Me personally...
I don't see how any harmful material could survive re-entry.
Then again,
Who the fudge know what the hell the US military have up there?!
Don't forget
Columbia 5 years ago. It is not necessarily what's on the debris, but what's IN it. Some compnoents are inside something inside something else shielded by the outside component, know what I mean? Chemicals for propulsion are highly toxic in their docile state, even before ignition.
Then, on to the what's ON. Hydraulic fluid can poison the soil, let alone a living organism. Lead is used in parts of shielding for radiation-protection purposes. Heavy metals used for structural integrity on the outside could be doused with radiation from space, making them toxic to touch.
Lots of possibilities really.
Seanie.
  