Retention in soils, sediments, and rocks

The pcrtechnctate ion will not likely be sorbed in significant amounts by soils and suspended bottom sediments of predominantly negative charge, but will be highly mobile in soils and waters and thus available for uptake in biota. The c level in soil down to a depth of 25 cm was estimated in 1979 to be 10 g/g of soil 18j. Tliis concentration was calculated from the known relative fission yield and the measured levels of Sr and Cs in soil, assuming that these fission products from nuclear bomb tests have nearly the same retention rates in soil. 

Recently, distribution coefficients Kd for Tc in Canadian Shield lake sediments were determined under oxic and anoxic conditions in a laboratory study. Untreated Winnipeg River water was used. For the oxic treatment, sediment and water were shaken for 24 h, spiked with 932 Bq of shaken for another 48 h. The 

0 1-kg for the organic sediment. Under anoxic conditions the mean values were 96.7. 0.8, and 6.2 % of Tc in solutions, corresponding to values of 14, 9200, and 210 I kg . respectively. Consequently, considerable quantities of technetium may be sorbed to the sediment under the anoxic conditions expected for Canadian Shield lake sediments 20]. 

Concentrations of I c caused by global fallout in the surface layer ( 20 cm) of paddy field. soil samples in Japan collected in 1991 and 1992 near Ogata, Omagari, Morioka, Imari, and Kawazoc were measured by inductively coupled plasma mass spectrometry (ICP-MS). On a dry weight basis the Tc concentrations ranged from 0.02-0.11 Bq per kg soil. The activity ratios of Tc/ Cs varied from 2.0 10 to 5.2 10 I The theoretical activity ratio is about 3.0 10 The mechanism of I c accumulation in paddy fields may be explained by the reduction of TcOj under the reducing conditions of paddy field soil [22.  

The sorption of under aerobic and anaerobic conditions was determined for 34 soils that were selected from across central Canada to represent a broad range of chemical and textural characteristics. The aerobic values were 0.0 and 0.5 1/kg for mineral and organic soils, respectively, the anaerobic values were 18 and 68 l/kg, respectively. The values arc given by 

---