5. What other effects can depleted uranium have on human health?
Isotopes are chemically identical, so all the isotopes of uranium have the same chemical toxicity. As DU has lower radioactivity than untreated uranium, chemical toxicity is the main problem likely to arise.
Toxicity of uranium compounds is highly dependent on their solubility. The metal normally combines to form uranium oxides which are largely insoluble, and so have low toxicity. Soluble compounds of uranium which are ingested in food or drink become concentrated in the kidneys and the bones. Uranium particles in the air can lodge in the lungs.
Toxicity of uranium is well-studied. Most uranium is rapidly eliminated by excretion, but animal tests indicate kidney damage after long-term administration. High doses can also cause decreased fertility, toxicity to the foetus (in mice), some behavioural effects and developmental variations. Laboratory tests have also indicated the possibility of genotoxic effects, although these have not been confirmed by an increase in cancers either in lab animals or in human studies. It is thought that an increase in cancer incidence among uranium miners is due to breathing radon gas rather than inhalation of uranium particles.
These studies and others have been used to establish No-Observed-Adverse-Effect-Levels and Lowest-Observed-Adverse-Effect-Levels for uranium, which have been converted into a Tolerable Daily Intake (TDI) of 0.6 micrograms per kilo of bodyweight per day. This TDI is reckoned to give a hundred-fold safety margin.
The TDI is derived from studies which are relevant to human health because they meet the criteria for risk assessment. These include applying the chemical under scrutiny by a route of exposure relevant to humans, for a significant part of the lifespan of the experimental animal. Of the numerous recent studies specifically addressing DU toxicity, the committee found that many confirm that DU toxicity is identical to naturally occurring uranium. Others do not meet these criteria, and in the committee’s view do not yield new relevant information.
Outside the laboratory, there is evidence on health effects of lower DU exposures from medical monitoring of Gulf War veterans. Some have embedded DU shrapnel, and have much higher concentrations of uranium in their blood than civilians or soldiers without direct exposure to DU. So far, no serious health effects have been observed after 16 years monitoring.