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Study shows danger to soldiers from depleted uranium aerosols is low

February 2005
During a routine patrol, streaks of flame light up the night sky as a depleted uranium projectile streaks towards its target, an Abrams tank. The tank takes a direct hit. The projectile pierces the tank's turret, missing the crew but showering them in depleted uranium dust and tank debris. Should they evacuate the tank, facing possibly dangerous and even deadly conditions, to escape the radioactive dust? Or, are they safer staying put and waiting for assistance from their compatriots? Thanks to a recent study led by Pacific Northwest National Laboratory, crews now have confirmation that if they stay inside the tank, they're not likely to suffer adverse health effects from the depleted uranium aerosols. These aerosols are produced when a depleted uranium penetrator pierces an armored vehicle or when the depleted uranium armor protecting a vehicle is perforated. The successful use of these heavy metal, weakly radioactive weapons during the 1991 Gulf War helped bring about a swift end to Iraqi tank battles. However, misidentification of U.S. forces in distant vehicles led to some incidents in which U.S. armored vehicles were struck by these new projectiles. The Department of Defense commissioned a five-year, $6M study in response to concerns from 1991 Gulf War veterans about inhaling and ingesting the depleted uranium particles from these incidents. "PNNL was selected to lead this high-profile, data intensive study because of our experience and field work with depleted uranium," said Project Manager MaryAnn Parkhurst. Team members, including health physicists, aerosol physicists, computer modelers, toxicologists, and engineers, were selected from PNNL, the U.S. Army, other national laboratories, and private companies. Characterizing the Particles The critical step in determining the health effects of depleted uranium aerosols was to determine the quantity as well as the size, chemical form, and other properties of the particles the armored vehicle crew would be breathing and ingesting if their vehicle was perforated. The form determines how the particles react within the body and their chemical toxicity, primarily to the kidneys. To characterize the depleted uranium aerosols, the team used innovative sampling techniques, advanced modeling methods, and emergency risk standards and guidelines. At the Army's Aberdeen Proving Grounds in Maryland, the team fired large-caliber depleted uranium penetrators at an Abrams tank and a Bradley fighting vehicle. Ballistic vehicles, which are structurally identical to functioning vehicles but contain no expensive electronic equipment or flammable materials, were used in all but the last test. In that test, a fully functional target vehicle was used. Before depleted uranium weapons were fired, the crew compartment of each vehicle was equipped with numerous aerosol samplers. Cyclone samplers collected aerosols continuously for 2 hours after each shot was fired. Cascade samplers and filter cassettes collected aerosols at sequential preset, computer-controlled intervals from 10 seconds to 1 hour, providing information on how quickly the depleted uranium aerosol concentration decreased with particle settling. A camera inside the vehicle captured the images of the nearly instantaneous formation of the aerosols as fine metal fragments oxidized. The samplers had to be rugged enough to survive the percussion of the projectile's impact, and most had to be sophisticated enough to collect and sort the particles by size. To protect these samplers from impact with metal fragments immediately following vehicle perforation, the team designed louvered steel shields and remote-controlled doors that dropped open a few seconds after each shot was fired. Parkhurst's team analyzed more than 8,000 samples including the aerosol samples and wipes of vehicle interior and exterior surfaces. They used a battery of research equipment, including mass spectrometers, atomic emission spectrometers, x-ray diffraction instruments, scanning electron microscopes, alpha and beta counters, and a gamma spectrometer. Most chemical and physical tests were performed at PNNL's Radiochemical Processing Laboratory in Richland, Washington. In vitro solubility tests of some aerosols in simulated lung fluid were performed at Lovelace Respiratory Research Institute. The Aberdeen Test Center's Radiological Laboratory conducted the alpha and beta analysis. The U.S. Army Center for Health Promotion and Preventive Medicine Laboratory confirmed alpha and beta measurements and conducted gamma and mass spectrometry. The team's results showed the uranium aerosols settle out of the air and onto surfaces relatively quickly, reducing concentrations typically by a factor of 100 within 30 minutes. The uranium particles in the aerosols were uranium oxides, most of which were fairly insoluble. Understanding the Health Effects So, what does inhaling uranium oxide particles mean to the tank's crew? To calculate the risks, the research team used particle properties and internationally recognized biokinetic and internal radiation dosimetry modeling to evaluate the deposition and distribution of the uranium particles in the body and the associated health effects from continual exposures ranging from 1 minute to 2 hours after the incident. Separate evaluations were made for other military personnel who respond immediately after a tank has been hit and mechanical repair crews who enter several hours to several days later. Ingestion exposures, from incidental hand-to-mouth transfer of deposited material, for the crew and these personnel were also estimated. The team developed a new methodology to estimate the risks from the uranium concentration in the kidneys. This methodology was needed because U.S. uranium exposure guidelines are for "peacetime" settings, not military conflicts where the risks may be imminent and of much greater magnitude. In military conflicts, the greatest risk may come from leaving the source of the radiation (that is, the dust inside the tank) and being exposed to enemy fire. In peacetime, the greatest risk may come from continued presence near the source. The study determined that the depleted uranium exposure, received immediately after the weapon's impact and continually for up to 2 hours later, was not likely to cause health problems. Exposures occurring after this time are even less likely to cause health effects. However, the risks are not zero. Any handling of fragments and oxide power should be done with care to minimize intake because at sufficiently high levels of inhalation or ingestion, depleted uranium can adversely affect the kidneys. Based on the risk assessment, the team suggests that the personnel inside an armored vehicle that has just been perforated with a depleted uranium penetrator take the following steps:
  • If the ventilation system is off, turn it on.
  • If it is safe to do so, exit the vehicle while the dust settles.
  • If it is not safe to exit the vehicle, stay inside.
The summary of the study, the health assessments, and the study's field data and particle characterizations will be published by Battelle Press. These documents will allow soldiers, medical staff, and other researchers in the U.S. and international communities to study the complete data set and the results. Contact: Kelvin Soldat, Environment, Safety and Health Systems Product Line Manager.

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