TABLE 16-1 Physical and Chemical Properties of Propylene Glycol

Chemical formula:

CH3CHOHCH2OH or C3H8O2

Chemical name:

Propylene glycol

Synonyms:

1,2-propanediol, 1,2-dihydroxypropane, methyl glycol

Molecular weight:

78

CAS number:

57-55-6

Boiling point:

187°C

Vapor pressure:

0.07 mm Hg at 20°C; 0.13 mm Hg at 25°C

Concentration in air at saturation:

170 ppma at 25°C

Conversion factor:

1 ppm = 3.2 mg/m3, 1 mg/m3 = 0.31 ppm, 1 mg/L = 313 Ppm

aCalculated from the vapor pressure at that temperature.

Source: Data from Rowe and Wolf 1982.

OCCURRENCE AND USE

PG is commonly used as an additive in cosmetics and in medicinal agents. It is thought to have low toxicity and is used as a vehicle for intravenous (IV) medications, topical medications, and cosmetics. The Food and Drug Administration considers it safe for use in medication and cosmetics. It is also antibacterial, which makes it useful as a preservative and disinfectant. PG is the principal component of aircraft deicing and anti-icing fluids and of motor vehicle antifreeze. As the general weight of evidence in the toxicology literature supports the conclusion that PG will be less toxic than ethylene glycol, PG-based coolant is strongly considered for use in NASA Constellation Program transport vehicles.

PHARMACOKINETICS AND METABOLISM

No data, human or animal, describing the toxicokinetics of PG exposure through inhalation are available. Because the solubility of PG in water is high, one might expect that any inhaled vapor reaching the lungs would be very well absorbed by the lung and metabolized by the liver in a fashion similar to its metabolism from an ingested dose, although one might expect some quantitative differences. Cavender and Sowinski (1994) described a work in which humans were exposed to 10% PG in a mist tent with labeled deionized water. Less than 5% of the mist entered the body and, of this amount, 90% lodged in the nasopharynx and disappeared in the stomach; very little was found in the lungs. It appears that most of the inhaled PG aerosol becomes trapped in the upper respiratory tract and does not reach the lungs.

For orally administered PG, the metabolites are lactic acid and pyruvic acid, which the body uses as an energy source (either through oxidation by the



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