TAB N - Summary of Health Estimates
Health risk assessments for 13 identified exposure events are being prepared that describe the activities of the participants, specify the sources of potential DU exposure, and estimate the dose from inhalation, ingestion and wound contamination, as appropriate for each exposure category. The US Army Center for Health Promotion and Preventive Medicine (CHPPM) is conducting these exposure assessments. These assessments will incorporate information from a RAND Corporation review of the current understanding of health effects associated with DU. These will be described in plain language by CHPPM. Most of the health risk-related studies are currently in progress.
This tab summarizes the exposure assessment information prepared by CHPPM for the Level I participants inside combat vehicles as they were struck by DU. Activities of these participants are described, hazards assessed, and exposure assessment (chemical and radiological) and dose response information is reviewed, along with a summary of the risk characterization reflecting the current body of knowledge.
Level I soldiers, injured or not, were in or around combat vehicles at the time they were struck by DU sabots, or immediately afterward. Besides the embedded fragments from wounds, these individuals may have inhaled DU aerosols generated by fires or by the impact of the DU projectile penetrating the target. The following discussion briefly summarizes the activities of Level I participants and provides pertinent details such as types of vehicles involved and the circumstances under which they were mistakenly targeted by US tank crews. For a more in-depth discussion of the incidents described, please see Tab H.
Level I participants are separated into two categories: soldiers who were in or on combat vehicles at the time they were struck by DU rounds; and soldiers who entered those vehicles immediately afterwards to rescue wounded comrades. The former group is currently believed to have incurred the highest risk from embedded DU fragments and/or inhalation of the DU aerosols resulting from penetrator impact.
1. Occupants of Vehicles When Struck
a. Summary of Activities
Armor crewmen and the "dismounted" infantry transported in M2/M3 Bradley Fighting Vehicles supplied the offensive striking power for Operation Desert Storm. The highly mechanized US armored and mechanized infantry units counted on the speed, mobility, and firepower of their Bradleys and Abrams to maintain a rapid rate of advance while engaging and neutralizing enemy formations who tried to block Coalition troops from achieving their objectives.
b. Hazard Identification:
The activities of Level I vehicle occupants indicate that the combinations of personnel location, form of contamination, and route of exposure shown in Table 8 were possible. Additional details of the scenarios and assessments will be contained in the CHPPM risk assessment paper when published. Members of this group were potentially exposed through all possible routes of entry, including wounds.
|Route of Exposure
Soluble and Insoluble oxides
Occupants of the vehicles were subjected to wounds from flying fragments, inhalation of airborne soluble and insoluble DU aerosols, ingestion of soluble and insoluble DU residues by hand-to-mouth transfer, and contamination of wounds by contact with contaminated clothing and vehicle interiors.
c. Dose Assessment
Soldiers in or on vehicles struck by DU munitions were possibly exposed through four routes: direct wounding, inhalation, ingestion, and contamination of wounds. Individuals with direct wounds who retained fragments of DU are currently being evaluated in the DU Follow-up Program. The remaining participants in this category could have been exposed to inhalation, ingestion, and wound contamination whether DU penetrated the crew compartment or not.
Many variables must be considered when estimating the dose received by these individuals. A basic approach, however, involves consideration of test data produced under conditions similar to the scenarios being evaluated. For Level I participants, USACHPPM reviewed over 80 published reports. The characteristics of DU oxide particles, such as chemical composition, particle size, isotopic composition, equilibrium of progeny, and solubility in lung fluid, were identified and considered. These show:
CHPPMs preliminary review of the test data allowed estimates of the airborne DU inside heavy armor M1A1 tanks to be determined for three scenarios: 1) the upper bound (worst case) (maximum air sample observed) exposure when one DU penetrator enters the crew compartment of a heavy armor M1A1, 2) the most likely (average air sample observed) exposure when one DU penetrator enters the crew compartment of a heavy armor M1A1, and 3) the average (most likely) exposure when one DU penetrator strikes a heavy armor M1A1 but does not enter the crew compartment. Using the test data for DU penetrators impacting on DU armor is considered to be a conservative approach because no penetrations of DU armor were noted for the friendly fire incidents during the Gulf War. However, in several cases, non-DU armor was penetrated by more than one DU round. Since Bradley Fighting Vehicles have much lighter armor than Abrams tanks, penetrations by DU normally produce less aerosol. However, there is not enough data at this point to provide a reliable estimate for Bradley penetrations. Therefore, the data for single and multiple penetrations of an Abrams Heavy Armor tank are considered to represent a worst case.
A review of the test data shows that concentrations of DU in the air under the two scenarios for the DU penetrator entering the crew compartment, with an estimated stay time of 15 minutes and standard breathing rates, yield an estimated maximum intake of 26 milligrams (mg) of DU and an average intake of 12 mg from a single DU penetrator hit. When the DU penetrator did not penetrate the crew compartment the intake was 0.042 mg or 42 micrograms (m g) or almost a thousand times less than when the penetrator enters the crew compartment.
The medical significance of these exposures is discussed below under dose response and risk characterization. It is important to realize that these estimated intakes of 26 mg, 12 mg, and 0.042 mg are for total DU oxide. If the intakes are then converted to radiation doses using the Lung Dose Evaluation Program (LUDEP), a lung dosimetry computer modeling program, CHPPMs estimate of the radiation doses were 0.48 rem (maximum), and 0.23 rem (average) when the penetrator entered the crew compartment; and 0.0005 rem when there was no entry of the crew compartment. For two hits, the intakes were doubled to 52 mg, 24 mg, and 0.084 mg, respectively, which produced radiation doses of .96 rem, 0.46 rem, and 0.001 rem.
To evaluate the heavy metal dose, the total DU oxide was divided between soluble and insoluble components. Based on the results of the solubility analysis of the DU oxide (83% insoluble and 17% Class D soluble), CHPPMs estimate of the intake values for a single DU penetrator hit were 22 mg insoluble/4 mg soluble, 10 mg insoluble/2 mg soluble, and 0.035 mg insoluble/0.007 mg soluble for the three cases.
For the ingestion route of exposure for individuals who were in the vehicle when a single DU penetrator entered the crew compartment, intake by hand-to-mouth transfer was estimated to be 16 milligrams of DU based on measured surface contamination levels, estimates of the hand to mouth transfer factors, and the assumption that 83% of the intake was of the insoluble "Y class" and 17% of the intake was of the soluble "D class". This intake results in an estimated radiation dose equivalent of 0.000002 rem. For two hits, the intake and associated radiation dose are 32 mg and 0.000004 rem.
Estimates of the intakes from DU contamination of wounds are continuing. This is primarily caused by the gaps in the available data on transfer of contamination from surfaces to wounds. Estimates of the intakes from this route are expected to be included in a follow-up version of this report.
d. Dose Response
The medical effects literature on depleted uranium was reviewed by RAND and will be discussed in their forthcoming report. Their preliminary review indicates that for the level of radiation exposure from depleted uranium in the Gulf War cancer and genetic effects are the main concern. Scientific studies have shown that these effects occur with a total incidence of 7.3 x 10 -4 per rem.
1. Radiation risk.
The exposure for Level I individuals (excluding those with embedded DU fragments) inside an Abrams M1A1 tank when a DU penetrator enters the crew compartment, is conservatively estimated to be 0.48 rem for a 15 minute exposure from a singe DU penetrator or .96 rem from two DU penetrators. Using the dose response factor of 7.3 x 10-4 per rem, the combined risk for all fatal cancers, non-fatal cancers, and genetic effects is 0.0007 (which is determined by multiplying 7.3 x 10-4 medical effects per rem by .96 rem = .0007). This should be considered an upper limit for the worst case involving two DU penetrators. This estimate is preliminary and will be refined as more data become available.
For comparison, the average radiation exposure to a member of the US population from background radiation is 0.3 rem per year.So this maximum estimated exposure of .96 rem is about the same as living in the United States for about three years and is less than one-fifth of the annual limit for workers of 5 rems.
When the crew compartment was not penetrated, the estimated dose (0.001 rem) is much smaller; the same as the radiation exposure from one day of background radiation.
Another way to describe the effects on health is by calculating a persons increased probability of experiencing the effects (dying from cancer, contracting other cancer, or producing genetic effects in future generations). For the maximum case above, the probability is 0.0007. This means that the exposed person would experience an increased chance of 1 in 1,427 of experiencing the effect. For comparison, the chance of dying from all causes of cancer during his or her lifetime is 23% (1 in 4.3); or about 300 times higher than the highest estimated risk from DU. Therefore, assuming the cancer risks were cumulative, the lifetime cancer risk for personnel inside the tanks at impact would increase from 23% to 23.07%. This is for the worst case example of two DU munitions penetrating a DU armored tank creating maximum aerosolization of the DU penetrator. The quantity of DU aerosols generated by impact on non-heavy armor tanks and lightly armored Bradley Fighting Vehicles would be less. Therefore, the increased lifetime cancer risk of 1 chance in 1,427 would also be worst case when compared to the actual exposures in the friendly fire incidents encountered in the Gulf War.
2. Chemical risk.
The chemical exposure for Level I individuals inside an Abrams M1A1 tank when two DU penetrators entered the crew compartment is conservatively estimated to be 52 mg intake of DU particles for a 15 minute exposure. The 52 mg intake contains about 9 mg of soluble DU based on test data indicating that up to about 17% of the airborne DU produced from impacts is soluble (ICRP Class D). For individuals who were in the vehicle when the DU penetrator did not enter the crew compartment, intakes of soluble DU are calculated to be much less, in the microgram range (14 mg).
A comparison of the risks from radiation with the possible kidney effects of soluble uranium illustrates that heavy metal toxicity effects predominate over the radiological concerns.
3. Additional Comment
The risk estimates discussed above are for soldiers who could have inhaled soluble and insoluble DU produced when a heavy armor M1A1 is struck in its DU armor by two 120 mm DU penetrators. This scenario is believed to produce the highest exposure for a single event. That belief is based on the following considerations:
Additional work is required to refine the following parameters as well as others that may be identified as the analysis proceeds:
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