TASTRAK spectroscopy of polonium-210 alpha-particle activity at bone surfaces: evidence for a concentrated surface deposit less than 3 microns deep.

The technique of alpha-particle spectroscopy by CR-39 type TASTRAK plastic has been used to study the depth distribution of natural alpha-particle emitters at the surface of human bone. The predominant component of this alpha-particle activity was 210Po supported by 210Pb, although a smaller activity of 226Ra was also detected. Autopsy samples of human femur and cranium were obtained from subjects age 63 to 86. Both cortical and trabecular surfaces were analyzed. The results indicate that 210Pb-supported 210Po is concentrated at the surfaces of human bone from elderly subjects, in a narrow band 3 microns deep or less, by a factor of about four. As a result, the alpha-particle dose to the nuclei of cells lining bone surfaces is around 1.8 times greater than that calculated for a uniform volume distribution. Polonium-210 activity indicates the distribution of 210Pb, and of stable lead, received by continuous intake throughout life at a very low level. A persistent bone surface concentration of lead and other osteotropic metals may be associated with the hypermineralized layer about 1 micron thick which occurs at the surface of resting bone mineral.