Interplay of Metals and Organics in E-Cigarette Aerosols Enhances the Production of Reactive Oxygen Species within Ultrafine Particles: Implications for Passive Vaping Exposures

Recent work has shown that the atmospheric aging of vaping emissions in indoor environments produces organic hydroperoxides via the ozonolysis of terpene flavoring chemicals. These peroxide species decompose to form radicals upon aqueous dissolution. While the mechanism responsible for producing these radicals has yet to be fully elucidated, one prevailing hypothesis to support this phenomenon is Fenton-like reactions between redox-active metals and peroxides. Vaping emits various redox-active metals, which may play an important role in mediating these types of aqueous reactions. Here, we observed that the production of radicals resulting from the aqueous decomposition of aged e-cigarette aerosols was found to be highly dependent on the presence of redox-active metals, indicating the reliance of Fenton-like reactions on mediating the formation of radicals. Additionally, we observed that peroxides and metals are enriched within the ultrafine particles (UFPs) of aged vaping emissions, which leads to a drastic enhancement of their ability to generate radicals. This work provides a mechanistic perspective regarding the oxidative ability of aged e-cigarette aerosols, as well as potential negative implications associated with their inhalation and subsequent deposition in aqueous regions of the lungs.