Transuranic element uptake and cycling in a forest over an old burial ground

The consequences of returning the Savannah River Site (SRS) burial ground area to general public access at the time of completion of the SRS mission is being investigated. This study was established with the objective of determining the uptake of buried, low-level, transuranic waste from unlined earthen trenches by forest vegetation. From SRS startup in 1953 through 1974, solid waste contaminated with α-emitting transuranic nuclides was buried, unencapsulated, in earthen trenches. Burial records show that this material includes plutonium-238 (238Pu), plutonium isotopes 239 and 240 (239,240Pu), americium-241 (241Am), and neptunium-237 (237Np). In 1979, two tree plots were established, one over a trench in the burial ground and the other in an area without trenches. In the 2 years following establishment of the tree plots, 1979 and 1980, whole trees of each species were collected from each plot and analyzed for 239Pu and 238Pu. Beginning in 1986, needle samples were collected from selected pine trees in each of the plots. Because of poor growth and survival, the hardwood trees were not sampled after 1980. The results of data analysis support the conclusions that: (1) there is more 238Pu uptake by pine tree seedlings than the other species, (2) there is greater transuranic radionuclide uptake in grown pine trees than in seedlings, and (3) there are greater concentrations of transuranic radionuclides in the grown pine trees on the trench plots than in the pine trees on the control plot. These data indicate that tree roots will extract transuranic isotopes from buried, low level waste. The amount of radioisotopes moved from the trenches to the surface is small and the level in the trees is low enough that dose from direct exposure will be very small. A model was developed to estimate the potential for the transfer from the SRS alpha trenches. The results suggest that even following 100 years of transport, the transuranic, alpha dose from consuming food crops grown in the contaminated soil will be less than from naturally occurring isotopes