Sec. 28.6 ELEMENTS NOT KNOWN TO BE ESSENTIAL TO LIFE 535 



No biological studies have as yet been carried out with radioactive species 

 of the rare-earth elements not occurring in fission, nor of several fission ele- 

 ments of lighter weight (gallium, germanium, tellurium, rhodium, palladium, 

 etc.). 



Extensive work has been carried out by Hamilton and coworkers [Bal,Cel, 

 2, etc.] on the distribution of fission-product elements in rats, particularly 

 in the liver and bone. Most of these are not taken up in significant amounts 

 from the digestive tract after oral administration, exceptions being stron- 

 tium, tellurium, iodine, barium, and cesium. Following parenteral injection, 

 however, many are accumulated in the skeleton and eliminated very slowly: 

 strontium, yttrium, zirconium, columbium, barium, lanthanum, cerium, 

 praseodymium, and prometheum, but not ruthenium, tellurium, iodine, or 

 cesium. Initially lanthanum, cerium, praseodymium, and prometheum 

 accumulate in the liver, but are quite rapidly excreted from this organ. Of 

 the fission elements concentrating in bone, those .not taken into the body in 

 appreciable amounts from the digestive tract are retained for long periods 

 of time in the pulmonary tissue when administered intratracheally or by 

 aerosols. Most of what is absorbed deposits in the bone. This has con- 

 siderable significance in the public-health aspects of atomic-energy installa- 

 tions, especially as chronic radiation of bone by radioactive isotopes localized 

 there has long been known for radium and recently demonstrated for stron- 

 tium and plutonium [Srl5,PulO] to cause osteosarcomas. 



Studies on Se 75 metabolism have been restricted to two papers on the dis- 

 tribution of labeled selenate injected into the rat [Sel, 2]. It was found that 

 selenate labeled with Se 83 (30-min half-life) is rapidly converted in the body 

 into volatile organic compounds and eliminated in the breath. Studies 

 on tellurium with the isotope Te 121 (125-day half-life) [Tel] and a mixture of 

 the isotopes Te 127 (90-day half-life) and Te 129 (32-day half-life) [Te2] have 

 shown, on the other hand, that at first the urine is the principal route of 

 elimination and later is almost equal to the feces; tellurium is concentrated 

 most highly in the blood, liver, and kidneys, apparently whether administered 

 in the tellurous or telluric state. 



Radioisotopes of yttrium and zirconium have been used in colloidal form 

 in the study of blood mixing time and volume (Y2,Zr2). They also have 

 found, or been suggested for, preliminary therapeutic application in the 

 treatment of leukemias (see Chap. 29). 



28.6. New Rare-earth Elements (Actinide Series). The new rare-earth 

 elements or actinide series begins with actinium (element 89) and includes 

 the heaviest known elements. So far eight have been discovered: actinium, 

 thorium, protactinium, uranium, neptunium, plutonium, americium, and 

 curium. Biological studies have been carried out for all except actinium 

 (which, however, has species in the natural radioactive series, which thus 



