1- There has been some studies, for example, some studies on mice inhaling propylene glycol (an ingredient in mouse
eliquid) showed no measurable differences from the control group:
The safety of propylene glycol (PG) when inhaled through an electronic cigarette. Studies on the effect of the inhalation of propylene glycol through a personal vaporizer.
2- Most eliquids contain no toxins in their unvaped form, not counting nicotine which you are not asking about
Some studies have been done and the vapor produced here is some info on that
4- I recomend US made
eliquid, I wouldn't trust chinese as they use a variety of ingridients. If your just
vaping PG/VG, there shouldn't be much to worry about.