Metallic dissolution of a civil war bullet embedded in a sternum

The contemporary trend of converting departments of anatomy into departments of cell biology has brought with it the task of examining archive collections and storage facilities to figure out how to best utilize the available space. During one such inspection at the University of Louisville School of Medicine, a human sternum containing a dull metal projectile was uncovered. The projectile was easy to characterize as a bullet that had been deeply embedded in the bone. Less clear, however, were the circumstances detailing how the bullet had become lodged in the sternum, or how long the sternum might have been in storage at the University of Louisville. Radiographs of the sternum revealed a halo of surrounding density that dissipated in intensity from the margins of the bullet. Our initial hypothesis was that lead had been leached from the bullet into the bone matrix. To better assess what in fact contributed to this density, the sternum and the bullet were analyzed by energy-dispersive spectroscopy (EDS) to determine their elemental composition. That the bullet was composed of lead and aluminum was not surprising, but the extent to which the presence and dissolution of the bullet had affected the composition of the bony sternum was not entirely expected. The contribution of metal ions from the bullet to the inorganic matrix of bone was most notable for aluminum but nearly negligible for lead. This finding confirmed that bone affinity for metals is dependent upon the metal and supports previous reports that have suggested that lead is released from bone as soluble blood product during bony remodeling, whereas aluminum results in a significant elevation of bone density.