What is it and where is it found?
Acetaldehyde has both natural and manufactured sources.
Naturally it occurs as a product of plant respiration, in some ripe fruits, cheese and heated milk. The highest concentration in food products occurs in alcohol (in particular calvados, sherry and cider) and fermented foods.
It also occurs as a by-product of combustion (wood in fireplaces, coffee roasting, and smoking tobacco). It is generated in vehicle exhaust as well as many industrial processes. Newly renovated or constructed buildings tend to have much higher levels of measured acetaldehyde since it occurs in many building materials (laminate, flooring and paints).
It is an intermediate product of higher plant respiration and formed as a product of incomplete wood combustion in fireplaces and woodstoves, coffee roasting, burning of tobacco, vehicle exhaust fumes, and coal refining and waste processing.
Acetaldehyde is also manufactured as the first step in producing other useful chemicals such as acetic acid. It is used in the manufacture of drugs, perfumes and disinfectants. It is added to fruit juices to strengthen the flavour. It is also used in the silvering of mirrors, in leather tanning, in fuel mixtures, as a fish or fruit preservative, and in the manufacture of dyes, plastics and synthetic rubber.
All humans are exposed to and generate acetaldehyde. One major source of production is in the breakdown of sugars and ethanol. It has been suggested that both the behavioural and the toxic effects of alcohol consumption may be attributable to acetaldehyde.
How harmful is it and what are the effects?
Acute inhalation effects include irritation to the eyes, skin and respiratory tract. With increased exposure comes inflammation of the skin, coughing, and the accumulation of fluid in the lungs. Chronic exposure to toxic levels of acetaldehyde produces symptoms similar to alcoholism. Acetaldehyde has been classified as a probable but not proven carcinogen.
Where can it occur in e-cigarettes?
In the Burstyn survey, 7 studies using smoking machines had measured concentrations ranging from .00004 to .001 ppm (parts per million) which at the highest level represented only .03% of the recommended Threshold Limit Value (TLV) of 25 ppm. In the one study in which a vaper volunteered, the measure for the “estimated concentration in the breathing zone” came out at .07 ppm or about .3% of the TLV. (The highest level found so far in ECTA member assays have come in at an estimated .014 ppm.) The TLV level is the level set at which a worker can safely operate for 8 hours a day and 40 hours a week.
In two comparative studies it was found that the concentration of acetaldehyde in the reference e-liquid was in one case 450 times less and in the other 1144 times less than in cigarette smoke. As another useful comparison the EPA found levels of .032 ppm in the air of Los Angeles.
What is a recommended threshold for this constituent?
As a food additive the FDA considered acetealdehyde as GRAS (Generally Recognized as Safe). The most conservative limit has been set at 25 ppm as being harmful with 2000 ppm as being immediately dangerous to life and health.