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A few days ago, we talked about dry burning of bare coils and mentioned that such practice may cause the release of particles to the inhaled aerosol. The quality of these particles is linked to the material the resistance wire is made of, Chromium, Molybdenum, Cobalt, Iron, Copper… The quantity is certainly very small but a cumulative effect on the long term may not be excluded.

A US research team from the University of California Riverside investigated e-cigarette aerosols for the presence of metals (tin, copper, zinc, silver, nickel, and chromium) and used qualitative and quantitative elemental analysis techniques to identify their origin [1].

Assembling value and the aerosol’s quality

Their motivation was to link the assembling quality to the quality of the aerosol and to demonstrate that poor/cheap material and procedures used during the manufacturing process heavily weight on the quality of the products in use. One of their objectives is to advise improvements in the quality of the device to minimize the risk of contamination with metals.

The exposure to metals by inhalation with e-cigarettes remains unknown but extreme cases have previously been described for welders in occupational medicine reports.

It is stated by the authors that trace metals like cadmium, nickel, lead, tin, zinc and copper, are present in cigarette smoke at higher levels than in e-cigarettes.

Among the metals under study, tin (Sn) was of particular interest because it was present in the fluid of one of the brands investigated, in the fibers and in the aerosol. Its presence was not only in the form of atoms but also as particles up to 0.5 μm.

A study on old cartomizers but an actual concern

As often, their “subjects” are from earlier generations of e-cigarettes. Here, they got interested in some cartomizer models available on the market between 2009 and 2014. Cartomizers are e-cigarettes were the atomizer and cartridge are combined into a single unit; they are probably not the best e-cigarette ever but they are characteristic of the market in the early 2010s. Since then, several improvements have been made but the problems of aerosol contamination by trace metals remains of actuality.

The authors, by dissecting some models of e-cigarette, determined that lots of different metals were present, some of them being in direct contact with the e-liquid.

Tin, copper, zinc, silver, nickel and chromium concentrations. Silver was found in the highest concentration (about 4,500.0 μg/10 puffs). Tin was the most variable component (up to 0.40 μg/10 puffs) since the other elements ranged between undetectable levels to 0.20 μg/10 puffs. Copper was the third highest concentration (up to was the most remarkable contaminent, followed by zinc and nickel.

Safety tips to minimize metal contamination:

  • Silver: A wire coated with plastic instead of silver reduced contamination,
  • Zinc: Wires joined by brazing, not by a brass clamp, reduced the contamination,
  • Copper wires, present in all products, and the copper-containing clamps,
  • Tin: Faulty solder joints were found to be a major cause of contamination, tin coating of copper wires was se second cause..
  • Dense fibers retain the biggest metal particles in their network. Poly-fil alone did not provide an effective filter.
  • Physically separated battery and atomizing chambers avoid the contamination of the aerosol with metals (released by the battery or used in the assemblage).

Tin, the most worrisome compound

Tin solders are present in all devices, especially to connect wires to LEDs or to assemble different metallic parts. It is important, for the best vaping quality, that aerosol and e-liquid remain out of reach of any type of alloy, especially tin solders. Tin has a low melting point (232°C), which may be exceeded by some of the most powerful devices, leading to degradation of the solder joints.

Replacing wire-to-wire tin solder joints with brass clamps significantly reduced tin levels without significantly increasing copper and zinc because brass is more stable than tin solder.

The authors noticed that not all cartomizers perform similarly [2]. By dissecting devices, they show that the wiring quality affects the production of aerosol and the densest production is the most enjoyable by the user that will discard the device that is not doing vapor. The most efficient wiring is often obtained with tin solder that needs to be carefully inspected.

If possible, do prefer brazed assembly instead of tin. Even if tin poisoning cases are almost absent from literature, their absence doesn’t mean that poisoning does not exist but rather that no link has been made between tin and diseases. Tin is also present in organotin compounds, some of which being as toxic as cyanide (CN).

Another identified source of metal was the e-liquid itself. The presence of metal in the blend may come from the manufacturing process, for example the use of metal containers for storing individual ingredients or the whole mixture. The manufacturing procedure must be carefully analyzed, step-by-step, in order to minimize the contamination risk.

In conclusion

A considerable scientific effort is being made to elucidate key points of aerosol quality. This is, for example the case for flavors but also for metals.

Currently available evidence indicates that electronic cigarettes are by far a less harmful alternative to smoking and significant health benefits are expected in smokers who switch from tobacco to electronic cigarettes. This is true for toxicants, for carcinogens and also for metals. However, as a general guideline, we all are in contact with metals and metal particles in our everyday’s life; each effort to reduce their impact on our body and health is valuable, especially when little awareness makes the biggest difference.


[1] Williams M., To A., Bozhilov K., Talbot P., 2015. Strategies to Reduce Tin and Other Metals in Electronic Cigarette Aerosol. PLOS One. DOI: 10.1371/journal.pone.0138933

[2] Williams M., Villareal A., Davis B., Talbot P., 2015. Comparison of the Performance of Cartomizer Style Electronic Cigarettes from Major Tobacco and Independent Manufacturers. PLOS One. DOI: 10.1371/journal.pone.0149251.

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