There have been a ton of studies noting that PG is safe.
The EPA report noted by Kristin, is an excellent one and here are some of the most relevant quotes from it:
"the Agency has concluded that there are no endpoints of concern for oral, dermal, or inhalation exposure to propylene glycol." It was also noted that "A review of the available data has shown propylene glycol to be negative for carcinogenicity in studies [and] therefore, no further carcinogenic analysis is required."
The studies they refer to are studies the EPA did themselves.
There are other quotes noting that pg, when inhaled, does not pass through, nor harm the unborn fetus.
The overall read of the EPA RED Report, is that the EPA would PREFER to see PG used in products as it dissipates extremely quickly into the ground water, leaving no harmful affects on the environment nor on those living in the environment. THAT is why it is in de-icer. THAT is why they want it in Anti-freeze. PG in those products is NOT the active ingredient. It is inert. And since PG does not freeze... it is perfect for solutions that need to be used in cold applications. Have you ever wondered why your tooth paste and lotions don't freeze when they are in the belly of a plane at very cold temperatures?
PG is simply a carrier product. It carries scents for lotions, it carries pharmaceuticals for medications, it carries nicotine for eSmokers, and yes, it carries chemicals for anti-freeze and plane de-icer.
Also... here is another great PDF that summarizes all of the studies that were done up until 1946:
http://www.e-cig.org/pdfs/1946-Synopsis-On-PG-As-Disinfection-Vapor.pdf
Most importantly from this is the study done on the childrens ward. That study was done over a period of 3 years. That IS a long term study. The above link also includes other studies that are worth reading...
EDIT: DEG is found in PG when the PG is not of the highest quality and yes... we don't need food grade or higher PG for deicer or anti-freeze because it is not meant to be ingested.
http://www.cdc.gov/mmwr/preview/mmwrhtml/00043194.htm DEG does not have to be found in PG and frankly, the FDA did something good by pointing out that one company might possibly be getting a lower grade PG than they should. Also relative is that DEG IS ALLOWED in US products.
http://docs.google.com/gview?a=v&q=...&sig=AFQjCNHaz9EWZWGXdUivvElc_H_ikh0g_w&pli=1 According to this FDA document, DEG IS allowable to .1% when mixed with other glycerins.
However, due to their lack of knowledge, the FDA should have also discovered that the product used by nJoy which did not test positive for DEG, is supplied by DeKang and Smoking Everywhere's product is not. So if nJoy's product is made by the supplier who makes up 90% of the imported market... where is SE getting their product? To jump to a conclusion that a company using a product from a manufacturer in the other 10% of the market share, is like saying that because the Peanut Butter Corp had salmonella in their peanut butter, all peanut butter must be bad so let's pull it all.
