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

摘要

Soil columns (50 X 15 cm) were used to determine the potential for ~(95m)Tc (as a surrogate for ~(99)Tc 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 ~(99)Tc is less important than radionuclides such as ~(129)I and ~(36)Cl 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 ~(99)Tc has accumulated should not be overlooked.