zoiDman, what follows is from wikipedia and other informational websites, plus some figuring on my part (I'm sorry, but I have to get into the weeds here to interpret and comment on the results -- and bear in mind, I'm working right at the limits of my knowledge):
- Methylethylketone (AKA MEK, or butanone, or model "cement," is a solvent widely used in many industrial processes). In 2005, the EPA removed MEK from the list of hazardous air pollutants, concluding "potential exposures to butanone [i.e., MEK] emitted from industrial processes may not reasonably be anticipated to cause human health or environmental problems." MEK can cause lung irritation and birth defects in mice, but at concentrations of 3,000 parts per million (ppm) (or greater), with no problems reported below 1,000 ppm. The ClearStream study reported 4.2 (for regular cigarettes) or 4.4 (for e-cigarettes) micrograms per cubic meter. A cubic meter of air at sea level weighs 1.2 kg. If you do the math, the 4.2 or 4.4 micrograms per cubic meter reported work out to a concentration of 0.0035 or 0.0036 ppm (assuming I did the math right).
- 1-ethyl-3-methylbenzene (AKA benzene, comprising several percent of most gasoline blends). OSHA has set a safe limit of 1 ppm in air per 8-hour workday and 40-hour workweek. The ClearStream study reported 0.2 or 3.4 micrograms per cubic meter, which works out to 0.000167 or 0.00283 ppm (again, assuming I've done the math correctly).
- Longifolen (misspelled, it's actually spelled "longifolene," is an aromatic hydrocarbon found in pine resins and in lapsang souchong tea and used for making perfumes and flavorings, among other things). Longifolene is a tricyclic sesquiterpene, a member of the large terpene family of hydrocarbons. Many of these compounds are found in living things and appear to be necessary to properly functioning metabolisms. The only reference I could find about exposure limits was the LD50 (lethal dose for 50% of the test animals) numbers for oral ingestion by rats and dermal exposure on rabbits. In both cases, the LD50 is greater than five grams per kilogram of body weight.
These three compounds seem to be totally innocuous in the tiny concentrations reported in the ClearStream study. Hopefully, Kurt (who is a biochemist in real life) will wander by to point out any errors in my analysis.
budynbuick, the study cited by tenshi in post #12 and shack22 in post #16 came from the National Institutes of Health, which is about as good as it gets.