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IP11 Investigations of the Columbia River and Estuary (USA)
(IP088) Uptake and depuration of 90Sr/90Y by Columbia River periphyton communities.
Fellows, R1, Bunn, A1, McKinstry, C1, Degerman, T1, Miller, B1, 1 Pacific Northwest National Laboratory, Richland, WA, USA
ABSTRACT- Low amounts of strontium-90 (90Sr) are currently entering the Columbia River at the U.S. Department of Energys Hanford Site in eastern Washington State. As part of a comprehensive study on the biological fate and transport of 90Sr at the Columbia groundwater/river interface, periphyton communities were collected from the Columbia River and cultured on glass slides. These were exposed to river water containing differing concentrations (1.0x105, 5.0x104, and 1.0x104 pCi L-1) of 90Sr (as SrCl2). Exposures lasted for 120 h followed by 72-h depuration periods in non-labeled river water. At selected time intervals, periphyton was scraped from slides into centrifuge tubes, washed with sterile river water, dried, weighed, ashed and counted using liquid scintillation. In the environment, 90Sr (t=28.2 yr) exists in secular equilibrium (equal counts from both) with its daughter product yttrium-90 (90Y; t=64.1 h). Most studies of Sr uptake employ 85Sr, 89Sr, or chemically separate 90Sr from 90Y to avoid interference of 90Y on the counting process. We counted all samples within 60 h of sampling and again after 27 d (> 10 half-lives of 90Y). The 60-h counts were consistently 2 to 3 times greater (pCi g-1 dry wt.) than those of the same samples after 27 d. Removal of the 90Sr/90Y from the exposure system produced depuration curves closely resembling 90Y decay kinetics. Calculations using counts and 90Y decay correction indicated that assimilation and retention of 90Y by the periphyton was almost an order of magnitude greater than 90Sr. The - decay product of 90Y (935 keV average, 2.26 MeV max) is much more energetic than the - of 90Sr (196 keV average, 546 keV max) and accounts for most of the radioisotope dosage imparted to a biological organism following 90Sr incorporation. Effects of such a higher dose to the primary producers of a freshwater ecosystem are unknown.
Key words: Strontium-90, periphyton, Yttrium-90, Columbia River
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