Synopsis of French Experimental and in Situ Research on the Terrestrial and Marine Behavior of Tc

Abstract

Terrestrial environment studies have been essentially concerned with the evolution of soil deposition and soil-plant transfers. Experimentally determined coefficients of distribution in soils are low: 60-80% of Tc remains hydrosoluble during the first months. Technetium emissions resulting from microbiological activity have been quantified. Antagonistic effects on Mo and Tc retention by soils are dependent on their respective concentrations. Four areas of soil-plant transfers have been studied: 1) root absorption kinetics relative to deposition of Tc, 2) interaction of stable Mo (environmental parameter) with the transfer of Tc to plants, 3) interaction of some long-lived radioisotopes (effluent parameters) with the transfer of Tc to plants, and 4) long-term soil-plant transfer and aging of deposited material. Of aquatic systems, only the marine environment has been studied. Under anoxic conditions in the presence of reducing sediments, the distribution coefficients (Kd) were very high (10(3)). Concentration factors (CF) from water to organisms were generally very low (1 to 10); however, CF greater than 1000 have been observed for some biota such as macrophytic brown algae, worms and lobsters. Biochemical analysis showed that Tc was essentially free and partially bonded to proteins. The transfer factors between sediments and species were very low (TF less than 0.5). The biological half-time was determined in some marine organisms that had accumulated Tc from water, food or sediments; the loss is biphasic. Uptake in edible parts was low. The physiochemical form affects the accumulation and loss of Tc. Analyses have quantified 99Tc in marine fauna and biota in the English Channel in relation with releases of the reprocessing plant of La Hague. Brown algae are the best bioindicators for following 99Tc dispersion in marine ecosystems.

Dynamic model for the assessment of radiological exposure to marine biota

“…Again, the assessment model was run both with and without default biokinetic parameters, with the macrophyte and winkle reference organisms chosen to illustrate the comparison. For these organisms, the default T B1/2 for 99 Tc in winkles is set to 142 days (Swift, 1989), whilst Tc in macrophyte is modelled with a biphasic release with T B1/2 s of 1.5 and 128 days, respectively (Masson et al, 1989;Busby, 1998;Topcuoglu and Fowler, 1984).…”

Soil availability, plant uptake and soil to plant transfer of 99Tc—A review

“…Further, Masson et al (1989) reported that, during long-term percolation experiments on a calcareous soil, Mo applied to the soil surface (2 µg-200 µg kg Ϫ1 soil) increased the soil water migration of Tc, thus revealing a competitive effect between the two anions in the soil. Further work by Masson et al (1989) found that soil to plant transfer of 99 Tc in Lactuca sativa was inversely proportional to the soil molybdenum concentration applied. These data indicate that it might be useful to investigate further the role of MoO 2Ϫ 4 nutrition in 99 Tc uptake by plants.…”

“…Oxidation of 99 Tc compounds is probably so slow that accumulation of 99 Tc is possible in soils that are subjected to periodic waterlogging Muramatsu, 1993, 1995;Tagami and Uchida, 1999). However, there are a number of reports of 99 Tc being remobilised from marine sediments (Masson et al, 1989;Leonard et al, 1997;Morris et al, 2000). Low redox potentials can also cause TcO Ϫ 4 to react with hydrogen sulphide to form Tc 2 S 7 which is not available to plants (Brookins, 1988;Tagami and Uchida, 1996;Tagami and Uchida, 1997).…”

“…In fact, numerous studies have shown that, regardless of the Tc concentration in the soil, there is a maximum concentration of about 0.1 mg kg Ϫ1 plant Masson et al, 1989;Echevarria et al, 1997;Krijger et al, 1999). Bell et al (1988) reported that Tc levels in Pisum sativa did not exceed 0.07 ppm.…”

Phase I remedial investigation report for the 300-FF-5 operable unit, Volume 1

“…In acid soils, both the water-soluble and the organic forms of technetium-99 are predominant, whereas water-extractable forms seem to predominate in calcareous soils (Masson et al 1989). The solubility and plant availability of technetium-99 are reduced over time, suggesting that it undergoes reduction (+4) and reoxidation (+7) in surface soils (Cataldo et al 1989).…”