They typically entered vehicles well after the initial suspended aerosol had dissipated or settled on interior surfaces. They may have inhaled DU residues that were resuspended by their activities, ingested DU through hand-to-mouth transfer, or spread contamination on their clothing.
Level III is an “all others” group whose exposures were brief or incidental.
The Capstone program performed a series of experiments to provide information on the amounts and characteristics of aerosols generated in or near vehicles hit by DU munitions. The experiments (Parkhurst et al. 2004a,b) involved 12 firings of large-caliber (LC) DU cartridges into Abrams tanks and a Bradley fighting vehicle. Specifically, the scenarios involved firing into three types of stripped-down vehicles (with no operating ventilation systems): an Abrams tank with conventional armor, a Bradley fighting vehicle with conventional armor, and an Abrams tank with DU armor. In addition, one shot was fired into an operational Abrams tank with DU armor that had an operating ventilation system. Aerosols were sampled in the vehicles by using filter cassettes, eight-stage cascade impactors, a five-stage cyclone separator, and a moving filter sampler. Sampling outside the vehicles was accomplished with high-volume air samplers or cascade impactors, and wipe samples were collected to evaluate potential DU ingestion.
Aerosol samples were collected in the target vehicles as a function of elapsed time after the shot, and the samples were analyzed for uranium content, particle size distribution, and other chemical and physical characteristics. The resulting dataset formed the basis of estimates of the amount and characteristics of aerosols that might be inhaled by soldiers in vehicles struck by DU munitions. The total quantity of DU aerosol generated by impact with armor cannot be measured directly, because of losses of absorption into or spallation of the DU onto the target. Using aerosol data, the Capstone study estimated that a maximum of 7% of the LC-DU penetrator was aerosolized inside the heavily armored Abrams tank and a maximum of 1% in the lighter-armored Bradley vehicle.
DU intakes, chemical concentrations, and radiation doses to selected organs were calculated for each phase (vehicle type), shot, and sampling position for each scenario. The intakes were based on scenarios of human exposure (described below) that included exposure duration and breathing rates. The time histories of uranium concentration in key organs (including maximal concentrations in kidneys) and the resulting radiation doses were estimated with human biokinetic models developed by the International Commission on Radiological Protection (ICRP). Specifically, three models were integrated in the computer programming to mathematically describe the toxicokinetics of uranium: the human respiratory tract model, the gastrointestinal tract model, and the uranium systemic biokinetic model. The respiratory and gastrointestinal tract models are described below, and the uranium systemic biokinetic model is described in Chapter 2.