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

Military Medicine, Aug 2000 by Kalinich, John F

After the extraction procedure, the following components are added to the reaction tube to the indicated final concentrations: CAPS buffer (pH 11; 200 mM), sodium citrate (10 mM), EDTA (10 mM), and ethylhexadecyldimethylammonium bromide (25 mM). The CAPS buffer is required to bring the pH within an acceptable range for the detection reaction to occur. Metal binding to the pyridylazo dye is extremely pH dependent, with the acceptable range between pH 8 and 12. CAPS buffer, added to a final concentration of 200 mM, not only neutralizes the nitric acid extracting agent (0.1 mL of 100 mM) but also maintains the pH of the reaction mixture within the acceptable range. Sodium citrate and EDTA are used as "masking agents" to prevent the binding of metals other than DU with the pyridylazo dye. They are added to a final concentration of 10 mM each. The ethylhexadecyldimethylammonium bromide is added as a solubilizing agent to prevent the assay components from precipitating out of the solution.

Br-PADAP is used to detect the presence of DU in the extract. The structure of this pyridylazo dye is shown in Figure 3. The absorbance maximum of Br-PADAP, in the absence of metals, is approximately 444 nm. When DU is present, Br-PADAP binds to the metal to form a Br-PADAP/DU complex that exhibits a very broad absorbance maximum at 578 nm. The effect of various concentrations of Br-PADAP on the detection of DU extracted from metal fragments in shown in Figure 4. Increasing the Br-PADAP concentration from 10 to 50 LM increased the 578-nm absorbance of a nitric acid extract of DU fragments by almost 50%. However, increasing the Br-PADAP concentration to 100 pM did not result in any further increase in absorbance. Therefore, Br-PADAP is added to the reaction mixture to a final concentration of 50 AM.

The length of time required for maximum color development/ absorbance of the detection assay was also determined (Fig. 5). Color development occurs rapidly, within 5 minutes, and maximum absorbance is reached by 10 minutes. After this time, no additional increase in absorbance was observed. Once formed, the Br-PADAP/DU complex is stable. As seen in Figure 6, the absorbance of the reaction mixture shows only a slight decrease after 3 hours.

The ability of other metal fragments to be extracted with this procedure and bind to Br-PADAP was also investigated. Some metals are either inert to the extraction or, if extracted, do not react with Br-PADAP. These metals are listed in Table I. Other metals can be solubilized by the extracting agent and are reactive with Br-PADAP. However, the interaction between the metal and the Br-PADAP can be prevented by the use of masking agents. These metals are also listed in Table I. The use of an extracting agent such as nitric acid, masking agents, and a pyridylazo dye that has a stronger affinity for DU than for other metals eliminates interference by practically all militarily relevant metals.

Discussion

The expanded use of DU in weapons systems has increased the potential for embedded DU shrapnel wounds. Studies of the health effects of embedded DU fragments have led to a proposed revision in shrapnel removal guidelines.5 Any change in the fragment removal policy would also require a procedure to easily and rapidly detect the presence of DU in metal fragments. Unfortunately, current techniques fail in this regard. However, we have developed a process by which DU in metal fragments can be rapidly extracted and detected. This process does not require extensive sample preparation or the use of complicated instrumentation and can be conducted by someone with minimal technical training.