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| IDUST TUTORIAL CENTER | Updated 3/16/03 |
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One of the primary misconceptions relating to biological effects of radiation exposure is the assumption that it behaves in the same way as chemical toxins. In reality, they are two very different animals. Chemical toxins and drugs are biologically active substances; that is, they react chemically with specific molecules normally present in the body, altering their function. Thus they are usually very specific in the organs they affect and the symptoms they produce. Arsenic, for example, promotes cancers in the skin, lung, liver and bladder. Symptoms of arsenic poisoning include headache, confusion, sleepiness, vomiting and diarrhea. Nitroglycerine, used for relief of angina, works specifically by dilating the heart's blood vessels so more oxygen can get to the heart.
In contrast, radiation exposure is PHYSICAL in nature. Radiation from radioactive substances consists of alpha and beta particles, neutrons and gamma radiation. Alpha and beta radiation consist of tiny particles that are expelled from an atom's nucleus at more than 10% the speed of light, giving them tremendous momentum. They are, in effect, sub-atomic bullets. They are also electrically charged particles, so-called "ionizing radiation." Because they are charged, they can damage molecules, such as DNA, enzymes, hormones, etc. without actually smashing into them. Simply by passing near enough to a molecule, the ionic charge can rip bonding electrons out of that molecule, causing it to break apart. Since this is the case, a single particle of ionizing radiation leaves a whole trail of damaged molecules in its wake before it finally comes to rest.
Gamma radiation is high energy electromagnetic radiation, much like the more familiar X-rays. It is not charged, and, since it consists of photons of energy, when a gamma ray photon strikes a molecule, its entire packet of energy is temporarily absorbed by the molecule. The molecule subsequently releases this energy by expelling one of its electrons (causing the molecule to break apart into free radicals) and releasing a gamma ray photon that has somewhat less energy than the original photon. The electron released is identical to a charged beta particle, so the gamma ray has, in effect, been responsible for creating ionizing radiation in its path. The new gamma ray photon that is released is free to bombard another molecule. This cycle can continue until the resulting gamma ray no longer has enough energy to cause the bombarded molecule to break apart. Thus a typical gamma ray emission from depleted uranium can result in formation of several beta particles.
Uranium is a substance that is both a chemical and radiation hazard. As a heavy metal, it exhibits chemical toxicity directed at the kidneys, bone marrow (thus affecting both blood production and the immune system), liver and endocrine system, particularly the gonads and thyroid. These are the locations within the body where uranium is most likely to become chemically incorporated as part of existing body tissue. Once in place, the uranium is likely to reside there for years. Over time, it can extract a great toll on the local tissues, both chemically and radiologically. As the uranium decays, it provides a continuous source of high-energy alpha and beta particles and gamma rays that unremittingly bombard molecules and cells in the surrounding tissue. The effects of radiation exposure are known to be cumulative over time.
Natural uranium is a mixture of three isotopes: 99.3% uranium-238, 0.7% uranium-235, and a trace of uranium-234. Depleted uranium (DU) differs from natural uranium in that more than half of the more radioactive U-235 has been removed. It is 99.8% U-238, with only 0.2% of U-235 remaining. It is still radioactive, though only about 60% as radioactive as natural uranium. U-238 decays by emitting an alpha particle.
It is important to remember that when a radioactive substance decays, the decaying atom gets transformed into a different substance. If that substance is itself radioactive, then additional radioactive particles will be produced. In the case of U-238, the decay product is thorium-234 (Th-234), which is also radioactive and which has a very short half-life (24.1 days) compared to the half-life of U-238 (4.51 billion years). Thorium-234 decays by emitting a beta particle and a gamma ray, producing protactinium-234 (Pa-234). Protactinium-234 is radioactive (half life 6.75 hours) and it also decays by beta particle and gamma ray emission, producing uranium-234, which has a half life of 247,000 years. In fact, there are 14 steps between U-238 and lead-206 which is a stable, non-radioactive substance. These first three steps can be depicted with the following equation:
U-238 -(alpha)--> Th-234 -(beta & gamma)--> Pa-234 -(beta & gamma)--> U-234
For all practical purposes, the decay pathway then gets hung up at U-234 due to its long half-life. Thus exposure to a small particle of depleted uranium in the body results in the nearby cells being bombarded by five radiation products for every single atom of U-238 that disintegrates-one alpha particle, two beta particles and two gamma rays.
What this means is that the specific organ or body function to be affected by radiation exposure depends on where the radiating isotope is located, how much of the isotope is present, how long the exposure lasts, and how effective the individual's genetic tolerance toward cancer cell formation is. The end results fall in the realm of statistical probabilities. Four people could have identical exposure to the same radioactive substance, with one getting leukemia, another suffering from lymphoma, the third getting thyroid cancer and the fourth remaining healthy. To say that DU is harmless because it is less radioactive than other radioactive substances with shorter half-lives is to ignore the fact that damage due to radiation exposure is driven by probabilities.
For example, uranium miners, exposed to both uranium ore (which contains only a small percentage of uranium) and to radon gas (one of the radioactive products in the uranium decay chain), have a higher probability of getting lung cancer than the general population due to their exposure to the radon. However, radon, a gas, is inhaled, then exhaled. Exposure only occurs when the miners are in the mine working, 8 hours a day, 5 days per week. Furthermore, the lungs are the only internal tissues exposed, and these are not overly sensitive (see below) to radiation damage. It makes no sense to compare radiation exposure to radon with radiation exposure to a heavy metal that takes up lodging in a sensitive area, such as bone marrow, and irradiates surrounding tissues 24 hours a day, 7 days per week. Yet these differences are frequently glossed over, even in scientific studies.
To better understand the effects of a radioactive particle embedded within body tissue, imagine a game of reverse Russian roulette. Someone stands in the middle of a room, blindfolded, and you are to stand at some fixed location around the edge of the room. The person in the center is given a gun. He must spin around and fire the gun. You are (probably) pretty safe. But even with one bullet, you COULD get injured or killed. Give him more bullets and let him shoot in any direction he desires, and your chances of getting hit increase.
Now consider depleted uranium. 1 mg of DU (a barely visible dust particle) fires not 1 but 850 alpha bullets every MINUTE, or over 8 million bullets in a single week. Not only that, if the DU particle has been sufficiently "aged" for, say five months after leaving the uranium purification plant, sufficient thorium and protactinium will have built up to also be firing their beta bullets and gamma rays, bringing the bullet count up to 40 million per week. (However, this increases the risk of biological damage by only 40%. This is because it is currently believed that the larger, more highly charged alpha particles are 10 times as effective at damage as beta particles.) And if the DU is contaminated by other more radioactive isotopes, such as plutonium or americium (as admitted by the Department of Energy), the odds of radioactive particles causing critical biological damage become significantly greater.
With external exposure to DU, the alpha radiation is effectively blocked by the skin, and most alpha bullets would miss the body anyway. Beta particles from the thorium and protactinium decay products, do penetrate the skin as far as 2 cm. Gamma rays are capable of passing completely through the body. These all have some possibility of causing damage, but again, most of the radiation misses the body entirely unless the radioactive object is closed in one's fist or dangling from a chain around one's neck as a souvenir.
Inside the body, however, EVERY bullet, alpha AND beta, strikes soft tissue and EVERY gamma ray passes through living tissue. Most damage is to molecules that don't matter, like molecules in a cell wall. But remember that alpha and beta particles are sized on the order of an atomic nucleus (alpha) or smaller (beta) and that at molecular scales, most matter is empty space. So particles have no problem getting through so-called cell "walls" and damaging substances within the cells. Some are BOUND to strike or pass close enough to DNA or RNA molecules to cause molecular damage to these blueprints of life. And no matter what molecules are damaged, the molecule fragments are free radicals, which themselves can be quite damaging to their surroundings. In fact, current research has been focusing on free radicals as being one of the primary culprits in initiating cancers.
Fortunately, nature has evolved ways for DNA to repair itself - most of the time. Here, timing also enters into the picture. If radiation damage takes place just as a cell or molecule is about to carry out a function, there might not be time for repair to take place and the damage then persists, either causing a cell to die or propagating that damage on to the next generation of cells. This factor explains why cells that divide most rapidly, such as sperm cells and those in bone marrow, are most sensitive to radiation damage and why children, are much more sensitive to radiation exposure.
In the last four years it has been discovered that sometimes damaged DNA, which SEEMS to have repaired itself, propagates normally for a few generations before suddenly showing signs of abnormality. This effect, known as radiation induced genomic instability, is a disturbing discovery that is not understood at the present time, but is quite relevant to this discussion.
Invariably, the topic of natural background radiation comes up in discussions about the dangers of radiation exposure. We are exposed to natural radiation (as from radium, radon, and yes, even natural uranium), all the time and we don't all die of leukemia or lymphomas, thanks to the body's wonderful mechanisms for self repair. However, leukemia, lymphomas, birth abnormalities, etc. are not new to the twentieth century, and it is reasonable to assume that some percentage of these cases are due to exposure to natural radiation. Unfortunately, we have no way to accurately determine what the actual toll might be.
Total background radiation exposure can be estimated. For example, 360 millirem per year is cited by the Canadian health service as the average annual background radiation dose of the general public in Canada. The difficulty with figures such as this is that they combine radiation from all sources, including cosmic rays, X-rays (medical), television sets and consumer products, all of which act on the body in ways quite different from ionizing radiation, and they include all ionizing radiation sources, such as radon gas and radium (instrument dials) and natural uranium together with no regard to the different pathways these substances take within the human body.
In spite of this, however, proponents of the use of depleted uranium (DU), such as the United States Army, propose that additional radiation in the environment resulting from use of DU munitions is nothing to worry about because it comprises only a small percentage of the background radiation to which we are all exposed. They also ignore the fact that a certain percentage of the population has been dying since the beginning of time due to radiation exposure from natural sources. Any increase in environmental radiation load will unquestionably result in an increase in that toll. So how can any action that increases our overall exposure to radiation be simply "nothing to worry about?"
So where does DU end up? Aerosol DU, formed when the DU projectiles burn their way through heavy armor, quickly turns into oxides of micrometer size which are readily inhaled in the lungs and readily dispersed over large areas, contrary to the army's assertions that these particles are so "heavy" that they aren't dispersed beyond 25 meters of impact. Monitors in New York state detected DU oxide particles 25 miles downwind of a DU munitions fabrication site.
Once in the lungs, these relatively insoluble particles can remain there for many years, dissolving into the blood stream very slowly, as evidenced by the fact that DU is STILL found in the urine of veterans 9 years after the Gulf War. Once in the blood, much is transferred to the kidneys, where they cause chemical damage by combining with certain essential proteins. But uranium also reacts somewhat like calcium and becomes deposited in the bones. There, located next to bone marrow (a site of rapid cell division), its ionizing radiation can severely effect both white blood cell formation (and thus the immune system) and be responsible for leukemia.
Finally, the question of how much DU is present in the body also enters the picture. If 1 mg of DU and its daughter isotopes can produce 24 million bullets per week, then 10 mg, for all practical purposes, produce 240 million bullets. Obviously, the greater the concentration, the greater the exposure, and the greater the risk of radiation damage. By dumping DU into the environment in relatively small areas (military targets, such as a tank), we are increasing the uranium concentration in these locations significantly above the natural background amounts, in spite of the army's assertions to the contrary. This will lead to greater radiation exposure anywhere in the vicinity of an exploded DU shell or bomb and a greater incidence of radiation damage. There IS NO THRESHHOLD below which the probability of radiation damage is zero.
We have turned the battlefields of recent wars into radioactive wastelands. Areas within Kuwait, Iraq, Bosnia, Kosovo and Afghanistan have been shelled with DU munitions. We have also left a radioactive legacy from DU in the United States. Consider the fact that the Starmet DU fabrication plant outside of Concord, MA is now a superfund site with the local population showing unusually high cancer rates, the fact that Jonesborough, TN and Colonie, NY have DU fabrication plant workers suffering from exposure to DU and whatever other toxic reactor waste (e.g. plutonium and americium) are contaminating the DU, (general fatigue, pain in bones and joints, elevated leukemia and lymphoma rates), the fact that the people of Socorro, NM, 2 miles outside a DU testing range, are also showing elevated incidence of cancer hydrocephalus, and the fact that workers from all of these sites are experiencing similar maladies to many Gulf War veterans, and to British and Italian soldiers returning from Bosnia and Kosovo, not to mention hundreds of Iraqi citizens. And do we dare mention the alarming number of unusual birth defects that have appeared in the offspring of some of our Gulf War veterans and Iraqi civilians since the 1991 war? How many eye-witness reports from reliable citizens returning from visits to Iraqi hospitals will it take to debunk the government's assertion that reports of thousands of suffering and dying children are nothing but "Iraqi propaganda"?
Since no specific epidemiological data on these population groups seems to be available, the evidence may be considered by some as "circumstantial" and "inconclusive". But when there is such a preponderance of anecdotal evidence pointing to depleted uranium (and/or contaminating radioactive materials such as plutonium and americium) as the source of these problems, one can only be amazed that such studies have not been authorized.
It is long past time that a thorough study of the effects of chronic exposure to inhaled depleted uranium (contaminated with the same radioactive waste found in military munitions DU) to biological organisms be undertaken. Complete and unadulterated statistics on Gulf War veterans must be made available by the military and Veterans Administration so that complete epidemiological studies can be made by an unbiased and independent group of scientists. Access to Iraqi doctors and citizens must also be made available to permit a similar study of the military and civilian victims of DU exposure there. Similar studies at other sites throughout the world, including within the United States, where DU munitions have been used, fabricated, and/or tested are required.
In the meantime, it is morally, ethically and legally necessary to place a total ban on further use, production, and distribution of these radioactive weapons. To do anything less can only be considered a war crime of major dimensions.