534 ISOTOPIC TRACERS AND NUCLEAR RADIATIONS [Chap. 28 



of dietary lead [Pb5], etc. Studies with Pb 212 have been on the uptake of 

 lead by erythrocytes [Pbl,2] and the general distribution of lead in normal 

 and tumor-bearing mice [Pbl,6]. 



g. Bismuth. The use of bismuth as an antisyphilitic and antiprotozoal 

 agent renders tracer studies of considerable importance. So far only two 

 tracer studies for the element [Bil,2] have appeared, both done with Bi 210 or 

 RaE (5-day half-life) of uranium series. Bismuth was found upon parenteral 

 injection to be eliminated in the urine and feces, about twice as much in the 

 former as in the latter, and to concentrate most highly in the kidney and 

 somewhat less in the liver. 



h. Radium. Radium has presented a toxicological problem particularly in 

 the watchmaking industry in connection with the painting of luminous dials. 

 No attempt has been made here to cover the extensive literature on the 

 toxicology and radiation effects of this element. Ra 226 is the common isotope 

 (1,596-year half-life). A few tracer studies have been carried out using 

 Ra 224 or ThX (3.64-day half-life) and Ra 228 or MsThi (6.7-year half-life). 



28.4. Noble Gases. The use of radioactive isotopes of three of the heavier 

 gases — argon, krypton, and xenon — has made possible important studies on 

 respiratory gas exchange and the pattern of blood mixing in the mammal 

 [A1,2,K1,5, etc.]. The marked solubility of xenon in fat has been shown 

 with the radioactive isotopes Xe 127 (34-day half-life) [Xe4] and Xe 133 (7-day 

 half-life) [Xel]. 



Isotopes of radon— Rn 220 or Tn (54.5-sec half-life) and Rn 222 (3.825-day 

 half-life) — have been measured or used in studies on the fate of descendants 

 of the thorium and uranium series, respectively (see Hevesy, [Gen76]). 



28.5. Rare-earth Elements (Lanthanide Series) and Other Elements in 

 Fission. The fission of uranium and plutonium results in the production of 

 isotopes of elements ranging from number 30 (zinc) to number 63 (europium). 

 Fission products therefore include species of almost half the rare-earth ele- 

 ments (numbers 57 to 71) or lanthanide series. Thus elements for which 

 very little biological interest existed before the large-scale utilization of the 

 fission process now have assumed considerable importance by virtue of the 

 dangers of contamination by, and irradiation from, their radioactive species 

 as produced in atomic-energy installations. A number of the elements 

 occurring in large yields in fission have already been considered, e.g., stron- 

 tium, columbium, xenon, and iodine. Other elements occurring as fission 

 products for which biological studies have been carried out include {i.e., 

 those not already considered previously) the rare earths lanthanum, cerium, 

 praseodymium, and promethium and the elements selenium, yttrium, 

 zirconium, ruthenium, tellurium, gallium, and barium. Studies with all 

 these except selenium, yttrium, zirconium, and tellurium have been limited 

 to one or two investigations concerned with fission-product problems. 



