Transfer of Metals to the Aerosol Generated by an Electronic Cigarette: Influence of Number of Puffs and Power

Abstract

Electronic cigarettes (e-cigarettes) are increasing in popularity despite uncertainties about their health hazards. Literature studies have shown that e-cigarettes may be a source of toxic heavy metal exposure to the user, but the mechanism by which metals are transferred from the e-cigarette parts into the aerosol plume that is inhaled by the user is poorly understood. The goal of this study was to quantify the potentially harmful heavy metals chromium, nickel, copper, and lead systematically during the simulated use of a mod-type e-cigarette in order to better understand the mechanism of metal transfer from the e-cigarette parts into the aerosol plume and into the liquid in the storage tank. Aerosol was collected and aliquots of the remaining liquid in the storage tank were collected from 0 to 40 puffs in 10 puff increments and analyzed with atomic absorption spectroscopy. It was found that the concentration of metals increased in both the aerosol and tank liquid the more times the e-cigarette was puffed, but at varying rates for each element and depending on the power applied to the heating coil. For copper, lead, and nickel, the concentrations of metals in the aerosol and tank increased with increasing power but for chromium, the concentration varied with power. Additionally, it was observed that chromium and nickel concentrations were greater in the aerosol than in tank liquid, consistent with the direct transfer of those metals to the aerosol from heating of the nichrome coil element used in this study. For copper and lead, the concentrations were similar or greater in the tank compared to the aerosol, consistent with transfer first into the storage tank liquid, followed by vaporization into the aerosol.

Keywords: aerosol; electronic cigarette; inhalation; metals; particulate matter.

Figure A1

Mean of concentrations of chromium (Cr), nickel (Ni), copper (Cu), and lead (Pb) in the e−liquid placed in the tank measured before firing the e−cigarette. Error bars represent standard deviations of triplicate measurements. The dotted lines represent the Limits of Quantitation (LOQ) of the measurements.

Figure A2

Concentrations of lead (Pb), nickel (Ni), and copper (Cu) for e-liquid over time with coil placed in e−liquid. Error bars represent standard deviations of triplicate measurements of individual liquid samples. Chromium concentration was less than the LOD in all cases and is not shown.

Figure 1

Schematic diagram of Vaporesso Revenger Mini E-cigarette used in this study. (a) General assembly with storage tank, coil assembly, and battery. (b) Magnified view of the coil assembly. For clarity, the assembly shown here has only one coil, while the GT8 coil assembly used in this study had four nichrome heating coils that heated simultaneously. Airflow through the device is indicated by red arrows.

Figure 2

Experimental apparatus. Red arrows indicate direction of air flow through the system. A flow meter was used to measure the flow rate through the device, while a flow control needle valve was used to set the flow rate. A high-efficiency particulate air (HEPA) filter was placed in the line to remove excess particles before air flow entered the pump.

Figure 3

Results. Solid blue circles represent the concentrations in the collected aerosol and open orange squares represent the concentrations in the tank liquid. Note the varying vertical axes for different metals. Error bars are ± the standard deviations of three independent puffing experiments.

Figure 4

Mean concentration of metals in the aerosol (solid markers) and tank (open markers) from 10 to 40 puffs plotted as a function of power. Note: Error bars are ± the mean standard deviation of each concentration.

Figure 5

Aerosol/tank concentration ratio plotted for each element, power, and number of puffs. The error bars represent standard deviations of repeated puffing experiments.

Figure 6

Mean aerosol/tank ratio plotted for each element and power. The gray horizontal line indicates an aerosol/tank ratio of one. The error bars represent the standard deviation of the mean aerosol/tank ratio over 10–40 puffs for each power.