YTTRIUM 



317 



Intake Levels. Yttrium is not an important naturally occurring con- 

 stituent of biological materials. A primary interest is concerned with 

 the radioisotopes of this element, produced by fission, and their tendency 

 to deposit in the bones of animals. The metabolism of Y^°, which is a 

 radioactive daughter of Sr^", may well be governed by the metaboHsm of 

 the parent strontium. There has been some interest in the use of Y^° 

 colloids for therapeutic purposes. The LD50 values for three yttrium 

 compounds ranged from 117 to 395 mg/kg administered intraperitoneally 

 to rats (Y-1). Intravenous dosage of 20 to 30 mg/kg of yttrium nitrate 

 was fatal to rats. 



Radioassay. Yttrium 91 appears to be the preparation of choice, 

 primarily on account of the high specific activity, unless a shorter-lived 

 activity is required. Routine beta or gamma counting can be used. 

 With an end-window counter, the measurements on soHd samples were 

 about four times as sensitive as on 10 ml solution in a 5-cm petri dish. 



Chemistry. No losses have been observed upon routine wet- or dry- 

 ashing. Stable yttrium has been determined spectrographically in bone 

 ash (Y-2). As noted below, care must be taken in the preparation of 

 solutions for administration to the biological system on account of tend- 

 encies for colloid formation and adsorption onto glass. 



Typical Methods. Immediately before use, the yttrium solution was 

 neutralized with XaOH to about 0.1 A'' HCl (Y-3). Rats were given 

 about 30 /iC per animal, and livestock were dosed with 1.4 mc/100 lb body 

 weight. With cattle, the isotope was mixed with the animal's own hep- 

 arinized plasma, which was then reinjected. Blood, urine, and milk 

 samples were counted directly or, if low in activity, were dried in Coors 

 No. 1 capsules and dry-ashed. Feces and tissue samples were either wet- 

 or dry-ashed. 



