Soil migration and plant uptake of technetium from a fluctuating water table

Soil columns (50 X 15 cm) were used to determine the potential for Tc-95m (as a surrogate for Tc-99 which is an important component of some radioactive waste) to migrate from a contaminated, fluctuating water table, through sandy loam soil and into perennial ryegrass. Upward migration was significantly retarded with, generally, only the bottom few centimetres of soil becoming contaminated over the 6 months of the experiment. This is thought to have been due to the presence of anoxic conditions within the water table leading to the reduction of pertechnetate to Tc-IV species which are relatively insoluble. However, some evidence of very slow upward migration over time was found. Only a small and inconsistent transfer of activity into the perennial ryegrass was observed. Whilst these observations would suggest that Tc-99 is less important than radionuclides such as I-129 and Cl-36 in terms of the risk associated with radioactive waste disposal; the potential for a slow upward migration, and/or a pulse-release following the re-oxidation of reduced soil in which Tc-99 has accumulated should not be overlooked. © 2005 Elsevier Ltd. All rights reserved.