Royal Society Report on Depleted Uranium. Parts I and II

Synopsis

Summary:

Copies of both parts of the report, and a combined summary of Parts I and II, are available from:

6 Carlton House Terrace

London SW1Y 5AG

They can also be seen on the Royal Society's website ( http://www.royalsoc.ac.uk - access via the "Science Policy" menu.) together with the annexes to both parts.

Please note that the annexes to the report are only available on the website.

Summaries of Part I, Part II and the recommendations of the report, and a note on the NRPB's contributions, are given below.

Part I (May 2001)

The Royal Society published the first part of its report on The Health Hazards of Depleted Uranium in Munitions in May 2001. That part dealt with the amounts of depleted uranium (DU) to which soldiers could be exposed on the battlefield, the risks from radiation and what is known from epidemiological studies, especially those on uranium workers. DU is known to be toxic, as are other heavy metals, and also weakly radioactive.

Questions and answers page on DU.

In response to public concern and discussion about the consequences for health arising from the use of DU weapons, in late 1999 the Royal Society convened an independent expert Working Group to review the present state of knowledge about the health and environmental effects of DU. The objectives were to inform public debate, and to provide the public with an independent opinion of the possible health hazards.

The Working Group was chaired by Professor Brian Spratt, FRS, Wellcome Trust Principal Research Fellow, Department of Infectious Disease Epidemiology, Imperial College School of Medicine.

Assessment of intakes

To provide an independent and transparent assessment the approach taken was to draw on original reports of studies so far as possible, and to provide details of the source information and methods used. Because of the lack of measurements of exposures in or soon after the conflicts in which DU has been used, the Group estimated intakes in a number of exposure scenarios, covering a wide range of situations that might occur. Thus Level I (high exposure) applies to soldiers in vehicles struck by DU penetrators; Level II (moderate) applies to personnel working on vehicles contaminated with DU, and Level III (low) applies to the majority of soldiers who might be downwind of impacts or fires involving DU, inhale resuspended DU-contaminated soil, etc. For both the assessments of intakes and for doses per unit intake, two assessments were made: a 'central estimate', based on what were considered to be the most likely situations, and which would be typical of the group involved, and a 'worst-case', which it was considered unlikely that any individual would exceed.

On this basis the following conclusions were reached.

• For most soldiers, intakes of DU were likely (central estimate) to be small (less than 1 milligram), and so were effective doses (less than 1 millisievert - the average annual effective dose from natural background radiation is about 2 millisieverts).
• The risks of radiation-induced cancer are also likely to be small (less than 1 in 10,000) and would not be detectable amongst the cancers that would occur in such a group without exposure.
• High exposures to DU should only apply to a small fraction of soldiers, such as survivors in vehicles struck by DU weapons. For them the central estimates give a lung cancer risk of about 1 in 1000. However, under worst-case conditions, the estimated risk of radiation-induced lung cancer up to about 1 in 15 could not be excluded, even though it results from inhaling a few grams of DU dust. This risk is similar to the rate in the general population, and so would approximately double the lung cancer risk.
• In all exposure scenarios considered, the risks of death from leukaemia and other cancers are much smaller than (
• Many soldiers could be exposed to low levels of DU, downwind of impacts or fires, from which the estimated risks of radiation-induced cancer are very low, less than 1 in 1,000,000. Even if the risks were 100 times higher than estimated, it is unlikely that any excess would be detected in a cohort of 10,000 followed for 50 years.

Epidemiological studies

Epidemiological studies have been conducted of tens of thousands of workers exposed to uranium in the processing of uranium from its ore to reactor fuel elements over several decades. (Studies of uranium miners are less relevant here because of their exposure to radon gas and its radioactive decay products as well as uranium ore particles.) The clearest finding from the studies of uranium process workers is the expected 'healthy worker' effect: diseases and death rates tend to be lower than in the general population. There is no clear and consistent evidence for any increase in cancer, or serious kidney disease. However, in most studies the uranium workers were not categorised by the extent of their exposure. It was recognised that these studies cannot detect small increases in cancer risks, but support the view that exposure to DU is unlikely to increase the risks of cancer greatly.

Part II (March 2002)

The Royal Society published the second report of its assessment of the potential hazards to military personnel and members of the public from the use of depleted uranium (DU) in weapons on 12 March 2002. Further information is provided in a press release on its website www.royalsoc.ac.uk. Part II considers the chemical toxicity of uranium, the environmental impact, and some responses to Part I of the Report.

Chemical toxicity

The toxicity of uranium has been studied extensively in experimental animals. These studies, supported by limited human data, indicate that toxic effects mainly arise from kidney damage. The biokinetic models of the International Commission on Radiological Protection were therefore applied to calculate the uranium concentrations in kidney resulting from the various scenarios described in Part I. The Group was unwilling to rely on animal data to assess the consequences of these uranium kidney concentrations, because of marked differences between species in their susceptibility. It therefore reviewed the literature to find cases of human exposure to uranium that produced effects on the kidneys, and in each case the maximum uranium concentration in the kidneys was estimated. Although the number of cases was small and diverse (accidental inhalations and skin burns, volunteer experiments, and an attempted suicide), a consistent pattern of increasing severity of kidney damage with increasing uranium concentration was found. Concentrations above a few tens of micrograms per gram of kidney lead to kidney failure, which could be fatal without prompt medical treatment. Concentrations around a few micrograms per gram of kidney lead to changes in kidney function that can be detected by tests on urine samples (dysfunction) while the uranium concentration remains high: whether such levels would have any long-term effect on health is not known, but considered to be unlikely. It was estimated that for most soldiers, exposures to DU would result in kidney concentrations less than 0.1 microgram uranium per gram of kidney and no effects would be expected. For soldiers in struck vehicles the concentrations could well reach a few micrograms per gram, leading to dysfunction detectable in urine tests. The possibility of large intakes (a few grams of DU) in 'worst-case' level I and II scenarios leading to kidney concentrations above 50 micrograms uranium per gram of kidney could not be excluded. Such concentrations would be expected to lead to kidney failure, and the Group was not aware that any such cases had occurred.

Environmental impact

A review of information relating to the environmental impact of DU battlefield use was conducted, but assessments of intakes, doses and risks other than for inhalation of resuspended soil, were not made, because it was considered that the pattern of contamination and its subsequent behaviour were too variable, depending on the nature of the military action and the local conditions (soil type, etc). Surveys conducted in Kosovo indicate that contamination is mainly confined to the immediate vicinity of penetrator strikes. It is recommended that areas should be cleared of visible penetrators and the contamination around them, particularly to avoid contamination of children at play. Many penetrators fired from aircraft miss their targets and may be deeply buried (a metre or more). If more than about 30 cm deep they can be very difficult to locate, and removal could be expensive and environmentally damaging. They pose little immediate hazard, but there is concern that in some circumstances groundwater could become contaminated, perhaps after several decades. Monitoring of water and milk supplies in affected areas is therefore recommended.

Responses to Part I

Several issues raised at the public meeting which followed publication of Part I of the report, and in correspondence and meetings with experts and veterans are addressed.

The use of modelling to provide quantitative assessments of exposures and risks in the absence of measurements of exposure, or of an exposure-response relationship for DU aerosols (as exists for radon) is explained. The possibility of radiation effects on the immune system is addressed, and it is considered that such effects are very unlikely from battlefield exposure to DU.

Evidence was taken from a former member of a US army unit involved in damage assessment and clean up of contaminated vehicles. He suggested that even the 'worst-case' estimates might in some cases be too low. He considers that vehicles were typically struck by four or five large rounds (rather than the one or two that had been assumed). He also claimed that men in his unit worked in or around DU-contaminated vehicles all day, every day for about three months, resulting in 600 hours exposure compared to the 100 hours 'worst-case'. This evidence conflicts with information in official US reports, but nevertheless assessments of its consequences were made.

Information was provided to the Group on measurements made in Canada of uranium isotopic ratios and concentrations in urine samples from UK veterans, about half of which indicated the presence of DU. A serious limitation of this study is the lack of corresponding measurements in a control group, which the Working Group considered essential in view of the potential difficulties in measuring the isotopic ratio in the tiny amount of uranium present in a urine sample. The results, however, suggest that modern mass spectrometric techniques could identify intakes of DU ten years earlier, that are well below the amounts likely to cause kidney damage or a detectable increase in cancer risk, and emphasised the need to validate such measurements.

Recommendations

A number of other recommendations for research and actions are made in both parts of the report. These include obtaining more information on the air concentrations (and hence intakes) of DU arising from penetrator impacts and by resuspension in contaminated vehicles (such tests are known to be under way in the USA and France, but the results are not yet available), better information on the dissolution of inhaled DU particles in the lungs, and information on the corrosion of DU penetrators in the environment.

Contributions from NRPB

Dr Michael Bailey, then Head of the Dose Assessments Department at NRPB, was a member of the Working Group. In Part I, his main contribution (with support from other NRPB staff) was to the assessment of intakes of DU and calculation of the resulting radiation doses to tissues. In Part II the main contributions of NRPB staff were in assessing uranium concentrations in kidneys from the use of DU weapons, and those which arose in reported cases of high intakes leading to kidney damage or dysfunction; and assessment of intakes from inhalation of resupended soil by people living in an area contaminated with DU.

Last reviewed: 30 October 2009