A procedure for the rapid detection of depleted uranium in metal shrapnel fragments

Military Medicine, Aug 2000 by Kalinich, John F

Depleted uranium is now widely used in the armor of military vehicles as well as in kinetic-energy penetrators designed to defeat enemy armor. As a result, the potential that personnel will be wounded by depleted uranium fragments has increased. Because toxicities associated with depleted uranium fragments may ultimately require different treatment protocols than those used for traditional metal fragment injuries, a method to rapidly detect the presence of depleted uranium in surgically excised shrapnel fragments is required. By treating the shrapnel fragment with an extracting agent, such as nitric acid, for 5 minutes in an ultrasonic cleaner, sufficient metal is solubilized to allow for colorimetric detection using a pyridylazo dye. Although several metals are capable of being detected under these conditions, the reaction can be made specific for depleted uranium through the use of masking agents such as sodium citrate and ethylenediaminetetraacetic acid. This procedure allows for the rapid (

Introduction

Uranium, as found in nature, consists primarily of three isotopes in the following percentages (by weight): 218U (99.283%), z5U (0.711%), and (34U (0.005%). As produced for power generation and nuclear weapons, uranium contains greater than 0.711% 235U and is considered "enriched" uranium. Uranium containing less than 0.711% 235U is considered "depleted" uranium. Depleted uranium (DU), obtained as a byproduct of the enrichment process for nuclear reactor- and weapons-grade uranium, usually contains less than 0.3% 235U and therefore is less than half as radioactive as natural uranium. Because it is extremely dense (1.7 times the density of lead), DU has several applications, including the armor plating of military vehicles. Its mass and pyrophoric properties under conditions of extreme temperature and pressure also make it useful for penetrator munitions designed to defeat enemy armor. These munitions saw their first combat use in the Persian Gulf War. Only the Allied forces possessed such weapons. Unfortunately, as a result of several friendly fire incidents, a number of Allied military personnel were injured with internalized DU fragments. At that time, existing Department of Defense shrapnel removal guidelines advised that fragments be left in place unless they were a present or future health threat. However, because of the lack of information on the health risks associated with long-term retention of DU fragments, several medical research projects were initiated to examine this policy. Preliminary findings from those studies have shown that, in a rodent model, embedded DU fragments solubilize and redistribute to a wide variety of tissues.' This redistribution begins as early as 1 day after implantation. As might be expected based on studies with other forms of uranium, kidney and bone exhibit the highest uranium concentrations. However, other tissues, including brain, lymph nodes, testicles, spleen, liver, heart, lung, and muscle, also show significantly higher concentrations of uranium. Urine from DU-implanted animals has significantly higher uranium levels than that from control animals, and this urine is mutagenic as determined by the Ames test.3 In addition, treatment of a cultured human osteoblast cell line with DU transforms the cells to a tumorigenic phenotype.4 The speed at which DU solubilized and redistributed, as well as its mutagenic and carcinogenic potential, led to proposed changes in the DU shrapnel removal policy. It is now advised that DU fragments greater than 1 cm be removed unless the medical risk is determined to be too great.5 In addition, patients with or suspected to have embedded DU fragments should be on a urine uranium bioassay program and should have their hepatic and renal functions monitored.6 Any change in shrapnel removal and treatment guidelines would require a procedure to detect the presence of DU in metal fragments. However, at present, there is not a rapid and convenient method to detect DU in metal fragments.

Examination of radiographs and magnetic resonance images can be used to detect metallic fragments embedded in tissues.' Unfortunately, neither of these imaging procedures can determine if DU is present in the embedded metal fragment. The technique of X-ray fluorescence can be used to identify subcutaneous DU fragments.89 This system uses a cobalt (^sup 57^Co) source to excite the uranium to produce X-rays and is capable of determining whether embedded fragments contain DU, provided that the fragments are embedded no deeper than 3 to 4 cm. However, with deeper shrapnel, there is a rapid decrease in signal intensity as a result of absorption by the overlying tissue. In addition, to obtain an accurate reading, measurement times on the order of 1 hour are required. The technique of differential attenuation has also been proposed as a possible method to determine if metal shrapnel fragments contain DU.10 This procedure requires the use of a whole body gamma-ray counter with hyperpure germanium detectors to determine the presence of DU in an embedded fragment.