Metals in electronic cigarette vapor: new review of the scientific literature

Two researchers looked at several studies analyzing the amounts of metals in steam. Their conclusions are clear: this research demonstrates an inappropriate methodology, which distorts their conclusions.

Many poorly conducted studies

For several years now, there has been a scientific consensus around the fact that vaping is less harmful than smoking. However, although the vapor produced by an electronic cigarette contains far fewer harmful substances than tobacco cigarette smoke, it is nonetheless composed of certain toxic molecules, and in particular carbonyls, nitrosamines, or compounds metallic. Since some research has already highlighted the detection of metallic compounds in e-liquids, at trace levels, it is not surprising that the vapor produced during vaping also contains them. Some parts of an electronic cigarette are even made of metal, which increases the chances of detecting it in the vapour.

A study to verify the methodology of other scientific work.

The subject of metals in the aerosol of a personal vaporizer has been widely studied by science since the appearance of the e-cigarette on the market. However, as is often the case when a subject is the fruit of numerous research works, the results vary according to the studies.

Last month, researchers Sébastien Soulet (Ingésciences, France) and Roberto A. Sussman (Institute of Nuclear Sciences, Mexico), carried out a review of the scientific literature (1) on this subject. The two experts looked at the results of 12 research studies carried out in laboratories and published after 2017. Their objective was to focus on the “consistency between their experimental design, real-life e-cigarette use, and appropriate exposure risk assessment”.

Among the studies studied, 9 had been carried out by researchers from academic and governmental institutions in the United States, 1 in China, and 1 in France. Finally, only one was funded by the vape industry.

An unsuitable methodology

After carefully analyzing the results of the studies reviewed and their methodology, the researchers note that all relied on very specific puff protocols, called CORESTA (Cooperation Center for Scientific Research Relative to Tobacco), or CORESTA type. Experts point out that since this method is “Incompatible with the large airflows and high wattage required to operate subohm devices, it is not surprising that high levels of certain metals (nickel, lead, copper, manganese) were found, particularly at the maximum power of the device, exceeding the strict toxicological references applicable to the general population”.

Thereby, these results would not be realistic, because they come from experiments whose protocols are incompatible with the real use of the tested devices.

The results obtained with the CORESTA method would, on the other hand, be realistic when it is used with electronic cigarettes of the pod and starter kit types (because they are intended to operate at low power, editor’s note). In these studies, the authors note that the levels of metals included in the aerosols were “well below stringent toxicology markers in all self-consistent lab tests”.

Some tests are not relevant to assess the health risks of users.

Finally, the 2 works that looked at the emissions of low-power electronic cigarettes, the results of which found metal levels higher than normal, were “tainted by methodological irregularities”. For example, the devices had been purchased 2 years before the study, without any data on their storage conditions having been communicated. It is thus possible that said devices are victims of corrosion. Furthermore, the researchers indicate that they have tested the materials with e-liquids without flavors or nicotineexcept that among the devices tested were a Juul pod and a Vapor4Life pod, which do not exist without flavors and/or without nicotine.

Not to mention the fact, among other irregularities, that some calculations are announced in the extract (summary, editor’s note) of the study, calculations that cannot be found anywhere in the complete study.

Sébastien Soulay and Roberto A. Sussman conclude:

“While laboratory tests under extreme conditions, unrelated to actual use, may be of theoretical and practical interest in themselves, they are not relevant for assessing the health risks of users”.

The reaction of Sébastien Soulet, co-author of the study and researcher at Ingésciences

On the left, Doctor Sébastien Soulet, Ingésciences. On the right, Doctor Roberto A Sussman, Institute of Nuclear Sciences, National Autonomous University of Mexico.

Reading this analysis, many questions naturally come to mind. How can such disparities in the methods used to carry out these studies be explained? How can we justify that several studies, dealing with the same subject, arrive at totally different conclusions? We contacted Dr. Sébastien Soulet, co-author of the review, to get his opinion on the matter.

Each researcher who studies the electronic cigarette can apply the vaping regime they want.

For him, the problems are multiple. If the industry vape “sudden” science, he explains, is because of a lack of organization of the latter, first of all. It does not really have a scientific organization which would bring together all its players, and which would have enough weight to “counteract bad studies”.

The sector would also be a victim of the lack of “standards”. The absence of the latter means that at present, every researcher who studies the electronic cigarette can “apply the ‘inhale’ (called vaping regimen in the lab) that he wants”, emphasizes the researcher. A fact he illustrates with the following example:

Each study will explain having analyzed a high-powered subohm device, except that one will have done so with more consistency of use than the other.

“A study looking at aerosol degradation products from a subohm device at 200W (despite it being recommended for 40-80W) can estimate that 1000 µg of a molecule is inhaled in a volume of 55 ml (approximate figure of a volume in indirect inhalation) by the vaper. A similar study, carried out by another researcher, could conduct the same study, but relate this quantity to a volume of 500 ml per puff (approximate figure for a volume in direct inhalation).

Add to that that there is not only one molecule considered, you get a repeated error leading to an overestimation of the real risks.

This first case will then give a concentration of exposure to this molecule of degradation 10 times greater than that of the second study, since the volume of the puff studied is 10 times smaller. However, each of them will explain having analyzed a high-power subohm device, except that one will have done so with more consistency of use than the other.

Add to that that there is not only one molecule considered, you get a repeated error leading to an overestimation of the real risks. And finally, we cumulate with a potency tested well beyond the recommended values, seriously questioning the relevance of the conclusions made with a toxicological analysis carried out under these conditions. Although it may seem exaggerated, this case comes from one of the criticized papers ».

© Ingesciences

A new question then arises, when will standards be put in place? According to Sébastien Soulet, also an expert in the AFNOR, CEN and ISO committees on vaping products, some could appear as early as next year, in particular “that necessary to analyze devices designed for direct inhalation”. If there is no way to force anyone to use them, they will at least have the merit of existing, of being able to serve as ” guide “and will make it easier to challenge searches that have chosen not to use them.

Some research would also be simply incomplete. As the doctor reminds us, a study is supposed “provide all the information necessary for its reproduction” by peers. However, some do not.

It is important not to cite and not rely on this type of study whose toxicological analysis results from conditions inconsistent with actual use.

Finally, concerning the question of knowing why the general media never speak of positive studies on the vape, but are happy to put on the front page those which are alarming, for the researcher, it is quite simply, because the negative makes sell more than the positive. Here again, according to him, the sector would need “to train to understand how these studies are biased and above all to organize themselves to conduct coherent studies and relay good studies”.

For his part, Roberto A Sussman wanted to add to our editorial staff that “Some of these studies are widely cited and used by public bodies”. For him, “it is important not to cite and not rely on this type of study whose toxicological analysis results from conditions inconsistent with actual use”.


(1) Soulet, S.; Sussman, RA A critical review of recent literature on metal content in e-cigarette aerosols. Toxic 2022, 10, 510.

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