- Metallic uranium (U) is a silver-white, lustrous, dense,
weakly radioactive element. It is ubiquitous throughout the
natural environment, and is found in varying but small
amounts in rocks, soils, water, air, plants, animals and in
all human beings.
- Natural uranium consists of a mixture of three radioactive
isotopes which are identified by the mass numbers 238U
(99.27% by mass), 235U (0.72%) and 234U (0.0054%).
- On average, approximately 90 µg (micrograms) of uranium
exists in the human body from normal intakes of water, food
and air. About 66% is found in the skeleton, 16% in the
liver, 8% in the kidneys and 10% in other tissues.
- Uranium is used primarily in nuclear power plants.
However, most reactors require uranium in which the 235U
content is enriched from 0.72% to about 1.5-3%.
- The uranium remaining after removal of the enriched
fraction contains about 99.8% 238U, 0.2% 235U and 0.001%
234U by mass; this is referred to as depleted uranium or DU.
- The main difference between DU and natural uranium is that
the former contains at least three times less 235U than the
- DU, consequently, is weakly radioactive and a radiation
dose from it would be about 60% of that from purified
natural uranium with the same mass.
- The behaviour of DU in the body is identical to that of
- Spent uranium fuel from nuclear reactors is sometimes
reprocessed in plants for natural uranium enrichment. Some
reactor-created radioisotopes can consequently contaminate
the reprocessing equipment and the DU. Under these
conditions another uranium isotope, 236U, may be present in
the DU together with very small amounts of the transuranic
elements plutonium, americium and neptunium and the fission
product technetium-99. However, the additional radiation
dose following intake of DU into the human body from these
isotopes would be less than 1%.
Applications of depleted uranium
- Due to its high density, about twice that of lead, the
main civilian uses of DU include counterweights in aircraft,
radiation shields in medical radiation therapy machines and
containers for the transport of radioactive materials. The
military uses DU for defensive armour plate.
- DU is used in armour penetrating military ordnance because
of its high density, and also because DU can ignite on
impact if the temperature exceeds 600°C.
Exposure to uranium and depleted
- Under most circumstances, use of DU will make a negligible
contribution to the overall natural background levels of
uranium in the environment. Probably the greatest potential
for DU exposure will follow conflict where DU munitions are
- A recent United Nations Environment Programme (UNEP)
report giving field measurements taken around selected
impact sites in Kosovo (Federal Republic of Yugoslavia)
indicates that contamination by DU in the environment was
localized to a few tens of metres around impact sites.
Contamination by DU dusts of local vegetation and water
supplies was found to be extremely low. Thus, the
probability of significant exposure to local populations was
considered to be very low.
- A UN expert team reported in November 2002 that they found
traces of DU in three locations among 14 sites investigated
in Bosnia following NATO airstrikes in 1995. A full report
is expected to be published by UNEP in March 2003.
- Levels of DU may exceed background levels of uranium close
to DU contaminating events. Over the days and years
following such an event, the contamination normally becomes
dispersed into the wider natural environment by wind and
rain. People living or working in affected areas may inhale
contaminated dusts or consume contaminated food and drinking
- People near an aircraft crash may be exposed to DU dusts
if counterweights are exposed to prolonged intense heat.
Significant exposure would be rare, as large masses of DU
counterweights are unlikely to ignite and would oxidize only
slowly. Exposures of clean-up and emergency workers to DU
following aircraft accidents are possible, but normal
occupational protection measures would prevent any
Intake of depleted uranium
- Average annual intakes of uranium by adults are estimated
to be about 0.5mg (500 μg) from ingestion of food and
water and 0.6 μg from breathing air.
- Ingestion of small amounts of DU contaminated soil by
small children may occur while playing.
- Contact exposure of DU through the skin is normally very
low and unimportant.
- Intake from wound contamination or embedded fragments in
skin tissues may allow DU to enter the systemic circulation.
Absorption of depleted uranium
- About 98% of uranium entering the body via ingestion is
not absorbed, but is eliminated via the faeces. Typical gut
absorption rates for uranium in food and water are about 2%
for soluble and about 0.2% for insoluble uranium compounds.
- The fraction of uranium absorbed into the blood is
generally greater following inhalation than following
ingestion of the same chemical form. The fraction will also
depend on the particle size distribution. For some soluble
forms, more than 20% of the inhaled material could be
absorbed into blood.
- Of the uranium that is absorbed into the blood,
approximately 70% will be filtered by the kidney and
excreted in the urine within 24 hours; this amount increases
to 90% within a few days.
Potential health effects of exposure to
- In the kidneys, the proximal tubules (the main filtering
component of the kidney) are considered to be the main site
of potential damage from chemical toxicity of uranium. There
is limited information from human studies indicating that
the severity of effects on kidney function and the time
taken for renal function to return to normal both increase
with the level of uranium exposure.
- In a number of studies on uranium miners, an increased
risk of lung cancer was demonstrated, but this has been
attributed to exposure from radon decay products. Lung
tissue damage is possible leading to a risk of lung cancer
that increases with increasing radiation dose. However,
because DU is only weakly radioactive, very large amounts of
dust (on the order of grams) would have to be inhaled for
the additional risk of lung cancer to be detectable in an
exposed group. Risks for other radiation-induced cancers,
including leukaemia, are considered to be very much lower
than for lung cancer.
- Erythema (superficial inflammation of the skin) or other
effects on the skin are unlikely to occur even if DU is held
against the skin for long periods (weeks).
- No consistent or confirmed adverse chemical effects of
uranium have been reported for the skeleton or liver.
- No reproductive or developmental effects have been
reported in humans.
- Although uranium released from embedded fragments may
accumulate in the central nervous system (CNS) tissue, and
some animal and human studies are suggestive of effects on
CNS function, it is difficult to draw firm conclusions from
the few studies reported.
Maximum radiation exposure limits and
their limited application to uranium and depleted uranium
The International Basic Safety Standards, agreed by all
applicable UN agencies in 1996, provide for radiation dose
limits above normal background exposure levels.
- The general public should not receive a dose of more than
1 millisievert (mSv) in a year. In special circumstances, an
effective dose of up to 5 mSv in a single year is permitted
provided that the average dose over five consecutive years
does not exceed 1 mSv per year. An equivalent dose to the
skin should not exceed 50 mSv in a year.
- Occupational exposure should not exceed an effective dose
of 20 mSv per year averaged over five consecutive years or
an effective dose of 50 mSv in any single year. An
equivalent dose to the extremities (hands and feet) or the
skin should not surpass 500 mSv in a year.
- In case of uranium or DU intake, the radiation dose limits
are applied to inhaled insoluble uranium-compounds only. For
all other exposure pathways and the soluble
uranium-compounds, chemical toxicity is the factor that
Guidance on exposure based on chemical
toxicity of uranium
WHO has guidelines for determining the values of health-based
exposure limits or tolerable intakes for chemical substances.
The tolerable intakes given below are applicable to long-term
exposure of the general public (as opposed to workers). For
single and short-term exposures, higher exposure levels may be
tolerated without adverse effects.
- The general public's intake via inhalation or ingestion of
soluble DU compounds should be based on a tolerable intake
value of 0.5 µg per kg of body weight per day. This leads
to an air concentration of 1 µg/m3 for inhalation, and
about 11 mg/y for ingestion by the average adult.
- Insoluble uranium compounds with very low absorption rate
are markedly less toxic to the kidney, and a tolerable
intake via ingestion of 5 µg per kg of body weight per day
- When the solubility characteristics of the uranium
compounds are not known, which is often the case in exposure
to DU, it would be prudent to apply 0.5 µg per kg of body
weight per day for ingestion.
Monitoring and treatment of exposed
- For the general population, neither civilian nor military
use of DU is likely to produce exposures to DU significantly
above normal background levels of uranium. Therefore,
individual exposure assessments for DU will normally not be
required. Exposure assessments based on environmental
measurements may, however, be needed for public information
- When an individual is suspected of being exposed to DU at
a level significantly above the normal background level, an
assessment of DU exposure may be required. This is best
achieved by analysis of daily urine excretion. Urine
analysis can provide useful information for the prognosis of
kidney pathology from uranium or DU. The proportion of DU in
the urine is determined from the 235U/238U ratio, obtained
using sensitive mass spectrometric techniques.
- Faecal measurement can also give useful information on DU
intake. However, faecal excretion of natural uranium from
the diet is considerable (on average 500 μg per day,
but very variable) and this needs to be taken into account.
- External radiation measurements over the chest, using
radiation monitors for determining the amount of DU in the
lungs, require special facilities. This technique can
measure about 10 milligrams of DU in the lungs, and (except
for souble compounds) can be useful soon after exposure.
- There are no specific means to decrease the absorption of
uranium from the gastrointestinal tract or lungs. Following
severe internal contamination, treatment in special
hospitals consists of the slow intravenous transfusion of
isotonic 1.4 % sodium bicarbonate to increase excretion of
uranium. DU levels in the human, however, are not expected
to reach a value that would justify intravenous treatment
any more than dialysis.
- Following conflict, levels of DU contamination in food and
drinking water might be detected in affected areas even
after a few years. This should be monitored where it is
considered there is a reasonable possibility of significant
quantities of DU entering the ground water or food chain.
- Where justified and possible, clean-up operations in
impact zones should be undertaken if there are substantial
numbers of radioactive projectiles remaining and where
qualified experts deem contamination levels to be
unacceptable. If high concentrations of DU dust or metal
fragments are present, then areas may need to be cordoned
off until removal can be accomplished. Such impact sites are
likely to contain a variety of hazardous materials, in
particular unexploded ordnance. Due consideration needs to
be given to all hazards, and the potential hazard from DU
kept in perspective.
- Small children could receive greater exposure to DU when
playing in or near DU impact sites. Their typical
hand-to-mouth activity could lead to high DU ingestion from
contaminated soil. Necessary preventative measures should be
- Disposal of DU should follow appropriate national or
Provides a summary of the scientific literature on uranium and
guidance on exposure to depleted uranium [pdf 394kb]
Provides information on medical treatment from excessive DU
exposure and advice for programme administrators sending
personnel to DU contaminated areas.