Thorium concentration in human tissues from two geographic locations of the United States

The naturally occurring alpha-emitting isotopes of thorium (Th-228, Th-230 and Th-232) have been determined in 22 sets of human tissue samples obtained at autopsy from Grand Junction, Colorado and 10 sets from Washington, DC. Lung, pulmonary lymph nodes, liver, kidney, bone and spleen were obtained for most cases. Personal data for each individual's age, sex, smoking history and occupation were obtained whenever possible. Thorium was determined by a procedure utilizing solvent extraction and alpha-spectrometry following tissue digestion and coprecipitation of thorium with iron. Th-229 was used as an internal tracer. The concentration of thorium isotopes is as follows: lymph nodes > lung > bone > kidney > liver for Th-230 and Th-232 and lymph nodes > bone > lung > kidney > liver for Th-228. The organ distributions are discussed in relation to geochemical abundances, metabolism and physico-chemical forms of the sources