Is the Harvard E-Cigarette Buttery Flavor Study Credible?

A month ago, I warned vapers to avoid e-liquids containing buttery flavorings diacetyl (DA) and acetyl propionyl (AP, also known as 2,3-pentanedione) – chemicals associated with bronchiolitis obliterans, a serious, sometimes fatal lung disease seen in workers producing buttered popcorn. 

This week, faculty at the Harvard School of Public Health reported that DA, AP and/or acetoin (a similar flavoring) are present in popular e-cigarettes’ aerosols.  The study, whose lead author is Joseph G. Allen, appears in Environmental Health Perspectives (abstract here).

If true, the report would implicate major e-cigarette manufacturers, but there are irregularities in the researchers’ methods and findings. 

Allen used a custom lab device “that drew air through the e-cigarette for eight seconds at a time with a resting period of 15 or 30 second [sic] between each draw. Eight seconds was chosen to make certain that each draw had adequate time for the entire contents to be forced out of the smoking device and through the sampling media…The samples were collected until the e-cigarette cartridges or cartomizers were exhausted, determined by the lack of visible emissions in the chamber.”  (emphasis mine)  In other words, the researchers used an aggressive procedure that vaped the samples dry.  Each “puff” was eight seconds long – an unrealistic length of time that could have produced higher-than-normal temperatures, combustion and smoke.

This is significant because at least two previous studies by Fujioka and Shibamoto (here) and Pierce et al. (here)  found that cigarette smoke contains both DA and AP.  Pierce reported that the smoke of a single cigarette has up to 1,037 micrograms of DA and 165 micrograms of AP.  She noted that DA is approved as a cigarette tobacco additive in Germany and the UK, and AP is also permitted in the UK.  However, according to Pierce, this “strongly suggests that pyrolysis products of tobacco and other cigarette components comprise a substantial fraction of the [DA] and [AP] concentrations in mainstream smoke.”  If the Allen e-cigarette methodology generated smoke, their results could have been compromised.

Another quirk of the Allen study was the resampling of “several of the same flavors from the same package (ie, testing two e-cigarette cartridges from the same pack)” for six of the flavors in the table at left.  It is troubling that the researchers failed to adequately explain why they ran these extra samples on only some products. 

More importantly, they didn’t offer a valid explanation for a wide divergence in values.  The researchers found no acetoin in one Pina Colada sample, but it was present in other samples at 17, 46 and 130 micrograms.  One Classic sample had no detectable acetoin, while another had 38 micrograms.  Allen suggested that these differences might be due to “variable chemical doses.” 

That explanation would be questionable if the sampled products were produced by major manufacturers with tight quality control systems, which seems to be the case here.

While, inexplicably, the Harvard researchers did not identify the e-cigarette aerosol brands under study, the brands can be inferred from the data. They are likely:

A – Mark Ten

B – Vuse

C – blu

D – NJOY

E – White Cloud

F – South Beach Smoke

G – Volcano

H – Tasty Vapor

I – Unknown

 

Since Pina Colada is a blu e-cigarette from Lorillard, and Classic is a Mark Ten product from Altria, ingredients can be expected to be highly consistent among samples taken “from the same pack”, as was done in this study.  

Allen and colleagues also suggested that variability could be related to the fact the researchers “relied on a visual determination of emissions of the e-cigarette in the chamber” to determine that the e-cigarette was “fully spent.”  A maxim in toxicology is to use methods that have been validated for the products and agents under investigation.  Eyeballing a stop point is not a validated method.    

As I advised previously, vapers should only use liquids that are certified to be free of buttery flavors that are suspected respiratory toxicants.  However, laboratory investigations of e-cigarettes should use validated methods to assure credibility.  The results of the Harvard Buttery Flavor Study do not meet this standard.