"It depends on how much [exposure] we are talking about here," Brenner says. "I think you would probably get a bigger exposure just from being in your house than from almost any conceivable DU exposure." Similarly, he does not believe that temporary exposure to the radioactive aerosols will do damage. "If you just inhale radon gas, for example, the alpha particles would be in the air in your lung and would have no range to get to any significant, sensitive cells."
Of importance is where exposure to the aerosols occurs. "In an outdoor setting, like in a war or something, the concentrations would be very low," Brenner says. The worst-case scenario might be for the crew of a tank hit with DU ammunition. According to a study by the AC-Laboratorium Spiez, those soldiers could inhale up to 50 milligrams of uranium aerosol. Still, only about 25 percent of the particles with a diameter less than 10 microns would be deposited in the lungs. And as mentioned above, only a small percentage of them would be easily soluble. The rest would be incorporated into the mucus in the lungs, and coughed or sneezed back out in less than an hour.
To be certain, inhaling or ingesting uranium aerosols delivers some additional radiation to the body, but the real health threat may have nothing to do with radioactivity. "Uranium is a toxin that effects the kidneys," toxicologist Bruce Kelman says. "Once you get the uranium into biological fluids, it mostly goes to the liver and kidneys. It breaks down the tubules in the kidneys that allow you to filter the urine out."
It is difficult to say how little depleted uranium it might take to make a person sick, Kelman says, because it depends on its physical form and whether it was inhaled, ingested or shot into the body. "The U.S. EPA [Environmental Protection Agency] determined that the most appropriate oral measure to use was a study in rabbits indicating that the lowest level at which there was an adverse effect observed was 2.8 mg/kg/day"¿that is, milligrams per kilogram of body mass per day. To put that into perspective, Kelman observes, "in terms of making the environment dirty, I don't think it makes it any dirtier than any other kind of military munition, where you have lead scattered throughout the environment, where you have toxic components of explosives that are left over."
So thus far, the threat seems negligible, but a certain amount of caution is warranted. "There is a general known lag period between radiation exposure and when a cancer is going to occur, if it's going to occur," Brenner says. "And it's on the order of 20 years or so. So you wouldn't expect to see radiation-related cancers from, say, Kosovo now. That would be against everything we know about how radiation causes cancer." There are two exceptions to that rule: thyroid disorders and leukemia. "Radiation-induced leukemia occurs generally in the first five years."
Most of the controversy over Kosovo has, in fact, focused on leukemia. After several NATO soldiers who served in Kosovo were diagnosed, the World Health Organization investigated whether the number of leukemia cases in Kosovo had risen during the last few years. They came to the conclusion that it had not. But this past November, the United Nations Environmental Program followed up, sending a team of experts to Kosovo to take soil and water samples in 11 locations. "At eight sites the team found either slightly higher amounts of beta-radiation immediately at or around the holes left by DU ammunition, or pieces and remnants of ammunition," Pekka Haavisto, former Finnish environment minister and leader of the UNEP¿s Balkan Task Force team, said in a statement on January 11.