A review of constituents identified in e-cigarette liquids and aerosols

INTRODUCTION: Identification of chemicals present in e-liquids and aerosols is a vital first step in assessing the human health effects of e-cigarettes. We aim to identify the qualitative and quantitative constituents present in e-cigarette liquids and aerosols. METHODS: A comprehensive search of scientific databases included literature up to July 2020. A total of 28 articles met inclusion criteria; 18 articles assessed e-liquid constituents and 15 articles assessed aerosol constituents. Of these, 5 assessed constituents present in both mediums. We included English-language publications that examine qualitative and/or quantitative constituents in e-cigarette liquids and aerosols. RESULTS: In total, articles identified 60 compounds in e-liquids and 47 compounds in aerosols. A total of 22 compounds were identified in both e-liquids and aerosols. These are: acenaphthylene, acetaldehyde, acetol, antimony, benzaldehyde, benzene, chromium, copper, diacetyl, formaldehyde, glycerol, lead, limonene, naphthalene, nickel, nicotine, nicotine-N'-oxides, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), N-Nitrosonornicotine (NNN), propylene glycol, toluene, and vegetable glycerin. Some of the identified chemicals have been labeled as harmful, toxic, or cancerous through human, animal, and cell line studies. A variety of laboratory methods were used for analyses, which made reported levels less consistent. CONCLUSIONS: E-liquids and aerosols contain a variety of chemicals with potential health effects from inhaling them. Further, secondhand health effects are unknown because of limited understanding of the dose of exposure by non-users. Identification of constituents in e-cigarettes is the first step to determine their risks to humans and support evidence-based regulations and health policies.