“Third-Hand Vapor” Precautions Are Not Justified. Guest Post by Dr. Roberto Sussman

BR note.  Readers of this blog know that anti-tobacco activists greatly exaggerated the risks of second-hand smoke (here and here). 

Unfortunately, the scaremongering has expanded to include third-hand smoke (discussed here), third-hand smokeless (here) and third-hand vapor (here).   

Two weeks ago another exaggerated “third-hand vapor” study was published by University of California activists.  For a perspective on this study, I am happy to introduce Dr. Roberto Sussman, a scientist (physics) in the Institute for Nuclear Research at the National Autonomous University of Mexico. Dr Sussman is also the director of Pro-Vapeo México AC, an all consumer non-profit association representing Mexican vapers and consumers of non-combustible nicotine delivery products, and an active member of INNCO.


“Third-Hand Vapor” Precautions Are Not Justified
By Dr. Roberto Sussman 

A recently published article (abstract here) seems to suggest potential health hazards from what could be called “third-hand vapor” in parallel to analogous studies on third-hand smoke. Specifically: the estimated exposure to electronic cigarette exhaled aerosol residues (ECEAR) deposited on surfaces and fabrics in rooms that are adjacent to a vape shop.   While it is worrying that the study of such extremely minute potential exposures to vapor residues may contribute to justify extensive vaping bans, the present comment only deals with strictly scientific (not political or activist) issues. Specifically, the following three issues are worth commenting:

(1) E-cigarette vapor vs PM_2.5. The article provides some background on possible health hazards from e-cig vapor. The following texts appear in the introductory section:

Significant amounts of 1,2-propanediol, glycerin, nicotine and PM_2.5 particles were present indoors during 2 hours of vaping. Moreover, an indoor air quality study showed that a large room with active EC users contained PM_2.5 at concentrations that were higher than in hookah cafes and bars that allow cigarette smoking. .  

The text conveys a sense of alarm, as it alludes to “PM_2.5”  (particulate matter of diameters smaller than 2.5 microns) allegedly present in the e-cigarette aerosol. These particles are found in aerosols produced by combustion mechanisms, for example in air pollution or tobacco smoke. However, the text quoted above hints the existence of an equivalent concern on health effects from exposure to PM_2.5 found in environmental e-cigarette vapor.  This seems to be completely unwarranted, since the “particles” in electronic cigarette exhaled aerosol are liquid droplets, not proper particulate matter, even if “particle” counts and diameters are of the same order of magnitude as in environmental tobacco smoke. This is clearly stated in various reliable sources (for example, “Public Health Consequences of E-Cigarettes: a Consensus Report”,  National Academies of Sciences Engineering and Medicine, see page 72 of the report here.)

I wonder why an article whose task is to look at potential exposures to pollutants in electronic cigarette vapor does not mention, as relevant background information for the readers, the fact that “particles” in the EC aerosol are chemically distinct (liquid droplets) from solid PM_2.5 found in second hand smoke. It is an important fact, yet it is omitted. 

(2) Accumulated fabric exposures are not realistic exposures in humans. The article mentions the possibility of potential exposure to toxicants by ingestion or dermic contact with ECEAR (electronic cigarette exhaled aerosol residues) deposited in cotton towels, paper towels and air filters.  However, no actual human exposures are measured or even estimated; only short and long term accumulated concentrations of deposited ECEAR in fabrics and filters placed in various fixed positions that can be in the path for continuous ECEAR deposition, for short and long term periods specified in Table 1. The results of this accumulated deposition are given in figures 2 and 3 in terms of dimensionless  quantities proportional to “1 ng (nanogram = 10^-9 gm) per 1 gm of a fabric”, analogous to ppb (particle per billion) figures for concentrations in a gaseous medium.  To estimate actual human exposures to ECEAR, it would be necessary to estimate the time and fabric surface area in which human subjects are actually exposed (under realistic assumptions) to these accumulated concentrations. Under normal circumstances exposure times to pollutants by dermic manipulation or ingestion of these items is not continuous nor prolonged: people may ingest or dermically manipulate these items for brief intermittent time periods and along reduced mouth or skin contact surfaces. 

The accumulated deposits of nicotine, alkaloids and nitrosamines can only be translated into actual human exposures under the extreme maximalist assumption of continued ingestion or dermic interaction for the same period in which the toxicants accumulated in the filters and fabrics that were placed to collect the substances in fixed spots. Realistic total human exposure will be much less because the actual ingestion or dermic interaction is short timed and intermittent and contact or mouthed surfaces contain few grams of fabric.  As an example, the article reports that

“After 35 days in the field site, a cotton towel collected 4.571 micrograms of nicotine. If a toddler mouthed on 0.3 m² [squared meters] or about 1 squared feet of cotton fabric from suite #1, they [sic] would be exposed to 81.26 mg [micrograms] of nicotine”. 

From Table 1 and figure 2B this corresponds to sample SF35D, the quantity in the figure is 4571 ng per fabric gram, though 0.3 m² is not a square foot but 3 square feet (3000 cm²). The reported area of 1 gm of cotton towel is 13.4 X 12.5 = 168.75 cm², so that 3000 cm² corresponds to 3000/168.75 = 17.8 gm of fabric, which multiplied times 4.571 mg per fabric gram yields the reported 81.25 mg of exposure to nicotine. However, this estimation is extremely unrealistic:  a toddler does not mouth a cotton towel for a long time, and 3 square feet is a huge fabric surface for a toddler to mouth! To understand how the authors obtained this quantity, we assume a constant deposition rate for 35 days in which the fabric sample SF35D was exposed to ECEAR. This means 135 ng per 1 gm of fabric per day, hence the total deposition for 0.3 m² is 2.314 mg per day, and thus 81.25 mg of nicotine just exactly corresponds to 81.25/2.314 = 35.11 days of exposure to a continuous 35 days of ECEAR deposition. Hence, the authors assume that the 81.25 mg exposure to nicotine by a toddler mouthing 3 square feet is equivalent to a continuous 35 days exposure to nicotine by a 3 square feet surface area of the cotton fabric. This is wholly unrealistic and highly exaggerated; toddlers don’t mouth cotton fabric in this manner.   

If we follow the authors’ estimate of nicotine exposure but apply more realistic toddler-mouthing times and fabric surface area, we get far smaller exposure figures. For example, a toddler mouthing only 1 gm of fabric (168.75 cm²) for one hour per day – still a gross exaggeration – is exposed to 5.41 ng of nicotine (130 ng per day/24). For 35 days we get 189.35 ng, not the suggested 81,250 ng. 

Moreover, the assumption of one hour contact with 1 gm of fabric every day during for 35 days is still unrealistic. Under normal conditions the exposed items (towels and filters) do not sit statically in homes, shops and offices for such extended time periods, and their chemistry will change by interaction with multiple external agents, necessarily altering the deposited ECEAR amounts.  Filters are designed to trap pollutants, thus it is not surprising that they contain more ECEAR, but are touched and manipulated only for maintenance or for normal control/replacement operation (which takes seconds). Paper towels are disposable and cotton towels are periodically washed, so 81.25 mg of nicotine will never accumulate.

As far as I am aware, the tobacco-specific nitrosamines (TSNAs) are the most worrying compounds in ECEAR, yet the detected exposure by fabrics and filters collecting ECEAR is really minute. Even long term, it is below 15 ng per 1 gm of cotton fabric, or about 0.42 ng per day. Assuming daily exposure comparable to this deposition rate and one hour of dermic manipulation of the towel yields a very minute exposure to TSNAs of 0.0175 ng.  I doubt that such a small hazard signal can be separated from the background noise.    

(3) Does exhalation of large clouds release more nicotine?. The article states that 94-99% of nicotine is retained by the vaper (citing reliable sources), yet the authors mention that 

“... the extent of nicotine exhalation depends on the user’s propensity to produce clouds of aerosol. In our real world study, nicotine generated by vape shop occupants reached suite #1 and contributed to ECEAR"   

It is not evident that exhaling larger clouds releases more nicotine into the environment. True, a large cloud contains more mass of aerosol, and thus more nicotine, but exhaling large clouds also requires deeper inhalation, which would likely produce larger nicotine deposition in the respiratory system. It is not obvious that this could compensate the larger mass of exhaled aerosol + gas phase.  

Excessive usage of the precautionary principle. The article concludes with this statement:

“Building codes will need to be developed and enforced to protect those who do not wish to be exposed to ECEAR. Vape shop air quality is not currently regulated nor has it been thoroughly studied. Regulatory agencies should exercise authority over malls to ensure that employees and tenants do not receive unwanted exposure to EC aerosols and its residues”.

The results and actual measurements in this report were from exposures to static fabrics and filters, not realistic exposures to real people.  So the authors’ recommended regulations are excessive and unfounded.