THORIUM IN THE HUMAN RIBS - VARIATION WITH AGE

Rib bone samples of human accident victims were analyzed for thorium. The analysis was carried out using neutron activation technique to det ermine Th-232. The age of the victims ranged between 6 years and 65 ye ars. The thorium concentration was found to increase with age. The mea sured 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 c oncentrations were found to be 0.54 +/- 0.38 ng/g and 0.46 x/divided-b y 1.8 ng/g (by excluding the outlier high value of 65-year-old individ ual). These values are much lower in comparison to those reported by e arlier workers. Assuming the total skeletal weight as 14.3% of the bod y 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 tho rium 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 wit h age. However, the deviation of data in 40-50 and 50-60-year age grou ps was such that the data could also be fitted into a sub-linearly inc reasing curve. Both the fittings, however, show a considerably lower r ate of uptake in bone than that expected from substitution of Indian ( Bombay) intake data into the ICRP model of Th metabolism.