Environmental fate and distribution of technetium-99 in a deciduous forest ecosystem

The uptake of 99Tc by trees intercepting contaminated groundwater from a radioactive waste storage site was measured to identify the major 99Tc pools within the woodland ecosystem and to assess the relative mobility of 99Tc in the existing element cycle. The highest average 99Tc concentrations in vegetation were found in herbaceous plants. Tree wood was the major above-ground pool for 99Tc because of the high concentrations in wood as well as the large amount of wood relative to other biomass at the site. Technetium was not easily leached from the trees by rainfall and was not readily extractable from forest floor leaf litter by water. The relative importance of return pathways for 99Tc to the forest floor was leaf fall > stemflow > throughfall, indicating that 99Tc was conserved by the trees. Snails and millipedes from the leaf litter layer concentrated technetium 20- and 16-fold, respectively, above levels found in the soil. Pertechnetate was rendered less bioavailable after ingestion by a leaf litter macroinvertebrate (Porcellio sp.) common to the study site. (author)