Your car needs antifreeze because water increases in volume about 10% when it freezes, and this expansion can crack and ruin the engine block. To prevent cold-weather damage, ethylene glycol antifreeze is commonly added to the water that flows through the engine. When equal volumes of water and ethylene glycol antifreeze are mixed, the freezing point is lowered from the 0 �C (32 �F) of pure water to about -37 �C (-35 �F). Because outside temperatures rarely fall this low, your engine is protected from cracking.
Although vital for preventing engine damage, ethylene glycol antifreeze poses a serious threat to animals and humans. It is a rapid poison, quickly causing severe kidney and brain damage that often leads to death. It is also a powerful poison; as little as a few teaspoons of ethylene glycol is lethal to humans and wildlife. As poisons go, ethylene glycol has a particularly cruel and pernicious twist: It has a sweet flavor, which makes it appealing to many animals and children. Ethylene glycol "tastes very sweet," says veterinary toxicologist Larry A. Kerr, at the University of Tennessee in Knoxville. "Animals love to lick the stuff up." About 4,200 people-including more than 700 children age five or under-are poisoned by antifreeze annually, according to the federal Consumer Product Safety Commission. Twenty-nine people died of ethylene glycol poisoning in 1994, the most recent year for which data are available. Antifreeze ingestion is one of the most common causes of poisoning of pets and other domestic animals and is responsible for tens of thousands of animal deaths annually, says Kerr.
A study by researchers at Colorado State University found that ethylene glycol causes half of all poisoning deaths of pet dogs and cats. In January 1995, a cougar at a California wildlife preserve died from ingesting antifreeze. The cooling system in your automobile is a complex machine. The coolant solution flows through channels inside the hot engine block, then through a pump, several hoses, the passenger heater, and the radiator. If a car is several years old and has not had careful preventive maintenance, any of these components can develop a leak. The result is a puddle of ethylene glycol that is a threat to wildlife.
One proposal is to add a "bittering agent" to ethylene glycol to reduce the likelihood of poisoning. "If we make it taste really bad, we might prevent kids from taking a second sip," says Rose Ann Soloway, administrator of the American Association of Poison Control Centers. The search for a suitable bittering agent for engine coolants presents unique scientific challenges. The substance must be strongly distasteful but nontoxic, have no effect on the performance of engine coolant, and remain chemically stable through thousands of cycles of heating and cooling. An ideal bittering agent has not yet been identified, Soloway says.
A company based in Omaha, Nebraska, formulated a nontoxic antifreeze based on a different chemical-propylene glycol. Unlike its molecular cousin ethylene glycol, propylene glycol is almost harmless to humans and animals. In fact, propylene glycol is an approved ingredient for animal food, as well as human cosmetics, snack foods, candy, seasonings and flavorings. For several years, automobile antifreeze based on propylene glycol has been sold under the brand name Sierra. According to Joel Adamson, vice president of Safe Brands Corporation, which markets Sierra, it works just as well as the traditional ethylene glycol antifreeze. When mixed with an equal volume of water, propylene glycol prevents freezing down to -35 �C (-31 �F). It appears that other manufacturers are following the lead of Safe Brands Corporation. Recently Prestone Corporation, one of the largest makers of traditional antifreeze, introduced a propylene glycol-based product called Low-Tox. The drawback? Propylene glycol costs more than ordinary antifreeze, says Adamson. However, as more people buy the safer products, the price should come down.
Out of concern that coolant leaking vehicles could pose a risk to zoo animals, the American Zoo and Aquarium Association (AZA) launched a program to encourage conversion to propylene glycol antifreeze in vehicles used at their animal facilities. In 1995 they persuaded 14 zoos to make the switch and some 30 more are expected to join in 1996. "Antifreeze poisonings of wildlife and pets are a well documented threat," says Joan Embry, spokesperson for the San Diego Zoo. "Spills, radiator leaks, boilovers, and improper disposal are common sources of accidental poisonings. Converting to a less toxic product is another way zoos can help preserve wildlife."
Emergency Treatment
In humans and other animals, ethylene glycol is broken down by alcohol dehydrogenase. This is the same enzyme that acts on ethanol and propylene glycol, the safer antifreeze. But the metabolism of ethylene glycol is dramatically different. Ethylene glycol is metabolized by alcohol dehydrogenase into several toxic organic acids. One of the most important of these is oxalic acid, which reacts with calcium ions in the blood to form solid calcium oxalate in the bloodstream. The insoluble calcium oxalate crystals block the flow of blood and cause severe damage to the lungs, brain, heart, and kidneys. Although calcium oxalate crystals cause brain damage, the most serious injury is to the delicate blood-filtering structures
of the kidneys.
"What usually kills the animals is that it wipes out the kidney," says veterinary toxicologist Larry A. Kerr. "They die of uremic poisoning, if they survive the brain damage."
The ingestion of very small amounts of ethylene glycol can be fatal. Sixty mL of ethylene glycol-just 2 fluid ounces or 4 tablespoons-can kill a large dog or an adult human. A child can die by drinking 30 mL, about 2 tablespoons. One teaspoon (5 mL) can kill a cat.
A person who ingests ethylene glycol will soon be in severe pain and in critical condition; rapid intervention is needed if the person is to survive. The treatment is to administer ethanol-beverage alcohol. This treatment is recommended because the enzyme alcohol dehydrogenase has an affinity for ethanol that is 100 times greater than for ethylene glycol. The idea is to "saturate the enzyme" with ethanol, explains Rose Ann Soloway
of the American Association of Poison Control Centers. "You want to tie
up all the alcohol dehydrogenase so there won't be any available for the ethylene glycol."
As medical staff closely monitor the patient's status, ethanol is administered over a period of days or weeks while ethylene glycol is slowly eliminated from the body, Soloway says. Eventually, ethylene glycol will pass through the kidneys into the urine. In severe cases, hemodialysis with an artificial kidney machine may be used to filter ethylene glycol and toxic organic acids from the blood stream.
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