From the "YOU DOCS" section, Chicago Tribune, October 14, 2008.

BY MEHMET OZ AND MICHAEL ROIZEN

Q. Call me paranoid, but I refuse to use a microwave. Do they cause cancer? -- Lucy

A. No, but they do cause more than extreme pizza sogginess. About 90 PERCENT of Americans have plastic residue in their urine because they microwave in plastic (that residue is called phthalates), and its chemicals can migrate into food, especially at high temperatures. Only plastic containers specifically designed for microwave cooking should be used. Discard them when they show any signs of breaking down.

http://www.suntimes.com/lifestyles/health/youdocs/1219165,CST-FTR-docs14.article