New Study Investigates Emissions of Metals and Toxic Chemicals from E-Cigs and Tobacco Cigs

Emissions of Metals and Toxic Chemicals from E-Cigs and Tobacco Cigs


Anyone who follows the research on e-cigarettes is likely aware that the reporting of findings in the media is not a generally good indicator of what the studies actually show. This can range from manufactured panics about e-liquid poisonings to the wholly unsupported notion of vaping being a gateway to tobacco use, but one of the most familiar forms of this deception relates to the chemical content.


Another iteration of this misleading media tactic is upon us, with a new study reportedly finding that “E-cigarette secondhand smoke has ‘increased levels of toxic metals.'” This is the general message gleaned from media coverage, but as usual, taking the apparently controversial step of actually reading the findings reveals that vapers are, in fact, exposed to considerably smaller quantities of harmful components than smokers.




  • Researchers compared emissions between cigarettes and e-cigarettes (with and without nicotine) using a set puffing schedule in an ordinary, office-like environment, as well as taking simultaneous readings of outdoor air.


  • Levels of indoor particulate matter during smoking were four and a half times the outdoor count, whereas during vaping there was little difference between inside and outside.


  • Researchers found that levels of organic chemicals such as polycyclic aromatic hydrocarbons were below the limit of detection for samples collected during vaping, but ten times outdoor levels during cigarette smoking. Only background levels of n-alkanes, organic acids and a marker of biomass combustion were detected in vaping tests.


  • Out of 47 elements and metals tested, only 6 appeared to have an indoor source during vaping tests, with three of them being in significantly lower quantities than during the cigarette tests. Silver, nickel and zinc were detected in similar quantities in smoking and vaping tests.


  • The metals detected appear to be related to the heating element (coil) and other atomizer materials rather than coming from a component of the e-liquid.


  • Nickel and silver were emitted at a faster rate during vaping, and chromium and titanium were emitted from vaping but not from smoking. However, other toxic metals such as cadmium and lead were emitted at up to 1000 times higher rates from smoking.


  • Organic acids and alkanes were emitted at 100 to 1000 times higher rates from smoking than from vaping.


  • 13 times more particulate nicotine is released from cigarette smoking than from vaping, but the study didn’t measure nicotine in gaseous form.


  • The researchers concluded that e-cigarettes result in “much lower” exposure to toxicants and undesirable chemicals, and appear to be a public health improvement compared to smoking. They argue for regulation to ensure manufacturing standards to minimize harmful chemical exposure.


  • Despite media concerns about e-cigs and metal content, most of the potentially dangerous components detected in e-cig vapor, in this study and other research, are present in considerably smaller quantities, if at all.


  • The levels of the metals identified as being emitted from e-cigs in cigarette-like quantities are well within daily exposure limits set by the USP for medicines. Recreational nicotine products should not be held to this strict standard, but e-cigs fall within limits regardless.


Vaping vs. Smoking: Emissions of Metals and Organic Compounds


The study (full paper is paywalled) comes from researchers at the University of Southern California, who compared the emission rates of and second hand exposure to particulate metals and organic compounds between cigarettes and e-cigarettes. They tested this in an office-like room, with three fans placed strategically to ensure the e-cig aerosol and cigarette smoke were distributed evenly around it for sampling. They recruited three volunteers (two men and one woman), who smoked normal cigarettes and vaped an e-cigarette (specifically the Ovale Elips C Series) for the experiments, positioned away from the sampling equipment to ensure smoke or vapor wasn’t blown directly onto it. The room had an open window, and with the sampling pump running the indoor air was completely replaced in just under an hour. During the tests, samples were also taken from a terrace outside the room to enable researchers to determine the impact of ambient outdoor air levels on the findings.


Second-hand e-cig smoke compared to regular cigarette smoke

Photo credit: ScienceDaily


For the cigarette smoking, participants were free to smoke however they liked, which worked out to an average of one puff per minute for seven minutes, then there was a three minute break before they smoked another cigarette. For the vaping tests, participants had to keep this same pattern (one puff a minute for seven minutes, break, then repeat) to ensure the two could be compared fairly. They took six e-cigarette samples (three with 16 mg/ml and three without nicotine) and three cigarette samples, with each having a counterpart sample taken outdoors to compare the indoor levels to background concentrations.


What They Found – E-Cigarette Emit Much Less Toxic Components


The most basic part of the analysis concerned the amounts of particulate matter released from smoking and vaping in comparison with the levels detected outside the room. When cigarettes were smoked in the room, the indoor particle concentration increased by over 4.5 times compared to outdoor levels taken at the same time, whereas when participants vaped the levels indoors and outdoors stayed roughly the same. There was also very little difference between nicotine-containing and nicotine-free e-cigarettes in terms of particulate matter emissions – so either way, vapers emit many times fewer particles than smokers.


The type of emissions detected is the most important element, of course, because small amounts of something risky are more worrying than large amounts of something benign. For basic comparison, researchers split the components into elements and metals, polycyclic aromatic hydrocarbons (PAHs), hopanes, n-alkanes, organic acids and levoglucosan (a sign of biomass combustion). Graphs available in the main paper and the supplementary information document clearly show that in each group (aside from hopanes: chemicals associated with gasoline and diesel engines, which weren’t detected in either indoor condition), e-cigarettes emit much less of these chemicals than cigarettes. This is true whether you look at the concentrations per cubic meter of air or their concentrations per micro-gram of particulate matter. In other words, e-cigarettes emit fewer particles overall, but even if they emitted just as many, the quantities of these groups of potentially harmful components would still be lower than in cigarettes.


Organic Chemicals and E-Cigarettes


One particularly valuable finding is that PAHs, which are potential carcinogens, were undetected for samples collected during vaping. When participants smoked cigarettes, by comparison, the levels increased to ten times their proportions in outdoor air. Similarly, there were five to ten times more alkanes and organic acids in the cigarette smoking tests than in either the vaping or ambient outdoor air conditions.  These findings were further corroborated using another experimental technique, which looked at concentrations of black carbon using different wavelengths of light. This again showed that cigarette smoke contains a lot of organic material (especially material which absorbs ultraviolet light), but e-cig aerosol contains very little.


As you would expect since cigarette smoking involves the burning of biological matter and vaping doesn’t, levels of the tracer levoglucosan were 80 times higher after smoking than after vaping. The limited presence of the chemical during the vaping tests was assumed to be from outdoor air that ended up in the testing room. Out of the organic chemicals tested, only n-alkanes and organic acids appeared to be associated with vaping, but aside from two specific acids, these chemicals weren’t present in detectable levels in the e-liquid itself. The researchers say it’s impossible to determine the source of these on the indoor vaping tests based on their data, but speculate that the detected n-alkanes and acids were probably due to background indoor levels rather than vaping itself. Smoking, on the other hand, is a notable source of emission of these chemicals.


Inorganic Elements, Metals and E-Cigarettes


The most widely-reported finding from this study related to the quantities of various metals and inorganic elements detected in e-cigarette vapor. The researchers looked at 47 different elements, and along with their concentrations (indoors after smoking a cigarette or after vaping and the simultaneous outdoor reading) the researchers were able to analyze the data to determine whether their main source was indoors or outdoors. Out of these 47 elements, only six (nickel, zinc, silver, potassium, boron and lanthanum) were determined to have an indoor source during the vaping tests. If you look at the tables in the supplemental information document, it’s clear that many other elements (notably lead and cadmium) are produced in huge amounts during smoking but are barely (if at all) associated with vaping. For lead, outdoor concentrations were 13.28 nanograms per cubic meter, indoors during vaping 9.85 ng was present per cubic meter and during smoking it was a comparatively massive 182.22 ng per cubic meter.


As has been explained elsewhere, the presence of metals in e-cigarette vapor is not something to be surprised about, since all of them use metal for the heating element (the coil) and atomizers are generally metallic in construction. The authors looked into the relative contributions of the e-liquid and the device’s components, and in no case did the e-liquid alone cause the detected levels, with zinc, nickel, silver and lanthanum in particular being predominately related to components.


For the six main identified elements, the researchers compared the levels between smoking and vaping sessions. For boron, potassium and lanthanum, the levels found after cigarette smoking were significantly higher than those found after vaping. For zinc, nickel and silver, there was no verifiable difference between the two.


Rates of Chemical Emissions from Smoking and Vaping


The authors also calculated the rates of emission for various chemicals for both vaping and smoking. Generally, the authors note that the rates of emission for numerous elements that are harmful to health are substantially lower in e-cigarettes compared to cigarettes. For example, 1,012 ng per hour of lead is emitted from cigarettes, but for e-cigarettes this is just slightly over 96 ng per hour. For cadmium, just over 657 ng per hour is emitted from cigarettes, compared to only 0.480 ng per hour from e-cigarettes, a difference spanning three orders of magnitude. These are both very toxic metals, and it’s clear that switching to vaping drastically reduces your exposure to them.


Apart from nickel, chromium, silver and titanium, cigarette smoking emitted more than vaping across all of the elements tested. Titanium and chromium weren’t detected from cigarettes at all, and for silver, cigarettes emitted 14.65 ng per hour compared to 20.91 ng per hour for e-cigarettes – a difference of only about six billionths of a gram per hour. There was over 3.5 times more nickel emitted from e-cigarettes, but this was still just 130.5 ng per hour. Zinc and potassium were the elements emitted at the highest rates from e-cigarettes, but for both cigarettes release drastically greater quantities. For organic compounds, the emission rates of all alkanes and acids were 100 to 1000 times lower in e-cigarettes compared to cigarettes.


Nicotine Emissions from Smoking and Vaping


Finally, the authors looked at nicotine release from e-cigarettes and smoking, finding that smokers expose bystanders to 13 times higher particle-phase nicotine concentrations than vapers. There was also nicotine detected in the air while participants were vaping the no-nicotine liquid, but this was assumed to be due to background levels rather than from the e-cigarette itself.


They tested the nicotine in the e-liquid, labeled as 16 mg/ml, and found that it contained 17.2 mg/ml (with a 0.5 mg/ml uncertainty in the measurement), showing a close agreement between the advertised and measured amounts (despite frequent media claims to the contrary). Based on this and their calculation of the rate of liquid consumption (1.3 ml/hour), they determined that 22.36 mg/hour of nicotine would be released in either gas or particle form. The researchers suggest that the low observed emission of nicotine in particulate form (just 4,344 ng or 0.004344 mg/hour) shows that only a small fraction of the nicotine emitted is detected as second-hand particles.  They suggest more evidence is needed to determine how much nicotine bystanders are exposed to from vaping, but other research has also suggested that this is much lower than from smoking. Of course, a substantial amount of the nicotine released from the liquid is absorbed by the user (since that’s why we vape in the first place), so it wouldn’t be expected that all of this would be exhaled in either gas or particle form.


What Does This Mean for Vapers?


Pointing out the 10-fold reduction in inorganic element emissions and the 100-fold decrease in organic emissions compared to smoking, the authors conclude that “Based on our results, use of e-cigarettes from a public health perspective appears to be an improvement compared to normal tobacco-containing cigarettes, as exposure to most of the toxic and/or undesirable chemical species was found to be much lower than that for normal cigarettes.”


However, the authors argue throughout the paper that the presence of some metals in greater quantities in emissions from e-cigarettes due to the components shows the need for quality controls in the form of regulation. Although it’s questionable whether the limited amounts of metal detected are cause for concern, it’s fair to say that most vapers would actually be in favor of reasonable quality control standards to ensure exposure to impurities and trace metals is kept to a minimum.


The media is mainly pushing the metals angle, because saying “e-cigarettes expose users to four times more nickel than cigarettes” and naming some other toxic metals that are present but not mentioning their very low quantities makes it sound like e-cigs are a risk to users’ health. The simplest argument against this is the simple fact that nickel, silver, zinc and chromium aren’t the only things you’d have to worry about from smoking.


Even if all of these had been present in much greater quantities in e-cigarettes (if they’d all been more like nickel), then e-cigarettes would still have massive potential for harm reduction, because there are over 4,000 chemicals in cigarette smoke, with about 70 carcinogens among them. Lead and cadmium are two examples of very toxic metals present in cigarette smoke in much higher quantities than in e-cigarettes, and that’s before other components (like PAHs, nitrosamines and so on) are even considered. There is no doubt that making a big fuss about a handful of components being present in cigarette-like quantities unduly detracts from the massive likelihood of hugely reduced exposure and harm from vaping.


But this isn’t the only thing that’s a little stupid about getting up in arms about a few metals being emitted by a metallic device used by consenting adults. Pharmaceutical medicines have allowable limits for metal impurities, and if e-cigarette-like amounts were present in an inhalable medicine, there wouldn’t be an issue.


For a 50 kg (fairy thin) person, 1.5 micrograms (that is, 1,500 ng) of nickel is allowed in inhalable medicines, according to USP limits. In this study, continued use emitted just 130.5 ng per hour. This means you could vape for 11 and a half hours with this emission rate before approaching the daily limit, assumedly according to the 1.3 ml per hour consumption calculated in the study. Based on these figure, you’d need to vape about 15 ml of e-liquid per day to approach the allowable limit for nickel in medicines. For chromium, the same thin person is permitted to be exposed to 25 micrograms per day (25,000 ng) as impurities in an inhalable medicine, compared to just 28.1 ng (about 900 times less) per hour measured from vaping. These measurements were taken after exhalation, so this could vary depending on how much is absorbed by the user, but there is such a notable difference that it’s clear there’s nothing to be concerned about for either vapers or bystanders.


This really puts everything into perspective. If you just read about this study through the media, you’d see “more of certain metals than cigarette smoke” and think e-cigarettes were a cause for concern, but nobody would get in trouble if you inhaled about a hundred times more chromium per day as part of your medical treatment. The thorn in the side of these manufactured concerns about the metal content of e-cigs is that we don’t even need vaping to be safer than medicines (since it’s a recreational product, like cigarettes); the only thing that really matters is if it reduces harm in comparison to smoking, and that is without question. The authors themselves point out that the study supports the notion that e-cigarettes are much safer than smoking. One or two trace metals really don’t matter when you think about the big picture.




As always, what people learn from the news reporting of research is vastly different to what was actually found. This wouldn’t be annoying if it didn’t seem like these unfounded concerns are given much more prominence in the legislative debates about e-cigarettes than the very real benefit they could have to public health.


Yes, of course there are trace amounts of metals in e-cigarette vapor, but these are found in similar quantities in pharmaceutical products (including nicotine inhalers), and no, they really aren’t anything to worry about for either vapers or bystanders.


Also read: