Thorium in the human ribs-variation with age

Abstract

Rib bone samples of human accident victims were analyzed for thorium. The analysis was carried out using neutron activation technique to determine Th-232. The age of the victims ranged between 6 years and 65 years. The thorium concentration was found to increase with age. The measured concentration ranged from 0.20 ng/g fresh weight at age 6 years to 1.84 ng/g at age 65 years. The arithmetic mean and geometric mean concentrations were found to be 0.54±0.38 ng/g and 0.46x/÷1.8 ng/g (by excluding the outlier high value of 65-year-old individual). These values are much lower in comparison to those reported by earlier workers. Assuming the total skeletal weight as 14.3% of the body weight and taking the average Indian's body weights as 14.5, 38 and 50 kg at ages 5, 15 and >18 years, the estimate of total skeletal thorium was made.

A plot of the total skeletal thorium with age groupings 0–10, 10–20... 50–60 years could be fitted into a linear relation with age. However, the deviation of data in 40–50 and 50–60-year age groups was such that the data could also be fitted into a sub-linearly increasing curve. Both the fittings, however, show a considerably lower rate of uptake in bone than that expected from substitution of Indian (Bombay) intake data into the ICRP model of Th metabolism.