398 ANIMAL BIOCHEMISTRY 



except for the occasional formation of siliceous kidney stones in 

 castrated male cattle or sheep. 



Strontium is a widely dispersed btit rare element associated with 

 barium in bones. Some evidence suggests that Sr++ may be essential 

 for the calcification of bones. Although soluble salts are quite toxic, 

 natural levels present no problem. A special situation of potential 

 concern is discussed below. 



Vanaditnn occurs in minute amounts in plants, animals, and soils. 

 It has been implicated in the development of bones and teeth, and 

 if these findings are substantiated will be listed as an essential element 

 in general animal nutrition. There is no problem of toxicity. Vana- 

 dium is the metal in the respiratory blood pigment of the grotip of 

 marine animals called ascidians or Tunicata. Obviously it is an 

 essential element for these species. 



In addition to the normal elements, radioisotopes are important 

 in nutrition and metabolism. They are widely employed in studying 

 problems in these areas and are helping to add to our increasing 

 knowledge. More directly, the contamination that follows the use 

 of isotopes raises the levels ingested by animals and taken up by 

 plants. This increase may ultimately become serious for two reasons. 



First, the radiation produced by the decay of these unstable isotopes 

 alters near-by molecules absorbing this radiation. Obviously the 

 drastic change of sufficient numbers of molecules of critical kinds 

 can have far-reaching biological effects. Second, the incorporation of 

 certain unstable isotopes into biological molecules leads to destruction 

 of these molecules when the isotope decays. In this case the atom 

 changes into a different element, giving rise again to abnormal mole- 

 cules. 



These general considerations lead to concern over the slowly rising 

 level of radioactive elements. Although immediate and acute effects 

 are not expected except in specialized accidents, the biological future 

 is in doubt. A major problem in animals is expected to be the isotope 

 strontium-90, which accumulates and remains in bones. The bio- 

 logical retention of this element and the particular radiation emitted 

 when this isotope breaks down make it a long-time hazard. Unfor- 

 tunately, large quantities are formed during the explosion of hydro- 

 gen bombs and dispersed over the entire earth by atmospheric move- 

 ments. Since relatively imknown and unmeasurable biological hazards 

 must be measured against political imponderables, testing of hydrogen 

 bombs is under heated debate. Although of concern, the explosion 

 of nuclear weapons of other types does not present quite such serious 

 immediate and long-term problems. Yet even the use of radioisotopes 



