G. Echevarria et al., BIOAVAILABILITY OF TC-99 AS AFFECTED BY PLANT-SPECIES AND GROWTH, APPLICATION FORM, AND SOIL INCUBATION, Journal of environmental quality, 26(4), 1997, pp. 947-956
Bioavailability of Tc-99 to plants is believed to decrease with time i
n aerobic environments. This study was carried out to follow the fate
of Tc-99 in the soil-plant systems according to the form of applied Tc
-99 and the time of incubation in the soil. Two series of experiments
were conducted: (i) (NH4TcO4-)-Tc-99 was applied to two inceptisols (A
and B) at the levels of 0, 2.5, 25, and 250 kBq kg(-1) dry soil, and
ryegrass (Lolium perenne L.) (A and B) and winter wheat (Triticum aest
ivum L.) (A) were grown; and (ii) two forms of Tc-99 ((NH4TcO4)-Tc-99
and Tc-99 bio-incorporated in wheat leaves) were added to Soil A. Then
ryegrass was grown on this soil incubated for 0, 1, 3, and 6 mo. Plan
ts were harvested at maturity for wheat and monthly for ryegrass. Resu
lts showed that ryegrass shoots accumulated 62 to 78% of Tc-99 supplie
d as (TcO4-)-Tc-99. The fraction of soil Tc-99 taken up (y) fitted an
exponential model of biomass production (x):y = a + e(cx), showing tha
t bioavailability decreased with biomass production and not with time.
In wheat, 92 to 95% was accumulated in the leaves and less than 1.1%
in the grain. Technetium-99 bioincorporated in wheat leaves was highly
extractable by water (73%), and as available to ryegrass as (TcO4-)-T
c-99, suggesting that (TcO4-)-Tc-99 was the predominant form in leaves
. Total uptake of Tc-99 by ryegrass was not affected by incubation, sh
owing that mobility of Tc-99 was not changed by aerobic microbial acti
vity.