210 



BARIUM 



Intake Levels. Barium occurs naturally in foods at levels usually less 

 than 0.1 per cent. Crop plants may contain 3 to 1000 ppm. About 

 200 mg of soluble barium is toxic for man. About 335 mg/kg of ingested 

 barium chloride is fatal for rats. 



Radioassay. Preparation BaLa-140-P will probably be most useful 

 because of its high specific activity and because the daughter activity will 

 not interfere if the samples are allowed to stand for about 400 hr after 

 being taken, to allow attainment of equilibrium between Ba^^" and La^^". 

 Either hard-beta or gamma counting is satisfactory. 



Chemistry. Barium is usually isolated by use of the insoluble sulfate 

 or chromate. Biological tissues may be either wet- or dry-ashed. 



Typical Methods. An adult rat was fed 150 g of ration containing 

 3.3 per cent barium sulfate, the latter being labeled with 4 mc Ba^^" 

 (Ba-1) ; the entire amount was consumed in 5 days. The skinned and 

 eviscerated body was dried at 110°C and ashed at 600°C. Two and one- 

 half grams of ash was weighed into a shallow 3.7-cm-diameter aluminum 

 tray which had been placed in a steel die. The powder was evenly dis- 

 tributed by hand, and a piece of glassined paper placed over the die. 

 With a punch and laboratory press, the powder in the tray was com- 

 pressed at 1000 lb/in. 2, and the tray then forced out of the die. The 

 waxed paper could be removed without disturbing the ash, and the sam- 

 ple was then counted with an end-window tube. Standards were pre- 

 pared using the same amount of ash and known amounts of activity. 



In another study, goldfish were placed in solutions containing 0.1 to 

 5 Mc/ml (Ba-2). The tissues were dried at 100°C and ashed at 800°C. 

 In some cases, the ash was dissolved in HCl and transferred to capsules 



