Technical Commentary: Metal Emissions in E-Cigarette Aerosols

A recently published peer-reviewed article on ScienceDirect examined the relationship between coil resistance in electronic cigarettes and the presence of metals and oxidative potential in generated aerosols.

In this study, the authors report that higher-resistance coils were associated with increased metal concentrations and elevated oxidative responses in an air-liquid interface lung cell model. These observations are important and contribute meaningfully to the ongoing discussion around device design, aerosol composition, and potential biological effects.

That said, from a device engineering and materials perspective, the mechanistic interpretation benefits from additional technical context. The discussion below is offered to supplement the published findings using established principles of heater physics, manufacturing experience, and historical failure analysis in ENDS systems.

Resistance Alone Does Not Define Coil Temperature

Coil resistance is frequently treated as a proxy for operating temperature. In practice, resistance alone is not a sufficient surrogate for either coil temperature or thermal stress.

Actual operating temperature is governed by multiple interacting variables, including power delivery, heat flux, wire gauge, surface area, airflow, and wicking efficiency. Historically, lower-resistance heaters operate at higher power densities and generate greater aerosol mass per puff.

If coil temperature were the dominant driver of metal transfer into aerosol, higher metal yields would be expected in lower-resistance configurations due to increased thermal energy and vaporization rates. The inverse relationship reported in the study suggests that mechanisms other than uniform heating of the active coil region are likely contributing to the observed metal levels.

Metals Often Originate Outside the Active Heating Zone

Extensive experience in heater and atomizer design indicates that metals detected in aerosol frequently originate not from the uniform, active heating zone itself, but from non-heated or partially heated components of the heater assembly.

Common contributors include:

• •Coil legs and electrical leads
• •Base pins and connectors
• •Welds, crimps, and mechanical joints
• •Exposed base layers beneath protective plating

Manufacturing processes used for resistance marking or labeling, such as laser etching or mechanical abrasion, can locally remove protective coatings and expose base alloys. These exposed regions are particularly susceptible to corrosion and electrochemical leaching under repeated wetting, condensation, and reheating cycles.

Importantly, corrosion-driven mechanisms are often most active at moderate operating temperatures where liquid contact time is prolonged, rather than at peak coil temperatures.

Lower Aerosol Mass Can Increase Apparent Metal Concentrations

Higher-resistance configurations typically produce lower total aerosol mass. Under these conditions, corrosion-driven metal release and preferential partitioning into fine droplets can result in higher metal concentrations per unit aerosol mass, even when total metal release is unchanged or lower overall.

Without normalizing metal yields to total aerosol mass, or localizing the physical source of metals within the heater assembly, comparisons based solely on concentration risk conflating correlation with causation.

Resistance Is Often a Proxy, Not a Root Cause

In commercial ENDS products, resistance rarely varies in isolation. It commonly co-varies with:

• •Wire diameter
• •Alloy composition
• •Coil geometry
• •Surface treatments
• •Marking and post-processing methods

Each of these variables has a well-established influence on corrosion behavior and metal release. Treating resistance as a primary causal factor without experimentally decoupling these confounders oversimplifies a complex materials system.

A Device Engineering and Materials Perspective

From a device engineering standpoint, the reported findings are more consistent with materials exposure and corrosion phenomena associated with manufacturing and assembly features than with intrinsic coil resistance or bulk operating temperature alone.

This perspective is informed by long-standing development and failure-analysis work in aerosol-generation systems, including extensive experience with heater design, device reliability, and aerosol delivery technologies.