Diacetyl and Other Ketones in e-Cigarette Aerosols: Some Important Sources and Contributing Factors

Abstract

Background: Concerns over the presence of the diketones 2,4 butanedione (DA) and 2,3 pentanedione (AP) in e-cigarettes arise from their potential to cause respiratory diseases. Their presence in e-liquids is a primary source, but they may potentially be generated by glycerol (VG) and propylene glycol (PG) when heated to produce aerosols. Factors leading to the presence of AP, DA and acetoin (AC) in e-cigarette aerosols were investigated. We quantified direct transfer from e-liquids, examined thermal degradation of major e-liquid constituents VG, PG and 1,3 propanediol (1,3 PD) and the potential for AC, AP and DA production from sugars and flavor additives when heated in e-cigarettes.Method: Transfers of AC, AP and DA from e-liquids to e-cigarette aerosols were quantified by comparing aerosol concentrations to e-liquid concentrations. Thermal generation from VG, PG or 1,3 PD e-liquids was investigated by measuring AC, AP and DA emissions as a function of temperature in an e-cigarette. Thermal generation of AC, AP and DA from sugars was examined by aerosolising e-liquids containing sucrose, fructose or glucose in an e-cigarette. Pyrolytic formation of AP and DA from a range of common flavors was assessed using flash pyrolysis techniques.Results: AC transfer efficiency was >90%, while AP and DA were transferred less efficiently (65%) indicating losses during aerosolisation. Quantifiable levels of DA were generated from VG and PG, and to a lesser extent 1,3 PD at coil temperatures >300°C. Above 350°C AP was generated from VG and 1,3 PD but not PG. AC was not generated from major constituents, although low levels were generated by thermal reduction of DA. Aerosols from e-liquids containing sucrose contained quantifiable (>6 ng/puff) levels of DA at all sucrose concentrations tested, with DA emissions increasing with increasing device power and concentration. 1% glucose, fructose or sucrose e-liquids gave comparable DA emissions. Furanose ring compounds also generate DA and AP when heated to 250°C.Conclusions: In addition to less than quantitative direct transfer from the e-liquid, DA and AP can be present in the e-cigarette aerosol due to thermal decomposition reactions of glycols, sugars and furanonse ring flavors under e-cigarette operating conditions.

Emerging ENDS products and challenges in tobacco control toxicity research

“…In addition to the relatively well-characterised ingredients of pure e-liquids (PG, vegetable glycerine (VG), nicotine, nicotine acidifiers and flavourants), a wide range of chemical reaction products are present in the aerosol, both as a result of slow reactions during storage (eg, Maillard reaction and acetal formation) and of acute production at the heating coil during use 59 60. The heating coil material and temperature can catalyse the breakdown of PG and VG, and can itself shed toxic metals into the aerosol 61–63.…”

Xenobiotics Delivered by Electronic Nicotine Delivery Systems: Potential Cellular and Molecular Mechanisms on the Pathogenesis of Chronic Kidney Disease

“…Diacetyl is a member of organic diketones and is widely employed in the food industry to add buttery-based flavors to food [ 156 ]. Diacetyl has been detected in several ENDS; in some e-cigarettes, the aerosols can reach a concentration of 239 μg/e-cigarette [ 157 ].…”

“…With the exponential growth of novel ENDS flavors, it was observed that out of 51 e-cigarettes tested, 47 had detectable concentrations of diacetyl or its substitutes [ 157 ]. Diacetyl is the most common example of safe flavoring by oral ingestion, but not for inhalation [ 156 ]. Although the effects of inhaled diacetyl on ENDS users remain elusive, retrospective studies assessing the occupational exposures to heated and inhaled diacetyl indicate its potential toxicity, especially to the airways [ 158 , 159 ].…”

Making Every Single Puff Count—Simple and Sensitive E-Cigarette Aerosol Sampling for GCxIMS and GC-MS Analysis

“…Therefore, other sampling aids have been tested to remediate this discrepancy. These include cartridges coated with derivatization agents [ 18 ], silica gel traps [ 19 ], polymer sorbent tubes [ 20 , 21 , 22 , 23 ], SPME fibers in a static gaseous sample [ 24 ], solvent-filled impingers [ 25 , 26 , 27 ] or a combination of these [ 28 , 29 ]. As with regular smoking machines, the necessary suction is produced by a simple vacuum pump or a large-volume syringe pump.…”

“…The use of solvent-filled impingers results in a dilution of the collected analytes in a large volume of a solvent. This dilution requires collecting larger amounts of aerosol [ 25 , 28 , 31 ]. Unfortunately, the trapped substances can be unstable, leading to underestimations when using this method [ 31 ].…”