transform them into vapors. Those liquids — propylene glycol, glycerin or a mix of the two — are food-grade solvents laced with flavorings and usually nicotine.

The Berkeley team used two current models of e-cigs and three different commercially available e-liquids. The experimental setup mechanically drew air through the devices to create the vapors that a user would normally inhale.

Heating up

The higher an e-cigarette’s voltage, the more toxic aldehydes it produces in each puff of vapor. Once a certain threshold is hit, each voltage increase produces a disproportionate increase (see last bar) in acrolein, acetaldehyde and formaldehyde, three of the most harmful compounds in the vapor. 

Adapted from M. Sleiman et al/Environmental Science & Technology 2016

Toxic aldehydes (such as formaldehyde, acetaldehyde and acrolein) were at negligible levels in the starting e-liquids, Destaillats notes. But the chemistry of the vapors varied as the e-cig device heated up: The first puffs contained somewhat less of the aldehydes than later puffs.

The new data show that “through the process of vaping, you are generating almost 1,000-fold higher emissions of those same compounds. And that is from the thermal degradation of the solvents,” Destaillats says.

Some devices can vary the voltage used to heat their coils. Higher voltages produced hotter conditions and more of the toxic aldehydes, which are probable or suspected carcinogens. Acrolein is also a potent irritant of the eyes and airways.

With a rise from 4.3 to 4.8 volts, the jump in emissions “goes exponential,” Destaillats adds, particularly “for the three aldehydes that are among the most harmful compounds present in the vapor.” Users could inhale up to 165 micrograms of these aldehydes per puff, the study found.

In their first tests, the chemists used a new e-cigarette for each puffing session. But in a second set of tests, they used one device over and over at its high-voltage setting. After the ninth 50-puff cycle, the toxic aldehyde emission rate had climbed by another 60 percent. This was consistent with a buildup on or near the heating element of what has come to be known colloquially as “coil gunk,” the researchers say. “Heating these residues would provide a secondary source of the volatile aldehydes.”

The data on changes in the vapor composition of “aged” e-cigarettes “is something new,” notes toxicologist Maciej Goniewicz of the Roswell Park Cancer Institute in Buffalo, N.Y. And using a better analytical technique than others have employed, he says, the Berkeley team turned up new toxicants — such as propylene oxide and glycidol — which neither his group nor others had detected in e-cig vapors. 

Editor’s note: This story was updated July 28, 2016, to correct the name of one of the liquids used in e-cigarettes.