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Reply #97: #2 The bioavailability of cesium isotopes decrease quickly in soils. [View All]

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NNadir Donating Member (1000+ posts) Send PM | Profile | Ignore Sun Feb-20-05 07:13 AM
Response to Reply #92
97. #2 The bioavailability of cesium isotopes decrease quickly in soils.
The biological half-life of radiocesium isotopes, that is the half-life with which is available for incorporation into to living organisms, is considerably less than the physical radioactive half life. Millions of curies of Cesium-137 were released by the Chernobyl accident (and millions more by nuclear weapons testing in places like Nevada) and the behavior of this isotope, which has a half life of 30.07 years, has been extensively studied. The injection of this radioisotope into the environment, both deliberately and accidentally, has been of interest not only for its radiological health and environmental implications, but has also been used as a tracer to track things like ocean and atmospheric currents, river sedimentation patterns, convection, stratification and mixing in lakes, mineral flows in soils, ice flows in glaciers, growth patterns in forests, etc.

Chemists tend casually to think of the group one elements (Lithium, Sodium, Potassium, Rubidium and Cesium, and, oh yes, Francium) as being relatively simple in their chemistry. What is notable about these elements besides the fact that they have only two oxidation states, 0 and 1, is the high solubility of almost all of their salts, as noted above. This solubility gives cause for one to think, somewhat naively, that cesium, like sodium, would have a tendency to wash out and distribute freely wherever water flowed. Moreover, one would expect that cesium would encounter few barriers to biological uptake. On a little reflection however, it is clearly not the case that the biochemistry or geochemistry of these elements are identical. Obviously, for instance, the biochemistry of potassium and sodium are very different; owing to the differences one can have a potassium deficiency even if one soaks his or her French fries in table salt. Also the congener element Rubidium, which is also naturally radioactive, has the highest concentration of any element in tissue that has no known physiological role.

The physiological properties of Cesium reflect these subtle differences: It has been known for some time that to everyones surprise that after contamination of an ecosystem with radiocesium, the concentration of Cesium-137 in living tissues falls much faster than the half-life attributable to radioactive decay. The half life for uptake of cesium into plants growing in contaminated soils is considerably shorter than thirty years; it is actually about two years. (See, for instance, Environ. Sci. Technol., 33 (1), 49 -54, 1999.) This means that although almost 19 years after the Chernobyl accident about 64% of the cesium-137 injected into the environment still exists, less than 0.1% of that is actually available for biological uptake. The mechanism for this property, according to this paper, seems to result from the tendency of cesium to form stable complexes with minerals found in certain types of soils.

In any case, were one to ingest Cesium-137, unlike other radioisotopes, it has very little tendency to concentrate in organs. It is relatively easy to flush it out by increasing ones potassium intake. One could significantly lower ones internal Cesium-137 level for instance, by eating bananas.

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