278 PHOSPHORUS 



Phosphorus 32 (14.30 days) Beta 1.712 Gamma 



Cat. No. Sp. Act. Form Cost Chem. Cont. Radiochem. Cant. 



P-32-I 30mc/g KH2PO4 $33/215 mc — 100 mc K^M12.44 hr) 



Possibly phosphite 



P-32-P-1 40mc/mg H3PO4 $1.10/mc — — 



P-32-P-2 CF H3PO4 $3/mc — — 



MicaW. Int. C. Scint. C. 50% Self -abs. 



8.9 X 10-5 g_6 X 10-5 4 X 10-2 310 (detn.) 



Critical Org. Body Air Water Effect. T^ 



Bone 10 mC IX IQ-^ 2 X IQ-^ 14 days 



Intake Levels. The approximate daily intake of phosphorus for the 

 various species is as follows: man, 1.5 g; rat, 45 mg; laying hen, 1 g; sheep, 

 2.5 g; 100-lb pig, 8 g; and cattle, 15 g. In studies of oral administration 

 there is usually no problem in regard to administration of excess mass 

 because of the normal high intake and the high specific activities avail- 

 able. The whole blood in most species contains 35 to 45 mg/100 ml, 

 whereas the inorganic phosphorus of the plasma ranges from 4 to 9 mg/ 

 100 ml. Mass is usually not a problem with injection studies, since it 

 takes relatively large doses to produce toxic symptoms. Soft tissues of 

 animals contain 2 to 3 mg phosphorus per gram fresh weight, and bones 

 range from 40 to 130 mg/g. A recommended nutrient solution for plants 

 contains about 32 ppm, and crop plants usually range from 0.1 to 2 per 

 cent on a dry-matter basis. 



Radioassay. P^- has been one of the most widely used radioisotopes on 

 account of the biological importance of the element, the ease of produc- 

 tion, a convenient half-life, and the energetic beta emission. Preparation 

 P-32-I may have the advantage of low cost for large-scale fertilizer use, 

 but one must be careful that there are no significant amounts of labeled 

 phosphite in the particular preparation used. The K*- radiocontamina- 

 tion is ehminated by measurement of samples after a lapse of time sufficient 

 to permit decay. Preparation P-32-P-1 appears to be most useful for 

 general purposes and has a specific activity high enough to meet most 

 biological requirements. When extremely high specific activities are 

 required, preparation P-32-P-2 may be used, but care must be taken to 

 avoid loss of activity from these solutions by adsorption to glass walls of 

 beakers, pipettes, etc. It has been shown that such losses become 

 especially significant at low levels of total phosphorus and high pH values 

 (P-1). Under such conditions it may become necessary to coat all glass- 

 ware with a material like silicone. Routine hard-beta counting, including 

 direct liquid measurements, is entirely satisfactory for P^-, and self- 

 absorption corrections are not usually important. It is seldom necessary 



