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Technetium Sources and Behavior in the Environment¹

ABSTRACT

Technetium (Tc) may enter the environment as a result of nuclear weapons testing, nuclear power production, nuclear fuel reprocessing, nuclear waste storage, and pharmaceutical use. The isotope ⁹⁹Tc has a long half-life and relatively high fission yield, and an understanding of its behavior and effects in the environment is essential to complete assessment of the environmental impact of the nuclear fuel cycle. Although little is known of Tc environmental behavior, the aqueous chemistry of Tc is well understood and limited laboratory investigations have been conducted on its behavior in soils, plants, and waters. On the basis of this current knowledge, the behavior and implications of Tc in the environment are assessed and avenues of research are suggested.

The most stable chemical species of Tc in aqueous solution is the pertechnetate ion, TcO₄^–. As the pertechnetate ion, Tc is highly soluble in water and in soil, but reduced forms (dioxide and sulfide) have limited solubility; sorption is significant in surface soils of high organic C content and low pH and may be significant in subsoils and geologic media under reduced conditions. A fraction of the sorption measured in surface soils may also have been due to immobilization in microbial cells. The pertechnetate ion is readily available to microbiota, algae, and higher plants and is toxic to higher plants at relatively low soil levels (0.1 µg/g). In higher plants, it is transported largely as the pertechnetate ion and toxicity appears to be due to biochemical rather than radiation effects. Uptake and toxicity appear to be due to Tc functioning as a nutrient analog. Preliminary studies indicate that, in contrast to hydrolyzable radionuclides, incorporation of Tc in plants reduces Tc absorption in animals.

Ultimately, the mobility and availability of Tc to biota will be governed by the quantity and form emitted and its form and solubility over the long-term in soils, sediments, and waters. Uptake by biota will be dependent upon the rate and extent of Tc movement across biological membranes and its toxicity. Proper evaluation of these phenomena will be largely dependent on development of an understanding of Tc sorption mechanisms in soils and sediments and the determination of the stable forms of soluble chemical species that occur in the environment over the long term.

Key Words: nuclear reactors • nuclear waste • soils • sediments • water • plants • algae • animals • pertechnetate • mobility • availability

¹ This research was performed under U.S. Dep. of Energy Contract EY-76-C-06-1830.

² Manager, Scientist, and Senior Research Specialist, respectively, Environ. Chem. Sec., Ecosystems Dep., Battelle, Pacific Northwest Lab., Richland, WA 99352.

Received for publication July 1, 1978.

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