I have discussed a study reporting that smokeless tobacco contains trace levels of several metals, including cadmium, arsenic, nickel, chromium and lead.  Now, researchers at the University of California-Riverside report that the aerosol from an undisclosed e-cigarette contained numerous metals.

The study, whose lead author is Monique Williams, appears in PLoS One. It notes a “total of 22 elements were identified in EC [electronic cigarette] aerosol, and three of these elements (lead, nickel, and chromium) appear on the FDA’s ‘harmful and potentially harmful chemicals’ list.  Lead and chromium concentrations in EC aerosols were within the range of conventional cigarettes, while nickel was about 2–100 times higher in concentration in EC aerosol than in Marlboro brand cigarettes.”

The article implies that e-cigarettes are the source of inhaled toxic metals.  But, as pointed out previously by Boston University’s Michael Siegel, the amount of metals delivered to e-cigarette users is lower than the daily exposures permitted by the authoritative U.S. Pharmacopeial Convention (USP) for inhalable medications.

Williams and colleagues reported that 10 aerosol puffs, the equivalent of one cigarette, contained 0.017 micrograms (ug, one-millionth of a gram) of lead.  This means that a pack-a-day equivalent (200 puffs) contains 0.34 ug of lead.  According to the USP, it is permissible for an inhaled medication to deliver up to 5 ug of lead per day to a 50 kilogram (~ 100 pound) person.

The same holds true for nickel, chromium and copper.  For nickel, Williams reported the pack-a-day e-cigarette level at 0.1 ug, while the USP allows 1.5 ug per day in inhaled medicines.  For chromium, Williams reported that e-cigarettes deliver 0.14 ug, while the USP allows 25 ug in inhaled medicines.  For copper, the Williams-reported level is 4.06 ug; the USP allows 100 ug.

Tin is another metal Williams reported in e-cigarette vapor, at 0.74 ug per 200 puffs. The CDC reports that the average U.S. daily intake of tin by inhalation is 3 ug.

To be clear, the problem with the Williams study is not that it reported trace concentrations of metals in e-cigarette vapor.  That is useful information.  The problem with this study, as with most works of this kind in the past 20 years, is that it was published without context.  As the above quote shows, e-cigarettes were compared to traditional cigarettes without any reference to exposure from other inhalation settings and/or products.

Such demonization of e-cigarettes is inappropriate, and authors and journal editors share culpability.  Greater effort should be made to avoid bias in reporting of scientific data, particularly when public health is at stake.

Featured Publications