C-14 AND TRITIUM IN PLANTS OF A WETLAND CONTAINING CONTAMINATED GROUNDWATER

Although plants obtain essentially all of their C from the atmosphere, they can also become contaminated with C-14 in settings where the soi l is contaminated with C-14. Attempts to characterize this transfer of C-14 from soils to plants using the traditional concentration ratio h ave proven problematic because the soil-atmosphere-leaf pathway likely ; dominates in most hypothetical contamination scenarios. This study i nvestigated plant concentrations of C in a wetland that has been conta minated by groundwater C-14 and H-3 over the past 30 a. The accumulati on of 3H in the plants is by the soil-root-leaf pathway, and variation s in the C-14/H-3 ratio in the plants would suggest that another pathw ay is dominant for C-14 accumulation. The vertical distribution of H-3 in cedar (Thuja occidentalis) foliage was quite constant, 46.7 +/- 4. 8 Bq g(-1) dry weight, while the C-14 decreased with height, from 6.9 Bq g(-1) at 2.2 m to 1.5 Bq g(-1) at 11.2 m. Along a transect through the wetland, the C-14/H-3 ratio in the pore water was uniform whereas both moss and white spruce (Picea glauca) vegetation showed marked var iation. We conclude that the soil-atmosphere-leaf pathway was a major contributor to plant C-14, and speculate that this will be typical of releases from underground nuclear waste disposal. Crown copyright (C) 1998 Published by Elsevier Science Ltd. All rights reserved.