Which plastics are microwavable?

The answer may be none.

The Milwaukee Journal Sentinel, which has been investigating chemicals in consumer products in an award-winning series called "Chemical Fallout," tested 10 food containers that are labeled "microwave safe" or are marketed for infants. All 10 products leached BPA after normal heating in the microwave or oven.

What I found especially interesting in these results is that some of the products were plastic containers with the plastic identification numbers 1, 2 and 5. Anyone who's been following the news this past year knows that plastics with these numbers are supposed to be BPA-free. (Only #7 is said to contain BPA.)

So, how can that be?

The purpose of the plastic identification system is only to facilitate the sorting of discarded containers to aid in recycling should a recycling program be in place.

It is not intended to ensure consumers that a container actually is accepted for recycling -- let alone that it is BPA-free, does not leach chemicals or is in any way safe. Indeed, the usage guidelines from The Society of the Plastics Industry (SPI), which developed the code in 1988, explicitly states that manufacturers should "[m]ake the code inconspicuous at the point of purchase so it does not influence the consumer's buying decision."

However, health and environmental advocates have seized on the numbers as the only way of advising the public on which plastics to avoid.

If the U.S. had adequate safety standards in place for food packaging -- or even adequate labeling requirements -- this wouldn't be necessary. As it is, you really don't know what's in plastic containers and packages -- or what might migrate from them into the food and beverages you consume.

This is why Frederick vom Saal, the University of Missouri researcher who has been studying BPA for more than a decade and oversaw the tests for the Journal Sentinel, said, "There is no such thing as safe microwaveable plastic."

Similarly, the Environmental Working Group, which focuses on environmental health issues, especially for babies and children who are particularly vulnerable to endocrine disruptors like BPA, recommends that you never microwave plastic.