The U.S. Army, among others, has been using ammunition made from tungsten alloy metals in an attempt to find a “green,” non-lead ammunition.

It looks like the search may just have to continue, based on research recently published in the scientific journal Chemical Research in Toxicology.

Scientists had thought tungsten was relatively non-toxic, and that, once in the environment (as in an expended bullet) the metal stayed intact and didn’t leach into the surrounding soil. Yet, several years ago researchers found tungsten in groundwater at Camp Edwards, a Massachusetts National Guard base that switched over to tungsten-nylon training ammunition in the 1990s.

In this latest research, as reported by United Press International, “Laboratory mice given drinking water containing small amounts of a tungsten compound were examined to see where in their bodies the tungsten ended up. Researchers found the highest concentrations of tungsten were found in the spleen, one of the main components of the immune system, and in bone marrow, the initial source of all the cells of the immune system.”

The next step was to determine if tungsten may in fact harm a mammal’s immune system. If that was found to be the case? You can remove the word “green” from any discussion of tungsten ammo!