2. Zinc-65 



This isotope, an activation product, is found in the soil to the extent of about 

 10 mc/sq.mi. Zinc-65 has been detected in small quantities in fish, meat, and other 

 foods68. Trace amounts have been detected in plant tissue. Its presence in persons 

 dwelling near the Hanford Works"", in cyclotron operating personnel, and in the 

 natives of the Rongelap atoll has been detected by gamma- ray spectrometry. Absorp- 

 tion from the gastrointestinal tract of man appears to be greater than the 10 percent 

 assumed previously"' ''^. In a study of 6 human subjects, absorption ranged from 30 

 to 90 percent of the ingested amount. Considerable interest in this nuclide has de- 

 veloped as a result of observations that it is heavily concentrated from sea water by 

 certain mollusks' . 



3. Other Minor Radionuclides 



Traces of Zr^^ (and its Nb^^ daughter) are found in plants, and Zr^^ has been 

 detected in food^S. Contamination level in soil is around 50 mc/sq.mi. Its absorp- 

 tion from the intestine is exceedingly low. 



Antimony-125 is presently found in soil in concentrations around 25 mc/sq.mi. 

 It has so far not been detected in plants or in animals. 



Manganese-54 has been found in soil in very low concentrations. It was detected 

 in some marine organisms after Pacific weapon tests. 



Tungsten- 181 and W-*-"^ were generated in at least one bomb test as a tracer for 

 atmospheric studies. They have been found only in soil, where their total activity is 

 around 50 mc/sq.mi. 



Rhodium- 102 was also generated as an atmospheric tracer. It has not been found 

 in the biosphere, except in soil, where its concentration is around 15 mc/sq.mi. 



F. General Considerations 



Two problems of special concern in the area of radionuclide metabolism de- 

 serve mention. One is that of estimating the body content of a radionuclide from ex- 

 cretion rates; the other is that of accelerating the excretion of a deposited radio- 

 nuclide by therapeutic measures. 



Where total-body counting methods are inapplicable due to the radiation char- 

 acteristics of the nuclide, the measurement of levels in the excreta offers the only 

 practical means for estimation of body radionuclide content. The establishment of 

 relationships between body content and excretion rates, as a function of time follow- 

 ing exposure and route of exposure, is therefore an important practical objective of 

 studies in large animals and in persons who have received occupational exposures 

 resulting in detectable levels of radionuclide excretion '2. 



Recent efforts to increase the excretion of deposited radionuclides have been 

 encouraging with respect to certain heavy metals, such as plutonium, thorium, 

 yttrium, and the rare earths '^3, por these elements, the chelating agent diethyle- 

 netriaminepentaacetate (DTPA) has proven much superior to the earlier studied 

 ethylenediaminetetraacetate (EDTA) and should be a practically useful agent for the 



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