The Cloud Chasers
From e-cigarettes to emerging heated tobacco products, how safe are electronic nicotine delivery systems? We meet the scientists tasked with exploring the chemical composition of these complex aerosols.
Charlotte Barker |
Hugo Destaillats is a Staff Scientist at Lawrence Berkeley National Laboratory (LBNL) Indoor Environment Group (USA), where he studies multiple aspects of indoor air quality. The group has studied tobacco smoke for many years, and as the e-cigarette market started to expand in the early 2010s, they turned their attention to the composition of vapor. The uncertainty around the effects of vaping intrigued Destaillats: “Today, everyone agrees that smoking is harmful. With vaping, the evidence is much less clear cut, with scientists and health agencies still debating the health impacts,” he says.
Instrumental in the team’s e-cigarette research was Mohamad Sleiman, now an assistant professor at SIGMA Clermont (France), who has an interest in developing analytical methods for environmental applications.
What’s in the cloud?
“We decided to study the chemical composition of vapor, to predict how it might impact on the user and those around them,” says Sleiman. The team were particularly interested in following up on previous reports of potentially toxic aldehydes found in vapor, and wanted to discover how these compounds were formed. They looked at three e-liquids and two devices to see how the technology used would impact on the composition and emission of inhaled and exhaled vapor.
The aldehydes were captured by dinitrophenylhydrazine (DNPH)-impregnated silica gel cartridges, and analyzed by HPLC with UV detection. Other volatile organic compounds were captured using sorbent tubes and analyzed by TD-GC/MS. “To gather additional information on the source of the toxicants we used headspace GC-MS – heating propylene glycol, glycerin and complete e-liquid to see if we could recreate formation of specific toxicants, and track changes in chemical profile with increasing heat,” says Sleiman.
The team found a total of 31 potentially toxic substances in the vapors they analyzed (1). “Our findings were consistent with other studies, but we made some additional observations, including two toxicants (one in vapor and one in liquid) that hadn’t been previously detected,” says Destaillats.
“One novel finding was that propylene glycol and glycerin in e-liquids can undergo thermal decomposition under certain conditions to produce the aldehyde acrolein – a powerful irritant,” adds Sleiman. Acrolein can occur at relatively high levels, depending on how the e-cigarette is used, adds Destaillats. High levels of aldehydes are sometimes attributed to unpleasant-tasting “dry puffs”, where the liquid burns rather than turning to vapor. But the researchers found that acrolein was also present under conditions mimicking routine use. Detecting aldehydes was a special challenge, says Sleiman “Acrolein is very reactive and easily oxidized, so samples had to be dealt with promptly to avoid degradation.”
The researchers noted that emissions of acrolein and other toxic compounds increased as the voltage and temperature of the e-cigarette rose, and with repeated use – presumably a result of a buildup of residue within the device. “We hope that one outcome of our research has been to provide useful information to manufacturers to help them improve the safety of their devices,” says Destaillats.
In a follow up analysis, the group carried out a simple health impact assessment for the toxicants they found in vapor, using disability-adjusted life years (2). The results suggested that while vaping is significantly less harmful than tobacco smoking, it isn’t without risks.
Spoilt for choice
Destaillats and Sleiman are particularly concerned about the “unknown unknowns” in vapor. In their study they found two compounds that hadn’t been identified before – and there could be others. “There are hundreds of e-liquid flavors out there made up of a variety of compounds; add in poor quality control and there could be impurities that no-one would think to look for,” says Sleiman.
Even “safe” compounds must be regarded with caution when they are in used in ways very different to their original purpose. “For example, the solvents used in vaping are propylene glycol and glycerin – there is a large body of evidence to show that these compounds are safe to eat, but very little to prove that they are safe to inhale in large quantities over several years or decades,” says Destaillats. “Vaping is effectively a toxicological experiment being carried out with millions of people around the world – there may be no serious health impacts, but there may be risks that are only revealed with time.”
E-Cigarettes Versus Heat-Not-Burn
E-cigarettes heat e-liquid (usually containing nicotine, flavorings and humectants) to vaporize it, before it condenses into a droplet cloud with a similar particle size distribution as cigarette smoke. E-cigarettes are produced by myriad manufacturers and with hundreds of flavors of e-liquid to choose from.
In heat-not-burn products, cigarette-like sticks of tobacco and humectants are heated to around 240 degrees Celsius (conventional cigarettes can reach 950 degrees Celsius), releasing nicotine and volatile flavor compounds. These devices are made by tobacco companies, and are currently only available in selected countries.
The e-cigarette market and associated technology is evolving rapidly, says Sleiman. “Two conventional cigarettes of the same brand will be virtually identical, but e-cigarettes and e-liquids come in countless permutations, which makes it difficult to generalize findings.” That may change as more regulation comes in, he suggests, as only companies with the resources to carry out proper quality control will remain in the industry. Either way, there will be plenty of analytical challenges for the team to explore in the years to come.
Though Sleiman has now left the LBNL group to take up a position at SIGMA Clermont, France, he and Destaillats continue to collaborate on research into vaping and other environmental applications. “As long as electronic nicotine delivery systems (ENDS) continue to evolve, we will continue to provide an unbiased analytical view,” says Destaillats.
This article has three parts:
Analyzing Uncertainty, featuring Hugo Destaillats and Mohamad Sleiman
Industry Insights, featuring Chris Wright
The Human Element, featuring Lion Shahab
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- M Sleiman et al., “Emissions from electronic cigarettes: key parameters affecting the release of harmful chemicals”, Environ Sci Technol, 50, 17, 9644-9651 (2016).
- JM Logue et al., “Emissions from electronic cigarettes: Assessing vapers’ intake of toxic compounds, secondhand exposures and the associated health impacts”, Environ Sci Technol, 51, 9271-9279 (2017).