More than 400 pounds of depleted uranium have not been recovered by the Air Force following military exercises conducted on the massive Utah Test and Training Range over the past 17 years, prompting a local watchdog group to raise concerns.

One of the military exercises involved a cruise missile that missed its intended target during a test in 2000. The missile struck west of the training range in the state's far western desert region, on the side of a mountain near its summit, according to Air Force documents found recently by Steve Erickson of the Citizens Education Project.

Erickson, who loosely describes his group as "keeping an eye on everyone," said the "spooky" part of his finding is that missiles occasionally go off course on the training range. The depleted uranium is left in mostly government-controlled, remotely accessed parts of the state, he said Monday, and the uranium is "basically not an issue for the general public to be concerned about."

But people ought to know, Erickson said, that depleted uranium was used in the Gulf War and is currently used in the Iraq war. Depleted uranium is the tough, high-density metal left over after removal of the more potentially dangerous enriched uranium. The military uses depleted uranium as defensive armor plating or in ordnance intended to pierce armor or ignite upon impact, according to the World Health Organization.

The use of the substance in munitions raises concerns over possible lingering health risks for Iraqis.

No one authorized to speak for Hill Air Force Base was available Monday for comment.

The Associated Press reported last year that of 2,100 soldiers tested after returning from the Iraq war, only eight had depleted uranium in their urine, according to the Department of Veterans Affairs. An estimated 286 tons of munitions with depleted uranium were used in the Gulf War and about 130 tons of depleted uranium used in ordnance had been fired in the Iraq war as of last August, the AP report said.

Whether storage and disposal methods are safe for workers also should be a concern, Erickson noted. The United States is storing an estimated 1.5 billion pounds of depleted uranium in hazardous-waste storage sites across the nation, the AP reported.

The World Health Organization states on its Web site that depleted uranium is "weakly radioactive" and that inhaling "very large amounts of dust" with the chemical present, or long-term exposure to depleted uranium, would be required for an increased health risk to humans. However, the health organization also says, "Probably the greatest potential for DU (depleted uranium) exposure will follow conflict where DU munitions are used."