In the mid-90's, the U.S. Army started to replace their lead bullets with ones made of tungsten, a metal they thought to be less environmentally damaging.
Unfortunately, it looks like tungsten wasn't such a great choice -- new research suggests the dense brittle metal greatly increases the risks of cancer.
Tungsten bullets have been in widespread use for 15 years, soldiers have fired off nearly 100 million training rounds of the stuff. It's used in missiles and larger-sized shells and is prized for the small sharp fragments it shatters into on impact. Oddly, the army is considering plans to use tungsten to replace depleted uranium at the same time they are phasing it out of use in bullets.
The Army should be applauded for recognizing the problems associated with the dispersal of lead, but might want to think about throwing their environmental research department more resources. It'd be nice if their next "green" replacement was, you know, actually green.