Slow, silent killer

While the proven risk from radiation exposure is an increased likelihood of developing cancer, some studies have noted other health effects too.

ON January 4 this year, European Commission President Romano Prodi became the latest European leader to demand an investigation into claims that depleted uranium (D.U.) used in the North Atlantic Treaty Organisation's (NATO) munitions had caused deaths o r illnesses among Balkan peacekeepers.

Public concern over the health hazards caused by D.U. munitions dates back to the Gulf war, when D.U. was first used in combat. Exposure to D.U. has been suggested as one of the causes for the massive crisis in public health in Iraq following the war. Th is is somewhat unlikely to be the case. The larger danger is to soldiers who were in vehicles hit by D.U. munitions, their rescuers and individuals who spent extended periods of time in these vehicles as part of clean-up. Indeed, in the years following t hat war, several U.S. war veterans have complained of a variety of medical problems, which have collectively been given the name 'Gulf war syndrome'. While the Pentagon has by and large maintained that there is no evidence to suggest that D.U. is linked to the syndrome, it is likely that at least some subset of the symptoms is related to exposure to D.U.

Uranium as found in nature has two significant isotopes (isotopes have the same number of protons in their nuclei but differ in the number of neutrons). The primary isotope is uranium-238 (U-238) which constitutes approximately 99.3 per cent of the total available uranium. The remaining 0.7 per cent is uranium-235 (U-235). To use uranium in nuclear weapons or in nuclear reactors, it has to be enhanced in the U-235 fraction. Depleted uranium refers to the "waste" material (and therefore available for fre e) left behind when natural uranium is enriched in its U-235 content. A typical D.U. composition has 99.8 per cent U-238 and 0.2 per cent U-235. The principal component, U-238, has a radioactive half-life of 4.5 billion years.

The choice of D.U. for use in munitions is made mainly because of its high density, about twice that of lead. During the Gulf war, D.U. was used to make tank-fired shells (with 4-5 kilogram D.U. penetrator rods) and 30-millimetre rounds (with a 0.3 kg D. U. penetrator) fired by "tank killing" aircraft. When these strike a hard target, such as a tank, a large fraction of their energy is converted into heat in a very short period of time, converting much of the D.U. into small, hot fragments and particles. The smaller fragments can burn, generating D.U.-oxide aerosol. D.U. is also used as an armour component in some tanks.

Exposure to uranium could be of two kinds - external, that is, when the uranium is outside the body, and internal, when uranium has entered the body through air, food, wounds, embedded shrapnel and so on. The health hazard due to exposure to uranium woul d result from its radioactivity and chemical toxicity. When the uranium is outside the body, only its radioactive properties are pertinent; chemical toxicity comes into play only in the case of internal exposures.

Radiation from the decay of uranium and various resultant radioactive isotopes can be of three kinds - Alpha, Beta and Gamma. Alpha particles cannot penetrate the inert outer layer of the human skin. They do not contribute to any external radiation thre at. They are hazardous only if there is internal consumption. Beta particles are usually hazardous only if bare uranium comes in direct contact with the skin. Gamma rays are far more penetrating and could deliver external radiation doses.

Because the primary decay mode of uranium is through Alpha particles, radiation doses from external exposure are relatively insignificant. It has been estimated that people living in the vicinity of damaged vehicles would receive external doses of at the most 10 per cent of the background radiation dose that all of us receive. However, D.U., when it is in contact with bare skin for long periods of time, could result in a significant Beta radiation dose. For example, children in Iraq play in abandoned ta nks or with shell fragments, thus putting themselves at greater risk.

Radiation doses could be much larger in the case of internal exposure. Ingestion of D.U. is a less significant risk since almost all of the uranium is excreted within a few days. More serious is the inhalation of very small D.U. particles, which can stay imbedded deep in the lungs, typically for months or even years. Since 10-35 per cent of the oxide produced when D.U. munitions strike a target and burn is in the form of particles that are respirable, people who are inside tanks that are hit or those wh o enter such tanks later on are likely to inhale these particles.

The kind of damage caused by such inhalation depends on the particles' solubility in body fluids, which determines the rate at which inhaled or ingested D.U. is absorbed into the bloodstream. Fine, insoluble aerosols result in higher radiation doses, whi le soluble aerosols pose greater risks of chemical toxicity because they are absorbed into the bloodstream quickly. Once in the blood, uranium concentrates in the kidneys and bones.

In the kidney, the chemical toxicity effects of D.U. can cause renal damage. The threshold concentration level that results in damage to the kidney is a matter of controversy. The literature on D.U. frequently cites 3 micrograms/gram of kidney tissue (t hat is, 3 ppm) as a threshold even though renal change in animals following exposure to uranium has frequently been observed at levels well below the threshold. In the case of other toxic elements like lead, as the sensitivity of measurements increase, s tudies have recognised very small effects at lower levels of exposure. It may, therefore, be premature to assume the existence of a firm threshold, below which adverse effects will not occur.

Assuming no significant damage below 1 ppm, physicists Steve Fetter and Frank von Hippel use a combination of rough estimates and test data to estimate the amount of uranium that individuals might inhale under various circumstances (Science and Global Security Volume 8:2 (1999), pp.125-161). For individuals who are outside vehicles struck by D.U., they conclude: "It is virtually impossible that any U.S. soldier outside of a struck vehicle could have inhaled a dangerous amount of D.U.-aerosol from penetrator impacts. It seems unlikely that even Iraqi soldiers on the "highway of death" between Kuwait City and Basra, other than those in vehicles struck by D.U. munitions, could have received doses in excess of U.S. occupational radiation or toxicity standards." However, in the case of those inside a vehicle that has been hit, Fetter and von Hippel estimate that they could potentially inhale large enough amounts leading to kidney damage or other toxic effects.

Another group of individuals who are potentially affected are those who have shrapnel of D.U. embedded in their bodies. Removing such shrapnel is often quite difficult and so there is a constant radiation dose. Over time, the embedded shrapnel gradually dissolve and lead to uranium accumulation in the kidney. Of these, the radiation dose is likely to be significant in them. A final category of individuals who could breathe in considerable amounts of D.U. are those who enter vehicles after they have been struck, either to rescue fellow-soldiers, remove munitions or equipment, or to clean or repair damaged vehicles.

There are many uncertainties that have to be factored into these estimates and damage assessments. First, there is uncertainty about the exact number of soldiers who were exposed to D.U. through one or more of these routes. Hence it is not possible to ma ke precise estimates about how many may be affected. In typical fashion, the Pentagon did not take any urine samples from soldiers for nearly two years, thereby making it impossible to estimate how much D.U. different individuals had been exposed to.

Second, there are uncertainties about the behaviour of uranium in the body. Multiple models have been proposed with significant variations. A comparison of uranium distribution in the body of a dead employee of a uranium workshop and the International Co mmission on Radiological Protection (ICRP) model found in autopsy that the presence of uranium in the lungs and lymph nodes was less than 1 per cent of the predicted values [Health Risks of Radon and Other Internally Deposited Alpha-Emitters (BEIR IV) (Washington DC: National Academy Press, 1988), p. 282].

There are also significant differences between different species in the matter of sensitivity; this becomes important because the question of which animal (dog or rat) is a better model for uranium effects in humans is yet to be settled. Gender sensitivi ty has also been noted in the case of rats, with the male requiring on an average about 2.5 times more uranium for lethality than the female.

Third, while the well-proven risk from radiation exposure is an increased likelihood of developing cancer, some studies have noted other health effects too. For example, chromosome aberrations, that is, genetic effects, have been reported in uranium mine rs and there is some evidence that uranium may affect the immune system. Uranium exposure has been found to result in developmental defects in mice, and a decrease in weight and length in dogs as well as an increase in the number of still births.

Finally, there are potential synergistic effects that could be caused by exposure to both D.U. and chemicals from the widespread bombing of petrochemical factories and fertilizer plants, and the many oil wells that were set on fire. Interestingly, U.S. t roops involved in the Gulf war were administered pyridostigmine bromide, a relatively new vaccine, to protect them against biological and chemical weapons; a survey underwritten by the Pentagon has linked the Gulf war syndrome to this vaccine. There is s ome evidence from experiments in mice and dogs that the combination of Alpha radiation from uranium and chemical toxicity produces a greater toxic effect on the kidney than either does separately (Health Risks of Radon and Other Internally Deposited A lpha-Emitters, p. 286). Given the almost complete lack of data, it is impossible to confirm or rule out such synergistic effects, let alone quantify the risks.

In the light of these uncertainties, the claim by the U.S. Department of Defence that the few veterans being monitored are "not sick from the heavy metal or radiological toxicity of D.U." is definitely overstated. As the U.S. National Academy of Sciences ' Biological Effects of Ionising Radiation Committee noted, the available epidemiological studies involving uranium exposure had only limited power to detect increased rates of either serious renal disease or increased rates of malignant tumours. The com mittee also recommended that "at present, it is premature to attempt a risk estimate for the probability of developing renal damage, and there is an evident need for well-controlled epidemiological studies." It is worth recalling that over the course of the previous century the level of occupational radiation dose considered "safe" has decreased by approximately a factor of 30 as better studies of health effects were conducted.

In the final analysis, though it is unlikely to be the primary cause for widespread sickness in Iraq or among Gulf war veterans, one can say that D.U. is unsafe and clearly poses health risks to people exposed to it. When the much more evident suffering due to sanctions have failed to evoke any change in policies or even sympathy - best epitomised by former U.S. Secretary of State Madeline Albright's 1995 statement that the half a million (or more) Iraqi children killed by the sanctions were "worth it" - it is no surprise that the much smaller health impacts as those from the exposure to D.U. have been disregarded by U.S. authorities, and now by NATO. The development and use of D.U. munitions is yet another instance of how the U.S. nuclear industry wo rks together with the military industrial complex to support U.S. imperialism around the world, regardless of the consequences. For this political reason, in addition to its health impacts, the use of D.U. must be opposed.

M. V. Ramana works at the Centre for Energy and Environmental Studies, Princeton University, United States.