Abstract
Plutonium was discovered and first synthesized in the early 1940's. Several isotopes of plutonium are used in nuclear technologies, (238)Pu for heat generation and (239)Pu for energy production and weapons. Both isotopes emit alpha particles, which pose a significant radiation hazard when incorporated into the body. Alpha particles emitted during (239)Pu decay deposit energy along a very short path in biological tissues (≈45 μm in soft tissues). Thus, defining the anatomical locations of these deposits is essential to identify the cells at risk of radiation damage and potential malignant transformation. Bone is a primary site for plutonium deposition and retention. Plutonium exposures are associated with increases in osteogenic cancers. Plutonium is preferentially deposited on endosteal and endocortical bone surfaces, particularly those surrounded by red versus yellow bone marrow. Red marrow is more vascularized with a sinusoid network, while yellow marrow is largely a closed capillary system. Cancellous bone in red marrow sites has greater bone turnover rates and relatively more plutonium-related bone cancers than in yellow marrow sites. The relationships of plutonium deposits in bone and potential alpha particle exposures to cells that include osteoclasts, reversal cells, canopy cells, osteoblasts, bone lining cells, and osteogenic progenitors of the basic multicellular unit during bone modeling and remodeling are reviewed. Differences in distributions of (239)Pu versus naturally occurring tumors in humans and experimental animals are noted. This review emphasizes the importance of the anatomical locations of plutonium deposition and retention in the skeleton and the potential relative radiation risks from alpha particles to bone cells and their progenitors.