8 January 2001
Material on Depleted Uranium (DU)
by Dr. Michael H. Repacholi
of the World Health Organization, Geneva
What is DU?
Uranium is a naturally occurring element used, among other applications,
in the generation of nuclear power. Naturally occurring uranium has three
principal radioactive isotopes, namely U-238, U-235 and U-234. Depleted
uranium (DU) is a by-product of the process of uranium enrichment in the
nuclear power industry in which nearly all the radioactive isotopes U-234
and about two thirds of the U-235 are removed. Thus, DU is almost entirely
U-238 and is about 40% as radioactive as natural uranium. Chemically,
physically and toxicologically, the metallic form of DU behaves in the
same way as the metallic form of natural uranium. Fine particles of the
metal ignite easily, producing oxides.
It is used for heavy tank armour, anti-tank munitions, missiles and projectiles
due to its high density and availability. DU weapons are regarded as conventional
weapons and as such can be freely used by the armed forces. Depending
upon the type of impact a fraction of the DU may be released in the form
of small, relatively insoluble particles of uranium oxide as well as relatively
large pieces of metallic uranium.
Peaceful applications of DU include counterweights in aeroplanes and
boats, shields against radiation in medical radiotherapy units and for
transport of radio isotopes.
by the use of DU
DU is released from fired weapons in the form of small particles that
may be inhaled, ingested or remain in the environment. The use of DU weapons
in the Balkans, particularly in Kosovo, has raised concerns about the
health risks of the populations living in the affected areas. There is
speculation that the "Gulf War Syndrome" is linked to exposure
to DU, but no causal relationship has been established.
DU as ballast in planes that crashed (e.g Amsterdam in 1992.; Stansted,
UK in January 2000) has raised the concern of governments and NGOs. The
report of the Dutch commission of enquiry concluded that some of the DU
unaccounted for had been dispersed as small particles which could have
been inhaled by rescue workers and local populations.
What are the
effects of DU on human health?
They are complex, due to the chemical, radiological and physical characteristics
of DU. Sound scientific information on various health and environmental
effects is limited since most data refers to the health effects of uranium.
However, since uranium and DU are essentially the same except for the
composition of their radioactive components, scientific studies on metallic
uranium will be applicable to DU.
Health effects depend on the type of exposure (internal or external),
route of exposure (ingestion, inhalation, wounds), characteristics
of DU (soluble or insoluble particles), and setting (military,
External exposure occurs during the physical handling of DU metal (e.g.,
working in a munitions store or vehicle equipped with DU munitions or
DU armour) or through contact with dusts created following explosion or
impact. Effects due to external exposure only (no ingestion or inhalation)
would be limited to ionizing radiation.
Internal exposure occurs by ingestion, inhalation and also through wounds.
Effects are caused by both chemical and radiological toxicity.
Inhalation and ingestion of large quantities of soluble compounds
of DU may produce acute effects on the kidneys. Even for soluble forms,
only a few percent of ingested uranium is absorbed into blood. [ICRP Publication
69]. Of this, about 10% is deposited in bones, kidneys and other tissues,
and this retention of uranium could potentially cause long-term effects,
including cancer. However, at low doses the risks of cancer are minimal.
Long-term exposure has been shown to result in damage to kidney function.
The ingestion of insoluble particles of DU poses a much lower chemical
health risk, as the fraction absorbed is lower still and nearly all the
material is eliminated through the GI tract.
Absorption by inhalation depends on the size and solubility of the particles.
Generally, inhaled uranium oxide particles larger than a few micrometers
in diameter will mainly deposit in the upper respiratory tract (nose,
mouth and larger airways), from which they quickly pass into the digestive
system. For smaller particles, a larger fraction will deposit in the lungs,
where they main remain for months or years, unless they dissolve. Very
small amounts may be retained in the lymphatic system for longer. For
soluble compounds deposited in the lungs the fraction absorbed into blood
is generally higher than when ingested, and can be greater than 50%. Insoluble
particles pose a higher radiation risk owing to the longer stay in the
In the military environment, wounds represent an additional route of
exposure if caused by the impact of DU projectiles or armour. Military
personnel are exposed to shrapnel as well as dusts that can be inhaled,
ingested or deposited on wounds.
toxicity and exposures
DU decays mainly through emission of alpha particles, which cannot penetrate
the external skin layers but may affect internal body cells (more susceptible
to the ionizing effects of alpha radiation) when DU is ingested or inhaled.
However, from the studies undertaken on uranium workers, no negative health
effects have been established after internal exposure to radiation through
ingestion and inhalation of DU particles or through skin lesions and wounds
contaminated by DU.
There is a theoretical possibility that exposure to alpha and beta radiation
from inhaled insoluble DU particles might lead to lung tissue damage and
increase the probability of lung cancer. Similarly absorption into blood
and retention in other organs, notably the skeleton, is assumed to carry
an additional risk of cancer, depending on the level of radiation dose.
Media reports suggest that soldiers in the Kosovo conflict may be at
a higher risk of leukaemia from radiation exposure to DU. (Leukaemia occurs
in adult populations at an incidence rate of about 50-100 cases per million
per year for the age group range of 20-45 years). From current evidence,
this is unlikely for several reasons:
- While ionizing radiation exposure is known to cause leukaemia, significant
radiation exposures are necessary. Some 15 years after the Chernobyl
nuclear reactor accident, the main cancer resulting was a very steep
increase in childhood thyroid cancer. No increase in leukaemia has been
detected in the exposed population. No radiation-related increases in
leukaemia have been established in uranium miners or workers milling
uranium metal to make nuclear fuel elements.
- Generally several years (normally at least 2-5 years) are needed
between exposure to ionizing radiation and clinical detection of leukaemia.
- Inhalation and ingestion of DU contaminated dust, even under reasonably
extreme conditions, and shortly after bombing, as determined by the
amount of dust that can be inhaled, it has been calculated to result
in a radiation exposure of less than about 10 mSv. This represents about
half the annual dose limit for radiation workers. If this amount of
soluble DU was inhaled, then severe kidney malfunction would occur below
this radiation dose.
While from the science it does not appear that leukaemia would result
from exposure to DU, WHO does not have any information on the exposure
situation regarding military personnel in Kosovo to make definitive conclusions.
Detailed surveys are needed to determine the numbers of soldiers exposed,
the amount of DU used, how much exists on the surface, how much is buried
in the ground, what is the composition of fine and course particle etc.,
before better conclusions can be made. Breathing ultra-fine particles
could lead to a theoretical risk of cancer.
DU in the
In arid regions, most DU remains on the surface as dust. It is dispersed
in soil more easily, particularly in the areas of higher rainfall. Cultivation
of contaminated soil and use of contaminated water and food may pose health
risks, but these are expected to be limited. Chemical toxicity would be
expected to be the main health concern rather than the radiation exposure.
Children rather than adults may be considered to be more at risk of DU
exposure when returning to normal activities within a war zone through
contaminated food and water, since typical hand-to-mouth activity of inquisitive
play could lead to high DU ingestion from contaminated soil.
WHO has been involved in the setting of guidelines on uranium that would
apply to DU. Currently these are:
- Guideline for drinking-water quality (2 ng/litre), a value considered
to be protective for sub-clinical renal effects reported in epidemiological
studies (WHO, 1998)
- Tolerable Daily Intake (TDI) for oral exposure to uranium of 0.6
ug/kg of body weight/day WHO (1998).
- Limits of ionizing radiation exposure of 1 mSv/year for the general
public and 20 raSv/year averaged over 5 years for radiation workers
(Basic Safety Standards, 1996).
- Extensive literature review undertaken to determine the generic health
consequences of exposure to Uranium and DU and preparation of a monograph
summarising the results of the review (to be peer-reviewed and published
before end of February 2001). Preparation of a WHO Fact Sheet.
- The terms of reference of the scientific review included a requirement
to identify gaps in knowledge requiring further research in order to
make better health risk assessments of human exposure to DU. A high-level
scientific expert group will be convened by WHO to review these requirements
for research and make proposals for in-depth research on this issue.
- Provision of advice to the UN Balkan Task Force (UNEP)
- Provision of advice on possible environmental health consequences
of the gulf war.
Interim research needs identified so far by the WHO review include:
- Clarifying our understanding of the degree of kidney damage associated
with changes in renal function (and its reversibility) in human populations
subject to different levels of uranium exposure
- Investigating the chemical and physical form, physiological behaviour,
leaching and subsequent environmental cycling of specific forms of uranium
from various industrial and military sources (e.g. depleted uranium
alloys, UFe, phosphate byproducts). To link such data to the existing
extensive knowledge base of the environmental and physiological behaviour
of uranium compounds produced by the nuclear industry.
- Improving our understanding of the reproductive, mutagenic and carcinogenic
properties of uranium and, by inference depleted uranium.
Dr Michael H Repacholi
Coordinator, Occupational and Environmental Health
Protection of the Human Environment (PHE)
World Health Organization, CH-1211 Geneva 27, Switzerland
Tel: +41 22 791 3427, Fax: +41 22 791 4123, E-mail: email@example.com
In consultation with Dr Elisabeth, International Agency for Research
on Cancer, Lyon, France and many reviewers for WHO.
08 January 2001