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

Abstract

Abstract Bioavailability of 99 Tc to plants is believed to decrease with time in aerobic environments. This study was carried out to follow the fate of 99 Tc in the soil‐plant systems according to the form of applied 99 Tc and the time of incubation in the soil. Two series of experiments were conducted: (i) NH 4 99 TcO − 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 99 Tc (NH 4 99 TcO 4 and 99 Tc 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 99 Tc supplied as 99 TcO − 4 . The fraction of soil 99 Tc 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 99 TcO − 4 , suggesting that 99 TcO − 4 was the predominant form in leaves. Total uptake of 99 Tc by ryegrass was not affected by incubation, showing that mobility of 99 Tc was not changed by aerobic microbial activity.