This was posted at [log in to unmask] Dr. Geoff Helliwell MB ChB CIH FFOM MIOSH Medical Director WellWork Ltd. UK -----Original Message----- From: Otto G. Raabe [mailto:[log in to unmask]] Sent: 10 January 2001 17:12 To: [log in to unmask] Subject: Depleted uranium projectiles January 10, 2001 Davis, CA There are several reports in the news about the implied toxicity of depleted uranium used for projectiles and shielding material in modern warfare. It has been suggested to be a potent carcinogen and leukemia inducer. 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 nephrotoxicity associated with deposition in the kidney tubules and glomeruli damage at high doses. The radiation doses from depleted uranium (specific activity only 15 Bq/mg)(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), "Depleted Uranium In The Gulf": http://www.gulflink.osd.mil/du_ii Otto ********************************************** Prof. Otto G. Raabe, Ph.D., CHP Institute of Toxicology & Environmental Health (Street Address: Bldg. 3792, Old Davis Road) University of California, Davis, CA 95616 E-Mail: [log in to unmask] Phone: (530) 752-7754 FAX: (530) 758-6140 ***********************************************