A Nest of Vapers

As debate over whether vaping is a healthier alternative to smoking rages on, a team from Lawrence Berkeley throw a little more fuel onto the fire, finding that the hotter an e-cigarette gets, the more likely it is to release irritants – and a couple of carcinogens to boot.

The indoor environment group at LBNL has been working on tobacco chemistry and exposure in indoor environments for about 30 years, but with the increasing popularity of e-cigarettes, they started looking at the chemical composition of both direct and passive (exhaled vapor) emissions. In particular, they focused on the effect of heating on the composition – as well as how the design of the device and nature of liquids can affect the levels of chemicals in the vapor. The overall objective? To assess the impact of the vapor on indoor air quality and estimate the health outcomes of exposure for both users and non-users.

The team identified 31 compounds in vapor, including glycidol – a probable carcinogen – and acrolein – a powerful irritant. Neither of the compounds had been identified in vapor previously. Emission rates ranged from tens to thousands of nanograms of toxicants per milligram of e-liquid vaporized, and they were significantly higher for a single-coil vs a double-coil vaporizer (by up to an order of magnitude for aldehydes). 

GC-MS was selected as an appropriate technique to measure the partitioning of volatile compounds in the e-liquids to the gas phase. “Headspace analysis allowed us to quantify the fraction of each constituent that is emitted at different temperatures but also to mimic the heating of the e-cigarette – verifying if some chemicals undergo thermal decomposition or if new chemicals are formed during heating,” says Mohamad Sleiman, Environmental Chemist and a Research Scientist at LBNL. “And by comparing direct injection with the headspace analyses for standard mixture and e-liquids, we were able to determine the percentage composition of the major constituents of the e-liquids.”

Thermal desorption GC-MS (TD-GC-MS) was used to analyze the vapors emitted by e-cigarettes and exhaled by users. “The technique uses sorbent tubes containing, for example, a carbopack C bed, which traps and preconcentrates a wide range of volatile organic compounds (C3-C14),” Sleiman says. The trapped compounds were thermally desorbed at 250-300 C and separated and identified through GC-MS.

What else did the LBNL team ‘smoke out’?

• Increasing voltage leads to higher emissions. 
• By increasing the voltage applied to a single-coil device from 3.3 to 4.8 V, the mass of e-liquid consumed doubled from 3.7 to 7.5 mg per puff and the total aldehyde emission rates tripled from 53 to 165 μg per puff, with acrolein rates growing by a factor of 10. 
• Harmful emissions increased with device age Aldehyde emissions increased by more than 60 percent after the device was reused several times, likely due to the buildup of polymerization byproducts that degraded upon heating. These findings suggest that thermal degradation byproducts are formed during vapor generation.
• Thermal dehydration of e-liquid solvents at high temperatures was the major source of toxicants.
• Glycidol and acrolein were primarily produced by glycerin degradation. Acetol and 2-propen-1-ol were produced mostly from PG, while other compounds (for example, formaldehyde) originated from both. Because emissions originate from reaction of the most common e-liquid constituents (solvents), harmful emissions are expected to be ubiquitous when e-cigarette vapor is present.

But before vapers are forced to put that in their pipe and smoke it, it is worth noting that irritant levels were still lower than in conventional cigarettes. What’s more, Sleiman suggests that since harmful emissions originate from heating the common constituents present in every e-liquid, protection of users may be gained by simply improving e-cigarette design to reduce coil and vapor temperatures. “Research into e-cig vapor’s impact on health is needed to better assess the risks,” he says.