K-40 -Reply

[FRAMEP@ORAU.GOV]

 Barbara Hamrick wrote:

>Does anyone know the average concentration of K-40 in human urine,
>or the normal range of concentrations?

A couple of approaches:

1. ICRP 30 suggests the daily potassium ingestion is 3.3 grams and that
the absorption fraction is 1. Because K-40 is under such tight
homeostatic control we can assume that what goes in also goes out. 
What then would be the amount excreted in urine and sweat?  The
concentration of potassium in sweat is about 0.0007g per ml.  Because
we (I mean men here) spew out 650 mls per day of sweat, this
translates to 0.5 grams of potassium each day in sweat. The rest of the
potasium, 2.8 grams, I will assume, goes via the urine. This 2.8 grams of
K in 1400 mls (men ) of urine becomes 2 E-3 g/ml. This translates to 2.34
E-7 g of K-40/ml (percent abundance of K-40 is 0.0117%) and this
becomes 1.6 pCi/ml (K-40 specific activity is 6.81 E-6 Ci/g).

Well, the bottom line seems to be the daily intake, and that can vary a fair
bit. I'd double check my numbers if I were you, thats for sure

2. My second approach was to ask Mike Stabin. He points out that ICRP
23 lists urinary potassium in 32 normal subjects as varying between
1.09-4.91 g/day with an average of 2.8 g/day. This he translated into a
range of 0.7 - 3.1 pCi/ml with an average of 1.8 pCi/ml.

Take care

Paul Frame
Professional Training Programs
ORISE
framep@orau.gov