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NEW YORK – Toxicologists have long considered ethylene glycol, the active ingredient in many antifreeze and engine coolant formulas, to be a seductive and uniquely dangerous poison.

For one thing, it’s sweet. “We actually had a mechanic who developed a taste for it,” recalled Dr. Marsha Ford, director of the Carolinas Poison Center in Charlotte, N.C. “He’d pour himself a little and sip it. And he kept doing that until he got sick.”

That’s the other danger: Ethylene glycol is a slow-acting poison. Even after a high dose, symptoms can take up to 48 hours to appear.

The country’s poison control centers record more than 5,000 ethylene glycol ingestions annually; some 2,000 cases require medical treatment. Most are accidental, but ethylene glycol figures in hundreds of suicide attempts every year – not to mention the occasional murder. Recently an Ohio woman was convicted of killing her fiancé by spiking iced tea with antifreeze.

The situation for animals has been even more dangerous. According to the Humane Society of the United States, as many as 90,000 pets and wild animals are poisoned annually by drinking spilled or carelessly stored products containing ethylene glycol.

Now the manufacturers of those products have determined to do something about all the carnage. They are making antifreeze taste awful – so very bitter it will be nigh impossible to drink by accident.

Seventeen states require manufacturers to add bittering agents to ethylene glycol products. The Consumer Specialty Products Association, which represents the key manufacturers, has voluntarily agreed to require members to add these agents to all consumer products containing the compound sold nationwide. The first batches of unpalatable antifreeze started hitting store shelves last year; this year customers can buy only the bitter versions.

The action came about in part because of a surprisingly warm relationship between the Humane Society and the CSPA. Both groups had worked together to propose federal legislation requiring bittering agents in antifreeze. But after repeated failures, they realized that an industry agreement was a more likely resolution.

Representatives of the two groups settled on an old-time compound, denatonium benzoate, as the best way to make antifreeze taste terrible. The compound is not considered especially toxic, is obnoxiously bitter, and has been shown not to damage engines.