I agree with Kirk. I would like to add the following:
"Ethylene glycol (IUPAC name: ethane-1,2-diol) is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, liquid. Ethylene glycol is toxic, and ingestion can result in death."
And to continue:
"Ethylene glycol is moderately toxic with an oral LDLO = 786 mg/kg for humans.[6] The major danger is due to its sweet taste, thus unlike for other poisons, children and animals are more inclined to consume large quantities of it. Upon ingestion, ethylene glycol is oxidized to glycolic acid which is, in turn, oxidized to oxalic acid, which is toxic. It and its toxic byproducts first affect the central nervous system, then the heart, and finally the kidneys. Ingestion of sufficient amounts can be fatal if untreated."
But OTOH:
"Propylene glycol is used:
* As a solvent in many pharmaceuticals, including oral, injectable and topical formulations. Notably, diazepam, which is insoluble in water, uses propylene glycol as its solvent in its clinical, injectable form.[5]
* As a humectant food additive, labeled as E number E1520
* As an emulsification agent in Angostura and orange bitters
* As a moisturizer in medicines, cosmetics, food, toothpaste, mouth wash, and tobacco products
* As a carrier in fragrance oils
* As an ingredient in massage oils
* In hand sanitizers, antibacterial lotions, and saline solutions
* In smoke machines to make artificial smoke for use in firefighters' training and theatrical productions
* In electronic cigarettes, it is used to deliver vaporized nicotine
* As a solvent for food colors and flavorings
* As an ingredient, along with wax and gelatin, in the production of paintballs
* As a moisture stabilizer (humectant) for snus (Swedish style snuff).
* As a cooling agent for beer and wine glycol jacketed fermentation tanks
* As a less-toxic antifreeze in solar water heating systems
* As a solvent used in mixing photographic chemicals, such as film developers
* In cryonics
* As a working fluid in hydraulic presses
* As a coolant in liquid cooling systems
* To regulate humidity in a cigar humidor
* As the killing and preserving agent in pitfall traps, usually used to capture ground beetles
* As an additive to pipe tobacco to prevent dehydration.
* To treat livestock ketosis
* As the main ingredient in deodorant sticks.
* To de-ice aircraft.[6]
* As an ingredient in UV or blacklight tattoo "
And:
"Propylene glycol is metabolized in the human body into pyruvic acid, which is a normal part of the glucose metabolism process and is readily converted to energy.
The oral toxicity of propylene glycol is very low, and large quantities are required to cause perceptible health damage in humans. Serious toxicity will occur only at plasma concentrations over 4g/L, which requires extremely high intake over a relatively short period of time. It would be nearly impossible to reach toxic levels by consuming foods or supplements, which contain at most 1g/kg of PG. Cases of propylene glycol poisoning are related to either inappropriate intravenous use or accidental ingestion of large quantities by children.
The potential for long-term toxicity is also low. In one study, rats were provided with feed containing as much as 5% PG over a period of 104 weeks and they showed no apparent ill effects.[9] Because of its low chronic oral toxicity, propylene glycol was classified by the U. S. Food and Drug Administration as "generally recognized as safe" (GRAS) for use as a direct food additive.
Prolonged contact with propylene glycol is essentially non-irritating to the skin. Undiluted propylene glycol is minimally irritating to the eye, and can produce slight transient conjunctivitis (the eye recovers after the exposure is removed). Exposure to mists may cause eye irritation, as well as upper respiratory tract irritation. Inhalation of the propylene glycol vapors appears to present no significant hazard in ordinary applications. However, limited human experience indicates that inhalation of propylene glycol mists could be irritating to some individuals. Therefore inhalation exposure to mists of these materials should be avoided. Some research has suggested that propylene glycol not be used in applications where inhalation exposure or human eye contact with the spray mists of these materials is likely, such as fogs for theatrical productions or antifreeze solutions for emergency eye wash stations."
But:
"Veterinary data indicates that propylene glycol is toxic to 50% of dogs at doses of 9mL/kg, although the figure is higher for most laboratory animals (LD50 at levels of 20mL/kg).
However, propylene glycol may be toxic to cats in ways not seen in other animals. The U.S. Food and Drug Administration has determined that its presence in or on cat food has not been shown by adequate scientific data to be safe for use. Any such use is considered an adulteration of the cat food and a violation of the Federal Food, Drug, and Cosmetic Act."
So, in the final analysis we probably ingest a lot of PG daily but it is harmless at the levels we ingest due to the metabolic path it takes. Pyruvic acid is a lot less toxic than Oxalic acid. Oxalic acid, I have been told, can actually congeal blood by reaction with calcium in the body. It is found in Rhubarb leaf and during WWII, many people died taking the mistaken advice of the government to consume Rhubarb leaf as a green vegetable.
I got these simple facts from Wikipedia. I have known them in that detail since Biochemistry in grad school.
PE