Diethylene glycolYou may have heard that the FDA found traces (1%) of diethyleneglycol in a pre-filled cartridge of the "Smoking everywhere" brand. Diethylene glycol is certainly a highly toxic substance used in the manufacture of tobacco (and antifreeze), but NOT used for the manufacture of liquid electronic cigarette . Because it is used in making tobacco, cheaper, less refined nicotine may have been contaminated with diethylene glycol residues. It can also be a byproduct of low grade propylene glycol manufacture. It is the most likely explanation of how a cartridge may have been contaminated.
In the other 17 cartridges of other brands tested by independent laboratories no traces of contamination with diethyleneglycol were found.
Many cigarette-liquid manufacturers use USP-grade nicotine (the same as that used in FDA-approved nicotine patches and chewing gum) and USP-grade propylene glycol and do not contain any trace of diethyleneglycol.