Aluminium, copper, nickel, lead and zinc in e-liquids from contemporary disposable vapes

Although concerns have been raised about the health and environmental impacts of e-cigarettes (vapes), little is known about the latest, fourth generation of disposable pod devices. In this study, e-liquids from 44 used and three new e-cigarettes from different manufacturers and of different flavours were extracted in dilute nitric acid and analysed for metal(loid)s by inductively coupled plasma-optical emission spectrometry. While some metal(loids) (e.g., As, Ba, Cd, Co, Cr, Mn, V) were rarely detected and concentrations never exceeded 10 mg per kg of e-liquid, others (Al, Cu, Ni, Pb, Zn) exhibited variable concentrations that spanned several orders of magnitude. Of particular concern were contents of Ni and Pb or Cu and Zn that regularly exceeded 100 mg kg^-1 or 1000 mg kg^-1, respectively. Leaching from metallic components of e-cigarettes in contact with the e-liquid could account for the presence of Ni but not Cu, Pb and Zn. Strong correlations between the latter elements and an increase in their concentration with decreasing extract mass suggested that e-liquids are generally contaminated by Cu, Pb and Zn and that concentrations in residual liquids progressively increase as e-cigarettes are used. Exposure to the user is unclear but mass balance calculations comparing e-liquids from new and used products of the same brand and flavour suggest that, per device, up to 8000 μg, 500 μg and 6000 μg of Cu, Pb and Zn, respectively, could be inhaled. Residual e-liquids enriched in these metals also pose a localised environmental hazard on improper disposal and an occupational risk during storage, handling and component dismantling. Better monitoring and regulation of harmful metals in e-liquids more generally are called for.