Three decades of in vivo x‐ray fluorescence of lead in bone

In vivo measurements of lead in bone were first made in the early 1970s. Of the three systems that have been used ( 57 Co excited K, 125 I or polarized excited L, 109 Cd excited K), 109 Cd excited K x‐ray fluorescence has been most widely adopted. Bone lead measured in vivo has been shown to reflect cumulative exposure, but the rate of input to bone varies with level of exposure. Chelated lead does not relate directly to bone lead. Endogenous exposure has been highlighted by bone lead measurements and this release of lead from bone and hence the half‐life of lead in bone have been shown to depend on age and on intensity of lead exposure. Thus x‐ray spectrometry has made a significant contribution to the understanding of long‐term human lead metabolism.