Effect of NO3- on the fate of (TcO4-)-Tc-99 system in the soil-plant system

This work was undertaken to study the effect of NO3- fertilization on the uptake of (TcO4-)-Tc-99 by plants. Rye-grass (Lolium perenne) was grown in a growth chamber on a silty loam soil to which were added increasing quantities of ammonium nitrate (21, 50 and 100 mg N kg(-1)). Soil samples were then amended with (TcO4-)-Tc-99 at a constant level of 29.6 kBqkg(-1) dry weight. Total initial NO3- content was 43.3, 57.8 and 82.8 mg N kg(-1), and total NH4+ content was 24.7, 39.2 and 64.2 mg N kg(-1). Three cuts were made at 4-week intervals, and aerial biomass was analysed for total Tc-99 and N, Results showed that total uptake of Tc-99 was decreased by increasing mineral N additions at the first cut, as mineral nitrogen was not a limiting factor for plant growth at this stage. Technetium-99 content in plants varied from 64% of the total applied Tc-99 with the lowest NO3- content to 31% with the highest. However, at the third cut, cumulative Tc-99 uptake reached the same level for the three treatments (80-83%) with no further effect of initial N applications, as NO3- was depleted in the soil. Therefore, (TcO4-)-Tc-99, was diluted in the pool of soil NO3- and was absorbed proportionally to nitrate by rye-grass. Copyright (C) 1997 Elsevier Science Ltd.