There is essentially no risk from external exposure, even from pure metal. The amount of respirable dust that can be contained in the lungs at any one time is limited to less than a gram. If this was all DU, it would be equivalent to only about 6 times the radioactivity of naturally occurring potassium-40 in our bodies. A person exposed to a maximum lung intake of DU oxide aerosols would not receive a lung radiation dose much greater than that from naturally occurring radon levels in many residences. Lung cancers arising from inhalation are therefore unlikely and have never been observed in occupational groups working with uranium.
Uranium exists naturally in the body and is transported in solution.
A small fraction deposits in bone but, because of its very low specific activity and the limited penetration of alpha emissions, it does not irradiate bone marrow very efficiently. There have been occupational studies of groups who have ingested radium, another alpha-emitter which is taken into bone in higher concentration than uranium. For high intakes of radium, these studies have shown an increased incidence of bone sarcomas, but not of leukemias. Calculations of possible radiation exposures arising from the use of DU munitions have been performed by the Swedish Radiation Protection Institute, indicating that doses would be generally small fractions of those arising from natural background radiation. It is therefore very unlikely that bone cancers would arise from small DU intakes, and there is no evidence to suggest that DU exposure could cause leukemias under any circumstances.