Hong Kong biology professor cannot understand the difference between mLs of e-liquid and mLs of breathing air


By Dr Farsalinos

Today I received a large number of messages about a new scary story in the media, coming from Hong Kong. The story says that e-cigarettes are “a million times” more harmful than outdoor air. I was intrigued to see what kind of a story that was, and once again I was shocked. Not only it is another story far distanced from the truth but, if the statement of an assistant professor of biology is accurately reported, it is a complete disgrace for the scientist, the department and the university.

Without publishing any details and without reporting anything on the methodology and the samples tested, scientists from the Baptist University in Hong Kong said they tested 13 types of e-cigarettes available in the local market and found polycyclic aromatic hydrocarbons (PAHs) at levels of 2.9 to 504.5 ng per mL (ng/mL). Trying to compare this to outdoor air levels, Dr Dr Chung Shan-shan, assistant professor in the university’s biology department said: “ [Level of PAHs] in e-cigarettes is at least one million times more than roadside air in Hong Kong”. But how exactly is this comparison made?

First of all, the definition of PAHs is: “a class of environmental pollutants created primarily from incomplete combustion of various organic materials including tobacco”. We all know that there is no complete or incomplete combustion of any material in e-cigarettes, so I really doubt whether their findings are valid. Of course, there is no study published, no methodology or any other detail mentioned; this is just a media story. Beyond that, I made a quick search online to find the levels of PAHs in outdoor air in Hong Kong (sorry, I have better things to do and I cannot waste more of my time for this report). I found a paper from 1998, finding levels of PAHs up to 48 ng/m3 (cubic meter = 1,000,000 (million) mL) in Hong Kong. So, the levels in outdoor air are 48 ng per 1,000,000 mL. Obviously the scientist quoted in the media story compared mLs of air with mLs of e-liquid. This is not misinformation, not misinterpretation and not a mathematical mistake. It is simply and outrageously ridiculous…

The average volume of air breathed daily by humans is 20m3 (=20,000,000 mLs). Contrary to that, an average vapers consumes 3mLs of liquid (according to our survey). Thus, the levels in outdoor air in Hong Kong would result in total daily exposure of 960 ng. The levels of exposure from e-cigarette liquids (as tested by the Hong Kong university and assuming they are correct) are 9-1500 ng. This is from 99% less up to 50% more than exposure to outdoor air (or, to express it differently, 100 times less to ½ time more). So, the statement “1,000,000 times higher levels” is completely false.

Let’s not forget that e-cigarettes are (and should be) used as smoking substitutes. The authors said they measured PAHs in tobacco cigarettes and found 5.6-6.3 ng/mL. First, tobacco cigarettes are solid, not liquids or gas. Thus, there is no mL of tobacco cigarettes, they should mention weight of tobacco.  But here is the catch: tobacco cigarette smoke is known to contain about 1.6 ug PAHs per cigarette (that is, 1600 ng/cigarette). To measure this, we smoke the cigarette according to ISO (1 puff of 35mL volume every 60 sec). In 10 puffs (usual number of puffs to consume 1 cigarette), you take about 350 mL volume of tobacco cigarette smoke. Thus, if you express the level of PAHs per mL puff volume, you get: 1600/350 = 4.5 ng/mL. In fact, they found a bit more than that (about 2200 ng/cigarette), but pretty close. But how can you compare mLs of inhaled tobacco cigarette smoke with mL of e-liquid? It is simply a joke. The truth is that 1 tobacco cigarette contains by far more PAHs than what they reported they found in 1 mL of liquid (which is 1/3rd the daily consumption).

There are only two possibilities: either the scientists have no idea about what they are talking about, or they are deliberately misinforming the public and the regulators. Even worse, they are creating panic to vapers (the vast majority of whom are former smokers), with the risk of making them relapse to smoking. This is a typical case of gross misinformation and extremely poor science. Literally, a public health disgrace… The reporters of this “study” (not authors, because there is no published study) need to immediately apologize to the public for creating this story out of nothing.



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