Answer to Question #13183 Submitted to "Ask the Experts"

Category: Radiation Basics

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

Q

I am having difficulty finding out the biological half-life of radium-228 (228Ra) and lead-210 (210Pb) and was wondering if the Health Physics Society may be able to help with this?

A

There are easy and complex answers, and I provide both below.

The concept of biological half-life was developed for early mathematical models developed prior to and for Publication 2 by the International Commission on Radiation Protection (ICRP), published in 1959. This was to accommodate the primitive (as we would now view it) calculational capability, such that only one organ or tissue "compartment" could be evaluated. The results of metabolic research were used to identify a set of organs where deposition was prevalent that were evaluated to calculate a "maximum permissible concentration" that if an individual was exposed to for a working year would result in a "maximum permissible dose." The most limiting of these organs would be the "critical organ" and the corresponding biological half-life that for the element (biological parameters are defined for elements, not specific radionuclides). In the ICRP Publication 2 system, the critical organ for lead was kidney and biological half-life 531 days for soluble material. For radium, the critical organ was the bone and biological half-life 16,400 days, also for soluble material. The lung was the critical organ for both for inhalation of insoluble material and was evaluated assuming a 120-day biological half-life.

As you might guess, modeling capability has improved greatly since the 1950s, and with it the complexity of metabolic models. Three series of models have been developed in the 1970s, 1990s, and now, in fact, a new series of metabolic data has been published in several ICRP publications beginning in 2015 (ICRP Publications 130, 134, 137, and future publications). To properly use these models, it is appropriate to develop intake retention functions (Skrable et al. 1988) from them that can be evaluated to estimate the intake based on measurements. This has, in fact, been done for the 1990s series and published by Potter (2002).

While I have provided the requested biological half-lives, I would not recommend their use due to the fact that the concept has been superseded three times since their publishing. I would recommend review of the second provided reference and use of intake retention fractions for prospective and retrospective intake and dose evaluation.

Charles "Gus" Potter, PhD, CHP

References

Skrable KW, Chabot GE, French CS, LaBone TR. Intake retention functions and their application to bioassay and the estimation of internal radiation doses. Health Phys 55(6):933–950; 1988.

Potter CA. Intake retention fractions developed from models used in the determination of dose coefficients developed for ICRP publication 68—particulate inhalation. Health Phys 83(5):594–789; 2002.

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