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ABSTRACT A major concern of managers of low-level waste burial sites is the translocation of radioactive contaminants by deep-rooted plants to the soil surface. This study investigates the uptake of strontium (90Sr), a biologically mobile element, by chamisa (Chrysothamnus nauseosus), a deep-rooted shrub plant, growing over a former liquid waste disposal site (Solid Waste Management Unit [SWMU] 10-003[c]) at Los Alamos National Laboratory (LANL), Los Alamos, New Mexico. Surface soil samples (0 to 5 cm depth) were also collected from below (understory) and between (interspace) shrub canopies. Both chamisa plants growing over SWMU 10-003(c) contained significantly higher concentrations of 90Sr than a control (background) plant--one plant, in particular, contained 3.35 x 106 Bq kg-1 ash (9.05 x 104 pCi g-1 ash) in top-growth material. Similarly, soil surface samples collected underneath (ave. = 4,237 Bq kg-1 dry [114.5 pCi g-1 dry]) and between (ave. = 529 Bq kg-1 dry [14.3 pCi g-1 dry]) plants contained 90Sr concentrations above upper limit background (30 Bq kg-1 dry [0.82 pCi g-1 dry]) and LANL screening action levels (>163 Bq kg-1 dry [4.4 pCi g-1 dry]); this probably occurred as a result of chamisa plant leaf fall contaminating the soil understory area followed by water and/or winds moving 90Sr to the soil interspace areas. Although some soil surface migration of 90Sr from SWMU 10-003(c) has occurred, the level of 90Sr in sediments collected downstream of SWMU 10-003(c) at the LANL boundary was still within regional upper limit background concentrations.
KEYWORDS: radioecology, 90Sr, plant uptake, chamisa, Chrysothamnus nauseosus
This paper is from the Proceedings of the HSRC/WERC Joint Conference on the Environment, May 1996, published in hard copy and on the Web by the Great Plains/Rocky Mountain Hazardous Substance Research Center.
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