Huh, I was wondering what happened to the Early Ammonia Servicer (EAS)
I think that "space debris mass per launch" - China is #1 as the worst space polluter. In terms of total space debris mass - I think Russia might be ahead of the U.S. by a moderate amount. But, these are just guesses as I'm not sure who is keeping track of debris per mass - it looks like Aerospace Corporation has just quantity of incidents.
In following up on a discussion on today's podcast, the following site was mentioned in the referenced slashdot thread about the ammonia tank jettisoned from the International Space Station that is due for re-entry into tech atmosphere:
The Center for Orbital and Re-entry Studies
The space debris in question could be followed here http://www.reentrynews.com/1998067ba.html