[ RadSafe ] carcinogenicity of uranium

[Otto G. Raabe]

April 17, 2010

It is amazing how much crap can be published based on nothing more 
than wild imagination and hyperbole concerning uranium and DU.

While in graduate school at the University of Rochester I had the 
opportunity to observe the inhalation studies being conducted with 
uranium oxide using various animal species. The Rochester studies 
began in the 40's as part of the Manhattan project and were still in 
progress when I was a graduate student in the 60's. Two of the key 
papers summarizing the uranium dioxide inhalation studies were 
published by Leonard Leach and his associates. The references are 
Heath Physics  18: 599-612 (1970) and Health Physics 25: 239-258 (1973).

The opening sentence of the Abstract of the 1973 paper states: 
"Inhalation studies show that dogs, monkeys and rats can breathe a 
natural uranium dioxide (UO2) aerosol of approximately 1 um mass 
median particle diameter at a mean concentration of 5 mg U/m3  (25 x 
TLV or 28 x MPCa), for periods as long as 5 yr with little evidence 
of serious injury."   There is no major effect on the bronchial 
airways!. THESE WERE MASSIVE DOSES DELIVERED OVER SEVERAL YEARS!

Natural and depleted uranium are chemically and biologically 
identical in their behavior and radiologically very similar.  DU is 
not unique in any way. Uranium is present in all the soil and rock on 
the face of the earth, and small amount are in our food. There is 
over 70 years of excellent toxicological research on uranium and 
uranium oxide that seems to be ignored in recent  alarmist papers. 
Uranium oxide, the form to which people might be exposed is neither 
very toxic and nor a known carcinogen,

Kathren et al, beautifully summarized with extensive historical data 
the trivial toxicological properties of uranium. Kathren, Ronald L.; 
Burklin, Richard K., Health Physics. 94(2):170-179, February 2008, 
Acute Chemical Toxicity of Uranium.

Inhaled uranium risk can be summarized as a trivial inhalation for 
exposure to traces of depleted uranium dioxide, a relatively inert 
form of uranium in the U(IV) oxidation state characterized by very 
low biological toxicity. Because of the extremely long half lives of 
the uranium isotopes, 4.5 billion years for uranium-238, depleted 
uranium is barely radioactive and presents no radiological hazard.

The studies by Malenchenko et al. (1978) utilized high doses of the 
most toxic uranyl ion (UO2--) chemical form of uranium in the U(VI) 
oxidation state to show an auto-immune response. THESE WERE HEROIC 
DOSES, NOT REALISTIC DOSES.

You might be confused by studies that show that sarcoma is produced 
by relatively large pieces off uranium are surgically placed into the 
body. This is a well known phenomena that occurs when any large 
irritant object is placed in body tissues in which there is 
continuous cellular proliferation leading to neoplasia. A similar 
result could be obtained with a large piece of plain iron surgically 
placed into body tissues.

Uranium metal and the oxides is not a dangerous carcinogen or 
toxicant. URANIUM OXIDE IS NOT A POTENT TOXICANT OR CARCINOGEN!

There is no need to consider the internal radiation dose from 
depleted uranium because it is mostly U-238 (99.28 percent U-238, 
0.71 percent U-235, and 0.0058 percent U-234 by mass and the half 
life of U-238 is 4.5 billion years which makes its specific activity 
tiny (specific activity only 0.4 microcuries per gram or 15 Bq/mg). 
Heavy metal poisoning in possible at really high intakes, but the 
radiation dose is really irrelevant.

The toxicity of uranium has been under study for al least 50 years 
including life span studies in small animals. Depleted uranium is 
only very weakly radioactive, and virtually all of the observed or 
expected effects are from mild nephrotoxicity associated with 
deposition in the kidney tubules and glomeruli damage at high doses. 
The radiation doses from depleted uranium (U-238 has a 4.5 billion 
year half life) are very small compared to potential toxic effects 
from uranium ions in the body (primarily damage to kidney tubules). 
The main route of potentially hazardous exposure is inhalation since 
gastrointestinal uptake is very small (<1/10,000).

Consider, for example the deposition of a respirable particle of 
depleted uranium dioxide in the human lung. If that particle is 
approximately spherical and has a diameter of 1 micrometer 
(aerodynamic diameter about 3 micrometer), it will emit an average of 
only one alpha particle every 100 days. Meanwhile the cells of the 
lung are being irradiated in a milieu of even more energetic alpha 
particles from natural radon and its decay products that are present 
in all the air on the surface of the earth. The total radiation dose 
to the lung from even relatively high exposures to airborne depleted 
uranium particles is not remarkable. The TLV is 0.2 mg/cubic-meter 
based on chemical toxicity.

After inhalation, uranium will be slowly mobilized and enter the 
systemic circulation. The uranyl ion is the form of mobile uranium 
within the body. It deposits at bone surfaces and remains in the bone 
matrix with a half time of up to one year. It is slowly cleared to 
the blood and excreted via the kidneys. While in the bone, alpha 
radiation is emitted, but with very low intensity since depleted 
uranium is not very radioactive. The range of alpha radiation in the 
bone is about 30 micrometer and the radiation is very diffuse, so the 
bone marrow is not effectively irradiated by uranium in the bone. 
Radiation induction of leukemia requires effective high dose-rate 
irradiation of the bone marrow. There is no known or expected 
leukemia risk associated with small amounts of U-238 in the bone 
because the marrow is not efficiently irradiated. [The same is true 
for much more highly radioactive radium-226 and plutonium-239.]

As to its "heavy Metal" toxicity, the closest analogy is lead. 
However, metallic lead has considerably higher toxicity than metallic 
uranium. Compounds of lead are much more hazardous than compounds of 
uranium since uranium tends to form relatively insoluble compounds 
which are not readily absorbed into the body. Also, lead within the 
body affects the nervous system and several biochemical processes, 
while the uranyl ion does not readily interfere with any major 
biochemical process except for depositing in the tubules of kidney 
where damage occurs if excess deposition occurs. Glomeruli damage has 
been reported at high doses as well. The kidney damage is dosage 
dependent and somewhat reversible. Lead bullets are probably more 
dangerous than uranium bullets.

References: "Handbook of the Toxicology of Metals", Friberg et 
al.(1990), "Uranium, Plutonium, Transplutonium Elements", Hodge et 
al. (1973), "A five year inhalation study with natural uranium 
dioxide", HEALTH PHYS 25, 230-258 (1973), "Acute Chemical Toxicity of 
Uranium", HEALTH PHYSICS 94:170-179 (2008), "The Capstone Depleted 
Uranium Study of Aerosols From Impact With Armored Vehilces", HEALTH 
PHYSICS 96: 207-409 (2009) and "Depleted Uranium In The Gulf": 
http://www.gulflink.osd.mil/du_ii

The penetrating radiation (beta and gamma) are very weak for DU, 
although it can certainly be found with a Geiger counter. 
Gastrointestinal uptake is very small because DU and its oxides are 
relatively insoluble. Inhalation of finely divided oxide particles is 
the most likely route of exposure that can lead to biological 
effects. The possible biological effects are associated with really 
large inhalation exposures and are limited. The 33 military personnel 
under study at the Baltimore VA hospital were exposed to high 
concentration of fresh dust of oxide particles formed after burning 
of DU during the Gulf War. There have been no ill effects reported to 
date in these heavily exposed persons. For the details see "Depleted 
Uranium In The Gulf": http://www.gulflink.osd.mil/du_ii


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Prof. Otto G. Raabe, Ph.D., CHP
Center for Health & the Environment
University of California
One Shields Avenue
Davis, CA 95616
E-Mail: ograabe at ucdavis.edu
Phone: (530) 752-7754   FAX: (530) 758-6140
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