low concentrations exist in the body fluids and bone. Tissue distribution studies have 

 shown that the muscle mass contains the largest portion (perhaps 60 percent) of the 

 body cesium, with visceral organs, brain, blood, bones, and teeth following in that 

 order^"^. 



Cesium salts are quite soluble and are quickly and completely absorbed, more 

 or less independently of route of administration. The ion is excreted by the kidney, 

 except in ruminants where a considerable portion is excreted by way of the gut. Tracer 

 studies in the cow show that about 13 percent of a single dose will find its way into the 

 milk within 30 days^'^. 



D. Iodine- 131 



Iodine-131 is produced abundantly in fission and, because of its volatile nature, 

 it is readily liberated. The tendency of iodine to concentrate in the small volume of 

 the thyroid gland is, of course, the primary cause of the hazard of 1^3 1. 



A situation involving I^^l ig illustrated by the Windscale reactor incident in 

 England in 1957. ^5 An accident during reactor operation allowed the release of fis- 

 sion products from the reactor stack. The fission product escaping through the filters 

 was almost entirely I^^l. Significant downwind contamination covered an area of about 

 200 square miles. The major vector for human intake of 1^3 1 was milk. Following 

 the incident, milk samples containing more than 1 )j.c/liter were obtained from nearby 

 farms. In order to limit the radiation dose to the thyroids of children to 20 rads, it 

 was necessary to use 0. 1 ^jlC of I^^l/iiter of milk as the maximum permissible con- 

 centration (assuming an intake of 1 liter/day). This necessitated discarding a con- 

 siderable quantity of milk over a period of 6 weeks. 



The adult thyroid has been found to tolerate quite large doses with no discernible 

 ill effects, but evidence from children treated with X-ray doses in the vicinity of 

 200 r in the region of the neck suggests that this dose may produce carcinoma of the 

 thyroid in a small proportion of exposed individuals, and, perhaps, under specific 

 conditions of irradiation66. In the child's thyroid weighing around 5 g, 1 (iC of I /g 

 of thyroid will yield an integrated dose of about 130 rads. 



E. Other Radionuclides 



The presence of certain other fission or activation products in the environment 

 has been detected. It is sufficient to comment on some of these only briefly, since 

 they are considered to contribute negligibly to the irradiation of man at this time. 



1. Ruthenium- 106, Ruthenium- 103 



At present these nuclides exist in rather high concentration in the soil, their 

 deposition level being around 800 mc/sq. mi. They have been detected in low concen- 

 tration in meat and other foods and in marine organisms by gamma- ray spectrometry. 

 Ruthenium is absorbed from the rat intestine to the extent of about 3 percent. Its 

 uptake by plants is extremely low, which impedes its passage from soils to man. 

 There is some uncertainty as to the critical organ or tissue for this radionuclide, but 

 the available evidence implicates the gufo?. 



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