DISTRIBUTION OF PB-210 AT ENDOSTEAL SURFACES OF BONE FROM CANADIAN ARCTIC CARIBOU

alpha Particle energy spectra were measured at femoral endosteal surfa ces of Canadian Arctic caribou (Rangifer tarandus) to assess the profi le of concentration with depth of Po-210 supported by Pb-210. Femur sa mples from five caribou all showed a pronounced superficial concentrat ion of Po-210, in a layer 1.9-6.4 mu m thick. Within this layer Po-210 was concentrated 1.5-10 times with respect to diffuse volume-distribu ted Po-210. This result is consistent with an earlier study of Po-210 at human cranial bone surfaces, which showed Po-210 to be concentrated about four times in a surface layer <3 mu m thick. However, the prese nt results have higher precision than the human bone data due to the m uch greater concentration of Pb-210 and Po-210 in caribou bone. The va lidity of using Po-210 as a marker of Pb-210, and the in vivo Po-210/( Pb-210 ratio are discussed. As a result of the measured endosteal supe rficial concentration of Po-210 in, caribou, the alpha particle dose w as calculated to be enhanced by a factor of 1.06-1.96 (mean 1.48) for bone lining cells, and of 1.08-2.39 (mean 1.69) For soft tissue above the bone surface, assuming equilibrium between Pb-210 and Po-210. It i s suggested that an additional longer-lived compartment for bone surfa ce lead could be incorporated into bio-kinetic models for lead.