Depleted uranium toxicity

Background

Uranium is an alpha-emitting, radioactive heavy metal that occurs naturally in nearly all rocks and soil. Natural uranium is made up of the three naturally occurring isotopes of uranium namely ²³⁴U, ²³⁵U, and ²³⁸U. Naturally occurring uranium deposits are over 99% ²³⁸U. You eat, drink, and breather natural uranium on a daily basis.
Health hazards of natural uranium have been studied extensively since 1940s. Health impact of Depleted Uranium (DU) has been studied since the early 1970s.
Enrichment is the industrial process by which natural uranium is separated into enriched uranium which has an increased percentage of ²³⁵U and depleted uranium which has a decreased percentage of ²³⁵U.
- DU is a byproduct of the enrichment process.
- DU has 40% less radioactivity than natural uranium. It has a specific activity of 0.33 microCi/g.
- DU has the same chemical properties as naturally occurring uranium, it simply has different ratio of isotopes of ²³⁴U, ²³⁵U, and ²³⁸U.
- DU health effects will be the same as for natural uranium because the toxicity is primarily due to the chemical toxicity rather than radiotoxicity.
United States Armed Forces have used depleted uranium in the manufacture of ammunition, armor, and aircraft.
- DU's high density, self-sharpening quality and pyrophoricity make it a good choice for projectile munitions.
- DU's density makes it a good armor choice.
- DU's density also makes it a good choice for counterbalance weights used in aircraft and on helicopter rotors.

'	Natural Uranium	Depleted Uranium
Isotope	Concentration of isotope	Concentration of isotope
²³⁴U	0.0058%	0.0010%
²³⁵U	0.72%	0.20%
²³⁸U	99.28%	99.80%
Relative Radioactivity	1.0	0.6

Routes of exposure

Inhalation - minor route of exposure for general population. Major route for occupational population. On average in US individual daily intake of uranium is 0.007 micrograms by inhalation.
Oral - predominant route of exposure for general population through ingestion of food and drinking water. Average daily intake of uranium in US is 1.9 micrograms by ingestion.
Dermal - unlikely route of exposure for general population. Potential route of exposure for military service members.

Toxicokinetics

DU is poorly absorbed following inhalation, oral, or dermal exposure route.
- Amount absorbed heavily dependent on the solubility of the compound.
- <0.1-6% of uranium is absorbed following oral exposure.
67% of uranium in blood is filtered in the kidneys and leaves body in urine within 24 hours. Remainder is distributed to tissues primarily bone, liver, and kidney.
Retention half-time for uranium in bone is 70-200 days.
Retention in body skeleton (66%), liver (16%), kidneys (8%), other tissues (10%)

Radiation Toxicity

Alpha emitter thus not serious external radiation hazard. Alpha radiation has poor penetrating ability. Direct contact with bare DU for 250 hours is necessary to exceed annual occupational exposure limits.
Internal exposure via inhalation, ingestion, wound contamination or retained fragments warrants some concern.
Chronic exposure by inhalation is potential radiologic hazard to the lung and thoracic lymph nodes.
Genotoxicity, mutagenicity and reproductive effects are being studied.

Chemical Toxicity

Kidney dysfunction main chemically-induced effect of uranium
Can develop tubulopathy or renal tubular acidosis

Clinical Features

DU is a heavy metal like lead, tungsten or nickel which can damage the kidneys when present in large amounts.
DU exposure normally does not result in any symptoms as small amounts are quickly passed
DU make cause impairment of the kidneys if exposure is significant in short term

Differential Diagnosis

Alpha radiation exposure

Heavy metal toxicity

Evaluation

Patients who feel they have been exposed to high levels of DU should be evaluated
Assess the following in patient:
- Circumstances : date, time, route of exposure, amount
- Evidence of wound or embedded fragments?
- Has patient had any prolong skin contact i.e. through keeping of a souvenir?
Provide medical examination:
- Physical
- Determine kidney function (blood urea and creatinine)
- Conduct urine analysis
- Complete blood count
- Chest x-ray if history suggestive of significant inhalation exposure
Test for uranium exposure if history suggest proximity to source or large exposure or any abnormalities on about routine examination
- Check beta-2 microglobulin in 24 hour urine to check for tubulopathy
- Check urine uranium level if elevated than 24 hour excreted DU level should be accessed including isotope-specific methods to identify ratios of isotope of uranium

Management

Acute exposure manage as would for any heavy metal exposure
Remove patient from exposure
Externally decontaminate if residue present on patient
Base further treatment on symptoms observed
Renal tubulopathy treatment which needs to be applied early prior to fixation of uranium in the skeleton to be truly effective
- Sodium bicarbonate perfusion to alkalinize urine
- Consider heavy metal chelation therapy
- Monitor renal function

Disposition

Most cases of exposure have no permanent effect
Likelihood to develop any health effects is low
If exposure is via inhalation and significant amounts of insoluble uranium compounds deposited in lungs than patient will need long-term surveillance/follow-up

References

Agency for Toxic Substances and Disease Registry (ATSDR), Toxicological Profile for Uranium (Update), February 2013.
McDiarmid, M.A. (2001). Depleted uranium and public health. BMJ, 322(7279), 123-124.
U.S. Army Environmental Policy Institute (AEPI). (June 1995). Health and Environmental Consequences of Depleted Uranium Use in the U.S. Army: Technical Report.
Department of Defense. (August 4, 1998). Health Effects of Depleted Uranium - Fact Sheet.
U.S. Army Environmental Policy Institute, (AEPI). (June 1994). Health and Environmental Consequences of Depleted Uranium Use by the U.S. Army, Summary Report to Congress.
World Health Organization (WHO), Guidance On Exposure to DU- For Medical Officers and Programme Administrators, 2001.
World Health Organization (WHO), Depleted Uranium: Sources, Exposure and Health Effects, 2001.
World Health Organization (WHO), Depleted Uranium Fact Sheet, revised January 2003.

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