Not surprisingly, the use of ammunition containing depleted uranium (DU) in Kosovo and elsewhere in the Balkans has provoked disquiet in Europe. In the Netherlands, concern over the release of this material had already been aroused previously following the crash of the El-Al airliner in the Bijlmermeer district of Amsterdam in 1992. It was against this background that the President of the Health Council decided to set up a Committee charged with the task of reviewing the health risks of exposure to DU and the preventive measures required for individuals present in areas where DU has been released into the environment. The present advisory report provides this review.

Uranium and depleted uranium

In its pure form, uranium (U) is a heavy, silver-coloured, radioactive metal. It is ubiquitous in nature in its natural isotopic form, together with its radioactive decay products. These decay products are removed during the extraction of uranium from ore. Natural uranium consists principally of the isotope U-238 and, to a minor extent, the isotopes U-234 and U-235.
Depleted uranium is recovered as a by-product of natural uranium during the enrichment of uranium for use in nuclear power stations. DU is characterised by areduction to 0.2% of the percentage of the isotope U-235. The radioactivity per unit of mass (activity concentration) of DU is lower than that of natural uranium (the respective levels being 14.8 and 25.4 kilobecquerels per gram). DU behaves chemically (and with that also toxicologically) identical to uranium in its natural isotopic form.
    In residues of DU from Kosovo a small amount of U-236 (0.0028%) has also been detected. The contribution made by this isotope to the total activity concentration is so minute that it does not influence the radiological properties of DU. From information regarding the possible contamination of this DU with transuranium elements (including plutonium) and fission products we can surmise that these impurities do not play any significant role in the assessment of the risk of exposure to DU.

Uranium in the living environment

Uranium occurs naturally in the environment and therefore also in the human body. In the Netherlands, the concentration of uranium in the soil varies between 0.4 and 8 milligrams per kg of dry earth. Intake of uranium by humans principally occurs via the diet. Most of the orally ingested uranium is eliminated from the body in the excreta (principally in the faeces), but some accumulates in body tissues (mainly in bone).
    DU enters the living environment via specific events, like a fire of objects containing DU (example: Bijlmer disaster) and military use of DU (example: Gulf War). Following such events DU fragments might be found in the areas concerned and uranium dust, usually in the form of the slightly soluble oxides, might have spread around in the surroundings of the event. That can cause exposure of the population, in particular via consumption of foodstuffs which have been grown on the contaminated soil and via inhalation of resuspended dust containing DU. Relief workers and military personnel entering these areas might be exposed via inhalation of dust and by radiation from DU fragments.
    Exposure in the framework of other applications of DU will be limited to occupational exposure. These situations are not treated in the present advisory report. Exposure of soldiers during military actions is entirely left out of consideration. The DU exposure mentioned above comes on top of the exposure to natural uranium in the living environment.

Uranium in the body

Absorption, distribution and excretion in the human body are highly dependent on the chemical form of the uranium and on the manner in which it is entering the body. Thus slightly soluble compounds such as uranium dioxide are only slowly eliminated from the lungs and will therefore only burden other organs in minute quantities. Ingestion of slightly soluble compounds results in little or no contamination of the body, since there is very limited absorption through the intestinal wall, by far the greater part being excreted in the faeces. Soluble compounds, on the other hand, are able to enter partly the blood circulation via the lungs or the intestinal wall and they then accumulate in organs (especially in bone). However, the great majority is excreted relatively quickly in the urine.
    Concentrations of 1 to 3 micrograms of uranium per kg of wet tissue are typically detected in organs. Typical values for excretion range from 0.05 to 0.5 micrograms per day in urine and around 1.5 micrograms per day in faeces.

Health effects of exposure

When assessing the health effects of exposure to natural uranium and DU, it is necessary to consider both the radioactivity of the material and its chemical toxic effect. Based on existing knowledge of the radiological properties of uranium, it would appear that radioactive contamination of the lungs is the principal health effect to be considered in connection with exposure to slightly soluble uranium compounds in the atmosphere. In this context should be mentioned that the dose arising from exposure to DU is much smaller than from exposure to natural uranium per unit of mass. For soluble compounds, the chemical toxic effect in the kidneys is the primary consideration. The toxicological effects are to some extent concordant with those of other heavy metals.
    A substantial amount of work has been done with uranium since the mid twentieth century. Research involving large groups of workers in the uranium industry has produced valuable data about the risks of exposure to uranium, but it also displays the frequently unavoidable shortcomings: namely, substandard information about the actual exposure of the workers, substandard or non-existent information on exposure to other possibly harmful agents and unsatisfactory data on disruptive variables such as smoking habits.
    The epidemiological research has not produced any clear evidence that exposure to uranium leads to health impairment. According to the literature, the additional cases of lung cancer among workers in uranium mines are attributable to the inhalation of the radioactive decay products of radon, which is found in elevated concentrations in and around mines. Military personnel who took part in the Gulf War exhibit more health complaints than others do. The extensive investigations conducted among these veterans have produced no evidence that exposure to DU is a causative factor in these complaints.
    The Committee does not, therefore, anticipate that exposure to DU in the situations described above, also given the possible extent of the exposure, will result in a demonstrable increased risk of diseases and symptoms among exposed individuals as a result of a radiological or chemical toxic effect exerted by this substance.

Cancer

In view of the fact that DU emits ionising radiation in the form of alpha particles, the induction of cancer, in principle, needs to be taken into account in relation to individuals exhibiting internal contamination with DU. In case of inhalation of slightly soluble DU compounds, attention will in particular need to be focused on the lungs.
    The radiation dose caused by incidental exposure to DU in the outlined scenarios is in the most conceivable cases limited compared with the radiation dose received during a lifetime of natural uranium a contribution t the induction of cancer in the population cannot be shown it can be concluded that the same is true for exposure to DU in the outlined scenarios. This general conclusion is also valid for the appearance of lung cancer and for the appearance of leukaemia after the inhalation of dust containing slightly soluble uranium compounds. The radiation dose elicited in the bone marrow and with that the theoretical probability for cancer induction by slightly soluble compounds is three orders of magnitude smaller than that elicited in the lungs. 

Renal damage

For soluble compounds, the risk posed by exposure to DU is principally of a chemical toxic nature. In the case of increasing exposure, abnormalities will first of all appear in the kidneys. Exposure to small amounts (milligrams) of uranium over short periods will therefore result in changes in the kidneys whichlead to acute, usually reversible, renal impairment. No such dose-dependency has been observed, however, in the frequency of chronic renal disorders among population groups who are chronically exposed to –in general totally less than 1 milligram per year– natural uranium. Nor have studies involving workers in the uranium industry and ex-military personnel (including the group with shrapnel in the body) to date produced any evidence that uranium can cause renal impairment. Thus the present body of scientific data tends to suggest an absence of irreparable renal damage as a result of the intake of DU in the exposure scenarios considered.

Prevention

DU is, just like several other heavy metals, classified as a hazardous substance. It is, after all, evident from the foregoing findings that the risks associated with exposure to DU for the exposure scenarios outlined here are very limited. The fundamental principle adopted in the fields of industrial and environmental hygiene dictates that unnecessary exposure to a hazardous substance must be avoided. According to the so-called ALARA principle (As Low As is Reasonably Achievable), exposure must be avoided as far as is reasonably possible. ‘Reasonably’ implies that the efforts made must be commensurate with the achievable degree of risk reduction – i.e. the achievable reduction in exposure.
    As far as possible exposure to DU in contaminated areas is concerned (for example in the vicinity of a fire in which DU has been released or in an area where military actions involving the use of DU ammunition have occurred), the Committee considers the strategy for protection laid down in the rules and regulations governing radiation protection to be adequate, both as regards limiting radiological and chemical toxic risks. This means that the first priority is to determine the nature and the extent of the contamination. Has contamination actually occurred? After that questions should be raised like: If so, how extensive is it and which compounds are involved? Are there fragments of DU in the area? Is there a possibility that windblown DU compounds could be inhaled? And so on. Based on the answers to these questions, one can determine whether it is necessary to impose limitations on access to, and use of, the contaminated area, and whether or not individuals who need to enter the area in a professional capacity (relief workers, for example) should be regarded as radiological workers. This will presumably only apply be necessary in exceptional cases.
    The answers on the foregoing questions are not only of importance for experts and authorities but also for the population in the vicinity of the place where DU has been liberated and for persons who for occupational reasons have to stay there. Open communication can prevent unnecessary anxiety. For this the Committee refers to an other recently published advisory report of the Health Council ‘Local environmental health concerns’.