Yep, good old sewage sludge. Yahoo's Buzz is reporting that "Michelle Obama's 'organic' garden has been besieged by icky goo in the ground."
Sounds like, in its time, the Clinton gardening team fertilized with sewage sludge. However, before you gag, you should know it's a fairly common practice. On the other hand, that same sludge stands in the way of the White House vegetable garden ever getting certified as organic.
Also, the soil is, uh, a little toxic to boot. The National Park Service's tests on the garden soil found it to have "highly elevated levels of lead" due to sewage sludge use.
Sigh. This is no good.