* Astronomy

As the filament in an incandescent light bulb, tungsten can illuminate a room, but it hasn't been spotlighted as an environmental contaminant in the same way that lead or mercury has. In fact, in the mid-1990s, believing that tungsten is relatively insoluble in water and nontoxic, the Army replaced the lead core in military bullets with tungsten alloys through its Green Ammunition Program. Similar bullets became available to hunters soon after as states began to ban lead ammunition to protect birds from lead poisoning.
Recent studies, however, indicate that under certain environmental conditions, some forms of tungsten can move readily through soil, leach into groundwater, and induce greater biological effects than previously known. These findings do not definitively raise a red flag about tungsten, but they have spurred more study on the metal's effects because of the increased use of tungsten in military ammunition and in civilian applications ranging from tools to tire studs.

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