Influence of e-Liquid pH on Heavy Metal Emissions in Open-System Electronic Cigarette Aerosols and Associated Health...

Nicotine salt e-liquids are formulated at lower pH to enhance tolerability, but acidity may corrode device components and elevate exposure to inhaled metals. The relationship between e-liquid pH, aerosol metal concentrations, and user health risks has not been systematically characterized.

Nine refillable e-cigarette (EC) devices were tested at controlled pH values (8.0, 5.1, 4.0, 3.2). Aerosols were analyzed for aluminum, cadmium, chromium, iron, lead, nickel, and tin using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Risks were assessed using ICH Q3D inhalation permitted daily exposures (PDE) and US Food and Drug Administration excess lifetime cancer risk (ELCR) methodology.

The UK market survey identified pH 4 as representative of typical e-liquid. At pH 4, median aerosol concentrations were Ni 2649 ppb, Cr 20 ppb, and Pb 176 ppb, compared with Ni 28 ppb, Cr 3 ppb, and Pb non-detectable levels at pH 8. Chromium exceeded its inhalation PDE at pH 4, while nickel and lead remained below their respective thresholds; no other measured metals exceeded PDE limits. The mean combined-metals ELCR increased from 47 per 100 000 at pH 8 to 747 per 100 000 at pH 4.

E-liquid pH is a critical determinant of metal emissions and associated risk in open-system EC, while risks remain lower than smoking, exposures at market-representative pH can exceed regulatory thresholds.

These findings indicate that e-liquid acidity is a key determinant of metal emissions and metals-attributable cancer risk in open-system electronic cigarettes. While risks remain substantially lower than those associated with combustible smoking, exposures at market-representative pH values can exceed established inhalation thresholds for chromium and produce non-trivial excess lifetime cancer risk. Regulatory frameworks may therefore benefit from considering e-liquid pH, device material compatibility, and routine aerosol metals testing across relevant pH ranges to better align product standards with harm-reduction objectives.