The Worry The much-circulated Web warning about the health risks of plastics in microwaves and freezers has made it to the bulletin board of at least one large Northwest Washington pediatrician's office. The notice advises that Johns Hopkins has "recently" reported in its newsletter that freezing water in plastic bottles and microwaving food in plastic containers and plastic wrap cause cancer by releasing toxic chemicals called dioxins.

The Truth First, the newsletter: Never reported there, said Johns Hopkins School of Public Health spokeswoman Kenna Lowe. Next, the chemistry: There are no dioxins in plastic, said Rolf Halden, assistant professor in the Department of Environmental Health Sciences and the Center for Water and Health at the Johns Hopkins Bloomberg School of Public Health. Dioxin hazards in your freezer? This idea is even more ridiculous, says Halden, since the chemicals migrate only when heated.

Rest Easy? Not yet. Plasticizers, a group of chemicals found in plastic, do leach into food when microwaved, especially at high temperatures. Can they hurt people? Research is inconclusive. One study last month in the journal Environmental Health Perspectives found that prenatal exposure to phthalates -- one of the plasticizers -- caused a measurable difference in anal-genital distance in infant boys. (That's a new indicator to us, too.)

How to Nuke Safely The Food Safety and Inspection Service ( recommends using only cookware and plastics made for microwave use. Margarine tubs and other plastic containers should not be used. Other advice: Use only microwave-safe plastic wraps. Remove food from packaging during defrosting. Do not let plastic wrap touch food during microwaving. So we've sort of come full circle. Says Halden, "This hoax has persisted for such a long time because it contains a kernel of truth."

-- Elizabeth Agnvall

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Bum wrap for plastics: Dioxins aren't the problem.