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Ethylene vs. Propylene Glycol

Ethylene and propylene glycol are two forms of antifreeze additives. They are commonly found in car and truck coolant systems. Ethylene glycol has a high level of acute toxicity when taken orally. Because of its ill health effects in low doses, it is not used around food preparation or near water supplies. Propylene glycol has a very low toxicity level, so low that the U.S. Food and Drug Administration has classified it as an additive "generally recognized as safe" for use in food.

  1. Uses

    • In addition to use as an antifreeze and coolant in water-cooled engines, both ethylene glycol and propylene glycol are used as deicing agents for runways and aircraft. Most ethylene glycol is mixed with other ingredients to make polyester resins, fibers and films, while antifreeze accounts for approximately 25 percent of its use. Propylene glycol is also used to make polyester compounds, as well as an antifreeze where leakage may contact food. Pharmaceutical, cosmetic and food companies use propylene glycol to absorb water and maintain moisture in certain products. It is also used to produce artificial smoke or fog for firefighter training and theatrical productions.

    Properties

    • When used in antifreeze, ethylene glycol is brightly colored and tastes sweet. Propylene glycol is described by the Center for Disease Control as a "clear, colorless, slightly syrupy liquid at room temperature" that is practically odorless and tasteless.

    Animal Ingestion

    • According to the Veterinary Support Personnel Network (VSPN), propylene glycol is "the main ingredient in 'safer' forms of engine antifreeze/ coolants." It is about three times less toxic to dogs than ethylene glycol, with cats being more sensitive to it than dogs. The VSPN calls ethylene glycol "the most dangerous form of antifreeze." Ethylene glycol forms crystals in the kidneys that can lead to renal failure.

    Benefits

    • When used in antifreeze, ethylene glycol has certain characteristics that are superior to propylene glycol. Less antifreeze is necessary to reach the same freeze-point protection with ethylene glycol than if propylene glycol is used. Ethylene glycol also has lower viscosity than propylene, resulting in less pumping head loss.

    Considerations

    • To minimize the risk of exposure to ethylene glycol, the federal Department of Health and Human Services recommends keeping antifreeze out of the reach of children and animals. Do not leave bottles on or near the ground. Avoid spilling antifreeze and do not drain it onto the ground. Early diagnosis of ethylene glycol poisoning is necessary for effective treatment. Seek medical attention as soon as possible for actual or suspected cases of antifreeze ingestion.

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