The propylene glycol statement you made is not true, it is found in some anti-freezes. They either use one or the other in anti-freeze propylene glycol is becoming more common because it is non-toxic and environmentally friendly. So from a e-cigarette perspective it is safe to consume. It is actually found in many liquid medicine bases as well as cosmetics and even some toothpaste.
WIKI
The most common water-based antifreeze solutions used in electronics cooling are mixtures of water and either ethylene glycol (EGW) or propylene glycol (PGW). The use of ethylene glycol has a longer history, especially in the automotive industry. However, EGW solutions formulated for the automotive industry often have silicate based rust inhibitors that can coat and/or clog heat exchanger surfaces. The use of PGW as a coolant is becoming more common primarily because it is environmentally friendly and non-toxic. Ethylene glycol is listed as a toxic chemical requiring care in handling and disposal.
Ethylene glycol has desirable thermal properties, including a high boiling point, low freezing point, stability over a wide range of temperatures, and high specific heat and thermal conductivity. It also has a low viscosity and, therefore reduced pumping requirements. Although EGW has more desirable physical properties than PGW, PGW is used in applications where toxicity might be a concern. PGW is generally recognized as safe for use in food or food processing applications, and can also be used in enclosed spaces.
[edit]