NIOSH submits letter to the editor concerning our diacetyl study


By Dr Farsalinos

The National Institute of Occupational Safety and Health (NIOSH) submitted a letter to the editor of Nicotine and Tobacco Research journal concerning our diacetyl-acetyl propionyl study. As you may remember, that was a chemical analysis study evaluating 159 e-liquids from Europe and the US for the presence of diacetyl and acetyl propionyl. We found that 74.2% of the samples were positive for the presence of these chemicals. To assess the level of exposure, we used the NIOSH-established safety limits of occupational exposure and determined that the average daily exposure from the liquids tested was 100 and 10 times lower than NIOSH-set limits. The letter and our response were published by the journal today, but since they are not open-access, I will present the main points of the NIOSH letter and our response herein.

The main purpose of the NIOSH letter was to clarify that the limits set by the institute refer to occupational exposure and not to consumers or the general public and that the comparison between smokers (or vapers) and occupational exposure is not widely accepted. The authors of the letter supported that their Occupational Exposure Limits are not applicable to sensitive population subgroups but to people healthy enough to work. They added that the NIOSH-established safety limit is not a measure of absolute safety but a level of exposure that would result in less than 1 in 1000 workers developing lung dysfunction after 45 years of exposure.  Moreover, they expressed concern about the accuracy of the cigarette smoke content of diacetyl as measured by Pierce et al, implying that the levels in smoke are lower than what they measured. However, they provide no justification for this. Finally, they mentioned that in our calculations we underestimated the breathing volume of workers by considering that they have a basic resting ventilation rate. They argued that workers conduct manual activity during their working hours, resulting in significant elevation on breathing rate and volume.

In our response, we used the NIOSH arguments to further support the appropriateness of our approach. In particular, we mentioned that the targeted population for e-cigarette use is the smoking population. Whether sensitive or not, these people are exposed to a large number of toxicants on a daily basis for many years. Additionally, we emphasized that a risk level of 1 in 1000 developing lung dysfunction represents a tremendous benefit for smokers who have a 1 in 3-4 risk of developing chronic obstructive lung disease in their lifetime. Additionally, we provided further evidence from the literature on the levels of diacetyl in tobacco cigarette smoke. Studies by Fujioka and Shibamoto and by Moree-Testa and Saint-Jalm found diacetyl in smoke at levels similar to the study by Pierce et al. Finally, we accepted the argument by NIOSH that we underestimated the ventilation rate of workers. That was a conscious decision, because we wanted to use the most stringent criteria in the comparison. Thus, we used the worst-case scenario of resting ventilation rate, which underestimated the safety-limit exposure set by NIOSH. Based on mild and moderate activity, the NIOSH-estimated safety exposure limit would be 86micrograms/day (mild activity) and 302micrograms/day (moderate activity) for diacetyl, and 132micrograms/day (mild activity) and 638micrograms/day (moderate activity) for acetyl propionyl. Our initial calculations considering resting ventilation rate was 65micrograms/day for diacetyl and 137micrograms/day for acetyl propionyl. Thus, the NIOSH-set limits are approximately 50-400% higher than what we considered in our original study, using the worst case scenario.

 In conclusion, it is important to provide a comparative measure of exposure to diacetyl and acetyl propionyl from e-cigarette use, considering that the targeted population is smokers who have a high risk of developing disease and are continuously exposed to several toxins (including diacetyl and acetyl propionyl). In any case, we made clear that diacetyl and acetyl propionyl represent an avoidable risk and every effort should be made to remove them from e-liquids. In our opinion, the major impact of our study is that it alerted the industry to take care of this issue. Anecdotal evidence suggests that there is a lot of improvement in this area, and we believe that a future study is needed to evaluate and verify whether diacetyl and acetyl propionyl have been removed from e-liquids.



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