Answer to Question #12658 Submitted to "Ask the Experts"

I am a hands-on participant of a failed atomic cleanup. In 1978 at 20 years old I was a soil sampler in the United States nuclear proving grounds in the Marshall Islands. Besides the astronomical amount of ionizing radiation I was exposed to, I am particularly concerned with the inhalation and ingestion of strontium-90 (⁹⁰Sr) and cesium-137 (¹³⁷Cs). Is it possible to test and detect the presence of these elements in my body?

The bottom-line answer to your question is that it is very unlikely that any of the radioactivity of concern to you could be measured today, either by direct measurement of radiations from your body or by indirect measurements of excreta from your body.

By way of explanation, the ¹³⁷Cs (via its associated decay product barium-137 metastable, ^137mBa) is a gamma emitter and therefore relatively easy to detect in the body using a whole-body counter. However, the element cesium has a relatively short residence time in the body; it behaves chemically like potassium and has a biological half-time of only about 100 days. This means that via biological processes alone, one-half of the cesium is eliminated from the body in 100 days. The 40 years that have passed since your exposure are sufficient that essentially none of the cesium intake would remain (in fact, most of it would have been excreted from your body in one or two years). 

⁹⁰Sr (and its associated decay product yttrium-90, ⁹⁰Y) is a pure beta emitter and therefore difficult to detect with in vivo counting. Strontium tends to behave similarly to calcium in the body and remains in bones for a long time—only about 3% of the retained strontium is eliminated per year (not all that is ingested or inhaled remains; some is eliminated quickly). There are a few specially-designed whole-body counters in the world that can detect strontium in bones (using low-yield weak x rays created by the interaction of the beta particles with the bone itself). The limits of detection of these machines is on the order of 2,000 Bq (2,000 disintegrations s^-1 in the entire body). It is unlikely that (1) we could get you into one of these whole-body counters (the one I am most familiar with is in Siberia), and (2) that you would have been allowed to ingest enough strontium, even in 1978, so that there would be enough in you to detect with these machines today. Such machines are currently used to study people who were seriously overexposed in the 1950s and 1960s.

At this long time after a possible intake, other bioassay techniques such as analyses of urine or feces are also insufficiently sensitive to detect exposures so long ago. The cesium is definitely all gone, and the strontium probably so reduced as to be undetectable now.

Bruce A. Napier, CHP