During the war in Iraq, thousands of rounds of munitions made with depleted uranium have been fired from Abrams battle tanks, Bradley fighting vehicles and A-10 attack aircraft. The highly effective weapon can easily bore through an armored tank.

Depleted uranium was first used in combat in 1991 during the first Gulf War and again by the United States forces in the Balkans and Afghanistan. The uranium hardens the tips of bullets and artillery shells and greatly improves their ability to penetrate armored targets.

On impact, depleted uranium, a toxic heavy metal, bursts into flames and is dispersed as a dusty residue in the smoke. It sticks to vehicles and leeches into the soil. It can also be inhaled or ingested from contaminated food or water from anybody nearby. Dan Fahey, a U.S. Navy veteran who has written extensively about the potential health effects of depleted uranium, says in the 1991 Gulf War, most of the shooting took place in sparely populated desert regions. In Iraq, depleted uranium munitions were used in some densely populated areas.

"That included the strafing runs in downtown Baghdad and tank battles in cities," he said. "And that brings up the need for very rapid assessments of the environment in those areas, to cordon off areas of contamination to protect people from being exposed to depleted uranium that has been left behind."

Dan Fahey says studies of laboratory animals and human cells, research largely funded by the U.S. Department of Defense, show a high risk of disease with increased exposure to depleted uranium.

"It has been found that depleted uranium causes cancer. It causes DNA damage. It can cause cell death. It can cause neurological disorders and also reproductive effects," said Mr. Fahey. "And the scientists who have conducted these studies have called for studies to [learn more]."

Pentagon health official Michael Kilpatrick says that while laboratory animals exposed to depleted uranium have indeed developed tumors, there is no conclusive evidence that humans exposed to the material face a similar health risk.

"And, in one set of animals these tumors are in fact cancers, but these animals do develop tumors or cancers from other heavy metals also," said Mr. Kilpatrick. "So, these are not unique effects with depleted uranium being the only cause. I think that we need to do these studies, but I think there is a great deal of science that needs to go on before you can say that this in fact can translate into a health effect in a human being."

One such ongoing study, Dr. Kilpatrick says, focuses on veterans exposed to high concentrations of depleted uranium dust or bits of shrapnel in their bodies from the 1991 Gulf War.

"The study of some 70 of these individuals that has been conducted at the University of Maryland, Baltimore by Dr. Melissa McDermott, has not shown any medical effects due to their depleted uranium exposure," he explained. "And, this is now some 12 years after that exposure occurred. Those individuals who have fragments of depleted uranium in their body are excreting high levels of depleted uranium in their urine. But their kidneys have adapted and there is no sign of any kidney damage."

Nor, he said, has there been any sign of birth defects in their children.

Dan Fahey says the study is too small to produce any significant data. He wants that study expanded and another one begun on veterans of the current conflict.

"The proper way to address this problem is to do proper health studies and proper environmental studies and to let the scientists do what they need to do to clarify the effects of this issue," he said. "But unfortunately the way it has worked in this country is that despite what the scientists say on this issue, decisions are made at the political level. That has brought about the Pentagon's position that there is nothing to worry about on this issue, because their policies are driven by politics and not by science."

The Pentagon's Michael Kilpatrick counters that public research on the health effects of depleted uranium continues. And he says any veteran of the 1991 Gulf War with concerns about it can obtain a free analysis of their urine.

"And some 300 have sent samples in. And, those urines are almost across the board normal. Several [had] high levels, which was probably due to their dietary intake in an area of the country where they live," said Mr. Kilpatrick. "But, if we look at doing other studies, if the uranium level is normal in a person today, Dr. McDermott has said there is no reason to have any concern about their depleted uranium exposure."

Still, many experts are not convinced. The British Royal Society, Britain's premier scientific institution, has urged that more research be done on depleted uranium contamination. And a report released April 23, 2003 by the United Nations Environment Program called for a detailed scientific assessment of sites that were hit by the fortified weapons.

The UNEP report says intensive use of DU weapons "has likely caused environmental contamination of as yet unknown levels or consequences" and recommends that guidelines be distributed immediately on how to minimize the risk of accidental exposure.

In a written statement, UNEP Executive Director Klaus Toepfer said, "Not only do environmental hazards threaten human health and well-being, but they can impede aid operations."

Pentagon health official Michael Kilpatrick says depleted uranium contamination is not a major health concern of U.S. military officials right now, although he says fragments of depleted uranium penetrators embedded in the ground could pose a threat to soil and water. In post-war Iraq, he says, proper sewage, sanitation and clean water are far more urgent health issues, and should be addressed first.