Saturday, 15 July 2006

Natural Accumulators of Radionuclides in the Environment.

Martine C. Duff, Anna Knox, and Mary Lou Ramsey. Savannah River National Laboratory, Bldg. 773A, Rm. 217, Aiken, SC 29808

During the last 50 years, a large amount of information on radionuclide accumulators or “sentinel-type” organisms in the environment has been published. Much of this initial work was conducted to study the risks of food-chain transfer of radionuclides to higher organisms such as reindeer and man. More recent work has been associated with the environmental and ecological interests in addition to the health and safety aspects associated with radionuclides in the environment. The accumulation of radionuclides can occur through a number of processes. Examples of these are by entrapment of radionuclides in the form of particulates and by physical or chemical sorption by the accumulator surface at the water-accumulator interface. Accumulation can also occur when the radionuclide source term exists in soil, sediment, water or in food (living or not living). Radionuclide uptake in the form of a gas is also possible. Radionuclide uptake can be a function of media characteristics such as pH, potentially competitive dissolved inorganic and organic ions, ionic strength, nutrients for growth, etc…. This is because these media characteristics can influence the chemical speciation of the radionuclide and preclude or promote radionuclide uptake. There are other factors as that affect radionuclide accumulation. For example, interactions with materials or living species that have close relationships with the accumulators can also influence the accumulation of radionuclides—such as lichens (an accumulator) that grow on deciduous trees versus those that grow on coniferous trees. Season, climate, geographical location, distance from source, elevation and water depth can also affect radionuclide accumulation. In many cases, there are multiple reasons that favor the observed accumulation. Finally, bulk or average levels of radionuclides in some accumulators may appear low but specific portions or organs of these accumulators may possess high levels of radionuclides. For example, high levels of some radionuclides can occur within one portion of the organism, such as the soft tissue of a mollusk (as opposed to the shell), which one could potentially consume. This presentation will consist of a literature review of sentinel organisms (mainly) and other natural materials that demonstrate a high affinity for radionuclides (or their stable surrogate isotopes). Factors that influence radionuclide uptake will be presented in more detail.

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