Influence of microorganisms on the behavior of technetium and other elements in paddy soil surface water

The Geochemistry of Technetium: A Summary of the Behavior of an Artificial Element in the Natural Environment

“…Despite the relatively oxidizing conditions of most farm lands, technetium appears to be bound up in soil, especially in periodically wet conditions (Ishii et al 2004a;Ishii et al 2004b;Tagami and Uchida 1997;Tagami and Uchida 1999). The relative immobility of technetium in agricultural fields was first noticed by Henrot (1989), who proposed that microbial activity may be causing reduction with consequent sorption and precipitation in the soil.…”

“…Subsequently, a wide variety of anaerobic microbes have been shown to reduce Tc(VII), including Geobacter metallireducens (Lloyd and McCaskie 1996), Geobacter sulfurreducens (Lloyd et al 2000), Escherichia coli (Lloyd et al 1997), Desulfovibrio desulfuricans (Lloyd et al 1999), Shewanella putrefacians (Wildung et al 2000), Desulfovibrio fructosovorans (De Luca et al 2001). An additional number of investigators also noted that technetium behaves as a reduced form in near-surface terrestrial sediments that are periodically waterlogged (Ishii et al 2004a;Tagami and Uchida 1999) that would otherwise expected to be oxidizing. In these settings, oxidation of organic material by microorganism yields a local oxygen-depleted zone in which in which facultative anaerobic bacteria thrive and technetium is reduced.…”

Uptake of radionuclides and stable elements from paddy soil to rice: a review

“…The level of Tc in the soil solution collected from the flooded soil of rice pots decreased rapidly with time, whereas the Tc concentration in the soil solution of unflooded wheat pots decreased slowly, because the wheat plants were not grown in flooded conditions. When a Tc tracer was added to a flooded paddy soil sample as TcO 4 À , Tc was rapidly transformed to immobile forms due to the reducing conditions generated by microbial activity (Tagami and Uchida, 1996;Ishii et al, 2004). Thus the low TF observed for rice could have been caused by fixation of Tc in the soil.…”

Comportement de radionucléides (Cs, I, Sr, Se, Tc) dans le sol : proposition de valeurs de Kd par défaut

“…Ainsi, dans les sols de rizière, le technétium s'accumule en surface sous une forme extrêmement peu remobilisable (Tagami et Uchida, 1999). Ishii et al (2004) ont clairement mis en évidence l'effet des bactéries sur l'insolubilisation du technétium dans un sol réducteur. Dans certains cas, il peut y avoir fixation totale -irréversible ou très lentement réversible -de ces formes réduites aux sites de liaison des acides humiques (Landa et al, 1977).…”