Technetium-99 Cycling in Maple Trees: Characterization of Changes in Chemical Form

Archive description

Prior field studies near an old radioactive waste disposal site at oak ridge, tennessee, indicated that following root uptake, metabolism by deciduous trees rendered technetium-99 less biogeochemically mobile than expected, based on chemistry of the pertechnetate anion. Subsequently, the form of technetium in maple tree sap, leaves, wood and forest leaf litter was characterized using one or more of the following methods: dialysis, physical fractionation, chemical extraction, gel permeation chromatography, enzymatic extraction, or thin layer chromatography on silica gel. Chromatography of pertechnetate incubated in vitro with tree sap showed it to behave similar to pertechnetate anion. When labeled wood and leaf tissue were processed using a tissue homogenizer, 15% and 40%, respectively, of the technetium was solubilized into phosphate buffer. Most of the solubilized technetium passing a 0.45-micron filter also passed through an ultrafiltration membrane with a nominal molecular weight cutoff of 10,000 atomic mass units. A majority of the technetium in leaves and leaf litter was removed only by strongly alkaline reagents typically used to release structural polysaccharides from plant tissues. In the leaf, pertechnetate is converted to less soluble forms apparently associated with structural components of leaf cell walls. This conversion explains why technetium-99 is not easily leached by rainfall from tree foliage and why technetium-99 appears to accumulate in forest floor leaf litter layers at the oak ridge study site.