July 19, 1996 (last updated Feb. 21, 1999)
(reproduced here with permission)
This background information allows us to propose a plausible contamination model at a battle site. It consists of three steps: (1) a source of hundreds of kilograms of DU aerosols generated suddenly against concentrated Iraqi armor; (2) widespread rapid dispersal of DU aerosol particles by wind action; (3) inhalation and ingestion of DU particles by unprotected U.S. service personnel on the battlefield.
The U.S. military and its representatives claim that DU munitions are safe, but they have not publicly addressed health and safety issues that apply after DU munitions have been fired. Apparently the official view is that in a combat situation it is acceptable for unprotected personnel to be exposed to the combustion products of fired DU munitions and assume any health risks involved.
We mention that 22 U.S. service personnel have been reported to have suffered imbedded fragments of DU in their bodies from "friendly fire". More than 5 years after the Gulf War, few of these fragments have been removed and the long-term health situation for these veterans has not yet been determined. We note the astonishingly high incidence of serious birth defects in families of Gulf War veterans in the State of Mississippi.
Finally, we mention how commonly used DU flight control counterweights in aircraft and DU munitions can burn in intense fires and produce dangerous concentrations of airborne DU aerosol particles that can be inhaled and ingested.
The main purpose of this paper is to develop a physical model of how easily many Gulf War veterans could have acquired dangerous quantities of DU in their bodies. To accomplish this we review the pyrophoric nature of uranium metal and its radioactivity. We show how readily uranium aerosol dust can be transported great distances by wind action in the atmosphere, pathways that DU aerosol particles can take into the body and become absorbed, and the tonnage of DU munitions fired during the Gulf War. This information is used to construct a contamination model that explains how large numbers of soldiers very likely became contaminated on the battlefields in Kuwait and Iraq. We show how the U.S. military views the safety of DU munitions, and we close by mentioning some of the known exposures of U.S. soldiers to DU and noting the high percentage of severe birth defects in children conceived and born in many families of Gulf War veterans.
Uranium can burn in other ways to generate aerosol particles of uranium oxide. Because elemental uranium is pyrophoric, when DU metal is heated in air at a temperature of 500 deg. C it can oxidize rapidly and sustain slow combustion (Ref. 5). For example, the effects of fires at storage sites for DU munitions have been studied (Ref. 8). The burning of DU metal flight control counterweights at airplane crash sites and the possibility of exposing large numbers of people to kidney poisoning (nephrotoxicity) by uranium oxide particles has been studied by Parker (Ref. 9). In 1992 an El Al Boeing-747 crashed into an apartment building in Amsterdam, Holland and burned intensely. Approximately 273 kg of DU in the tail of the 747 is unaccounted for; it burned and contaminated the surrounding area (Ref. 10).
Table I. Isotopic composition of natural and depleted uranium
in atom percent.
U-234 U-235 U-236 U-238
Natural Uranium 0.0055 0.7196 0.0000 99.2749
Depleted Uranium 0.0008 0.2015 0.0030 99.7947
A trace of U-236 from reprocessed nuclear fuel may be present in some of the DU stockpile. The alpha activity in DU is about 43% less than it is in natural uranium because there is less U-234 and U-235, but DU always occurs in highly concentrated form and this more than makes up for its lower alpha activity. In contrast, natural uranium occurs in concentrations of 1-3 parts per million by weight in soils, where it is locked up in non-metallic form in minerals and is relatively inert to chemical action there.
Only the first three isotopes in the uranium decay series or chain headed by U-238 are important in determining the radioactivity of DU (Ref. 12). Uranium-238 decays into thorium-234 (Th-234), which decays into protactinium-234 (Pa-234), which decays into U-234, etc. down the decay chain. The 246,000 year half life of U-234 is too long for it to decay much during our lifetimes and produce significant numbers of decay progeny.
The U-238 decay chain is broken during the chemical reduction of uranium hexafluoride into DU metal and is broken again during the melting and processing of the metal into a penetrator. To determine the maximum time it takes to regain equilibrium in the partial decay chain, we assume a solid sample of uranium that initially contains only the U-238 isotope, i.e. no decay progeny. Using Bateman's equations, (Ref. 13), we calculate the growth of Th-234 and Pa-234 activities as a function of elapsed time in weeks. The results are given in Table II.
Table II. Radioactivity (disintegrations/second) in 1 gram of
U-238 with no decay progeny initially present.
Half lives used:
U-238 = 4.47e9 years
Th-234 = 24.10 days
Pa-234 = 1.17 minutes, 6.69 hours (two decay states)
U-234 = 2.46e5 years (Ref. 14).
Scientific notation is used, i.e. 2.46e5 = 246000.
Weeks U-238 ---> Th-234 ---> Pa-234 ---> U-234
0 12,430 0 0 0.000
1 12,430 2,270 2,150 0.000
5 12,430 7,890 7,840 0.001
10 12,430 10,770 10,750 0.004
15 12,430 11,830 11,820 0.007
20 12,430 12,210 12,210 0.010
25 12,430 12,350 12,350 0.013
30 12,430 12,400 12,400 0.017
After 25 weeks, Th-234 and Pa-234 have reached 99.4% of the decay rate of U-238 and for practical purposes have reached secular equilibrium with U-238, their parent isotope. Secular equilibrium means that the decay progeny of U-238 are being replaced at the same rate they are decaying; after 25 weeks all three isotopes are decaying at approximately the same rate. This is a maximum time; in reality, equilibrium will be reached much faster, since these two isotopes can never be separated totally from U-238. The isotope U-238 emits alpha particles and also emits some gamma rays. Its decay progeny Th-234 and Pa-234 each emit beta particles and gamma rays. An alpha particle is a fast helium atom with its two electrons removed, a beta particle is a high-speed electron and a gamma ray is like an X-ray.
From this analysis we conclude that in a solid sample of DU, six months at most after manufacture of a DU penetrator, or DU armor for a tank, or DU particles in a person's body, substantial additional radiation in the form of beta particles and gamma rays always will be present. In fact, most of the penetrating gamma radiation and all of the penetrating beta radiation from DU comes, not from uranium, but from the decay progeny of U-238 (Ref. 15). In a year, only one-thousandth of a gram (1 milligram or mg) of DU generates more than a billion alpha particles, beta particles and gamma rays. The U.S. Army has investigated the generation of DU aerosols in armored vehicles hit by DU cannon rounds. Their investigators report "...that personnel inside DU struck vehicles could receive a dose in the `tens of milligrams' range due to inhalation" (Ref. 16). This exposure results in an acute dose of uranium.
Gamma rays become absorbed in body tissue as follows. If their energy exceeds 40 keV, part of the gamma-ray energy is transferred to an atomic electron, setting it in high-speed motion (1 keV = 1000 electron volts energy). The remaining energy is carried off by a new gamma ray. This process, called the Compton effect, repeats until the gamma ray has an energy below about 40 keV where the photoelectric effect dominates and the remaining energy can be transferred to a photoelectron. For example, using Gofman's method, (Ref. 17) one can calculate that an 850 keV gamma ray absorbed in body tissue will produce a packet of high-speed Compton electrons and a fast photoelectron that on average can traverse 137 body cells. By contrast, according to Gofman, X-rays commonly used in medical diagnosis have a peak energy of 90 keV and an average energy of 30 keV (Ref. 17) A 30 keV X-ray in body tissue can be converted into a photoelectron of this energy, which on average can traverse only 1.7 cells. Ionization along the tracks of high-speed electrons in tissue can cause damage to genetic material in the nuclei of cells. Thus, a high energy gamma ray from Pa-234 is much more penetrating than a typical medical X-ray and can damage far more living cells. The many 2.29 MeV beta particles emitted by Pa-234 are extremely penetrating in body tissue (1 MeV = 1 million electron volts energy). Referring to the experimental data given by Gofman (Ref. 17), each one of these beta particles can traverse more than 500 body cells.
Alpha, beta and gamma radiations produce the same biological effects on cells and organs, and much of their radiation damage to body tissue can accumulate over the time of exposure (Ref. 18). Therefore, it seems reasonable that not only the continuous radiation of body tissue by alpha particles from U-238, but the energetic beta particles and gamma rays from its decay progeny Th-234 and Pa-234 must also be considered when assessing possible cancer risk and genetic damage.
In 1979 the author worked at the Knolls Atomic Power Laboratory (KAPL) in Schenectady, New York. While trouble shooting a radiological problem, he and his colleagues in the mass spectrometer component accidentally discovered DU aerosols collected in environmental air filters exposed at the Knolls site (Ref. 21). The origin of the DU contamination proved to be the National Lead Industries plant in Colonie, 10 miles (16 km) east of the Knolls site, on the western boundary of the city of Albany, NY. A local newspaper reported that NL was fabricating DU penetrators for 30-mm cannon rounds and airplane counterweights made of DU metal (Ref. 22). A total of 16 air filters at three different locations covering 25 weeks of exposure from May through October of 1979 were analyzed; all contained trace amounts of DU. Three of these air filters were exposed for four weeks each at a site 26 miles (42 km) northwest of the NL plant. This is by no means the maximum fallout distance for DU aerosol particles.
Totally unrelated to the discovery of DU in KAPL air filters, in February 1980, a court order by NY State forced NL to cease production, because they exceeded a NY State radioactivity limit of 150 microcuries for airborne emissions in a given month (Ref. 22). The plant closed in 1983 and is now being decontaminated and dismantled. The 150 microcuries corresponds to 387 g of DU metal. For comparison, one GAU-8/A penetrator in an aircraft 30-mm cannon round contains 272 g of DU metal (Ref. 5).
Using a special fission track analysis technique, 26 uranium-bearing particles were extracted from several air filters exposed at KAPL and were analyzed separately for their uranium isotopic content (Ref. 11) Four particles contained pure DU. They were approximately 4-6 micrometers in size, three were irregularly shaped and the fourth was a 3.8 micrometer diameter sphere. Probably it solidified from a molten state as uranium dioxide. The other 22 particles were enriched uranium associated with the radiological trouble-shooting problem. This widespread trace contamination of DU in the atmosphere was less than one percent of allowable limits. Its presence in the air filters did not concern us nearly as much as the sizes of the DU particles that were born ten miles by the wind from Albany to KAPL. The four DU particles were near the upper end of the respirable size range, which is about 5 micrometers. Respirable means that particles will pass through the upper respiratory airway to the lung and become deposited in various interior regions of the lung, where many will remain for many years. A 5 micrometer uranium dioxide particle can cause a high, localized yearly radiation dose from energetic alpha particles to lung tissue; it is a radioactive hot spot in the lung (Ref. 23).
The density of uranium metal is 19 grams per cubic centimeter; for uranium dioxide it is 11 grams per cubic centimeter, equal to the density of lead. How can a uranium dioxide particle with this density, or a uranium metal particle with a density 1.7 times that of lead remain airborne long enough to be transported by wind 26 miles (42 km)? It might seem a daunting challenge to answer this question, but a complicated physical theory is unnecessary.
Just as a parachute jumper in a free fall through the lower atmosphere quickly reaches a constant terminal velocity of approximately 120 mph, so too a micrometer-size uranium particle falling under gravitational attraction through still air will reach a constant terminal velocity that is determined by its size, density, geometrical shape and air viscosity.
Stokes' law provides an accurate and convincing scientific explanation of how micrometer-size DU particles can remain airborne for many hours. This physical law is well known to scientists and engineers who study fluid dynamics. It was published in 1846 and 1851 by Sir George Stokes, and is described in introductory textbooks on fluid flow (Ref. 24). It is given by the expression
2 G R^2 (S-A) V = ------------- 9 C where R^2 means R squared G = 980.4 centimeters per second squared is the acceleration of gravity, R = the radius of the sphere in centimeters, S = the density of the sphere in grams per cubic centimeter, A = 1.213e-3 grams per cubic centimeter is the density of air at one atmosphere and 18 deg. C, C = 1.827e-4 poise is the viscosity of air at one atmosphere and 18 deg. C.
The terminal velocity V is in centimeters per second if G, R, S, A and C are in the units shown. Stokes' law allows one to calculate the terminal velocity of a microsphere of uranium metal or uranium oxide of known radius and density falling through still air.
Stokes' law is valid for fluid flow described by a Reynolds number of 0.1 or less (Ref. 24). Experiments confirm this upper limit (Ref. 25) The dimensionless Reynolds number Re for a sphere is given by
2 R A V Re = ------- C
where the terms are defined above. A 10 micrometer diameter uranium metal sphere falls at 5.7 cm/sec in still air and Re = 0.038, which is much less than 0.1. Therefore, Stokes' law is accurate for all respirable spherical uranium metal or oxide particles 10 micrometers or less in diameter falling through air. Table III lists the fall rates for a range of particle sizes.
Table III. Terminal (constant) velocities for
uranium dioxide spherical particles in still air.
Diameters are in micrometers.
dia. cm/sec. ft./hr.
5.0 0.82 97
4.0 0.52 62
3.0 0.30 35
2.0 0.13 15
1.0 0.033 4
0.5 0.0082 1
Irregularly-shaped microparticles will fall more slowly than a sphere of the same density and weight. Depleted uranium particles one micrometer or smaller are virtually floating in air and can remain airborne for a very long time. The 3.8 micrometer dia. spherical uranium dioxide particle analyzed at KAPL had a fall rate of 56 ft./hr. It had to reach a height of only 200 ft. in the warm exhaust plume from the National Lead plant for a gentle breeze averaging 3 mph to carry it 10 miles (16 km) to KAPL.
Fallout range can be increased greatly by two more natural phenomena. First, frictional forces in the air or emission of an alpha particle from a uranium atom will electrostatically charge a DU particle. For example, it is well known that a high velocity ion striking a metal oxide surface will dislodge a pulse of secondary electrons from the surface (Ref. 26). An alpha particle is a high velocity helium ion, and it will generate a large number of secondary electrons below the surface of an uranium oxide particle as it passes through the surface. Many of the momentarily-free electrons just below the surface will escape from an airborne uranium oxide particle, leaving it in a positively-charged state. Like an electrostatic precipitator collecting dust in a room, an electrically-charged uranium dioxide particle and an oppositely-charged dust particle will attract each other and join together. The average density of the two particles together will be substantially less than 11 grams per cubic centimeter and the fallout range will be greatly increased. Fallout particles of DU also can become attached to sand or dust particles on the ground and then become resuspended in the air by wind or vehicle action and transported to new locations (Ref. 27). Desert sand in the Persian Gulf region is extremely fine (Ref. 28). Second, random motions of the atmosphere of a few cm/sec are of the same order of magnitude as the terminal velocities of micrometer particles of DU oxide or metal falling through air.
Exposure to gamma rays emitted from DU is another pathway into the body. Crews are exposed to the equivalent of one chest X-ray for every 20-30 hours they spend in an Abrams tank armed with DU ammunition (Ref. 30). The U.S. Army measured a gamma dose rate of 250 millirems per hour at the surface of a penetrator (Ref. 31). This dose rate is consistent with the 233 millirads per hour dose rate for an unspecified mass of DU listed on a U.S. Department of Labor Material Safety Data Sheet issued to Nuclear Metals, Inc. (Ref. 32). For gamma rays, the rad and rem dose units are equal. At body contact, the 250 millirems per hour is equivalent to a dose rate of up to approximately 50 chest X-rays per hour. Whole penetrators or large fragments of penetrators fired from tank cannon and left on a battlefield have this amount of surface radioactivity.
The U.S. Army and the Veterans Administration have shown an unwillingness to investigate health issues associated with the toxicity and radioactivity of inhaled and ingested DU aerosol particles that have become absorbed in the body. Both have refused to test large numbers of veterans for the presence of DU in their bodies; so far only a handful have been tested. According to Laura Flanders, as of January, 1995, at least 45,000 soldiers deployed to the Persian Gulf during the war are suffering from symptoms connected with their service (Ref. 37).
Workers in DU industrial processing plants and people living in communities surrounding these plants also have been contaminated by fallout of DU particles (Ref. 22). How rapidly contamination takes place depends on the magnitude of the airborne concentration and particle size of the uranium dust. The smaller the particle, the easier it can enter the body. In written testimony prepared for a 1982 New York State hearing on NL Industries, Dr. Carl Johnson, a principal investigator of the National Cancer Institute Project, stated that some of the workers at the NL plant had concentrations of uranium in their urine as high as 30 picocuries/liter (77 micrograms of uranium/liter). He said this concentration level indicated a very heavy body burden of uranium (Ref. 38).
The three references cited above clearly indicate that the U.S. military's concern for the safety of DU munitions ends at the muzzle of the cannon. Whatever happens becomes someone else's problem after a round is fired and its DU metal penetrator strikes armor, partially burns up and injects a huge number of chemically poisonous, radioactive DU aerosol particles into the atmosphere.
On an NBC Dateline program, (Ref. 6) Sgt. Daryll Clark describes how he and twelve others were in an advanced position in the desert when someone radioed them that 20 Iraqi tanks were approaching his forward radar unit. He called for air support, and shortly a flight of A-10 Warthogs arrived and destroyed all of the tanks with DU-tipped 30-mm cannon rounds. Clark describes how he and the men with him were coughing and choking on smoke from the burning tanks, but mixed with it was DU aerosol dust, which he and the others breathed. He has had chronic respiratory problems since the war and his daughter Kennedy was born in September 1992 with purple welts called hemangioma covering not only her face and body, but some internal organs as well. Kennedy has serious breathing problems and was born without a thyroid. Clark stated that a geneticist told him that he could have ingested some radiation and that it could affect sperm cells. Almost three years after his exposure to DU, Clark's urine tested positive for uranium.
Army nurse 1st. Sgt. Carol Picou also is featured in the NBC documentary. She and seven other women in her medical team were in a forward position, ahead of the main U.S. forces and surrounded by burning Iraqi tanks and vehicles when they stopped and became exposed to DU from the burning destroyed Iraqi armor. Doctor Thomas Callender of Lafayette, Louisiana has examined Picou and said on the program that her outcome bears a striking similarity to other individuals who had exposures to ingested radioactive elements. Picou has been given a medical discharge.
The 7 medical personnel with Picou and the 12 soldiers with Clark probably became contaminated with DU. These 21 soldiers are not included in the official list of those recognized by the U.S. government as having been exposed to DU. Given the large tonnage of uranium penetrators in cannon rounds that were fired on the battlefields in Iraq and Kuwait, it is likely that many thousands of other soldiers also became contaminated with DU. The U.S. Army and the Veterans Administration balk at giving urinalysis tests and "in vivo" tests (whole-body counting of gamma rays) to measure the amount of DU in the lungs and other body organs of Gulf War veterans.
An astonishingly high rate of birth defects in the families of Gulf War veterans is especially troubling. For example, Laura Flanders reports that the Veterans Administration conducted a state-wide survey of 251 Gulf War veterans families in Mississippi (Ref. 46). Of their children conceived and born since the war, 67% have illnesses rated severe or have missing eyes, missing ears, blood infections, respiratory problems and fused fingers. Flanders goes on to say that the birth defects are consistent with the effects of radiation from DU and infection from sand fly bites. Others blame experimental vaccines, chemical warfare pills, the insect repellent DEET and smoke from oil well fires for causing birth defects.
- 'Depleted' Uranium