CHAPTER 28 

 ELEMENTS NOT KNOWN TO BE ESSENTIAL TO LIFE 



Ellsworth C. Dougherty 



28.1. Introduction. Some 22 of the 96 known elements have been con- 

 sidered so far. The remaining 74 are not known to be essential to living 

 systems. However, as already noted in Chap. 24, there are certain elements 

 for which a vital role has been suggested on evidence of varying strength. 

 For purposes of this volume these elements (some 11) are considered in 

 Sec. 28.2. 



The remaining elements are grouped more or less arbitrarily into (1) ele- 

 ments of common pharmacological and toxicological importance, (2) the 

 noble gases, (3) elements of the lanthanide rare-earth series and others in 

 fission, (4) the actinide rare-earth series, and (5) other elements. 



For the main nuclear reactions producing the isotopes considered in the 

 following subsections, Sec. 7.12 should be consulted. 



28.2. Possible Micronutrient Elements. Eleven elements are treated here 

 as having been regarded as possible trace requirements for animals or plants. 

 This does not complete the list of elements for which such a role has been 

 suggested, but it does cover the principal ones. These elements are lithium, 

 fluorine, chromium, nickel, gallium, bromine, rubidium, strontium, colum- 

 bium, tin, and tungsten 



a. Lithium. No tracer work has been reported for lithium, which has been 

 found widely present in trace amounts in animals. It has no known radio- 

 active isotope of half-life greater than 0.88 sec; thus the rarer stable species 

 Li 6 will presumably have to serve for purposes where changes in systems 

 in dynamic lithium equilibrium are to be studied. Some studies have been 

 made with natural lithium on the effect of bombarding lithium in tissues with 

 slow neutrons [Lil-2]; like B 10 , the bombarded Li 6 nucleus splits with the 

 release of high specific ionization. These studies have given results similar 

 to those obtained with boron. 



b. Fluorine. The effect of fluorine in making teeth more resistant to 

 caries has led to its being postulated as an essential micronutrient in verte- 

 brates. A few studies have been carried out with F 1S (112-min half-life) on 

 the uptake of fluorine in bone and teeth [Fl-3], both in vivo and in vitro. 

 The secretion of fluorine in the submaxillary-gland saliva of the cat has also 

 been shown [Fl]. 



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