Bioavailability of Technetium-99 as Affected by Plant Species and Growth, Application Form, and Soil Incubation
- G. Echevarria,
- P. C. Vong,
- E. Leclerc-Cessac and
- J. L. Morel *
Laboratory of Soil and Environmental Sciences, ENSAIA-INRA/INPL, BP 172, 2, avenue de la forêt de Haye F-54505 Vandoeuvrelès-Nancy Cédex, France, Laboratory of Isotopes, ENSAIA-INRA/INPL, BP 172, 2, avenue de la forêt de Haye F-54505 Vandoeuvrelès-Nancy Cédex, France; Agence Nationale pour la Gestion des Déchets Radioactifs (ANDRA), Parc de la Croix Blanche, 1–7, rue Jean Monnet, F-92298 Châtenay-Malabry Cédex, France. Abstract
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) NH499TcO−2 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 99TcO−4. The fraction of soil 99Tc taken up (y) fitted an exponential model of biomass production (x):y = a + eex, showing that bioavail-ability 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 99TcO−4, suggesting that 99TcO−4 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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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