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19 June 2013

Answer to Question #1452 Submitted to "Ask the Experts"

Category: Alpha Emitters — Polonium

The following question was answered by an expert in the appropriate field:

What is a total activity of ²¹⁰Po and ²¹⁰Pb in the standard 70-kg person? What would the range of values in the United States be (Bq or pCi)?

According to the UNSCEAR 1982 Report "Ionizing Radiation: Sources and Biological Effects," 70 percent of the body content of ²¹⁰Pb is in the skeleton. UNSCEAR estimates the typical ²¹⁰Pb concentration in the skeleton to be 3 Bq/kg. This equates to a total skeletal activity of 15 Bq. The other 30 percent of the ²¹⁰Pb in the body, 6.4 Bq, would be distributed more or less uniformly throughout the soft tissues. The grand total of ²¹⁰Pb in the body is thus 21.4 Bq. In the skeleton, UNSCEAR 1982 assumes the ²¹⁰Po concentration to be 80 percent that of the ²¹⁰Pb concentration. As such, UNSCEAR estimates that the soft tissue concentration of ²¹⁰Po is 2.4 Bq/kg. This, in turn, translates to a total skeleton ²¹⁰Po activity of 12 Bq. In the soft tissues, UNSCEAR 1982 assumes a 1:1 ratio between ²¹⁰Po and ²¹⁰Pb. Hence the ²¹⁰Po activity in the soft tissues would be 6.4 Bq. The grand total of ²¹⁰Po in the body would be 18.4 Bq.

UNSCEAR, by the way, stands for United Nations Scientific Committee on the Effects of Atomic Radiation. The more recent UNSCEAR reports don't seem to contain as specific information about the body's ²¹⁰Pb and ²¹⁰Po content as the 1982 report.

The levels can be expected to be lower for women than men and lower for children than adults. Smokers have higher concentrations than nonsmokers.

An idea as to the variability of these activities in the U.S. population can be obtained from R.B. Holtzman's "Measurement of the Natural Contents of RaD (²¹⁰Pb) and RaF (²¹⁰Po) in Human Bone—Estimates of Whole-Body Burdens" (Health Physics 9(4):385; 1963). The ²¹⁰Pb concentrations measured by Holtzman in samples of bone ash ranged from 0.037 to 0.454 pCi/g. The average value was 0.146 pCi/g. The concentration in bone ash is approximately twice that in the skeleton (wet weight).

Paul Frame, CHP, PhD

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