Although consumers don’t give much thought about the kinds of containers they use in the microwave, not all plastics are safe, according to LSU AgCenter nutritionist Dr. Beth Reames. Fortunately, she says consumers can depend on the U.S. Food and Drug Administration for careful testing of microwave containers.
FDA testing includes microwave-safe plastic coverings that keep food from splattering and microwave-safe containers that hold frozen dinners. Even microwavable popcorn bags, which look like paper and contain a metalized plastic film that allows them to reach high temperatures so the corn can fully pop, are examined.
Under the food additive provisions of the Federal Food, Drug and Cosmetic Act, new substances used to make plastics for food use are classified as "food contact substances." They must be found safe for their intended use before they can be marketed, according to the LSU AgCenter nutritionist.
Edward Machuga, a consumer safety officer in the FDA's Center for Food Safety and Applied Nutrition, says, "Substances used to make plastics can leach into food. But as part of the approval process, the FDA considers the amount of a substance expected to migrate into food and the toxicological concerns about the particular chemical."
The agency has assessed migration levels of substances added to regulated plastics and has found the levels to be well within the margin of safety based on information available to the agency. The FDA will revisit its safety evaluation if new scientific information raises concerns. Reames says one chemical called diethylhexyl adipate has received a lot of media attention. DEHA is a plasticizer, a substance added to some plastics to make them flexible. Exposure to it may occur when eating certain foods wrapped in plastics, especially fatty foods such as meat and cheese. But the levels are very low, the LSU AgCenter nutritionist says, noting that the levels of the plasticizer that might be consumed as a result of plastic film use are well below the levels showing no toxic effect in animal studies.
Other claims have asserted that plastics contain dioxins, a group of contaminants labeled as a "likely human carcinogen" by the Environmental Protection Agency. According to the FDA, no evidence has been seen that plastic containers or films contain dioxins.
"Consumers should be sure to use any plastics for their intended purpose and in accordance with directions," Reames says, adding, "If you don't find instructions for microwave use, you should use a different plate or container that you know is microwave safe. Such containers are made to withstand high temperatures."
The American Plastics Council recommends that carryout containers from restaurants and margarine tubs should not be used in the microwave. Inappropriate containers may melt or warp, which can increase the likelihood of spills and burns. Also, discard containers that hold prepared microwavable meals after you use them because they are meant for one-time use.
Microwave-safe plastic wrap should be placed loosely over food so that steam can escape and should not directly touch your food. Some plastic wraps have labels indicating that there should be 1-inch or more space between the plastic and the food during microwave heating.
The LSU AgCenter nutritionist says always read directions, but also know that, in general, microwave-safe plastic wraps, wax paper, cooking bags, parchment paper and white microwave-safe paper towels are safe to use. Covering food helps protect against contamination, keeps moisture in and allows food to cook evenly. She cautions never to use plastic storage bags, grocery bags, newspapers or aluminum foil in the microwave.
Reames also recommends contacting an extension agent in your parish LSU AgCenter office to learn more about safe microwave containers. In addition, refer to the Family and Consumer Sciences section under the Louisiana Cooperative Extension Service at the LSU AgCenter Web site: http://www.lsuagcenter.com/.