Microwave experiments cause sponge disasters

Investigators at the University of Florida found that microwaving sponges for two minutes at full power can sterilize them (Microwave zaps germs). It appears that some, after hearing this, tried it for themselves with less than positive results: sponges catching fire, smoking up the house, and damaging the microwave.

It appears the home experimenters left out a crucial step. The university promptly issued an advisory:

"To guard against the risk of fire, people who wish to sterilize their sponges at home must ensure the sponge is completely wet. Two minutes of microwaving is sufficient for most sterilization. Sponges should also have no metallic content. Last, people should be careful when removing the sponge from the microwave as it will be hot."--CNN

I'm of two minds about trying this myself. Wetting them... no problem. But how the heck do I know if my sponges have metallic content? I don't recall the packaging listing their ingredients.