Tungsten-alloy shrapnel might cause cancer.

An alloy containing tungsten, cobalt, and nickel turns wounds cancerous within a few months, a test in rats shows. The finding raises questions about the current military practice by many countries of using this alloy in bullets and other ammunition as a replacement for uranium and lead.

Biochemist John F. Kalinich of the Armed Forces Radiobiology Research Institute in Bethesda, Md., and his colleagues surgically embedded pellets of the alloy, which is 91 percent tungsten, into the animals' leg muscles. Separate groups of rats received pellets made of predominantly of nickel or tantalum, a heavy metal.

Within 5 months, all the rats getting the tungsten-alloy pellets died of cancers that had spread from their wounds to their lungs. The nickel pellets also caused fatal cancers at the animals' wound sites, but not in their lungs. The rats with embedded tantalum didn't develop any malignancy and lived for a year. The researchers report the findings in an upcoming Environmental Health Perspectives.

Tungsten has no history of causing cancer, but nickel and cobalt do. "Whether the presence of tungsten is the key factor in the alloy's carcinogenicity needs further research," Kalinich says.