COBALT 



239 



Intake Levels. Ruminants recjuire about 0.1 mg/day of cobalt per 

 100 lb body weight, or about 0.1 ppm in the dry matter of herbage. The 

 requirements for nonruminants are not established, although cobalt 

 must be required to satisfy vitamin B12 needs. For rats, 0.4 ^tg/day is 

 adequate, and in rabbits deficiency symptoms were not produced on as 

 little as 0.0024 ppm. Crop plants range from 0.03 to 0.4 ppm on a dry- 

 weight basis. The glandular organs of animals usually show the highest 

 concentrations ranging from 0.2 to 3 ppm on a dry basis. The lethal dose 

 when injected into dogs is greater than 30 mg/kg. Fifty milligrams 

 cobalt injected intravenously into young calves produced temporary dis- 

 tress but no deaths (Co-1), and growing dairy animals were able to con- 

 sume up to 50 mg/100 lb body weight with no harmful effects (Co-2). 

 Under certain conditions, cobalt given to animals in amounts greater than 

 requirements, but by no means excessive, may produce polycythemia. 



Radioassay. Preparation Co-5758-P, which is cyclotron-produced by 

 bombardment of iron, is the one of choice provided the need for high 

 specific activity can justify the cost. Inert or radioactive iron contam- 

 ination will usually not be a problem. Preparation C0-6O-P is satisfac- 

 tory for general tracer work. Both of these radioisotopes can be counted 

 efficiently by soft-beta methods. However, in most cases the simplicity 

 of sample preparation for gamma counting will make it the procedure of 

 choice. 



Chemistry. The low concentrations of cobalt in plant and animal tis- 

 sues have stimulated considerable research on analytical methods. Wet- 

 ashing may be accomplished by the use of nitric and sulfuric acids or the 

 usual treatment with nitric, sulfuric, and perchloric acids. A method for 



