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Bioavailability of Technetium-99 as Affected by Plant Species and Growth, Application Form, and Soil Incubation

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.

^* Corresponding author (morel{at}ensaia.u-nancy.fr).

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 + e^ex, 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.