Answer to Question #560 Submitted to "Ask the Experts"

Cesium-137 from fallout and from the accident at the Chornobyl nuclear power plant can become incorporated in man mainly by ingesting meat from caribou and reindeer that ingest fallout on vegetation such as lichens. Other routes of intake for cesium include bread, eggs, leafy vegetables, root vegetables, milk, poultry, fish, and fruits. Ingested cesium has a short biological half-time in man (about 80 to 110 days in adults), but an even shorter half-time in children (57 days) and infants (19 days). The average amount of ¹³⁷Cs in our bodies from all sources in the environment and all food that we eat is about 20 picocuries per gram (or 20 nanocuries per kilogram) at equilibrium between intake and excretion, which gives an annual internal radiation dose to the whole body of about 0.4 mrem per year. In S.I. units, 0.74 Bq per gram as background ¹³⁷Cs results in a whole-body dose of about 0.000004 Sv or 0.004 mSv per year. According to studies with laboratory animals, the effects of high intakes of ¹³⁷Cs include most of the typical biological effects of radiation poisoning. The studies on beagle dogs that ingested food containing ¹³⁷Cs involved total radiation doses of 700 to 1100 rem (7 to 11 Sv). Whole-body doses of concern for short-term effects (such as chromosome aberrations in blood cells) could be seen at doses as low as about 25 rem (0.25 Sv). This dose level would correspond to an equilibrium deposition of about 1.25 microcuries ¹³⁷Cs per gram or 46,000 Bq per gram (46 KBq/g) in the body. Effects would be more life-threatening at whole-body doses of 1 to 5 Sv (a factor of 4 to 20 higher).

Darrell Fisher, PhD