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Depleted Uranium


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By Kent Gregory - Posted on 19 December 2008

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AUSTRALASIAN RADIATION PROTECTION SOCIETY

February 8 2001 MEDIA RELEASE
POTENTIAL HEALTH EFFECTS OF DEPLETED URANIUM IN MUNITIONS

Some military personnel involved in the 1991 Gulf War have complained of continuing stress-like symptoms for which no obvious cause has been found. These symptoms have at times been attributed to the use of depleted uranium in shells and other missiles, which are said to have caused toxic effects. Similar complaints have arisen from the more recent fighting in the Balkans, particularly the Kosovo conflict about a year ago.

Depleted uranium (DU) is natural uranium which is depleted in the rarer U-235 isotope (see below). It is a heavy metal and, in common with other heavy metals, it is chemically toxic. It is also slightly radioactive and there is therefore said to be a hypothetical possibility that it could give rise to a radiological hazard under some circumstances, e.g. if dispersed in finely divided form so that it is inhaled.

However, because of the latency period for the induction of cancer by radiation, it is not credible that any cases of radiation-induced cancer could yet be attributed to the Kosovo conflict. Furthermore, extensive studies have concluded that no radiological health hazard should be expected from exposure to depleted uranium.

The risk from external exposure is essentially zero, even when pure metal is handled. No detectable increases of cancer, leukaemia, birth defects or other negative health effects have ever been observed from radiation exposure to inhaled or ingested natural uranium concentrates, at levels far exceeding those likely in areas where DU munitions have been used. This is mainly because the low radioactivity per unit mass of uranium means that the mass needed for significant internal exposure would be virtually impossible to accumulate in the body – and DU is less than half as radioactive as natural uranium.

This position is well summarised in the concluding paragraph of a commentary by N D Priest on the "Toxicity of depleted uranium", published in The Lancet, Vol 357, January 27, 2001, which reads:

"It can be safely concluded that, at any conceivable level of uptake, depleted uranium will have no appreciable radiological or chemical carcinogenic potential. Moreover even if cancers were to be produced they would occur many years after intake, because the lag period between damage to the sensitive cells and the appearance of recognisable tumours. In man, for chronic irradiation from internally deposited alpha-emitting radionuclide, these latency periods would typically lie in the range of 10 years to several decades. In view of this latency, tumours in individuals exposed to depleted uranium for shorter periods - e.g. servicemen exposed to depleted uranium in the former Yugoslavia within the past decade - cannot be attributed to radiation from depleted uranium. Finally the only chemical toxic effect expected would be reversible damage to the kidney."

What is depleted uranium?

Naturally occurring uranium ores contain uranium in a mixture of isotopes. Natural uranium has about 99.3 % U-238 and 0.7 % U-235, and a trace of U-234. The fuel used in commercial light water reactors requires the proportion of U-235 to be enriched to 3 to 4 %. Some reactors, such as military reactors and research reactors, require considerably higher enrichment percentages, and uranium used in nuclear weapons requires a very high level of enrichment. Highly enriched uranium may also be used as fuel for fast reactors. The waste product from the enrichment process is uranium with a reduced content of U-235 and is therefore termed "depleted uranium" (DU). DU may also be produced as a by-product of reprocessing spent fuel to recover plutonium. DU is typically made up of about 99.8% U-238 and 0.2 % U-235. Traces of U-236 and transuranic elements might exist in DU recovered from spent fuel, because of incomplete separation.

Uranium decay products, which contribute much of the radioactivity in naturally occurring uranium, are removed by the processes that lead to the production of DU. The energies of alpha and gamma radiation emitted per unit time from DU are about 11 % and 1.4 % respectively of those from the U-238 decay series at equilibrium. The total activity of DU is about 60 % of the total activity of natural uranium metal.

In the US, the Department of Energy (DOE) recently reported that the DU stock it provided to the Department of Defense for manufacturing armour plates and munitions may contain trace levels (a few parts per billion) of transuranics. From a radiological perspective, the transuranic contamination in DU armour, prepared from this stock material, would contribute only an additional 0.8 percent to the radiation dose from the DU itself and is an insignificant addition.

Why is DU used in munitions?

Uranium has a density of 19.05 g/cm3, which is almost twice that of lead. Its metallurgical properties are such that projectiles made from it are able to withstand the high firing velocities of modern weapons. Uranium shells fired from tanks and aircraft are able to penetrate and destroy heavily armed tanks at greater ranges than other types of anti-tank shells.

DU is relatively cheap, available in large quantities and is safe to handle with simple precautions. Hence, it used in many applications requiring a dense material, such as counterweights and ballast in aircraft, sailing boat keels and shielding against x-rays and gamma irradiation. It has the same chemical properties as natural uranium, reacting readily with many non-metallic elements, so that components may need to be clad (e.g. in aluminium) for normal handling.

What are the risks from exposure to DU?

Most of the DU munitions that are fired do not strike hard objects. Hence, they are likely to become embedded in the ground as intact metal components which, in themselves, do not present a health hazard. However, uranium is pyrophoric, particularly when in finely divided form, i.e. it can ignite spontaneously at elevated temperatures. A DU projectile striking a hard object, such as an armoured tank, ignites on contact and some 10-35 % is converted to a finely divided oxide aerosol. Fragment of unburnt uranium may also form shrapnel. The aerosol is a trivial hazard to tank crew compared with blast, heat and shrapnel, but resuspended material could potentially present a hazard to persons subsequently in the area.

Most scientific concern focuses on the potential for toxic heavy metal effects on the kidney, particularly where fragments of DU have become embedded in the body. High exposure to uranium in laboratory animals has resulted in specific types of kidney damage. However, no significant relationship has been found between kidney function and urine uranium values in Gulf War veterans with embedded fragments, although "mobilization of DU from shrapnel is occurring on a slow but ongoing steady basis." No effects on renal function have been observed.

The potential for radiological effects from exposure to DU is doubtful, primarily because of the very low specific activity of the material. 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. For example, a study which followed up 19,000 workers who had been employed between 1943 and 1947 in a uranium munitions factory in the US, found no cases of lung cancer (or kidney disease) that could be attributed to uranium exposure.

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. Similarly, there is no reason to expect that radiation from DU could cause birth defects.

What are the observed health effects of exposure to DU from munitions?

The minimum latency period that would be expected for any case of radiation-induced leukaemia is about 2 years, and 5-10 years for other cancers. The median latency period is about 8 years for radiation-induced leukaemia and 2 to 3 times longer for solid tumours such as lung cancer. Hence, from this perspective alone, no case of cancer could yet be in evidence due to exposures during the Kosovo conflict. Solid tumours due to the Gulf War are unlikely to be in evidence.

The World Health Organisation (WHO) is working with the International Agency for Research on Cancer (IARC) and the UN Environment Programme (UNEP) to gather more information on:

* the effects of DU munitions used in the Balkans and Middle East,
* the evidence that exists on the health effects of DU,
* the incidence of neoplasia and other possible adverse health effects among civilians, and
* effects among humanitarian workers and military personnel who handled DU.

A fact-finding mission to Kosovo, undertaken in November 2000, did not find any evidence of DU contamination although it has been confirmed that DU munitions were used. Further studies and checks on the health of the local population were recommended. A task force is being sent to Iraq to investigate claims that thousands of civilians have contracted various forms of cancer and that babies have been born with deformities, due to DU contamination.

The possible effects of DU have already been extensively studied, along with other possible contributors to "Gulf War sickness" such as chemical and biological agents, oil well fires, pesticides, pyridostigmine bromide, immunisations, infectious diseases and stress. A British evaluation (see www.mod.uk/policy/gulfwar/info/du.htm), updated to February 1999, concludes:

"In the light of the known exposures to uranium in the uranium industry during and after World War II it would seem unlikely that the hazards of uranium have been underestimated. To date there is no indication that harmful overexposures to DU with respect to chemical toxicology or radioactivity have occurred either at the UK ranges or in the Gulf conflict."

In the USA, literature reviews of potential agents which might have given rise to illnesses were commissioned by the Special Assistant to the Deputy Secretary of Defense for Gulf War Illnesses. These reviews by the Rand Corporation covered not only DU but also agents noted above. The Rand report on DU published in late June 1999 (available at www.gulflink.osd.mil/library/randrep/du/cover.html) concludes, as follows:

* "Although any increase in radiation to the human body can be calculated to be harmful from extrapolation from higher levels, there are no peer-reviewed published reports of detectable increases of cancer or other negative health effects from radiation exposure to inhaled or ingested natural uranium at levels far exceeding those likely in the Gulf. This is mainly because the body is very effective at eliminating ingested and inhaled natural uranium and because the low radioactivity per unit mass of natural and depleted uranium means that the mass of uranium needed for significant internal exposure is virtually impossible to obtain.
* "External radiation takes the primary form of alpha radiation, but amounts of beta and gamma radiation also exist. Alpha radiation is not capable of penetrating cloth or skin and would therefore have no negative health effect. Beta and gamma radiation, which can have negative health effects, have been measured at levels below those expected to be of concern.
* "Large variations in exposure to natural uranium in the normal environment have not been associated with negative health effects.
* "Radiation-related effects from embedded fragments will depend on the size of the fragment and its proximity to vital organs.
* "Exposure to uranium and other heavy metals in large doses can cause changes in renal function and at very high levels result in renal failure.
* "In spite of these findings, no increased morbidity or frequency of end-stage renal disease has been observed in relatively large occupational populations chronically exposed to natural uranium at concentrations above normal ambient ones.
* "The cohort of individuals, about half of whom have embedded fragments, who are being followed at the Baltimore VA Medical Center as part of the DU Follow-Up Program, represents a group of Gulf War veterans who received the highest levels of exposure to DU during the Gulf War. Although many of these veterans have health problems related to their injuries in the Gulf War and those with embedded fragments have elevated urine uranium levels, researchers to date report neither adverse renal effects attributable to chemical toxicity of DU nor any adverse health effects they relate to DU radiation."

The conclusions of three authoritative overseas studies can be summarised as follows:

* RAND Corporation – There is no evidence of radiological health effects, or of increased kidney disease in troops with embedded fragments.
* US Department of Health and Human Services Agency for Toxic Substances and Disease Registry – No radiological health hazard is expected from inhalation, dermal or oral exposure to depleted or natural uranium.
* National Academy of Sciences Institute of Medicine – Studies of effects "are suggestive of no association" with DU.

 

Dr A C McEwan
President
Australasian Radiation Protection Society

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