Basics about Uranium and Depleted Uranium (DU) and Its Impact on Human Health

 
Uranium
Depleted Uranium (DU) and DU Weapons
Radiation and Its Effects on the Human Body

 
Uranium

Uranium occurs in trace amounts in nature about 3 parts per million (ppm) or 3 micrograms of uranium per gram of dry soil. The equivalent of 1 teaspoon of natural uranium per 5 tonnes of earth.

An infinitesimal quantity of natural uranium is ingested in the body on a daily basis. It passes through the body with minimal effects because it is absorbed very poorly in the gastrointestinal tract (only 2% absorption). Approximately 10 nanograms (a nanogram is 1 one-billionth of a gram) is excreted daily in human urine.

Once mined, it is refined into concentrated packets of almost pure uranium. It is this highly concentrated “natural” uranium which is processed to produce enriched uranium. The enrichment process increases the isotope U235 concentration to create Enriched Uranium (EU) which is more easily fissionable for use in nuclear weapons and power plants. This process also creates Depleted Uranium (DU) as a byproduct.

All uranium whether “natural”, “depleted” or “enriched” is a chemical and radiological toxic substance emitting alpha, beta and gamma particles. All forms of uranium differ from each other by only a fraction of one percent. Both Natural and Depleted Uranium are over 99% composed of the isotope U238. The ratio of isotope U235 /U238 gives the unique signature that determines whether the uranium is enriched, natural or depleted.

 
Depleted Uranium (DU)

DU is a byproduct of the uranium enrichment process.

Presently there is no acceptable solution for safe disposal of radioactive waste. The laws and precautions governing its use have largely been discarded since large-scale military use made them impractical. Depleted uranium is also now being made available to be recycled as an element going into manufacturing of consumer or industrial products.

The enrichment process also creates small quantities of the man-made isotopes U236 and Plutonium (Pu239). These isotopes are included in the “depleted” uranium mass as it is too expensive to extract them.

For every grams of enriched uranium that is produced there are 7 grams of Depleted Uranium. This results in huge stockpiles of radioactive waste. It is estimated that there is over one million tons of DU stockpiled in the U.S. The quantities of plutonium in these stockpiles are a well-kept secret. It is routinely measured but not publicly reported.

The properties and composition of natural uranium and DU are listed in Table 1.

Table 1
Isotope Composition, Chemical Half-lives and Isotope Ratios in Natural and Depleted Uranium.

ISOTOPE NATURAL DEPLETED HALF-LIFE
U-238 99.2749% 99.7947% 4.49 billion years
U-235 0.7196% 0.2015% 710 million years
U-234 0.0055% 0.0008% 248,000 years

The radiological decay processes in DU are given in Table 2 together with those for natural uranium.

Table 2
Radioactivity (disintegrations per second) in 1 milligram of U-238 at Secular Equilibrium.

U-238 Th-234 Pa-234 U-234
12.4 alpha particles 12.4 beta particles 12.4 beta particles 0.017 alpha particles

In the course of one year, 1 milligram of uranium emits 390 million alpha particles, 780 million beta particles and associated gamma rays. This is over one billion high-energy, ionizing, radioactive particles and rays which can produce extensive biological damage.

The energy of a single alpha particle exceeds the amount required to damage important macromolecules such as DNA, RNA, enzymes and proteins. It does this by breaking molecular bonds, chemical reactions, which alter or destroy the shape, organization and function of these molecules.

DU WEAPONS

Modern warfare since the Gulf War in 1991 has employed weapons which make use of DU for its properties:

  1. It is cheap and available to arms manufacturers free of charge.
  2. It has a very high-density which makes it superior armour piercing material.
  3. It burns upon impact producing intense heat and easily cuts through steel.
  4. It acts as a self-sharpening penetrator.

The danger posed by DU in Weapons

  1. When DU weapons hit a target, a fine aerosol of uranium oxides is formed. The majority of particles (46 - 70%) are less than 10 microns.
  2. The aerosol-like particles (dust) are easily inhaled into the lungs.
  3. These fine particles can be spread by the wind and are readily re-suspended by modest breezes or vehicle and personnel movements. There is no existing study measuring the distance traveled by such particles. However, there is a documented instance were particles were physically captured 42 km from a test site. (Dietz 1999).
  4. This only proves migration beyond the specific site but does not preclude the possibility that particles can travel a great many times more kilometers. Fluid dynamic studies report that particles fewer than 5 microns can remain almost permanently suspended in the atmosphere.
  5. While some of the DU is soluble, the majority (in the form of other oxides) is insoluble and remains in the body for years. Once in the body, DU slowly spreads from the lungs, mainly into the lymph nodes and bone. Excretion from the body is very slow.
  6. The uncontrolled use and spread of uranium goes against the scientifically established conventions for handling radioactive substances and contravenes international laws. See the case made by Karen Parker at the UN that DU weaponry is illegal under existing human rights and humanitarian (armed conflict) law
  7. It is estimated that 300 - 800 metric tons of DU were deposited in the battlefield in Iraq and Kuwait in 1991. Dr. Doug Rokke (DU expert and former US army physicist) estimated that 120 to 480 million grams of DU would be aerosolized if 40% of the DU were burnt up.
  8. These airborne and respirable sized particles will be radioactive for billions of years into the future.

 
Radiation and Its Effects on the Human Body

In terms of pure physics, radiation is the process of transport of energy across space. Radioactivity is the process of decay of a physical element and involves the emitting of "bundles of energy", which may have a mass or not and may have an electric charge or not.

Relatively few natural elements undergo this process and they are called "radioactive" elements. These include uranium, plutonium and a few other less well-known natural and man-made isotopic elements. There are many particles produced in nature either coming from the vastness of outer space (cosmic rays) or produced in the world’s high energy research laboratories. Alpha and beta particles, gamma and X-rays are the particles emitted when radioactive decay takes place.

These were the first particles discovered by scientists as humanity entered its current phase of scientific knowledge. When particles reach the human body they interact with its physical components. This interaction results in the deposit of part or all of the energy carried by the “intruder” particle. The particles are so tiny that their effect is not immediately sensed by the body. It is the consequences of this interaction that is felt inside the body - by disruption of the bonds that keep molecules together, by creating ions that further interact with our system.

Each particle emitted has a certain amount of energy. The energy multiplied by the total number of particles gives the total amount of "uninvited" energy released in the body. To illustrate this point, consider the number of alpha particles emitted by a single spherical pellet of Uranium Oxide (UO2) 0.0001 inch or 2.5 microns in diameter (equivalent to 1/40th the width of a human hair) and the dose rate it produces.

Tiny as it is, the 2.5 micron Depleted Uranium Oxide pellet contains 210 billion atoms (2.1 x 10 to the power of 11) of U238. Each year, the pellet will emit an average 32.3 alpha particles. It also contains U234, 235, 236 which together yield an additional 5.3 alpha particles per year. Thus a single pellet of Depleted UO2 will produce a total of 37.6 alpha particles per year.

The 37.6 alpha particles will deliver a radiation dose of 17 rads/year. With an RBE (Relative Biological Effectiveness) factor of 10, the dose rate is 170 rem/year for the surrounding body tissue. In the US, the Code of Federal Regulations regarding energy specifies an annual limit of 0.17 rem/year and a specific limit of 0.5 rem/year for an individual in the general population.

A quick calculation shows one single pellet delivers 1,000 times the annual limit. This number is multiplied by the total number of pellets present in the body. For example, if a single or series of exposures resulted in the presence of 10 pellets then the annual limit is exceeded by 10,000.

Another factor to consider is "permanence". Objects or particles less than 5 micron in diameter are considered respirable, meaning that it is small enough to enter into the lungs and become permanently trapped. If the body does not manage to somehow release it then the radiation is internalized and the dosage is permanent during the individual's lifetime and even remains in their physical remains after death.

For a review of hundreds of years of scientific literature on the medical effects of internal contamination with uranium see Dr. Durakovic's review paper Medical Effects of Internal Contamination with Uranium CMJ 1999, Vol 40, No 1