On 2016 Dec 18, Zvi Herzig commented:

The concerns for potential chronic toxicity in 2 of the 42 tested products refer to (1) terpene hydrocarbons in relation to Maximized Survey-Derived Intake (MSDI) levels and (2) diacetyl in relation to NIOSH-recommended safety limits.

MSDIs are the normal exposures considered when food safety standards are established. Exceeding them isn't necessarily hazardous, but it implies a level not considered in the assessment. Therefore, it's important to consider other available safety limits when possible.

The strictest 8 hr occupational exposure limit for terpenes is 20 ppm (111 mg/m3) Granström KM, 2010. Occupational safety limits consider a ~10 m3/workday respiration rate for active workers Kuempel ED, 2015. This corresponds to a safe terpenes inhalation limit of 1,110 mg/workday.

The highest concentration of terpenes in this study is 106.7 mg/g. A mean consumption of 3 g e-liquid daily among EC users is noted. This corresponds to terpene consumption of 320.1 mg/day for the highest terpene concentration e-liquid -- a fraction of the aforementioned safety limit.

Furthermore, with a high prevalence of switching between flavors Farsalinos KE, 2013, these quantities are further diluted in relation to chronic use. This study detected hydrocarbons at 2.5 mg/g on average, all hydrocarbons being terpenes. In contrast, a single cigarette delivers 4.9 mg of hydrocarbons, including 1.1 mg of terpenes Perfett TA, 2014. Despite the much higher exposure to terpenes in cigarette smoking, terpenes are not noted in any of the lists of cigarette smoke's notable toxicants.

With regards diacetyl estimated to result in 126 µg/day exposure in one case, it should be noted that tobacco smokers inhale 5700 µg diacetyl per day Farsalinos KE, 2015, 45 times greater than the exposure resulting from using the product with the highest diacetyl level among 42 liquids tested in this study.

On 2016 Dec 18, Zvi Herzig commented:

The concerns for potential chronic toxicity in 2 of the 42 tested products refer to (1) terpene hydrocarbons in relation to Maximized Survey-Derived Intake (MSDI) levels and (2) diacetyl in relation to NIOSH-recommended safety limits.

MSDIs are the normal exposures considered when food safety standards are established. Exceeding them isn't necessarily hazardous, but it implies a level not considered in the assessment. Therefore, it's important to consider other available safety limits when possible.

The strictest 8 hr occupational exposure limit for terpenes is 20 ppm (111 mg/m3) Granström KM, 2010. Occupational safety limits consider a ~10 m3/workday respiration rate for active workers Kuempel ED, 2015. This corresponds to a safe terpenes inhalation limit of 1,110 mg/workday.

The highest concentration of terpenes in this study is 106.7 mg/g. A mean consumption of 3 g e-liquid daily among EC users is noted. This corresponds to terpene consumption of 320.1 mg/day for the highest terpene concentration e-liquid -- a fraction of the aforementioned safety limit.

Furthermore, with a high prevalence of switching between flavors Farsalinos KE, 2013, these quantities are further diluted in relation to chronic use. This study detected hydrocarbons at 2.5 mg/g on average, all hydrocarbons being terpenes. In contrast, a single cigarette delivers 4.9 mg of hydrocarbons, including 1.1 mg of terpenes Perfett TA, 2014. Despite the much higher exposure to terpenes in cigarette smoking, terpenes are not noted in any of the lists of cigarette smoke's notable toxicants.

With regards diacetyl estimated to result in 126 µg/day exposure in one case, it should be noted that tobacco smokers inhale 5700 µg diacetyl per day Farsalinos KE, 2015, 45 times greater than the exposure resulting from using the product with the highest diacetyl level among 42 liquids tested in this study.