Graduate Thesis Or Dissertation

Radiotechnetium as an environmental contaminant : its metabolism by two freshwater species, the pearl mussel (Margaritifera margaritifera) and the rough-skinned newt (Taricha granulosa)

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  • There is an increasing world inventory of radiotechnetium (mainly ⁹⁹Tc) and it is inevitable that some of this will be released to the environment. However, little is known about the environmental behavior of this element. This work examined technetium's behavior in two representative freshwater species, the pearl mussel (Margaritifera margaritifera) and the rough-skinned newt (Taricha granulosa). The organisms were exposed to aqueous solutions of ⁹⁵mTc as pertechnetate, under chronic conditions. Uptake of the nuclide was followed for 63 and 51 days, respectively, by whole-body scintillation assay. The final whole-body concentration factors obtained were 0.9 for the mussel and 11.3 for the newt. The subsequent retention of this body burden by the two species was followed for 58 and 30 days, respectively. Both species exhibited two-phase retention patterns with long-lived components containing 65 and 75% of the initial activity, respectively. The biological half-lives for these long-lived components were calculated as 87 days for the mussel and 37 days for the newt. Tissue distribution data indicated that the soft tissues of the mussels contained more than twice the concentration of Tc activity as the shell, and that this ratio remained constant throughout both uptake and retention. This seemed to indicate a passive uptake and loss of the nuclide. In the soft tissues of the mussel the site of greatest Tc concentration was the foot-visceral mass, while the adductor muscle contained the least. The distribution of Tc in the tissues of the newt indicated that the major site of localization was the intestine. This activity was evenly distributed between the intestinal tissues and the contents of the gut. This study showed that, in the freshwater species studied, technetium is neither extensively concentrated nor tenaciously retained. It appears that uptake and loss are passive rather than due to an active metabolic mechanism. However, several unanswered questions were raised during this work which point out the need for continued research into the movement and behavior of technetium in freshwater ecosystems.
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