Comparison of body burden due to thorium estimated by whole body counting and urinalysis and its implications with regard to recommendations of ICRP-78

Studies have been carried out on the workers of a thorium/monazite processing plant, where workers are exposed to a mixture of S and M type of thorium compounds. It has been found that for a normalised whole body retention of 100 Bq, the corresponding urinary excretion rate is 23±5 mBq/d, which is 2.5 times higher for S type and 1.8 times higher for M type, when compared with the values provided by ICRP-78. As ICRP calculations are based on inhalation exposure to either S type or M type, under ideal conditions, it cannot be directly adopted in operating plants. As the present study has been conducted on workers who were under actual inhalation exposure to a mixture of S and M type compounds of thorium, the result obtained can be used to modify the recommendations of ICRP-78. (author)