Field studies on the terrestrial behavior of actinide elements in East Tennessee

Field studies on the comparative uptake of various actinide elements (232Th, 233U, 238U, 239Pu, 241Am, and 244Cm) by plants and animals inhabiting historically contaminated environments on the Oak Ridge National Laboratory (ORNL) reservation in East Tennessee are summarized. The present-day pattern of actinide element bioaccumulation from a flood plain site contaminated with Pu in 1944 is U > Th approx. Pu. Thus the environmentally dispersed 239Pu exhibits a transfer from floodplain soil to biota comparable to that of indigenous 232Th and less than that of the indigenous 238U. This ranking agrees with the chemical extractability of U, Th, and Pu from soil, using either weak acids or strongly basic reagents. The pattern of actinide element uptake from the shoreline of a historically contaminated pond is Pu < Am approx. Cm < 238U = 233U. This ranking also agrees with the chemical extractability of Pu, Am, Cm, and U from shoreline sediment, using weak acids. Results from field studies at ORNL agree with what has been generally inferred about the relative food chain transfer of the actinides, based on laboratory studies and field studies at other sites in the United States. Because they share the same valence state, there are apparent strong similarities in soil sorption, plant uptake, and animal uptake between trivalent Am and Cm and between tetravalent Pu and Th. Available evidence suggests that knowledge of the behavior of naturally occurring 232Th in the terrestrial food chain can be useful for predicting the long-term fate of environmentally dispersed 239Pu, while data on 238U might be used to place an upper limit on the expected long-term food chain transfer of all transuranic elements except Np. 33 references, 5 figures, 1 table