Intake Levels. Tungsten does not usually occur in biological mate- 

 rials With rats, 0.1 per cent tungsten as the oxide or tungstate in the 

 food produced slight weight losses in 70 days; 0.5 per cent as the tungstate 



caused death. 



Radioassay. For tracer work, either preparation W-185-F or VV-18/-i 

 would be satisfactory. For Wl«^ gamma counting is considerably less 

 sensitive than beta counting. However, if the samples contam sufficient 

 activity, gamma methods would ehminate problems of sample preparation 

 and self-absorption. 



Chemistry. Wet-ashing has been shown to be satisfactory. A methoa 

 for estimation of tungsten in biological material is as follows (W-1) : About 

 2 ml of blood, 10 ml of urine, or 2 g of tissue is used. The sample is heated 

 in a Kjeldahl flask with glass beads, 4 ml concentrated H2SO4, and 10 ml 

 HNO3-HCIO4 mixture. Heating is continued until all dense white fumes 

 are driven off Bones and feces may require more H2SO4, and if charring 

 occurs, additional HNO3-HCIO4 is required. The acid residue is made 

 alkaUne with NaOH and then diluted to contain about 0.1 mg W per 5 ml. 

 The solution is filtered, and an aliquot treated with potassium thio- 

 cyanate, concentrated HCl, and titanium trichloride reagent for develop- 

 ment and measurement of color. 



W-1 Aull J C and Frederick W. Kinard: The Determination of Tungsten in 

 Biological Materials, J. Biol. Chem., 135: 119-121 (1940). 



