Elements including metals in the atomizer and aerosol of disposable electronic cigarettes and electronic hookahs

Abstract

Objective: Our purpose was to quantify 36 inorganic chemical elements in aerosols from disposable electronic cigarettes (ECs) and electronic hookahs (EHs), examine the effect of puffing topography on elements in aerosols, and identify the source of the elements.

Methods: Thirty-six inorganic chemical elements and their concentrations in EC/EH aerosols were determined using inductively coupled plasma optical emission spectroscopy, and their source was identified by analyzing disassembled atomizers using scanning electron microscopy and energy dispersive X-ray spectroscopy.

Results: Of 36 elements screened, 35 were detected in EC/EH aerosols, while only 15 were detected in conventional tobacco smoke. Some elements/metals were present in significantly higher concentrations in EC/EH aerosol than in cigarette smoke. Concentrations of particular elements/metals within EC/EH brands were sometimes variable. Aerosols generated at low and high air-flow rates produced the same pattern of elements, although the total element concentration decreased at the higher air flow rate. The relative amount of elements in the first and last 60 puffs was generally different. Silicon was the dominant element in aerosols from all EC/EH brands and in cigarette smoke. The elements appeared to come from the filament (nickel, chromium), thick wire (copper coated with silver), brass clamp (copper, zinc), solder joints (tin, lead), and wick and sheath (silicon, oxygen, calcium, magnesium, aluminum). Lead was identified in the solder and aerosol of two brands of EHs (up to 0.165 μg/10 puffs).

Conclusion: These data show that EC/EH aerosols contain a mixture of elements, including heavy metals, with concentrations often significantly higher than in conventional cigarette smoke. While the health effects of inhaling mixtures of heated metals is currently not known, these data will be valuable in future risk assessments involving EC/EH elements/metals.

Fig 1

Internal anatomy of air-flow activated (A) and button-activated (B) disposable ECs/EHs. Both models included the LED light, battery, air-tube, thick wires, joints, wick, filament (thin wire), and sheath. The button-activated models also included the button and button circuit board. The internal anatomy of both ECs and EHs are similar.

Fig 2. Concentration of elements in disposable EC aerosol (first 60 puffs) and in Marlboro Red cigarette smoke.

The concentration of elements in aerosols from (A) Vype, (B) Square 82, (C) V2 Cigs, (D) Mistic, (E) BluCig, and in smoke from (F) Marlboro Red ISO, and (G) Marlboro Red CS are shown in the pie charts as a percentage of the total concentration of elements for each brand. The total concentration of all elements is given for each brand in μg/10 puffs beneath each pie chart. Numbers adjacent to each element are concentrations in μg/10 puffs for that element. For each brand, all concentrations are the average of three aerosol samples from three different ECs, and only elements that were higher than or equal to 0.002 μg/10 puffs are presented in this figure.

Fig 3. Elemental analysis of disposable ECs at low and high air-flow rates.

The concentrations of elements in the aerosol of NJOY King were measured at low (A) and high (B) air-flow rates, and are shown for each element in the pie charts as the percentage of the total concentration of all elements. Sodium was not measured in the aerosol from NJOY King puffed at a low air-flow rate. The total concentration of all elements is given at the bottom of each pie chart. Numbers adjacent to each element are concentrations in μg/10 puffs for that element. All concentrations are the average of three aerosol samples from three different ECs, and only elements that were higher than or equal to 0.002 μg/10 puffs are presented in this figure.

Fig 4. Concentration of elements in disposable EH aerosol and Marlboro Red cigarette smoke.

The concentration of elements in the aerosols of (A) Imperial Hookah, (B) Smooth, (C) Starbuzz (D) Tsunami, and in smoke from (E) Marlboro Red ISO and (F) Marlboro Red CS are presented in each pie chart as a percentage of total element/metal concentration. The total concentration of all elements is given in μg/10 puffs at the bottom of each figure for each brand. Numbers adjacent to each element are concentrations in μg/10 puffs for that element. All concentrations presented are the average of three samples, and only elements higher than or equal to 0.002 μg/10 puffs are presented in this figure.

Fig 5. Comparison of the concentrations of elements in the first and last 60 puffs of disposable EC/EH aerosol.

Four brands of disposable ECs/EHs were evaluated: (A, B) Square 82, (C, D) Luxury Lites, (E, F) V2 Cigs, and (G, H) BluCig. (A, C, E, G) Represent the concentration of elements in the first 60 puffs of each brand. (B, D, F, H) Represent the concentration of elements in the last 60 puffs of each brand. The total concentration of all elements is given at the bottom of the pie chart for each brand. Numbers adjacent to each element are concentrations in μg/10 puffs. All concentrations are the average of three independent aerosol samples from three different ECs/EHs, and only elements higher than or equal to 0.002 μg/10 puffs are presented in this figure.

Fig 6. Comparison of individual elements across brands of disposable EC/EH aerosol and conventional cigarettes.

The concentrations of 15 individual elements in EC/EH aerosol and Marlboro Red cigarette smoke (ISO and CS) are presented for each unit in each brand (A-O). Significant differences were evaluated by performing t-tests between the Marlboro Red group (ISO) and each individual EC or EH for each element. * = p < 0.05; ** = p < 0.01; *** = p < 0.001; **** = p < 0.0001. Absence of a dot indicates the value was below the limit of detection and the trial was treated as zero in the statistical analysis. Red = Trial 1, Green = Trial 2, Blue = Trial 3.

Fig 7. Scanning electron microscopy and energy dispersive X-ray spectroscopy analysis of disposable EC/EH wires and joints.

(A) Scanning electron micrograph of the clamp joining thick and thin wires (red arrow) in BluCig. The filaments (0.13 mm) were usually comprised of nickel (B) and chromium (C) as shown for BluCig. For all brands, the thick wire (0.33 mm) was comprised of copper (D) and silver (E). The clamps in all brands were comprised of copper (D) and zinc (F) (2.4 mm). The filament (0.11 mm) from Square 82 was unusual in that it was comprised of chromium (G), iron (H), and aluminum (I). In some brands, the thick wire and filament were joined by tin solder. The solder joint (J) (1 mm) in Square 82 was comprised of tin (K) and calcium (L). The solder joint (M) (1.8 mm) between the thick wire and filament in Imperial Hookah was comprised of tin (N) and lead (O). The solder joint (P) (2 mm) between the thick wire and filament in Luxury Lites was comprised of tin (Q) and lead (R). (S) Example of poorly manufactured solder joints, comprised of tin (T) (0.78 mm) in most EC/EH brands. White arrow = filament (thin wire); Orange arrow = thick wire; Red arrow = joints between the thick and thin wires. Data are summarized in Table 2.

Fig 8. Scanning electron microscopy and energy dispersive X-ray spectroscopy analysis of disposable EC/EH wicks and sheaths.

Examples are shown for BluCig which was representative of most brands. The sheath (A) in BluCig was comprised of silicon (B), oxygen (C), calcium (D), aluminum (E), and magnesium (F). For all brands, the wicks all had a similar composition as shown for BluCig. The wick (G) was comprised of silicon (H), oxygen (I), calcium (J), aluminum (K), and magnesium (L). Spectra of the composition of the sheath (M) and wick (N) are presented in this figure. All data are summarized in Table 2.