Thorium in man and environment uptake and clearance

Abstract

The intake and tissue distribution of thorium (^{2 3 2}Th) was studied in an urban (Bombay) population in India. From the analysis of 16 whole diet samples, the average daily intake through food was found to be 2 μg (range 0.8–4.3 μg·d⁻¹). The estimated intake through drinking water and inhalation comes out to be 0.03 and 0.02 μg per day. From the analysis of human autopsy tissue samples it is observed that the concentration ranges in lungs and bone are 1.5–16 μg/kg and 0.2–9.0 μg/kg fresh weight respectively. The average urinary concentration is 12 ng/1 (range 7–22 ng/l for 10 samples). Among the different body tissues, pulmonary lymph nodes were found to contain the highest concentration (geometric mean 53.4 μg/kg, range 31.4–85.5 μg/kg for 6 samples). Analysis of the samples was done by the neutron activation technique. 311.8 keV gamma photons of^{2 3 3}Pa which is the activation product of^{2 3 2}Th, were counted after chemical separation. A 54 cm³ intrinsic Ge detector coupled to 1024-channel analyser was used. Using the average lung content and the daily average intake values of thorium through inhalation, the clearance half-time from lung was estimated.