http://www.atsdr.cdc.gov/phs/phs.asp?id=1120&tid=240
I found this ^. It refers to humans.
However I also found many sites that said propylene glycol IS also used in antifreeze and IS toxic to us and to pets if ingested but I could not find numers of amount ingested and what the range of reactions might be.
http://www.snopes.com/critters/crusader/carryouts.asp
Snopes is interesting, it says Unproven, which of course means it isn't known if it's true or not.
It's so hard to figure out which internet site is correct.