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6 Radiologic Effects of Depleted Uranium
Pages 66-85

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From page 66...
... Because of the long half-lives of the various uranium isotopes (see Table 6-1) , DU has a low specific activity and hence is only weakly radioactive, with various uranium isotopes undergoing alpha decay and emitting x and gamma radiation.
From page 67...
... Stochastic risks posed by exposure to ionizing radiation include radiogenic cancers and genetic mutations. Deterministic effects are usually associated with high doses and typically occur relatively soon after exposure; thus, they are said to have a short latent period (time between exposure and manifestation of the effect)
From page 68...
... RADIATION DOSE As it decays, DU and its associated decay products emit alpha particles, beta particles, and photons of ionizing electromagnetic radiation (IER) , that is, x rays and gamma rays.2 Unlike ultraviolet radiation, used in the sunburn example above, IER has the ability to displace electrons in atoms or to remove electrons, thereby producing ionization or charged particles as it traverses matter, giving up in the process some of or all its energy.
From page 69...
... The dose from any ionizing radiation can be expressed as absorbed dose, but this is not a satisfactory method for relating dose to biologic effect or, in the case of stochastic effects, risk, because some kinds of radiation are more effective than other kinds in producing adverse biologic effects, and some tissues are more radiosensitive than others. Thus, two different kinds of radiation may result in the same absorbed or physical dose and have very different effects.
From page 70...
... The underlying logic is relatively straightforward and can be understood by noting that uniform irradiation of the whole body will produce a risk of a fatal cancer in each tissue, and the sum of the stochastic risks to all the tissues is equal to the total stochastic risk. If only a portion of the body is irradiated -- that is, one or two specific organs, as might be the case with a radionuclide incorporated into their tissues -- the total radiogenic stochastic risk comes from those irradiated tissues.
From page 71...
... EXTERNAL EXPOSURE TO DEPLETED URANIUM: DIRECT RADIATION The uranium isotopes that constitute pure DU all undergo decay by emission of alpha particles accompanied by x and gamma radiation. In addition, there is considerable ingrowth of the uranium decay-series progeny after 50 y.
From page 72...
... At or near the surface of a natural uranium slab, x and gamma radiation contributes about 10% of the dose; 10 cm from the surface, that fraction increases to about 20%; and 1 m from the source, the dose is almost exclusively from x and gamma radiation and about a few tenths of 1 mGy/h -- somewhat greater than observed by Fetter and von Hippel but still small enough to preclude, for all practical purposes, deterministic effects. Although deterministic effects of external exposure to DU are extremely unlikely, external irradiation of the skin by DU and its decay products would pose a risk of stochastic effects.
From page 73...
... That corresponds to an effective dose of about 0.67 mSv for an intake of 1 g of DU, which would produce a total stochastic risk, including both carcinogenesis and genetic risk, of about 3.3 × 10-5. In other words, the total risk of a stochastic effect from ingestion of 1 g of DU is about 33 in a million.
From page 74...
... Effective dose coefficients calculated according to ICRP (1994b) for class M and class F aerosols of DU with the same AMAD are 2.7 × 10-6 and 5.0 × 10-7 Sv/Bq, respectively, which are stochastic risks smaller than associated with class S material.
From page 75...
... and Risk Factors Route of Organ Intake Kidney Lung Bone Liver Effective Radiation dose (Sv) per milligram DU intake Inhalation Class M 1.80 × 10-5 3.17 × 10-4 5.00 × 10-4 6.72 × 10-6 4.09 × 10-5 Class S 2.41 × 10-6 9.48 × 10-4 6.44 × 10-6 8.78 × 10-7 1.14 × 10-4 Ingestion 3.60 × 10-6 3.47 × 10-7 1.00 × 10-5 1.35 × 10-6 6.29 × 10-7 Injection 1.80 × 10-4 1.73 × 10-5 5.02 × 10-4 6.77 × 10-5 3.15 × 10-5 Radiation-morbidity risk per milligram DU intake Inhalation Class M 1.32 × 10-8 2.06 × 10-6 4.96 × 10-9 7.70 × 10-9 2.12 × 10-6 Class S 1.46 × 10-9 5.70 × 10-6 5.50 × 10-10 8.33 × 10-10 5.70 × 10-6 Ingestion 2.84 × 10-9 1.56 × 10-9 1.39 × 10-9 1.68 × 10-9 2.45 × 10-8 Radiation-mortality risk per milligram DU intake Inhalation Class M 8.58 × 10-9 1.96 × 10-6 3.48 × 10-9 7.31 × 10-9 1.99 × 10-6 Class S 9.51 × 10-10 5.42 × 10-6 3.84 × 10-10 7.92 × 10-10 5.42 × 10-6 Ingestion 1.71 × 10-9 1.00 × 10-9 6.77 × 10-10 2.88 × 10-10 8.53 × 10-9 There is some suggestion that the biokinetic models put forth by ICRP and others may not completely characterize absorption and distribution in the tissues and thus may lead to inaccurate assessments of risk.
From page 76...
... In any case, for a given concentration in the kidneys, the risk of chemotoxic effects of DU far outweighs the risk of radiologic effects. Despite the above indications of potential shortcomings, the biokinetic models and dose-calculation methods are adequate to provide a good indication of the radiologic risks posed by DU.
From page 77...
... The studies have demonstrated none of the classic chemotoxic effects associated with uranium exposure or deterministic effects of irradiation. No cases of leukemia, bone cancer, or lung cancer have occurred in the 10 y of followup of 15 U.S.
From page 78...
... for Selected Cancers in 78 Uranium Workers Brain Leukemia Total Lung Hepatic and CNS Testicular and Study (Reference) Cancers Cancer Renal Cancer Cancera Cancer Cancer Bone Cancer Aleukemia Lymphomab Colorado Plateau uranium- 0.90 1.13 0.81 0.79 -- -- -- 0.66 2.29 mill workers (with no (0.78-1.04)
From page 79...
... Fernald: fabrication 1.09 1.01 0.63 1.62 1.24 0.67 0 1.16 1.81 of uranium products (0.98-1.22)
From page 80...
... : "Oak Ridge uranium conversion and enrichment, alpha and beta chemistry departments," because those workers were already included in the TEC/Y12 row for all workers.
From page 81...
... One possibility is that high smoking rates in the workers, which was confirmed by the few data available, may have led to increased overall rates of lung cancer. Nevertheless, it cannot be ruled out that inhaled uranium particles may lead to an increased incidence of lung cancer, especially given that alpha particles are emitted by uranium.
From page 82...
... There were nonsignificant suggestions of excess chronic nephritis in Mallinckrodt and Colorado Plateau uranium workers but a 15% deficit in chronic nephritis across all the studies. An increased mortality rate (SMR, 2.6)
From page 83...
... . Cancer mortality in that county -- including deaths in a number of uranium workers and those exposed to uranium dust, mill tailings, and so forth -- was compared with that in four other counties in the region that
From page 84...
... However, if they are present at all, the quantities of those contaminants are so small that the dose and risk associated with them are trivial and for practical purposes can be ignored. SUMMARY In summary, the following can be concluded with respect to the radiologic effects of DU: • DU is only weakly radioactive and does not pose a reasonable risk of acute deterministic effects.
From page 85...
... RECOMMENDATIONS Additional followup studies of exposed populations have the potential to improve knowledge of the health effects of DU. To permit an adequate assessment of the risks of cancer, renal toxicity, and other possible health effects faced by DU-exposed soldiers, a careful followup of the exposed groups should be continued, including the cohort of DU-exposed soldiers now being followed by the Department of Veterans Affairs.


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