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Bioavailability of technetium-99 as affected by plant species and growth, application form, and soil incubation
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Edité par CCSD ; Crop Science Society of America -
Bioavailability of 99Tc to plants is believed to decrease with time in aerobic environments. This study was carried out to follow the fate of 99Tc in the soil-plant systems according to the form of applied 99Tc and the time of incubation in the soil. Two series of experiments were conducted: (i) NH499TcO4- 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 aestivum L.) (A) were grown; and (ii) two forms of 99Tc (NH499TcO4 and 99Tc 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. Plants were harvested at maturity for wheat and monthly for ryegrass. Results showed that ryegrass shoots accumulated 62 to 78% of 99Tc supplied as 99TcO4-. The fraction of soil 99Tc taken up ( y ) fitted an exponential model of biomass production (x):y = a + ecx, showing that 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 99TcO4-, suggesting that 99TcO4- was the predominant form in leaves. Total uptake of 99Tc by ryegrass was not affected by incubation, showing that mobility of 99Tc was not changed by aerobic microbial activity.
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