Prepared for the
Hague Peace Conference, May 1999
By Dr. Rosalie Bertell, Ph.D., G.N.S.H.
Source of Exposure:
Uranium metal is autopyrophoric and can burn spontaneously at room temperature in the presence of air, oxygen and water. At temperatures of 200-400 degrees Centigrade, uranium powder may self-ignite in atmospheres of carbon dioxide and nitrogen. Oxidation of uranium under certain conditions may generate sufficient energy to cause an explosion (Gindler 1973). Friction caused by bullet or missile entry into a tank or armored car, for example, can cause the uranium to ignite, forming a concentrated ceramic aerosol capable of killing most personnel in the vehicle. Depleted uranium was used extensively in place of tungsten for ordnance by the US and UK in the Gulf War.
There is no dispute of the fact that at least 320 tons of depleted uranium (DU) was "lost" in the Gulf war, and that much of that was converted at high temperature into an aerosol, that is, minute insoluble particles of uranium oxide, UO2 or UO3 , in a mist or fog. It would have been impossible for ground troops to identify this exposure if or when it occurred in war, as this would require specialized detection equipment. However, veterans can identify situations in which they were likely to have been exposed to DU. Civilians working at military bases where live ammunition exercises are conducted may also have been exposed.
Uranium oxide and its aerosol form are insoluble in water. The aerosol resists gravity, and is able to travel tens of kilometres in air. Once on the ground, it can be resuspended when the sand is disturbed by motion or wind. Once breathed in, the very small particles of uranium oxide, those which are 2.5 microns [ one micron = one millionth of a meter ] or less in diameter, could reside in the lungs for years, slowly passing through the lung tissue into the blood. Uranium oxide dust has a biological half life in the lungs of about a year. According to British NRPB [ National Radiation Protection Board ] experiments with rats, the ceramic or aerosol form of uranium oxide takes "twice as long" or about a two year biological half life in the lungs, before passing into the blood stream. [Stradling et al 1988]
Because of coughing and other involuntary mechanisms by which the body keeps large particles out of the lungs, the larger particles are excreted through the gastro-intestinal tract in feces. The uranium compounds which enter the body either through the wall of the gastro-intestinal tract or the lungs, can be broken down in the body fluids, and tetravalent uranium is likely to oxidize to the hexavalent form, followed by the formation of uranyl ions. Uranium generally forms complexes with citrate, bicarbonates or protein in plasma, and it can be stored in bone, lymph, liver, kidney or other tissues. Eventually this uranium which is taken internally is excreted through urine. Presence of depleted uranium in urine seven or eight years after exposure is sufficient evidence to substantiate long term internal contamination and tissue storage of this radioactive substance.
Uranium is both a chemical toxic and radioactive hazard: Soluble uranium is regulated because of its chemical toxicity, measured by damage to the kidney and tubules. Uranium is a heavy metal, known to cause uranium nephritis. Insoluble uranium, such as was released in the Gulf War, is regulated by its radiological properties, and not its chemical properties. Because of its slow absorption through the lungs and long retention in body tissues, its primary damage will be due to its radiological damage to internal organs rather than chemical damage to the renal system. Obviously, both types of damage occur simultaneously, therefore it is a matter of judgment which severe damage, radiological or chemical, occurs at the lowest dose level. However, with the lengthening of the time during which the contaminant resides in the body and the low overall dose, the risk of cancer death becomes greater than the risk of significant damage to the renal system.
Uranium decays into other radioactive chemicals with statistical regularity. Therefore, in its natural and undisturbed state, it always occurs together with a variety of other radioactive chemicals, some of the best known being thorium, radium, polonium and lead.
Natural uranium in soil is about 1 to 3 parts per million, whereas in uranium ore it is about 1,000 times more concentrated, reaching about 0.05 to 0.2 percent of the total weight. Depleted uranium concentrate is almost 100 percent uranium. More than 99 percent of both natural and depleted uranium consists of the isotope U-238. One gram of pure U-238 has a specific activity of 12.4 kBq, which means there are 12,400 atomic transformations every second, each of which releases an energetic alpha particle. Uranium 238 has a half life of 4.51 E+9 (or 4.51 times 10 to the 9thpower, equivalent to 4,510,000,000 years).
Each atomic transformation produces another radioactive chemical: first, uranium 238 produces thorium 234, (which has a half life of 24.1 days), then the thorium 234 decays to protactinium 234 (which has a half life of 6.75 hours), and then protactinium decays to uranium 234 (which has a half life of 2.47E+5 or 247,000 years). The first two decay radioisotopes together with the U 238 count for almost all of the radioactivity in the depleted uranium. Even after an industrial process which separates out the uranium 238 has taken place, it will continue to produce these other radionuclides. Within 3 to 6 months they will all be present in equilibrium balance. Therefore one must consider the array of radionuclides, not just uranium 238, when trying to understand what happened when veterans inhaled depleted uranium in the Gulf War.
It should be noted that uranium 235, the more fissionable fraction which was partially removed in enrichment, makes up only 0.2 to 0.3 percent of the depleted uranium, whereas it was 0.7 percent of natural uranium. It is this deficit which enables one to use analytical methods to identify the uranium found in veteran's urine as depleted and not natural uranium. The U 235 was extracted for use in nuclear weapons and nuclear reactor fuel. Depleted uranium is considered nuclear waste, a by-product of uranium enrichment.
The difference in radioactivity between natural and depleted uranium is that given equal quantities, depleted uranium has about half the radioactivity of the natural mixture of uranium isotopes. However, because of the concentration of the uranium in the depleted uranium waste, depleted uranium is much more radioactive than uranium in its natural state.
Uranium and all of its decay products, with the exception of radon which is a gas, are heavy metals. Unlike some other heavy metals which are needed in trace quantities by the human body, there is no known benefit to having uranium in the body. It is always a contaminant. Ingesting and inhaling some uranium, usually from food, is inescapable however, in the normal Earth environment, and we humans basically take in, on average, 5 Bq per year of uranium 238 in equilibrium with its decay products. This gives an effective radiation dose equivalent to the whole body of 0.005 mSv. Using a quantitative measure, we normally ingest about 0.000436 g a year.[UNSCEAR 1988, 58-59] This is a mixture of soluble and insoluble compounds, absorbed mostly through the gut.
Regulatory limits recommended by the International Commission on Radiological Protection [ICRP] assume that the maximum permissible dose for members of the public will be the one which gives the individual 1 mSv dose per year. This is in addition to the natural exposure dose from uranium in the food web. Assuming that this dose comes entirely from an insoluble inhaled uranium oxide, and using the ICRP dose conversion factor for uranium 238 in equilibrium with its decay products, one can obtain a factor of 0.84 mSv per mg, or a limit of intake of 1.2 mg (0.0012 g) per year for the general public. This would give an added radiation dose of 1.0 mSv from uranium, and an increase of almost 2.75 times the natural uranium intake level. Nuclear workers would be allowed by the ICRP maximum permissible level, to reach an annual dose of 20 mSv, comparable to an intake of 24 mg of uranium, 55 times the normal yearly intake.
The maximum dose per year from anthropogenic sources can be converted to the maximum concentration permissible in air using the fact that the adult male breathes in about 23 cubic metres of air in a day [ICRP 1977]. The maximum permissible concentration in air for the general public would be: 0.14 microgram per cu metre, and for workers: 2.9 micrograms per cu m assuming the Gulf War situation of continuous occupancy rather than a 40 hour work week, and an 8 hour day. It is common in the US and Canada to refer to 2000 pounds as a "ton", whereas the British "ton" is 2240 pounds. Both are roughly 1000 kg. Just in order to understand the scale of the ceramic uranium released in Desert Storm, at least 300 million grams were "lost", and breathing in only 0.023 g would be equivalent to the maximum permissible inhalation dose for a nuclear worker to receive in a year under the 1990 recommendations of ICRP.
Medical Testing for
Depleted Uranium Contamination:
Potential testing includes: chemical analysis of uranium in urine, feces, blood and hair; tests of damage to kidneys, including analysis for protein, glucose and non-protein nitrogen in urine; radioactivity counting; or
more invasive tests such as surgical biopsy of lung or bone marrow.
Experience with Gulf War veterans indicates that a 24 hour urine collection analysis shows the most promise of detecting depleted uranium contamination seven or eight years after exposure. However, since this test only measures the amount of depleted uranium which has been circulating in the blood or kidneys within one or two weeks prior to the testing time, rather than testing the true body burden, it cannot be directly used to reconstruct the veteran's dose received during the Gulf War. However, this seems to be the best diagnostic tool at this time, eight years after the exposure.
Feces tests for uranium are used for rapid detection of intake in an emergency situation, and in order to be useful for dose reconstruction, must be undertaken within hours or days of the exposure. Blood and fecal analysis are not advised except immediately after a known large intake of uranium.
Whole body counting for uranium, using the sodium iodide or hyper pure germanium detectors, is designed to detect the isotope uranium 235, the isotope of uranium partially removed from depleted uranium. For lung counting, again it is the uranium 235 which is detected, and the minimum detection limit is about 7.4 Bq or 200 pCi. Since normally humans take in only 5 Bq per year, this is not a very sensitive measure. Seven or eight years after the Gulf War exposure, this method of detection is most likely useless for veterans.
Routine blood counts shortly after exposure, or during a chelating process for decontamination of the body are useful. This is not a search for uranium in blood, but rather a complete blood count with differential. This is done to discover potentially abnormal blood counts, since the stem cells which produce the circulating lymphocytes and erythrocytes are in the bone marrow, near to where uranium is normally stored in the body. The monocyte stem cells in bone marrow are known to be among the most radiosensitive cells. Their depletion can lead to both iron deficient anemia, since they recycle heme from discarded red blood cells, and to depressed cellular immune system, since monocytes activate the lymphocyte immune system after they detect foreign bodies.
Testing of lymph nodes or bone on autopsy would be helpful. However, invasive biopsies on live patients carry no benefit for the patient and are usually not recommended because of ethical considerations about experimentation on humans. If a veteran is recommended for bronchoscopy for medical reasons, it would be advisable to also take tissue samples for analysis for depleted uranium.
When chelation processes have been initiated the rate of excretion of uranium in urine will be increased and there is a risk of damage to kidney tubules. Therefore careful urine analysis for protein, glucose and non-protein nitrogen in important. Some researchers have also reported specifically finding B-2-microglobulinuria and aminoaciduria in urine due to uranium damage.
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