This chapter discusses the state of knowledge concerning DUŪs chemical and radiological toxicity to humans. Many scientists argue that chemical toxicity from internalizing DU particles is many times greater than the carcinogenic toxic effects that radiation exposure can cause. Others argue that the long-term carcinogenic toxic effects, due to internal radiation exposure from internalized DU, are the most critical DU-health issue. The Army is concerned about the health effects of both types of toxicity. We seek to describe the health concerns associated with both phenomena in this chapter. This chapter considers the following key areas:
Before using DU the Army evaluated the health risks of soldiersŪ external exposure to DU munitions and armor in training, operations and combat. The risk to soldiers handling DU was found to be insignificant and within applicable standards (Danesi, 1990). Current operational procedures ensure the health and safety of personnel by minimizing external exposure to intact DU armor and DU munitions during combat and training. (Some vehicles with DU armor are used in training; DU ammunition is not used in training). Current data reveal that DU presents a medical concern only if it enters the body.
The health risk of exposure to low-level radiation is a complex issue.
Many in the scientific community disagree over how to estimate the risk.
Some issues associated with the radiological and chemical toxicity of DU
used in Army weapon systems are not fully resolved (Daxon and Musk, 1992).
Many elements and chemical compounds can produce adverse health effects under certain conditions. Heavy metals are usually toxic. Some are in common use, such as chrome used for plating or cadmium in rechargeable flashlight batteries. DU is a heavy metal with the toxicological risks shared by other heavy metals such as lead, cadmium, nickel, cobalt and tungsten. While health risks from DU may be affected by individual susceptibility to uraniumŪs toxic effects and to concurrent exposure to other toxicants, the health risks from DU are largely dependent on three factors (ICRP, 1979):
If DU enters the body, it has the potential to generate significant
medical consequences. The risks associated with DU in the body are both
chemical and radiological. Small particles generated in fires or during
the impact of penetrators on armor may enter the body by inhalation, ingestion
(for example, by ingesting›contaminated food or water), and by deposition
in open wounds. During combat, soldiers may be wounded by metal fragments
that contain DU. The solubility of the DU-containing material in bodily
fluids is the primary determinate of the rate at which the uranium moves
from the site of internalization [lung for inhalation, gastrointestinal
(GI) tract for ingestion, or the injury site for wound contamination and
injection], into the blood stream and then to the organs. In most instances
solubility also determines how quickly the body eliminates uranium in urine
Experimental data from weapon system RDT&E and from field experience during Operation Desert Storm indicate that the potential for DU internal exposure during combat is directly related to the location of the soldiers exposed.
Soldiers in or near vehicles struck by DU munitions are most likely to receive internal DU exposures. The Operation Desert Storm fratricide incidents showed that soldiers in armored vehicles can survive DU penetrations and can have DU-fragment wounds and DU-wound contamination.
Recovery and maintenance soldiers working in and around DU contaminated vehicles can inhale or ingest resuspended DU particles. Monitoring of research workers, maintenance, and recovery soldiers has not evidenced internal exposures; however, the Army should conduct further experiments to better define the risks from resuspended particles. These experiments would provide sufficient information to develop maintenance protocols that include the use of personal protective equipment by workers, if appropriate. Soldiers may be incidentally exposed to DU from dust and smoke on the battlefield. The Army Surgeon General has determined that it is unlikely that these soldiers will receive a significant internal DU exposure.› Medical follow-up is not warranted for soldiers who experience incidental exposure from dust or smoke.
6.1.1›››› Health Risks from Radiation
This section provides information on the background exposure from natural radiation received by all inhabitants on earth. In the U.S., radiation from natural background sources exposes everyone to about 300 millirem per year (mrem/yr) [National Council on Radiation Protection and Measurments (NCRP), 1987b]. People who live at high altitudes and in areas rich in radioactive minerals receive several times the background dose of those who live in most coastal plains. However, regardless of location, we are exposed to naturally occurring radiation and radioactive elements (some of which are metabolized by our bodies). The NRCŪs standard for public exposure to man-made sources of radiation is 100 mrem/yr above background (10 CFR 20.1301). Distinguishing between natural background and exposure above background is sometimes confusing. Radiation levels are reported in rads, rems and roentgens. The prefix žmÓ (žmilliÓ), as in mrem, means 0.001 rem.
The scientific community agrees that the models for estimating cancer and genetic anomalies caused by low-level radiation exposure› overstate the actual hazards [Biological Effects of Ionizing Radiaton (BEIR), 1980, 1989, 1990; United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), 1986, 1988, 1993, 1994].› Risk estimates used for low-dose exposure are extracted from high-dose/high-dose rate data. Risks from acute radiation exposure (greater than 100 rem) are relatively well-established. Reports by ICRP and the National Research Council's Committee on the Biological Effects of Ionizing Radiation (BEIR, 1980, 1989, 1990) contain excellent summaries of the literature concerning the human health effects of radiation exposure. Because extracting the risk estimates at low doses is a theoretical and not an experimental process, experts disagree somewhat as to which models best describe different types of exposures (BEIR, 1980, 1989, 1990; UNSCEAR, 1986, 1988, 1993, 1994).
Several studies (summarized in BEIR, 1980, 1989, 1990; UNSCEAR, 1988, 1993, 1994) were conducted on populations receiving low- dose/low-dose rate radiations from occupational exposures, exposures to nuclear weapon's fallout, medical sources of ionizing radiation, and living in areas with high natural background radiation. In the assessment of the results of these studies, the BEIR V (BEIR, 1990) committee concluded that there was no detectable increase in cancer rates in these populations.› The committee did not conclude that there were no radiation effects; it did conclude that these results were consistent with their estimates of risk and indicated that risk estimates based upon high-dose/high-dose rate data do not underestimate the risk of low-dose/low-dose rate exposure.
All health and safety protection standards are set at levels below the risk of adverse health effects that is considered acceptable (ICRP, 1977; NCRP, 1993b).›The concept of acceptable risk is relatively straightforward for exposures that have a threshold level below which adverse health effects do not occur. These types of effects include chemical toxicity and some radiation effects such, as radiation burns or sickness. The severity of the injury increases as the exposure is increased.
Determining risks for radiation-induced cancer and genetic effects is complex. There is no threshold dose. There is a relationship between increased incidence of disease and radiation exposure.› Thus, unlike "threshold-effects," there is always risk associated with exposure for non-threshold radiation effects. The radiation protection standards that address "non-threshold effectsÓ represent a risk level that is considered acceptable through national and international agreements.› As such, these standards define the accepted risk level posed by non-threshold effects.
When compared to other common radioactive isotopes, health risks from internalized DU are small. Table 6-1 compares the relative radiation dose a person would receive, per unit mass internalized, for various common radionuclides. The radiation dose received from each of the following would be vastly different if a person were to internalize them: DU, uranium in the natural isotopic ratio, 226Ra, or americium-241 (241Am). Specifically, if the radiation dose from DU is taken as the base unit (1 unit), the dose from the same amount of natural isotopic uranium would be 1.7 units; the dose from 226Ra would be 200,000 units; and the dose from 241Am would be 30,000,000 units. Promethium-147 (147Pm) and 226Ra illuminate the instrument dials of Soviet tanks used by Iraq during Operation Desert Storm (FSTC, 1993). Americium-141 is used in many home smoke detectors.
Exposure to ionizing radiation exhibits two types of health effects:› žthresholdÓ (deterministic) and žnon-thresholdÓ(stochastic). The severity of a deterministic effect depends on the amount of exposure above a threshold. Below the threshold dose, no acute effects are observed. Normal skin burns are analogous to deterministic radiation effects. Specifically, a burn is first noticeable at a discrete threshold. As the temperature or length of exposure increases, the burn becomes more severe. A burn will occur each time the process is repeated (ICRP, 1984). Deterministic radiation effects include radiation sickness and burns.› These both require high doses (greater than 100,000 to 150,000 mrem) delivered at high dose rates (minutes to days). Deterministic effects are not important for DU because of their low-radiation dose rate.
Table 6-1.› Comparison of the Relative Radiation Dose per Unit Mass Internalized, for DU and Other Substances
Statistics and the associated inferences concerning the probability of occurrence are only as accurate as the sample size from which they are derived.› Large sample sizes yield greater levels of confidence in the projection of probability.› Therefore, the demography of large human populations is required to detect stochastic health effects with any significant degree of confidence. Cancer and genetic (hereditary) diseases are endemic in all human populations. The probability of occurrence for these types of diseases can be estimated using probability theory. If the probability of occurrence for a cancer or genetic disease increases in populations exposed to radiation, the increase is termed a stochastic health effect. Thus, an increase in the radiation exposure raises the probability of disease (BEIR, 1980, 1990; UNSCEAR, 1988, 1994). Stochastic health effects exhibit the following characteristics:
The primary external hazards from DU are›› and›› radiation. These emissions are generated by the radioactive decay of trace-levels of uranium daughter products. The radiation exposure that Army personnel receive depends on the amount of DU present, the DU component (kinetic energy penetrator, DU armor, etc.), the configuration (in manufacture, in storage, uploaded on a vehicle, bare penetrator, etc.) and the exposure time. All DU weapon systems used by the Army are shielded to control the›› radiation emitted from DU. The Army has aggressive programs for managing the radiation exposure potential from DU munitions and tank armor. Researchers have conducted investigations to evaluate radiation field strengths (Bratlett et al., 1979; Gray, 1978; Haggard et al., 1986; Hooker and Hadlock, 1986; Hooker et al., 1983; Mishima et al., 1985; Parkhurst et al., 1988, 1991; Parkhurst and Hadlock, 1990; Parkhurst and Sherpelz, 1993; Wilsey et al., 1993). These investigations sought to define the level of exposure for soldiers and other personnel operating or maintaining these weapon systems.
Danesi (1990) summarized the exposure potential from DU weapon systems. He concluded that intact DU weapon systems, both munitions and armor, presented very little external exposure risk for personnel working with them. Danesi (1990) further suggesed that soldiers and support personnel working with or using DU weapon systems are unlikely to exceed the exposure limit for the general population and will not approach the limit for occupational exposure (5,000 mrem/yr). The Army monitors soldiers and support workers according to NRC occupational exposure standards (10 CFR 20.1201).
Holding a spent DU penetrator (DU metal without shielding) would deliver a skin dose (› and› ) of approximately 200 mrem/hour (Coleman et al., 1983; Cross, 1991; Needham and Coggle, 1991; Piesch et al., 1986; Rohloff and Heinzelmann, 1986). The current occupational exposure radiation dose limit (› and› ) for skin is 50,000 mrem/yr. The only plausible way that a soldier or support person could exceed this skin dose would be if a piece of DU from an expanded penetrator were carried as a souvenir.
The radioactive properties of DU have the greatest potential for health impacts when DU is internalized. DU can be internalized through inhalation or ingestion. Inhalation can occur during DU munitions testing, during a fire involving DU munitions or armor, and when DU particles are resuspended by testing or fires. The inhalation potential of a particle depends on its dimensions and mass. The effective particle size is determined from the mass-mean particle size and the surface-mean particle size.› Ingestion occurs primarily from hand-to-mouth transfer or from DU- contaminated water or food. Fragment wounds containing DU metal and contamination of any wound with DU occur in combat.
Internalized DU delivers radiation wherever it migrates in the body. Within the body,›› radiation is the most important contributor to the radiation hazard posed by DU. The radiation dose to critical body organs depends on the amount of time that DU resides in the organs. When this value is known or estimated, cancer and hereditary risk estimates can be determined (ICRP, 1977).
The health risks of internal DU exposure are a function of the particle characteristics, route of exposure, duration of exposure, and the species of DU (Eckerman et al., 1988; ICRP, 1981). The rate at which DU is eliminated can be measured in the urine or, in the case of ingestion, in the feces. These data can be used to estimate the total amount of DU internalized. From this and other information, researchers can develop health risk models to estimate health risk for various types of internal DU exposure (Boecker et al., 1991; Eisenbud, 1987; ICRP, 1981, 1979; Kathren and Weber, 1988; Kocher, 1989; Leggett, 1989; Toohey et al., 1991; Wrenn et al., 1985).
6.1.2›››› Health Risks from Chemical Toxicity
Because the radioactivity of DU is very low, the chemical toxicity of DU may be the more significant contributor to human health risk. As previously indicated, DU and natural uranium have essentially the same chemical behavior and toxicity. Therefore, chemical toxicity data developed for any isotope of uranium are applicable to DU. Other heavy metalsůsuch as lead, chromium, tungsten and uraniumůare also chemically toxic. The toxic properties of DU and uranium have been broadly studied (Voegtlin and Hodge, 1949, 1953; Stokinger et al., 1981; Kathren and Weber, 1988; Leggett, 1989; Diamond, 1989; Kocher, 1989; Zhao and Zhao, 1990). Danesi (1990) contrasted the potential toxic effects of DU and tungsten when each was used in projectiles. While DU is more toxic than tungsten, Danesi noted that there were substantial data gaps concerning the toxic behavior of tungsten when alloyed with nickel, cobalt or iron.
As a means of comparison, Table 6-2 presents OSHA workplace time weighted average values for several airborne metals. These concentrations are considered to be acceptable exposure levels in the workplace over a normal working lifetime. Uranium and tungsten are the primary metals of interest in the table; however, all the other metals are used or have been used as alloys in DU penetrators or tungsten penetrators or both (29 CFR 1910.1000, 1910.1025). Toxicity is only one of the variables used in evaluating the risks from DU in the environment. Solubility and route of exposure are also critical. If the material does not migrate in the environment then the exposure potential is reduced and thus the impact of inherent toxicity is moot since the exposure potential dominates the calculation of the risk.
Table 6-2.› Comparison of the OSHA Time Weighted Average Values for the Elements Listed for Inhalation Exposures
The following conclusions can be made from Table 6-2 concerning the toxicity of heavy metals:
Table 6-3.› Uranium Content of the Body from Natural Sources
In the kidney, uranium binds to bicarbonate and proteins (found in blood and urine). This reaction plays an important role in the mechanism of uranium nephrotoxicity. At normal blood and body pH levels, most soluble uranium is bound to bicarbonate, with lesser amounts bound to serum proteins (Moore, 1984, Stevens et al., 1980; Wrenn et al., 1987). This binding helps prevent soluble uranium from interacting with most body tissues.
When the bicarbonate-uranium complex enters the kidney, it leaves the blood and becomes part of the freshly made urine found in a specialized renal collecting system called the renal tubules. The renal tubules generally have a more acidic environment than the rest of the body. As a result, the uranium is freed from the bicarbonate and is then able to bind with, and potentially damage, the tissues of the kidney (Stevens et al., 1980, Barnett 1949; Wrenn 1987).
The accepted threshold level for kidney toxicity of 3› g of uranium per gram of kidney mass was set by the ICRP in 1959 and is still used to establish uranium standards (Diamond, 1989; ICRP, 1960).› There is considerable discussion in recent literature concerning this limit, because the basis for choosing 3› g/g is unclear. Animal data indicate that toxic effects may occur at much lower levels› (Kathren and Weber, 1988; Stokinger, 1981; BEIR, 1988; Leggett, 1989; and Diamond, 1989).› There is general agreement however that the threshold in humans is between 1 and 3› g/g for acute, short-term exposures (Kathren and Weber, 1988).› The level at which chronic (lifetime) exposures can produce clinically significant end points is not as clearly defined (BEIR, 1988).
Work with animal models (rats and mice) shows the potential for chemically-induced teratogenic effects when the mother is exposed to high levels (approaching levels toxic to the mother) of uranium (BEIR, 1988; Domingo et al., 1989a, 1989b, 1989c).› Effects ranged from low birth weight to skeletal abnormalities for doses at which the mother exhibited signs of chemical toxicity.› The effects noted are believed to be chemically induced because estimated radiation exposure was too low (all less than 7 rads) to account for the anomolies noted (BEIR, 1988).› Extrapolation of these results to human exposures is difficult because of the limited amount of data on the placental transfer of uranium (BEIR, 1988).› There is substantial information available on the placental transfer of plutonium-239; however, the chemical differences are such that a direct extrapolation is not possible.
6.2 Reducing DU Toxicity
DU is inherently toxic. This toxicity can be managed but it cannot be changed. The Army uses good management practices, material control and encasement to limit personnel exposure to DU in armor and munitions.
6.2.1›››› Reducing DU Radiological Hazards
Technologies are available to reduce the 234U and 235U residuals in DU. These processes are very expensive and would not significantly reduce the radiation risks of DU to health or the environment. Current enrichment processes reduce the concentration of 235U and 234U by 71 and 82 percent (by weight), respectively. This reduction makes DU approximately 60 percent as radioactive as natural uranium (0.4› Ci/g compared with 0.7› Ci/g). Removing all the 234U and 235U (which is not possible) would reduce the specific activity of DU to 0.33› Ci/g (the specific activity of pure 238U). If this were possible, the resulting DU would be about half as radioactive as natural uranium.
6.2.2›››› Reducing DU Chemical Hazard
There is no known way to reduce the chemical toxicity of DU in the body. Technology cannot significantly affect the solubility of uranium oxides formed in an uncontrolled environment such as the battlefield or in a fire. When munitions are fired or burned and when armor is pierced during battle, DU released to the environment will react with other nearby elements. These chemical reactions may produce compounds with various chemical toxicities. While fires and high-energy penetrator impacts occurring in an uncontrolled environment result in uncontrolled dispersion of DU contamination, the potential toxicity of this contamination can be limited by preventing DU exposure.› Disrupting pathways of exposure can be achieved through personnel training, decontamination procedures and personal protective equipment.
The solubility and particle size of the DU species inhaled or ingested controls the impact of its toxicity. The body will excrete much of the soluble uranium within a few days; however, the kidney may be damaged by uranium ions, freed from the bicarbonate form, in the uric acid. This damage mechanism is supported by studies that show animals with alkaline urine have an increased rate of uranium excretion and a decreased level of uranium nephrotoxicity (Wills, 1949). This occurs because alkaline urine has high levels of bicarbonate, which stays bound to the soluble uranium and prevents it from interacting with renal tissue. Alkalization of urine provides a theoretical means of treatment for persons with high levels of soluble uranium in their bodies. By increasing the rate of DU elimination, uranium is prevented from binding to kidney tissue. This procedure has not been clinically demonstrated in humans.
Animal data also suggest that certain chelators, a group of medications used to help remove heavy metals from the body, are effective in removing uranium (a heavy metal). These types of medications have not been used to treat humans exposed to uranium.
6.2.3›››› Hazard Reduction Using Alternative Materials
Replacing the DU in weapon systems with a non- toxic material would mitigate the health risks associated with DU. This material, however, would need to meet the performance criteria for armor and munitions. It would also need to provide a substantial reduction in toxicity over DU. Tungsten is the only alternative material currently under evaluation as a substitute for DU. The RDT&E efforts have not successfully developed tungsten munitions or armor that perform at a level equivalent to DU. Furthermore, as previously indicated, tungsten is a toxic heavy metal which would present risks from chemical toxicity similar to DU.
6.3 Medical Evaluation of the Effects of DU
6.3.1›››› Embedded DU Fragments
Thirty-six soldiers wounded during Operation Desert Storm were reported to have wounds involving embedded DU fragments [General Accounting Office (GAO),1993]. Many of these fragments were not removed using standard surgical guidelines because the risks of surgery were too great (GAO, 1993; Daxon and Musk, 1992).› These guidelines were established based on experience with standard (non-uranium, non-radioactive) fragmentation injuries. Figure 6-1 illustrates the surgical difficulty associated with fragment removal.
Concern over the potential long term health effects of embedded DU fragments
led the Army's Surgeon General to request that the Armed Forces Radiobiology
Research Institute (AFRRI)› conduct an in-depth analysis of this issue
(DA, 1992).› The AFRRI review (Daxon and Musk, 1993)› found no compelling
evidence to change current surgical criteria for fragment removal.› Uncertainty
about the long- term health effects of embedded DU fragments warrants long-term
follow-up of these patients and further research.› Specific uncertainties
include chronic chemical toxicity and the effects of long-term, low-dose
rate irradiation of the tissues surrounding the fragment, including the
potential for carcinogenesis.
Figure 6-1.› Embedded DU Fragments
20 mm DU fragment› Multiple embedded DU fragments
The Army Surgeon General has taken the following actions to develop a medical support program for soldiers who may have received DU fragment wounds (Myers, 1993):
The Defense Authorizations Bill for fiscal year 1994 (Defense Authorizations Bill, 1993) directed the study of "...the possible short-term and long-term health effects of exposure to depleted uranium including exposure through ingestion, inhalation, or bodily injury...". The AFRRI and the Inhalation Toxicology Research Institute, Albuquerque, N.M. are currently working on projects initiated by the Army Surgeon General resulting from the Defense Authorizations Bill. The AFRRI has initiated pilot studies to evaluate the chemical toxicity, fetal effects and metabolic behavior of embedded DU fragments (Daxon, 1995).› The Army Surgeon General should continue to support these and other studies that seek to better define the medical significance of embedded DU fragment wounds.
6.3.2›››› DU Wound Contamination
Soldiers who are wounded in an environment contaminated with DU are likely to have DU particles in their wounds (Rokke, 1993; Melanson, 1993; Daxon, 1993a). Regular wound cleaning procedures should be effective in managing DU wound-contamination. However, they could be improved through the use of radiation detection equipment. Standard Army radiation detection equipment (AN/VDR-2) or other relatively inexpensive, commercial, radiation detection equipment can be used to assess removal of DU during wound cleaning or to detect DU contamination remaining in a wound (Rokke, 1993). This instrumentation could also be used to assist in screening personnel wounded by DU containing-materials.
6.3.3›››› Assessment of the Amount of DU Internalized
During Operation Desert Storm, the Army did not assess the level of DU that soldiers internalized until well after hostilities ended (GAO, 1993). The Army Surgeon General recommended that procedures be implemented for medical personnel to assess internalized DU in patients who might be exposed during operations in Somalia. There were no DU exposures during the Somalia deployment. The Army should formalize and continue this policy because:
The Army learned several lessons from the unfortunate DU friendly fire incidents during Operation Desert Storm. Early data (JTCG/ME, 1974) estimated the probability of surviving a DU-penetrator hit to be very low. In Operation Desert Storm at the first real combat data point, survivability was more than 90 percent for M1A1 tank crews and more than 80 percent for Bradley crews. While the high rate of survival was fortunate, the inaccuracy of the initial estimate presented medical personnel with the unexpected challenge of developing protocols for treating DU wounds.
Since DU weapons are openly available on the world arms market, DU weapons will be used in future conflicts. The Army will be required to treat soldiers with DU contamination in future conflicts. Therefore, additional guidance is required for medical personnel on treatment of embedded DU fragments, decontamination of wounds and necessary procedures to quantify the DU internalized. The Army Surgeon General provided interim guidance when the Army deployed DU-armored vehicles and DU munitions to Somalia (DA, 1993d). The guidance addressed fragment removal and procedures required to document exposure levels for personnel who may have internalized DU.
In evaluating the issues concerning DU use during Operation Desert Storm,
GAO stressed the need to educate personnel in the radiological and toxicological
properties of DU and in the methods required to treat patients with internal
contamination (GAO, 1993). Broad DU-related training requirements are addressed
in Section 6.5 and elsewhere in this report. The medical issues of importance
include the following:
6.4 Potential Hazards and Protective Measures
The Army has conducted numerous investigations over the past 25 years concerning worker and soldier exposure to DU. This section provides a summary of some pertinent investigations. Note that the various measuring units reported here (rads, rems and roentgens) and different estimates of annual training or work hours reflect different assumptions made by the investigators in the original studies. For describing exposure from gamma and X-rays, a roentgen is essentially the same as a rem. Dose units are reported in the units used in the respective citations.
6.4.1›››› Army Depot Workers
Some Army depot workers routinely work with weapons containing DU components. Virtually all radiation exposure from DU in munitions and armor is due to low-levels of gamma radiation emitted by the daughter products formed from the radioactive decay of DU. Munition storage containers are designed to minimize penetration by› and most particles.
The Battelle PNL measured the dose rates from single pallets of DU munitions and for palletized munitions arranged as they would be in storage (Parkhurst et al., 1993, 1994; ARDEC, 1991a). For large caliber munitions (120 and 105 mm) the dose rates in storage areas with multiple pallets can exceed 1 mrem/hr.› The highest dose rate was measured between two rows of M829A2 120 mm munitions, configured as they would be in a storage facility, at 1.24 mrem/hr. The highest dose rate measured, for the small caliber M919 25 mm munitions, was 0.108 mrad/hr in the spaces between multiple pallets. Personnel working in these facilities are required to follow procedures that minimize exposure as not to exceed the monitoring limit of 500 mrem/yr. These procedures include:
Bradley Fighting Vehicle crews and Abrams Tank crews spend different amounts of time conducting training and maintenance in and on their vehicles. The NRC requirements do not apply in combat (DoDI, 1989). However, the Army is committed to maintaining the safest possible environment for the soldier.
Bradley Fighting Vehicle Crew Exposure
The Fighting vehicle crews have annual occupancy rates of 845 hours for the M2 (Infantry) Bradley Fighting Vehicle and 1,109 hours for the M3 (Cavalry) Bradley Fighting Vehicle (Hixon, 1990). DU munitions are not part of a combat vehicleŪs basic load during field maneuvers or gunnery training. DU munitions are not authorized for training issue by the Standards in Training Commission (STRAC) and are not available for allocation/requisition, as specified in DA Pam 350-38, Training Standards in Weapons Training, February 15, 1993. Therefore, training in U.S. combat vehicles should not result in increased DU exposure.
In combat, the Bradley Fighting Vehicle will carry M919 25 mm DU ammunition. The Battelle PNL estimated that the highest dose to personnel in the Bradley (scout configuration M3A3) was 0.18 mrad/hr (Piper et al., 1993). At this dose rate a combat crew would not exceed the NRC 5,000 mrem/yr occupational radiation exposure limit if they stayed in the vehicle continuously (24 hr/day) for a year (Parkhurst, 1994a; Piper et al., 1993).
Abrams Tank Crew Exposure
A report published by the U.S. Army Ballistics Research Laboratory estimated that tank crews spend a maximum of 904 hours in combat vehicles during a training year (Fliszar et al., 1989). Tank crews also use their vehicles to rest, sleep, eat or pass the time, particularly in wet or cold weather.
The M1A1HA tank contains DU armor. With a full combat load mix of ammunition, the tank commander, gunner and loader each receive a radiation dose of 0.01-0.02 mrem/hr. The driver receives a radiation dose of 0.13 mrem/hr to his head if armor is overhead or 0.03-0.05 mrem/hr if ammunition is overhead. The same exposure exists for the M60A3 tank driver and the M1 and M1A1 (non-DU armored) tank driver when ammunition is overhead (ARDEC, 1990; Parkhurst and Scherpelz, 1993, 1994; Wilsey et al., 1993).
It is unlikely that either the 500 or 100 mrem/yr exposure level will
be exceeded for either tank during peacetime or wartime operations.› However,
more detailed estimates of the amount of time crews spend in their tanks
should be obtained to verify this assessment. The TACOM is
in the process of obtaining these estimates for the following (Gryna, 1994):
When an Abrams main gun or a Bradley 25 mm cannon is fired, some burnt gases enter the crew fighting compartment (PM TMAS, 1993). A bore evacuator removes these gases from the end of the Abrams main gun after each round is fired (FM 17-12-1). Blowers and nuclear, biological and chemical (NBC) protection systems in the Abrams and Bradley ventilate the crew compartment (FM 17-12-1;› TM 9-2350-252-10-2; TM 9-2350-284-10-2).
A small amount of DU oxidation may occur in the gun tube when a DU round is fired (Parkhurst, 1993; McGuire, 1993d; PM TMAS, 1993). Also, a small amount of DU is expelled when a DU round is fired (Mishima et al., 1990; Parkhurst, 1993; PM TMAS, 1993). Abrams and Bradley gun tubes and the bore evacuator of the Abrams may contain small DU residuals after firing various DU munitions (Mishima et al., 1990; Parkhurst, 1993; YPG, 1993; Elliott, 1993; NRC, undated; AMC, 1993). Measurements indicate that radioactivity is detectable but within NRC standards (Davis, 1993a).
When a DU projectile breaks up in a gun tube, DU contamination is concentrated near the end of the tube. The AMC tested the Bradley 25 mm gun to determine if this contamination migrates from the gun tube into the crew compartment. A draft study by Battelle PNL indicated that firing DU ammunition with a number of inbore breakups occurring produced a detectable level of DU aerosol particles in the crew compartment. Some of these particles were within the respirable range, but the concentration was within NRC guidelines (Parkhurst, 1993).
During September 1993 and February 1994, AMC tested DU migration into the Abrams tank turret. No DU intrusion was noted, even when the testing crew deliberately created flarebacks.
Possible Exposure to Soldiers Near DU-Contaminated Vehicles
Army field tests have shown that if a DU penetrator strikes a DU-armored vehicle and creates a fire or an explosion, it can contaminate nearby soil. Most of the DU contamination detected in these tests was within 5 to 7 m of the vehicle (4.7› g of DU per gram of soil following five tests at the same location) (Fliszar et al., 1989). DU contamination decreased to less than 0.5› g/g of soil at 30 m. To put this contamination in perspective, the normal uranium content in soil is about 5› g/g of soil (NCRP, 1987c). During these tests, some DU armor components were expelled 76 m from the vehicle. Soil contamination created by these tests did not require treatment or removal under NRC criteria (Fliszar et al., 1989).
6.4.3›››› Maintenance and Recovery Personnel
Vehicle maintenance and recovery personnel may be exposed to DU and other toxic substances in combat-damaged vehicles. The Army has not assessed the risks to recovery and maintenance personnel working in and around vehicles contaminated with DU particles. Inhalation and ingestion present a potential pathway for internalization of DU by these personnel. Good personal hygiene reduces the potential for hand-to-mouth internalization. The Army needs to further evaluate these risks and define appropriate protocols.
DU-contaminated vehicles that present the highest risks for maintenance and recovery personnel fall into three categories:
BRL attempted to evaluate DU-particle generation as a function of welding on DU-contaminated tank armor (Fliszar et al., 1989). The data confirmed that DU particles were generated during welding but were insufficient to determine their concentration.
BRL evaluated airborne DU exposure when damaged DU-armor packages were removed from the tank turret (Fliszar et al., 1989). This operation involved cutting metal and using a lift to remove damaged armor packages. Data indicated that airborne contamination generated by this operation could exceed the NRC occupational exposure criteria.
Members of the 144th Service and Supply Company performed maintenance
and recovery of U.S. vehicles damaged during Operation Desert Storm, including
vehicles contaminated by DU. The Army Surgeon General tasked USACHPPM to
obtain voluntary 24-hour specimens from personnel for radiochemical analysis.
As of May 1994, preliminary results from 9 of the 26 personnel, at the
time of specimen collection, were not positive for DU. Fluorometric analysis
was performed at USACHPPM and more sensitive›› spectral analyses were performed
at a leading DOE laboratory.
Field surveys were conducted in Southwest Asia on vehicles that were contaminated with DU (Rokke, 1993; Lindsay, 1993). Unfortunately, these surveys only classified the vehicles as contaminated or clean. The level of DU contamination was not ascertained.
Combat maintenance and recovery personnel from the 144th Service and Supply Company did not know that some of the vehicles retrieved during Operation Desert Storm were contaminated with DU (GAO, 1993). They had no guidance on the management of DU-contaminated equipment. The Army does not have a technical bulletin addressing procedures for retrieving DU-contaminated equipment during combat.
Peacetime operational procedures for managing DU weapon systemsŪ accidents are outlined in TB 9-1300-278, Guidelines for Safe Response to Handling, Storage, and Transportation Accidents Involving Army Tank Munitions or Armor Which Contain Depleted Uranium. However, these protocols were not intended to be applied in combat. This document describes procedures based on NCRP principles of radiation protection (NCRP, 1987a). U.S. radiation protection policy mandates that radiation exposures are below established standards and are ALARA without placing undue constraints on the industry or mission (3 CFR).
The Army applies the ALARA principle to peacetime accidents involving DU. For example, TB 9-1300-278 recommends that firefighters use respirators. This recommendation is not made because the risks from DU are high, but because respirators reduce the potential for inhalation without increasing costs, hindering firefighting operations or increasing the risk of injury to the firefighters. Most firefighters wear self-contained breathing apparatus at all fires. Conversely, TB 9-1300-278 does not recommend respirators for medical personnel attempting to save lives or to treat serious injury during a DU fire, because the delay in donning respirators would increase risks and exceed the potential benefits.
Combat is not a safe undertaking. The non-radiation risks of combat
are significantly higher than the risks used to set radiation protection
standards. Combat and DU risks must both be considered when developing
a TB for combat operations. Some of the salient issues that must be considered
6.5 Soldier Hazard Awareness Training
The GAO indicated that soldiers need additional training on the use and effects of DU armor and ammunition so that they will not expose themselves to DU oxides while working (GAO, 1993). In addition, the Army should train PEOs and PMs for DU-weapon systems on health and environmental issues associated with the DU-weapon system life cycle.
Before Operation Desert Storm, specific service schools or unit leaders provided some soldiers with limited training on DU. For example, service schools trained explosive ordnance disposal (EOD) soldiers, ammunition handlers and welders who might work on DU armor. Some unit leaders had given their troops limited training on procedures for handling tanks with DU armor that had experienced internal ammunition fires or armor penetration.
Before Operation Desert Storm, the Army had only addressed the hazards and handling of DU in military job-specific and branch-specific publications. As previously mentioned, TB 9-1300-278 provides procedures for handling equipment contaminated with DU. In addition, TM 9-2350-264-10-2, OperatorŪs Manual: Unusual Conditions, Trouble Shooting and Maintenance, Tank, Combat, Full-Tracked: 120 mm Gun M1A1 (2350-01-087-1095) General Abrams, Volume 2 of 2, warns of the potential hazards of DU. However, it is unlikely that most U.S. soldiers would have been aware of these documents. The typical armor, engineer, mechanic, infantry, transportation or medical soldier probably would not have read TB 9-1300-278 in normal training or duty. It is more likely that an EOD specialist, ammunition handler, firefighter, installation RPO or transportation officer would have been acquainted with TB 9-1300-278. Similarly, M1A1 tank crews, and possibly tank mechanics, may have noted the warnings and directives about DU in Volume 2 of TM›› 9-2350-264-10-2.
Neither FM 17-12-1, Tank Combat Tables, nor AR 385- 63, Policies and Procedures for Firing Ammunition for Training, Target Practice, and Combat, indicates that DU in the ammunition could be hazardous. Appendix G of FM 17-12-1 contains standard procedures for reducing crew exposure to DU oxides when incoming fire ignites munitions stored in a tankŪs bustle.
Before the GAO study, TACOM had published TM 9-2350-200-BD-1, Battlefield Damage Assessment and Repair for Tank, Full-tracked: 105 mm Gun, M1 (2350-01-061-2445) and Tank, Combat, Full-Tracked: 105 mm Gun, IPM1 (2350-01-136-8738) and Tank, Combat, Full-Tracked: 120 mm Gun, M1A1 (2350-01-087-1095) and General Abrams (Hull). This manual lists the procedures necessary to assess, recover and repair Abrams tanks from the unit maintenance level to the support maintenance level. It also contains an appendix on assessing and dealing with DU contamination.
Operation Desert Storm showed that, in combat, a broad range of military specialties needed to be made aware of the hazards and precautions required when dealing with DU and DU contaminated vehicles (GAO, 1993).› Soldiers require training on the hazards of DU, on methods to detect DU, and on field-expedient protection and decontamination measures. Moreover, the Army needs to revise its manuals for weapon systems that contain DU components so that the manuals clearly identify DU components, potential hazards, and requisite precautions for use and repair. The Army has initiated a program to accomplish these tasks. The Armor School, for example, includes a DU presentation in the Basic Noncommissioned Officer Course, Master Gunner Course, Officer Basic Course and Officer Advanced Course. The Chemical School added DU training to three instruction programs, and the Ordnance School began presenting a hazardous materials briefing that includes information on DU.
The Army is examining DU training requirements for the rest of the force. In July 1993, the Office of the Deputy Chief of Staff for Operations and Plans (ODCSOPS) desig- nated Training and Doctrine Command (TRADOC) as the ArmyŪs executive agency for DU training. The ODCSOPS provided guidance to TRADOC for developing training across the Army and tasked TRADOC to recommend a training strategy and implementation milestones by September 1, 1993 (DA, 1993a, 1993b).
Both DA and TRADOC are seeking funds and personnel to support a three-tiered DU training program. Tier one will provide general radiation awareness training for all Army personnel. Tier two will support the AMC contaminated equipment recovery plan. Tier three will provide training for Chemical Corps personnel (Commandant, U.S. Army Chemical School, 1993). The Army recently authorized the Chemical School, to produce two DU training films:› One film will provide general awareness training for all the Army. The second film, produced with the Ordnance School, will deal with equipment recovery on the battlefield (Battle, 1994).
Marking of individual items containing DU varies and is sometimes misleading. Tank ammunition is marked with the word žSTABALOY,Ó but 25 mm M919 rounds and M1A1 tanks with DU armor bear no special markings. As a result, soldiers cannot easily identify DU materials. This could lead to accidental exposures of soldiers to the potential hazards of DU, especially in combat. Moreover, using alternate names for DU such as žSTABALOYÓ can lead to confusion and to possible mishandling of DU materials. Standardized markings should be developed.
No available technology can change the inherent toxicity of DU or significantly reduce its toxicity.
Like natural uranium, DU presents toxicological and radiological health risks, which depend on the chemical and physical form of the uranium and the duration and mechanism of exposure. Radiological risks from external exposure to DU penetrators are low. Soldiers are internally exposed to DU if they inhale or ingest DU particles, if a DU fragment is embedded in the body, or if DU particles contaminate a wound. Radiological risks from internal exposures are greater than risks from external exposures and cannot be estimated without detailed knowledge of the physical and chemical properties of the DU internalized. DUŪs solubility in bodily fluids determines its movement into organs and its elimination from the body. Uranium is chemically toxic if sufficient quantities are internalized. The kidney is the most sensitive organ to uranium. The generally accepted threshold level for kidney toxicity is 3› g of uranium per gram of kidney mass.
Based on Operation Desert Storm experience, the Army learned that it needs to provide additional medical management guidance on:
Personnel in or near vehicles when the vehicles are hit by DU munitions are the most likely to receive internal exposures. Recovery and maintenance personnel working in and around DU-contaminated vehicles also can inhale or ingest DU. The potential for internalization is high enough that the Army should further investigate and analyze the risks. Other Operation Desert Storm personnel whose only possible DU exposure was through breathing fumes from burning vehicles or incidental contact with contaminated vehicles are not considered to be at risk by the Army Surgeon General. Studies indicate that tank crews and workers in DU weapons storage areas do not receive external radiation exposures in excess of NRC limits.
Soldiers need additional training on the use and effects of DU armor
and ammunition so they will not expose themselves to DU oxides while working.
In addition, the Army needs to update its TMs to provide more information
on DU. Finally, the marking of individual items containing DU should be
standardized and made more understandable.