Do you eat frozen dinners heated up in the microwave? And if so, how closely do you look at the packaging for those meals?

Recent concerns about BPA, an endocrine disruptor linked to everything from breast cancer to sexual dysfunction, have convinced many people to stop using plastic water bottles that aren't marked BPA-free. But if you're heating up plastic-encased food in your microwave, you could be using containers that contain BPA or phthalates, a plasticizer linked to genital deformities and other health problems.

These plastic concerns apply not only to items like disposable yogurt cups that were never intended for the microwave, but also to plastic containers specifically marketed as "microwave safe." That's what Good Housekeeping found back in November 2008 when it tested 31 plastic items that people are likely to use to reheat foods. While the majority of the items showed no traces of BPA or phthalates, three items were found to contain BPA: Rubbermaid EasyFind Lids container, Rubbermaid Premier container, and Glad Press'n Seal Multipurpose Sealing Wrap. One item — Glad Press'n Seal wrap — contained low levels of both phthalates and BPA.

The disturbing part of this experiment is that these questionable items are expressly marketed as BPA-free products by Rubbermaid and Glad. Rubbermaid, for example, includes its EasyFind Lids on a list of BPA-free items and contends its own experiments found no traces of BPA. Glad Press'n Seal wrap's FAQ also brags that their item contains no BPA.

In Good Housekeeping's tests, the BPA or phthalates in the containers weren't found to leach into foods. However, a similar test of 10 items — including a Rubbermaid multipurpose container — done by the Milwaukee Journal-Sentinal did find that BPA leached from "microwave-safe" plastics ranging from frozen food trays to plastic baby food packaging.

That's why many people are worried about putting plastics in the microwave. Last month, New York Times columnist Nicholas D. Kristof asked doctors at a symposium what they do in their own homes to reduce risks of diseases linked to environmental pollution, like cancer:

They said that they avoid microwaving food in plastic or putting plastics in the dishwasher, because heat may cause chemicals to leach out. And the symposium handed out a reminder card listing "safer plastics" as those marked (usually at the bottom of a container) 1, 2, 4 or 5.

Even those "safer plastics" may not be safe in the microwave, however, according to the Journal Sentinel's testing, which found BPA leaching in plastics marked 1, 2 and 5. Considering these uncertainties, it's easy to see why some may choose the precautionary principle, keeping all types of plastics out of the microwave. Florence Williams, the author of the Good Housekeeping story, says that her research has changed her habits in the kitchen:

Since learning more about the health effects of plastics, including how much we don't know, I've changed some habits …. I now store leftovers in ceramic or glass containers in the fridge, and I don't put anything plastic in the microwave because there's still a lot to learn about the interactions of heat and plastic — and it's easy to find an alternative …. I'd be happy to stop doing all this, but until the government starts testing household plastics in ways that will tell us what's safe and what's not, I will go on being a little obsessed.

With more environmentalists opting against plastics in the microwave, some organic frozen food companies have opted for less-plasticky packaging. Organic and natural frozen food company Amy's Kitchen, for example, says it shuns plasticizers and uses paper containers for its products, though these containers are still PET-lined and usually have a top film made of polypropylene. "These measures have been taken to ensure that all of our packaging material is safe for use," according to the FAQ on Amy's Kitchen's website. "However, if you would prefer not to cook in plastic, our products can be easily removed from the original container and cooked in glass."

Of course, an easy way to avoid plastic or plastic-lined containers for frozen meals is to avoid frozen meals altogether. Although many MNN readers like to make their meals from fresh ingredients, the big aisles of overpackaged meals and frozen dinners at supermarkets — and even Whole Foods and many local co-ops — makes clear that microwavable convenience foods are still quite popular.

Plastic in the microwave: Is BPA in your frozen dinner?
Concerns about BPA and phthalates have more people worried about heating plastics in the microwave.