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PM01 Phytoremediation and Risk Assessment
(PM003) Phytoremediation of Strontium-90 from the Columbia River shoreline at the Hanford Site in Washington State.
Fellows, R1, Ainsworth, C1, Goswami, D2, Herrington, R1, Barfuss, B1, 1 Pacific Northwest National Laboratory, Richland, WA, USA2 Washington State Department of Ecology, Richland, WA, USA
ABSTRACT- Past Plutonium production operations have left a radioactive legacy at the U.S. Department of Energy (USDOE) Hanford Site 100-N Area, located along the Columbia River in south-central Washington State. The plateau and bluff overlooking the river at 100-N are contaminated with approximately 75-Ci of Sr-90 while about 2 Ci of Sr-90 is present in the 10- to 20-m wide shoreline below. The USDOE, along with Washington State and Federal regulators, are exploring combined placement of a permeable barrier at the base of the bluff to stop Sr-90 groundwater movement to the river, and phytoremediation to remove the Sr-90 along the shoreline. Because of the shorelines rocky bank, almost 3-m daily water level fluctuations, and Sr-90 contamination above and below the water table, ultimate approval of phytoremediation will require a site-suitable plant species, proven Sr-90 extraction ability, and low potential for Sr-90 off-site transfer. There is no proven hyperaccumulator of Sr. Coyote willow (Salix exigua), a native plant, was selected for its rapid growth rate, root structure, stolon propagation, and phreatophytic nature. When grown in a sand-hydroponic test bed for 60-days, 30-cm cuttings of coyote willow reached almost 2-m in height and gained more than 2-g/day dry weight with most of the root mass located in the saturated zone demonstrating high biomass production under potential flooding conditions. An analog of Ca (up to 5% of plant dry weight), Sr may share a similar uptake mechanism and therefore the rhizosphere [Ca]/[Sr] ratio may affect total Sr accumulation. Studies are underway this year to determine [Ca]/[Sr] ratio effects, the potential for isotopic discrimination of Sr-90 from Sr, and amounts of Sr-90 uptake over several growth cycles from contaminated sediment. The potential of food chain interactions and development of management practices to minimize the risk will be addressed next year.
Key words: Strontium-90, Phytoremediation, Columbia River, shoreline
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