The primary health and environmental risks of using DU arise from the internalization of metal fragments and oxides generated by penetrator impacts, from fires involving DU munitions, and from oxidation of DU penetrators in the natural environment. To quantify these risks, one must know the quantity and the physical and chemical properties of the oxides generated and how these change with time, and use the appropriate environmental and health effects models to estimate the potential intake through each pathway.

Previous studies of the health and environmental consequences of the use of DU have indicated that the Army needs to conduct several additional investigations to more fully understand its consequences. The Army can improve the experimental procedures it uses in these investigations.

5.1 Findings of Previous Studies

Before the Army used DU in penetrators, the Office of the Director Defense Research and Engineering (ODDR&E) tasked the JTCG/ME to perform an initial assessment to ì... evaluate the medical and environmental implications of the use of depleted uranium and alternatives in a variety of conventional munitions. ...î The JTCG/ME was also tasked with analyzing each phase of the DU life cycle, including combat operations, and recommending research required to confirm any of its conclusions (JTCG/ME, 1974).

The JTCG/ME concluded that ìOverall, implementa- tion of the proposed action [the development and use of DU penetrators] is expected to have no significant medical and environmental impact. Depending upon conditions locally, significant impact can occur in the event of uncontrolled release of DU.î Specifically, it concluded that implementing the regulatory requirements of the Atomic Energy Commission (now NRC), DOT and OSHA would effectively control the internal and external hazards of DU for all peacetime activities (mining, manufacture, transportation, storage and RDT&E). The JTCG/ME further concluded that fires or accidents involving DU munitions and the use of DU munitions in combat could result in locally significant internalization (inhalation, ingestion and embedded fragments) (JTCG/ME, 1974).

The primary shortcomings of the JTCG/ME analysis were the following:

• The lack of data on the amount and characteristics of airborne DU that combat and fires could generate.
• The lack of definitive assessments of the environmental behavior of DU.

M.E. Danesi, the U.S. Army Pierre Committee, and the NMAB of the National Academy of Scienceís National Research Council each conducted similar evaluations (Danesi, 1990; Pierre Committee, 1979; NMAB, 1979). Each of these reviews concurred with the overall conclusions of the JTCG/ME on the health effects of military use of DU.

5.2 Depleted Uranium Characterization

The Army has conducted many tests to determine the characteristics of particles produced by hard and soft target impacts and by fires involving DU munitions and armor. Unfortunately, data that the AEPI reviewed did not contain the attributes required to estimate inhalation potential or environmental transport. AEPI is conducting an exhaustive review of existing particle data to better define data gaps.

The data from each burn test were consistent and reproducible. However, the technology for assessing health and environmental risk has advanced greatly in recent years. Therefore, these data are not sufficient to support the data needs of the new health and environmental risk assessment techniques. For example, tests designed to characterize the aerosols created when a DU penetrator strikes a combat target found significant differences in particle characteristics of the different types of rounds and different types of targets. Investigators made no attempt to critically evaluate the reasons for these differences. They assumed that differences in munitions and targets or errors in experimental design caused the inconsistent results. Unless researchers clearly understand these data, they are of limited use for evaluating health and environmental consequences.

Thus, after AEPIís critical review of the available particle characteristic data, studies must be designed to generate requisite data. These data must be suitable for use in calculating environmental and health risks from aerosols generated in fires and hard- and soft-target impacts, and they should identify and characterize the oxides formed when penetrators are exposed to the environment. At a minimum, these data would include chemical species, mass-mean size, surface-mean size, size distribution, specific gravity by species and particle shape factors.

5.3Ý Experimental Procedures

AMC has conducted many tests on the potential hazards of DU munitions and armor. However, these data have often been insufficientÝ for calculating health and environmental risks. Individual PMs decide when to investigate potential hazards, and researchers conduct experimental procedures and data analyses without external peer review to validate the quality or completeness of their work. Thus, the Army does not appear to closely coordinate the planning and performance of experiments for DU health and environmental assessments.

Many weapons performance experiments have also produced data for the Army to use in evaluating the potential health hazards of battlefield use of DU munitions and armor. Three investigation topics are particularly significant:
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• Radiological doses received by crews in tanks loaded with DU munitions (ARDEC, 1990; Parkhurst et al., 1991).

• DU aerosols generated by DU munitions (40 CFR 61; Jette et al., 1990).

• DU aerosols resulting from the impact of various types of munitions on DU-armored tanks (Fliszar et al., 1989).

Army studies need to review and assess similar previous investigations. For example, AEPI researchers identified four studies of DU aerosolization during munitions and armor testing that used similar experimental methods (Fliszar et al., 1989; GenCorp Aerojet, 1993; Gray, 1978; Haggard et al., 1986). Although the studies were otherwise excellent, none of the more recent studies compared their results with those from earlier studies. This comparison is necessary to check the validity of results and to force researchers to critically review differences and develop explanations for them. This step is essential in developing a fundamental understanding of particle characteristics and in developing predictive models.

The DU-particle resuspension has become a major concern since Operation Desert Storm. Particulate resuspension data were derived from air samples taken on single vehicle impact tests or fires. The resuspension potential for the test cases is not comparable with that on the battlefield. During a battle, multiple vehicles can provide a source for DU particles (fires and impacts) or can mechanically resuspend DU by their movements. Thus, without a firm grounding in aerosol mechanics theory, test results are only valid for the testing conditions and cannot be generalized over diverse environmental conditions (soil composition, vegetation, weather, etc.). The Army needs general models that are sufficiently robust to provide defensible estimates of the aerosol and particulate concentrations of DU on the battlefield.

Eriksonís work is a good example of how researchers should mix theory and experimentation (Erikson et al., 1990a). Erikson studied the mobility of DU at two U.S. test sites. The study had a firm theoretical basis that guided measurements and served as a bench mark to test the validity of the data. While the objective of the experiment was limited to two specific test sites, the methodology Erikson used makes the data more broadly applicable. These data can be used as a starting point for estimating the environmental fate and effect of expended DU penetrators under other environmental conditions. The only major shortcoming of the Erikson study was that it did not receive independent peer review.

The system developer PM should require peer review of all health and environmental aspects of proposals, data and reports concerned with DU contained in the weapon system. Peer review of proposals will ensure that the experimental approaches are sound and that the work is likely to yield new, valuable information. It will also ensure that the personnel performing experiments have the necessary expertise. Peer review of final reports will ensure that researchers conducted experiments correctly and drew scientifically defensible conclusions. Reports should be reviewed inside and outside DoD to increase the number of expert reviewers and to enhance the credibility of reports. Independent peer review is crucial because too often studies are performed by or for an organization that has a vested interest in the results.

For example, based partly on Coleís experimentation and analysis, Danesi concluded that soldiers can safely take refuge in a DU-contaminated vehicle (Cole, 1989; Danesi, 1990). Cole works for a DU munitions manufacturer, and Danesi cited an internal report, sponsored by the manufacturer, that did not undergo an independent review.

In spite of the high quality of Coleís report, its conclusions are less credible because they lack rigorous independent confirmation.

The Army has and is conducting many tests to assess the environmental and health hazards associated with all phases of DU use. It could improve the usefulness of the data already gathered and the quality, dependability and cost-effectiveness of future testing by taking four actions:
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• Critically reviewing all environmental and health hazard data obtained to date to ensure that it is consistent and scientifically defensible, to identify critical data gaps, and to recommend methods to fill these gaps.

• Emphasizing the development of theoretical models and their use in planning experimental research to maximize the cost effectiveness of experiments.

• Establishing a mechanism for scientific peer review of proposed experiments and their results.

• Identifying a focal point and repository for all information on the health and environmental effects of DU. This organization could consolidate available environmental data and thereby reduce duplication and ineffective experimentation.

Four previous studies have examined the health and environmental effects of the use of DU in conventional weapons: a 1974 study by the JTCG/ME, a 1979 study by the U.S. Army Pierre Committee, a 1979 study by NMAB of the National Academy of Scienceís National Research Council, and a 1990 study by Danesi.

The JTCG/ME study concluded that the overall use of DU penetrators would have no significant medical or environmental impact but that, depending on local conditions, an uncontrolled release of DU could have a significant impact. Further, it concluded that implementing regulatory requirements of NRC, DOT and OSHA would effectively control DU hazards during peacetime. It also concluded that fires or accidents involving DU munitions and the use of DU munitions during combat could cause locally significant internalization. The three later studies concurred with these conclusions.

The Army has conducted many tests to determine the characteristics of particles produced by hard- and soft-target impact and by fires involving DU munitions and armor. These tests have not produced all the appropriate data required to calculate scientifically defensible health and environmental risks. Many of these data were collected before modern risk assessment technologies were developed. The Army needs to establish a health and environmental data protocol to ensure that testing produces data that are appropriate for developing health and environmental policies.