REALLY? THE FACTS A widely circulated e-mail message has caused fears that heating plastics in the microwave can contaminate food with dioxins, a group of carcinogens. Experts say there is little truth to this: dioxins almost never turn up in commercial plastics. But Dr. Rolf Halden of the Johns Hopkins School of Public Health said another substance that gives many plastics their flexibility, called plasticizers, can migrate into food in small amounts. Plasticizers, unlike dioxins, are not known to be toxic. To be on the safe side, however, the Food and Drug Administration recommends that consumers use only plastic containers...