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uranium rounds, or were downwind of burning depleted-uranium ammunition (such as personnel at Camp Doha during the July 11, 1991, explosions and fire). Although these people could have inhaled airborne depleted-uranium particles, they are unlikely to have received an intake high enough to cause health effects.

Level III exposure is likely to be much lower than level I or II exposure. However, the number of military personnel with level III exposure may be much larger and the exposure range wider.

Direct measurement of exposure to depleted uranium in the battlefield is ideal but is not practical. To estimate exposure, field tests have been conducted to measure the range of depleted-uranium concentrations in vehicles that have been struck by large-caliber depleted-uranium rounds (USACHPPM, 2004). Aerosols were collected while Abrams tank and Bradley vehicle ballistic hulls and turrets with depleted-uranium armor or conventional armor were struck by depleted-uranium rounds. When an Abrams tank with depleted-uranium armor was struck, inhalation intake of depleted-uranium oxides by surviving crew members in 5 minutes is estimated to have been 20% greater than intake by the crew of a tank with conventional armor. When the less heavily armored Bradley vehicle was struck, inhalation intake was estimated to be 30% of the intake in the Abrams tank.

Residual concentration in a struck vehicle can be affected by ventilation of the vehicle. In one field test, inhalation intake of depleted uranium was reduced by about 90% in a struck Abrams tank with an operating ventilation system compared with that in a tank without one (USACHPPM, 2004). However, it is not clear whether the ventilation systems were active during friendly-fire incidents in the Gulf War. Without confirmed information on ventilation, estimation of exposure should be based on the cautious assumption of no ventilation.

All three reports mentioned above—the Capstone report, the Sandia report, and the Royal Society report—were based on an estimation approach, so they are all subject to considerable uncertainties in intake estimates and due to parameters chosen for modeling. The Royal Society report used the best data then available on initial air concentrations of depleted-uranium oxides in a struck tank and produced central estimates of intakes and risks for a number of exposure scenarios. Worst-case estimates were also provided by using values at the upper end of the likely range. The worst-case scenarios provide intakes and risks that are unlikely to be exceeded.

The Capstone report addressed inadequacy of the available data from test firings by conducting 13 new test firings of large-caliber depleted-uranium rounds against an Abrams tank and a Bradley vehicle. The Capstone study determined the airborne depleted-uranium concentration and size distribution in the struck vehicles as functions of time after impact. It provides a substantial database of airborne depleted-uranium concentration in struck vehicles and of the composition and particle size distribution. In addition, in vitro solubility of particles in the

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