Acetal Formation of Flavoring Agents with Propylene Glycol in E-cigarettes: Impacts on Indoor Partitioning and Thirdhand Exposure

SHUANG WU, Erica Kim, Ran Zhao, University of Alberta

     Abstract Number: 64
     Working Group: Indoor Aerosols

Abstract
The widespread popularity of e-cigarettes has led to a significant increase in teen nicotine use. A large number of flavorings are the main contributors; the most commonly-used agents are carbonyls, which are toxic upon inhalation and may cause lung diseases. In e-cigarette solvents (e-liquids), flavorings can react to form acetals with different chemical properties and unknown toxicologies. Once emitted indoors, these harmful flavorings and their acetals can cause secondhand and thirdhand exposures, defined as exposures occurring through evaporation or chemical partitioning. These processes are governed by partitioning coefficients. The recent discovery of a large volume of indoor reservoirs signifies the importance of indoor partitioning, which is responsible for thirdhand exposure. However, conversions of flavorings to acetals in e-liquids have been rarely identified and their chemical properties are still unknown.

This study focuses on the liquid-phase chemical reactions of flavor carbonyls with e-liquid components, namely propylene glycol (PG). This work is the first to estimate the conversion of α-diketones to acetals in PG. Further, this work aims to understand how acetal formation affects the indoor partitioning of flavor carbonyls. Specifically, proton nuclear magnetic resonance (¹H NMR) spectroscopy has been employed to monitor the liquid-phase reaction. Poly-Parameter Linear Free Energy Relationships (ppLFERs) have been used to estimate the partitioning coefficients. A chemical two-dimensional (2D) partitioning model has been applied to predict the indoor phase distribution of flavorings and evaluate the potential pathways of human exposure.

This research provides insights into secondhand and thirdhand exposure to e-cigarette emissions. Indoor partitioning of flavorings added in e-cigarettes is not only determined by flavorings but is also affected by adducts formed in e-liquids. It should be noted that persistent exposure can harm non-smokers without their awareness through various pathways indoors. Our study helps to better understand the potential health hazards caused by flavorings added to e-cigarettes.