What is it and where is it found?
Pentanedione is a ketone with similar structural properties to diacetyl and thus is likely to share its toxicity as well. Since exposure to diacetyl has been identified as an occupational hazard, manufacturers have been substituting similar substances to produce the same effect (a buttery flavour or scent).
Pentanedione occurs in butter, bread, milk, yogurt, chicken, meat, cocoa, coffee, potato chips, roasted almonds, pecans, beer, red and white wine, rum and whiskey. It can be described as creamy, penetrating, cheesy, oily, sweet, buttery, almond-like, brown roasted, and somewhat caramellic, with a fruity nuance. It also occurs in substantial levels in cigarette smoke.
How harmful is it and what are the effects?
Inhalation is probably not safe. Though the general public is unlikely to come into contact with pentanedione vapours, if its suspected similar risk profile to diacetyl holds true, chronic exposure could irritate the eyes, throat and skin and lead to lung disease. The similarity to diacetyl is quite probable though the exact effects of exposure to pentanedione are suspected rather than proven.
Where can it occur in e-cigarettes?
A buttery flavour or scent might indicate the presence of pentanedione. Once diacetyl was known to be harmful flavourers replaced it with pentanedione which contributed the same buttery flavour. Unfortunately “diacetyl-free” did not translate to harmless since pentanedione has the same risk profile.
What is a recommended threshold for this constituent?
It is recommended to observe the same threshold that exists for diacetyl. In the case of e-liquid, that recommendation is to keep it below detectable levels.