242 COPPER 



Intake Levels. Daily food intake for man is about 2 mg. Sheep, 

 cattle, and swine consume about 5 mg/day/100 lb body weight, which is 

 equivalent to about 6 ppm in the dry matter of herbage. About 0.1 mg/ 

 day is optimum for rats. About 12 mg copper sulfate fed daily to rats is 

 deleterious. One gram copper sulfate fed daily to sheep for 1 to 2 months 

 was fatal. Cattle are not injured by 2 g copper sulfate daily. Copper 

 mixed with feed is generally much less toxic, because of poor absorption, 

 than is soluble copper administered as a solution. A recommended nutri- 

 ent solution for plants contains 0.0127 ppm. Crop plants range from 3 

 to 75 ppm on a dry basis. 



Radioassay. Routine solution counting or gamma counting can be 

 used. Perhaps most useful, on account of the short half-life, is scintilla- 

 tion counting of the tissues themselves. The radiocontaminants may 

 become of importance if the measurements are made after considerable 

 decay has occurred or if there is a selective biological accumulation of the 

 contaminants (Cu-1). If necessary, these impurities can be eliminated 

 by electrolytic purification of the original preparation. On account of 

 the relatively low levels of copper tolerated by most biological systems, 

 it is often necessary to measure the Cu''* as soon as possible with a high 

 sensitivity, so that the dose can be made as small as possible. 



Chemistry. Biological samples can be either dry-ashed or w^et-ashed 

 according to the methods described in Chap. 5. Recoveries are usually 

 more certain with the wet-ashing procedures. A method for estimation of 

 copper in small plant or animal samples is as follows (Cu-2) : Five milli- 

 liters of blood, 1 to 5 g of wet tissue, or 1 g of dry tissue is oxidized with a 

 mixture of sulfuric, perchloric, and nitric acids. Any iron present is 

 deionized with ammonium citrate or pyrophosphate in strongly alkaline 

 solution. A color is formed by addition of diethyldithiocarbamate, and 

 the solution extracted with amyl alcohol for colorimetric evaluation. 



Typical Methods. For a study with cattle (Cu-3), the irradiation unit 

 of 0.32 g of copper wire was dissolved in 8 A'' HNO3 and neutralized with 

 2 N NaOH to the point of incipient precipitation. An amount of solution 

 containing about 250 mg Cu was used for oral dosage of 350-lb calves, and 



