Generation of Substantially Metal-Reduced but Aldehyde-Rich Aerosol for E-Cigarette Toxicity Studies

When e-liquid is aerosolized in an e-cigarette for inhalation by the user, the aerosol becomes contaminated by a mixture of toxicants, including metals and aldehydes. A method to generate e-cigarette aerosol with high aldehyde but low metal content is lacking, yet is needed to untangle the potential independent effects versus toxicological interactions of aldehyde and metal exposure from e-cigarette aerosol mixtures. The objective of this study was to establish a method for generating aldehyde-rich aerosols from e-liquids that lack, however, the large metal contamination typically found in e-cigarette aerosol. To aerosolize e-liquid at temperatures that promote aldehyde formation (up to 200 °C), a pneumatic atomizer was externally heated. Both a pure propylene glycol/vegetable glycerin (PG/VG) mixture and a commercial e-liquid were aerosolized. Aerosols were analyzed for known e-cigarette-associated toxicants, including 11 aldehydes using liquid chromatography-tandem mass spectrometry and 9 metals (Cr, Cu, Fe, Mn, Ni, Pb, Sr, V, Zn) using inductively-coupled plasma mass spectrometry. Aldehyde levels in aerosols from the pneumatic atomizer only reached those in a real-world e-cigarette aerosol if the commercial e-liquid was aerosolized at 200 °C. Metal levels in the aerosols from the pneumatic atomizer were then at least 8 times lower than in e-cigarette aerosol from a "Mod" device operated at 50 W. Cu, Ni, and Pb levels were particularly low across all aerosol samples, with some levels below the method detection limit (MDL). Aerosolization of a commercial e-liquid by a pneumatic atomizer at 200 °C produces aerosol that is low in metal levels (particularly Ni, Cu, Pb), but has aldehyde levels comparable to those found in a real-world e-cigarette aerosol.