Metal and silicate particles including nanoparticles are present in electronic cigarette cartomizer fluid and aerosol

Abstract

Background: Electronic cigarettes (EC) deliver aerosol by heating fluid containing nicotine. Cartomizer EC combine the fluid chamber and heating element in a single unit. Because EC do not burn tobacco, they may be safer than conventional cigarettes. Their use is rapidly increasing worldwide with little prior testing of their aerosol.

Objectives: We tested the hypothesis that EC aerosol contains metals derived from various components in EC.

Methods: Cartomizer contents and aerosols were analyzed using light and electron microscopy, cytotoxicity testing, x-ray microanalysis, particle counting, and inductively coupled plasma optical emission spectrometry.

Results: The filament, a nickel-chromium wire, was coupled to a thicker copper wire coated with silver. The silver coating was sometimes missing. Four tin solder joints attached the wires to each other and coupled the copper/silver wire to the air tube and mouthpiece. All cartomizers had evidence of use before packaging (burn spots on the fibers and electrophoretic movement of fluid in the fibers). Fibers in two cartomizers had green deposits that contained copper. Centrifugation of the fibers produced large pellets containing tin. Tin particles and tin whiskers were identified in cartridge fluid and outer fibers. Cartomizer fluid with tin particles was cytotoxic in assays using human pulmonary fibroblasts. The aerosol contained particles >1 µm comprised of tin, silver, iron, nickel, aluminum, and silicate and nanoparticles (<100 nm) of tin, chromium and nickel. The concentrations of nine of eleven elements in EC aerosol were higher than or equal to the corresponding concentrations in conventional cigarette smoke. Many of the elements identified in EC aerosol are known to cause respiratory distress and disease.

Conclusions: The presence of metal and silicate particles in cartomizer aerosol demonstrates the need for improved quality control in EC design and manufacture and studies on how EC aerosol impacts the health of users and bystanders.

Figure 1. Cartomizer anatomy.

(A) A dissected cartomizer. 1 = mouthpiece, 2 = air tube, 3 = solder joint between air tube and thick wire, 4 = solder joint between thick wire and filament, 5 = wick, 6 = filament, 7 = solder joint between the filament and thick wire, 8 = thick wire, 9 = solder joint where the thick wire would attach to the mouthpiece, 10 = inner fibers, 11 = black area on inner fibers, 12 = outer fibers with yellow electrophoretic band. (B) EDS spectrum showing that the filament is comprised of chromium and nickel. Insert shows the particulate surface of the filament. (C) Scanning electron micrographs (inserts) and EDS spectrum of the thick wire which is comprised of copper coated with silver. Asterisks (*) in the upper insert indicates area where silver coating is missing and copper wire is exposed; white box indicates the silver coating. Lower insert shows the surface of the copper wire at high magnification. (D) EDS spectrum showing that solder joints are comprised mainly of tin. Upper insert shows a typical poor quality solder joint between the filament and thick wire. Boxed area is shown at higher magnification in the lower insert and contains tin whiskers. (E–H) Images of fiber types, (E, F) inner fibers, and (G, H) outer fibers. (E, G) black deposits on fibers and (F, H) green coloration on both sets of fibers.

Figure 2. Elemental analysis of pellets, cartomizer fluid, and particles on fibers.

(A and B) Supernatants and pellets obtained by centrifuging outer fibers (A) and inner fibers (B) (inserts). EDS spectra showing that the pellets are comprised mainly of tin. (C) Cartomizer fluid with particles inhibited hPF attachment dose dependently. (D) Cartomizer fluid with particles inhibited proliferation dose dependently. (E).Cartomizer fluid with tin particles had a stronger negative effect on hPF survival in the MTT assay than fluid without particles.

Figure 3. EDS spectra of elemental analysis and SEM images of cartomizer fluid and particles on fibers.

(A–B) Micrographs of white and black particles from cartomizer fluid (inserts) and spectra showing that the particles in fluid contained mainly tin. (C) Spectrum and micrograph (insert) of tin whiskers found in cartomizer fluid. (D) Spectrum and micrograph (insert) of inner fibers showing that the particulate deposition on the fibers is mainly tin. (E) Green outer fibers showing particles coating the fibers. (F) Micrograph (insert) and spectrum of green coated outer fibers. Particles are mainly tin with a trace of copper. (G) Green outer fibers after centrifugation, which removed green coloration. (H) Micrograph (insert) and spectrum of centrifuged outer fibers at higher magnification. Particles on the surface of the fibers are mainly tin, without copper.

Figure 4. Particulate material in the aerosol: Size distribution of particles in room air (A) and in aerosol (B) is expressed as number of particles/(cm3*logD).

The number of particles/cm3 with diameters between logD1 and logD2 is equal to the area under the curve bounded by logD1 and logD2. (C–D) Low magnification SEM micrographs of particles from room air (C) and aerosol (D) viewed in the backscatter mode. (E–I) EDS spectra and SEM micrographs (inserts) of particles in aerosol. F (insert) shows aggregation of small silver particles. (J–M) EDS spectra and TEM micrographs (inserts) of tin (J–K), chromium (L), and nickel (M) nanoparticles in aerosol.