Hazardous chemicals in flavoured e-cigarette vapour

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The vapours produced by flavoured e-cigarettes liquids contain dangerous levels of hazardous chemicals known to cause cancer in humans, found a US study.

The thermal decomposition of flavouring compounds dominates the formation of toxic aldehydes during vaping, producing levels that exceed occupational safety standards.

Building on more than 30 years of air quality research in some of the most polluted urban environments on Earth, a team of atmospheric scientists at the Desert Research Institute (DRI) has turned their attention toward the growing e-cigarette industry and the unidentified effects of vaping on human health.

New research reports that the aerosols (commonly called vapours) produced by flavoured e-cigarettes liquids contain dangerous levels of hazardous chemicals known to cause cancer in humans. The study confirms that these toxic aldehydes, such as formaldehyde, are formed not by evaporation, but rather during the chemical breakdown of the flavoured e-liquid caused by the rapid heating process (pyrolysis) that occurs inside e-cigarettes or electronic nicotine delivery systems (ENDS).

“How these flavouring compounds in e-cigarette liquids affect the chemical composition and toxicity of the vapor that e-cigarettes produce is practically unknown,” explained Dr Andrey Khlystov, an associate research professor of atmospheric sciences at DRI. “Our results show that production of toxic aldehydes is exponentially dependent on the concentration of flavouring compounds.”

E-cigarette liquids have been marketed in nearly 8,000 different flavours, according to a 2014 report from the World Health Organisation. Recent reports have shown that many flavours, such as Gummy Bear, Tutti Fruitty, Bubble Gum, etc, were found to be especially appealing to adolescents and young adults.

The US Food and Drug Administration reports that 16% of high school and 5.3% of middle school students were current users of e-cigarettes in 2015, making e-cigarettes the most commonly used tobacco product among youth for the second consecutive year. In 2014, 12.6% of US adults had ever tried an e-cigarette, and about 3.7% of adults used e-cigarettes daily or some days.

Khlystov and his colleagues measured concentrations of 12 aldehydes in aerosols produced by three common e-cigarette devices. To determine whether the flavouring additives affected aldehyde production during vaping, five flavoured e-liquids were tested in each device. In addition, two unflavoured e-liquids were also tested.

“To determine the specific role of the flavouring compounds we fixed all important parameters that could affect aldehyde production and varied only the type and concentration of flavours,” explained Dr Vera Samburova, an assistant research professor of chemistry at DRI.

Samburova added that the devices used in the study represented three of the most common types of e-cigarettes – bottom and top coil clearomisers, and a cartomiser.

The study avoided any variation in puff topography (puff volume, puff velocity, interval between puffs) by utilising a controlled sampling system that simulated the most common vaping conditions. E-cigarette vapour was produced from each device by a four-second, 40-ml controlled puff, with 30-second resting periods between puffs. The e-cigarette devices were manually operated to replicate real-life conditions and all samples were collected in triplicate to verify and confirm results. Specific care was taken to avoid “dry puff” conditions.

To provide further proof that the flavouring compounds, not the carrier e-liquid solvents (most commonly propylene glycol and/or vegetable glycerin) dominated production of aldehydes during vaping, the authors performed a series of experiments in which a test flavoured e-liquid was diluted with different amounts of the unflavoured e-liquid. Liquids with higher flavour content produced larger amounts of aldehydes due to pyrolysis of the flavouring compounds.

In all experiments, the amount of aldehydes produced by the flavoured e-cigarette liquids exceeded the American Conference of Governmental Industrial Hygienists Threshold Limit Values (TLVs) for hazardous chemical exposure.

“One puff of any of the flavoured e-liquids that we tested exposes the smoker to unacceptably dangerous levels of these aldehydes, most of which originates from thermal decomposition of the flavouring compounds,” said Khlystov. “These results demonstrate the need for further, thorough investigations of the effects of flavouring additives on the formation of aldehydes and other toxic compounds in e-cigarette vapours.”

The growing popularity of electronic cigarettes (e-cigarettes) raises concerns about the possibility of adverse health effects to primary users and people exposed to e-cigarette vapors. E-Cigarettes offer a very wide variety of flavors, which is one of the main factors that attract new, especially young, users. How flavoring compounds in e-cigarette liquids affect the chemical composition and toxicity of e-cigarette vapors is practically unknown. Although e-cigarettes are marketed as safer alternatives to traditional cigarettes, several studies have demonstrated formation of toxic aldehydes in e-cigarette vapors during vaping. So far, aldehyde formation has been attributed to thermal decomposition of the main components of e-cigarette e-liquids (propylene glycol and glycerol), while the role of flavoring compounds has been ignored. In this study, we have measured several toxic aldehydes produced by three popular brands of e-cigarettes with flavored and unflavored e-liquids. We show that, within the tested e-cigarette brands, thermal decomposition of flavoring compounds dominates formation of aldehydes during vaping, producing levels that exceed occupational safety standards. Production of aldehydes was found to be exponentially dependent on concentration of flavoring compounds. These findings stress the need for a further, thorough investigation of the effect of flavoring compounds on the toxicity of e-cigarettes.

Andrey Khlystov, Vera Samburova

Desert Research Institute material Environmental Science & Technology abstract

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